webui_handler/

route_handler.rs

// Copyright (c) Microsoft Corporation.
// Licensed under the MIT license.

//! Route component inventory management for incremental route rendering.
//!
//! These helpers walk the normal render fragment graph. The request-aware path is
//! route-aware but state-agnostic: it follows the active route chain for the
//! current request path, while conservatively traversing `if`, `for`, and
//! attribute-template edges without evaluating runtime state.

use crate::{route_matcher, route_renderer, HandlerError, StateSelection};
use memchr::memchr2;
use route_matcher::CompiledRouteIndex;
use serde::de::{DeserializeSeed, IgnoredAny, MapAccess, SeqAccess, Visitor};
use serde::ser::SerializeMap;
use serde::Serialize;
use serde_json::{value::RawValue, Map, Value};
use std::borrow::Cow;
use std::collections::{HashMap, HashSet};
use std::fmt;
use std::sync::{Arc, OnceLock, RwLock};
use webui_protocol::{
    web_ui_fragment::Fragment, ComponentAssetStylePreload, CssStrategy, StateProjectionMode,
    WebUIFragmentRoute, WebUIProtocol,
};

fn partition_component_asset_style_preloads(
    protocol: &WebUIProtocol,
    preloads: &[ComponentAssetStylePreload],
) -> (
    Vec<ComponentAssetStylePreload>,
    Vec<ComponentAssetStylePreload>,
) {
    let mut shadow = Vec::new();
    let mut light = Vec::new();
    for preload in preloads {
        if protocol
            .components
            .get(&preload.root)
            .is_some_and(|component| !component.uses_shadow_dom)
        {
            light.push(preload.clone());
        } else {
            shadow.push(preload.clone());
        }
    }
    (shadow, light)
}
use crate::streaming::PreparedContinuationStatePlan;

// ── Protocol Index ──────────────────────────────────────────────────────

/// A decoded protocol with reusable deterministic indices.
///
/// Construct this once when a server loads `protocol.bin`, then reuse it for
/// full renders, partial navigation, component-template requests, and token
/// queries. Full renders borrow the immutable protocol without locking.
/// Authored route patterns are precompiled once and matched as immutable
/// absolute patterns or relative suffixes. Parsed template metadata is
/// populated lazily behind a read-write lock whose scope is limited to
/// individual metadata lookups.
pub struct Protocol {
    protocol: WebUIProtocol,
    style_metadata_error: Option<String>,
    css_strategy: webui_protocol::CssStrategy,
    /// Render plan prepared once at load: numeric fragment slots, per-fragment
    /// render targets, canonical component prop names, and route presence bits.
    render_fragments: crate::RenderFragmentIndex,
    component_asset_style_manifest: std::result::Result<String, String>,
    component_asset_style_links: String,
    component_index: HashMap<String, u32>,
    style_resource_index: HashMap<String, u32>,
    style_resources_requiring_escape: HashSet<String>,
    component_reachability: OnceLock<ComponentReachabilityIndex>,
    fragment_ids: Vec<Arc<str>>,
    fragment_slots: HashMap<Arc<str>, u32>,
    route_index: CompiledRouteIndex,
    boundary_declarations: OnceLock<HashMap<u32, BoundaryDeclaration>>,
    continuation_state_plans: OnceLock<Box<[OnceLock<PreparedContinuationStatePlan>]>>,
    template_metadata_cache: RwLock<HashMap<String, Value>>,
}

/// Build-time identity of one streaming boundary declaration.
///
/// Interned once per protocol so a discovered occurrence clones two pointers
/// instead of allocating the authored owner and name on every response.
pub(crate) struct BoundaryDeclaration {
    pub(crate) owner: Arc<str>,
    pub(crate) name: Arc<str>,
}

impl Protocol {
    /// Decode protobuf bytes and build the reusable protocol index.
    ///
    /// # Errors
    ///
    /// Returns a protocol error when `bytes` is not a valid WebUI protobuf.
    pub fn from_protobuf(bytes: &[u8]) -> std::result::Result<Self, webui_protocol::ProtocolError> {
        let protocol = WebUIProtocol::from_protobuf(bytes)?;
        if let Some(error) = Self::validate_component_style_metadata(&protocol) {
            return Err(webui_protocol::ProtocolError::Validation(error));
        }
        Ok(Self::new_with_style_metadata(protocol, None))
    }

    /// Create a reusable runtime protocol from an already decoded document.
    #[must_use]
    pub fn new(protocol: WebUIProtocol) -> Self {
        let style_metadata_error = Self::validate_component_style_metadata(&protocol);
        Self::new_with_style_metadata(protocol, style_metadata_error)
    }

    fn new_with_style_metadata(
        mut protocol: WebUIProtocol,
        style_metadata_error: Option<String>,
    ) -> Self {
        let css_strategy = protocol.css_strategy();
        let component_asset_style_preloads =
            std::mem::take(&mut protocol.component_asset_style_preloads);
        let (shadow_preloads, light_preloads) =
            partition_component_asset_style_preloads(&protocol, &component_asset_style_preloads);
        let component_asset_style_links = if css_strategy == CssStrategy::Link {
            crate::serialize_component_asset_style_links(&light_preloads)
        } else {
            String::new()
        };
        let component_asset_style_manifest = if css_strategy == CssStrategy::Link {
            crate::serialize_component_asset_style_manifest(&shadow_preloads).map_err(|error| {
                format!("failed to serialize component asset style metadata: {error}")
            })
        } else {
            Ok(String::new())
        };
        let component_index = build_component_index(&protocol);
        let style_resource_index = build_style_resource_index(&protocol);
        let style_resources_requiring_escape = build_style_escape_resources(&protocol);
        let route_index = CompiledRouteIndex::new(&protocol);
        let mut fragment_ids: Vec<Arc<str>> = protocol
            .fragments
            .keys()
            .map(|id| Arc::from(id.as_str()))
            .collect();
        fragment_ids.sort_unstable();
        let mut fragment_slots = HashMap::with_capacity(fragment_ids.len());
        for (slot, id) in fragment_ids.iter().enumerate() {
            // Record counts are bounded by the compiled graph, well inside u32.
            #[allow(clippy::cast_possible_truncation)]
            fragment_slots.insert(Arc::clone(id), slot as u32);
        }
        // Render slots reuse the continuation slot numbering, so the prepared
        // index shares the interned IDs instead of duplicating every string, and
        // resolves targets through the slot map instead of re-searching by name.
        let render_fragments =
            crate::RenderFragmentIndex::new(&protocol, &fragment_ids, &fragment_slots);
        Self {
            protocol,
            style_metadata_error,
            css_strategy,
            render_fragments,
            component_asset_style_manifest,
            component_asset_style_links,
            component_index,
            style_resource_index,
            style_resources_requiring_escape,
            component_reachability: OnceLock::new(),
            fragment_ids,
            fragment_slots,
            route_index,
            boundary_declarations: OnceLock::new(),
            continuation_state_plans: OnceLock::new(),
            template_metadata_cache: RwLock::new(HashMap::new()),
        }
    }

    pub(crate) fn protocol(&self) -> &WebUIProtocol {
        &self.protocol
    }

    pub(crate) fn ensure_style_metadata(&self) -> Result<(), HandlerError> {
        self.style_metadata_error
            .as_ref()
            .map_or(Ok(()), |error| Err(HandlerError::Invariant(error.clone())))
    }

    pub(crate) fn css_strategy(&self) -> webui_protocol::CssStrategy {
        self.css_strategy
    }

    /// Render plan built once when this protocol was loaded.
    pub(crate) fn render_fragments(&self) -> &crate::RenderFragmentIndex {
        &self.render_fragments
    }

    pub(crate) fn component_asset_style_manifest(&self) -> Result<&str, HandlerError> {
        match &self.component_asset_style_manifest {
            Ok(manifest) => Ok(manifest),
            Err(message) => Err(HandlerError::Rendering(message.clone())),
        }
    }

    pub(crate) fn component_asset_style_links(&self) -> &str {
        &self.component_asset_style_links
    }

    pub(crate) fn component_index(&self) -> &HashMap<String, u32> {
        &self.component_index
    }

    pub(crate) fn style_resource_index(&self) -> &HashMap<String, u32> {
        if self.style_resource_index.is_empty() {
            &self.component_index
        } else {
            &self.style_resource_index
        }
    }

    pub(crate) fn style_resources_requiring_escape(&self) -> &HashSet<String> {
        &self.style_resources_requiring_escape
    }

    pub(crate) fn component_reachability(&self) -> &ComponentReachabilityIndex {
        self.component_reachability
            .get_or_init(|| ComponentReachabilityIndex::new(&self.protocol, &self.component_index))
    }

    pub(crate) fn route_index(&self) -> &CompiledRouteIndex {
        &self.route_index
    }

    /// Resolve a compiled fragment record ID to its dense slot.
    ///
    /// Continuation frames carry slots instead of owned IDs, so descending into
    /// a component, condition, or loop body allocates nothing.
    pub(crate) fn fragment_slot(&self, id: &str) -> Option<u32> {
        self.fragment_slots.get(id).copied()
    }

    /// Borrow the compiled fragment record ID for a dense slot.
    pub(crate) fn fragment_id(&self, slot: u32) -> Option<&str> {
        usize::try_from(slot)
            .ok()
            .and_then(|slot| self.fragment_ids.get(slot))
            .map(Arc::as_ref)
    }

    /// Borrow the interned identity of one build-time boundary declaration.
    ///
    /// The table is built on first streaming use and shared by every later
    /// response, so discovering an occurrence never re-allocates the authored
    /// owner or name.
    pub(crate) fn boundary_declaration(&self, declaration_id: u32) -> Option<&BoundaryDeclaration> {
        self.boundary_declarations
            .get_or_init(|| build_boundary_declarations(&self.protocol))
            .get(&declaration_id)
    }

    /// Borrow the memoized continuation projection surface for one entry.
    ///
    /// The graph walk that decides which top-level state keys a continuation
    /// retains depends only on the compiled protocol, so it runs at most once
    /// per entry for the lifetime of this [`Protocol`]. Memoization is a
    /// slot-indexed table of [`OnceLock`] cells: after the first response for
    /// an entry, every later response reads the plan through one acquire load
    /// with no lock, no hash, and no reference-count traffic. The table itself
    /// is allocated on first streaming use, so protocols that never stream pay
    /// nothing. Failures are captured and replayed so the memo never re-walks a
    /// graph that is known to be unusable.
    pub(crate) fn continuation_state_plan(
        &self,
        entry_id: &str,
    ) -> Result<&PreparedContinuationStatePlan, HandlerError> {
        let slot = self
            .fragment_slot(entry_id)
            .ok_or_else(|| HandlerError::MissingFragment(entry_id.to_string()))?;
        let index = usize::try_from(slot).map_err(|_| {
            HandlerError::Invariant("continuation plan slot does not fit usize".to_string())
        })?;
        let plans = self.continuation_state_plans.get_or_init(|| {
            (0..self.fragment_ids.len())
                .map(|_| OnceLock::new())
                .collect()
        });
        let cell = plans
            .get(index)
            .ok_or_else(|| HandlerError::MissingFragment(entry_id.to_string()))?;
        Ok(cell.get_or_init(|| PreparedContinuationStatePlan::new(&self.protocol, entry_id)))
    }

    /// Borrow the build-time CSS token list.
    #[must_use]
    pub fn tokens(&self) -> &[String] {
        &self.protocol.tokens
    }

    /// Produce a complete partial-navigation response from serialized state.
    ///
    /// This variant validates serialized host input while borrowing selected raw
    /// values into the response. Rust callers that already own parsed state
    /// should use [`Self::render_partial`] instead.
    pub fn render_partial_json(
        &self,
        state_json: &str,
        entry_id: &str,
        request_path: &str,
        inventory_hex: &str,
    ) -> Result<String, HandlerError> {
        self.ensure_style_metadata()?;
        let mut index = self.request_index();
        let (response, state_selection, _) = render_partial_indexed_with_state(
            self.protocol(),
            entry_id,
            request_path,
            inventory_hex,
            &mut index,
        )?;
        serialize_partial_response(response, state_json, &state_selection)
    }

    /// Produce a complete partial-navigation response from parsed state.
    ///
    /// This ownership-taking variant moves selected values into the response
    /// instead of serializing and reparsing the complete state tree. Use it when
    /// the caller already owns a [`serde_json::Value`] for the request.
    pub fn render_partial(
        &self,
        state: Value,
        entry_id: &str,
        request_path: &str,
        inventory_hex: &str,
    ) -> Result<String, HandlerError> {
        let response = self.prepare_partial(state, entry_id, request_path, inventory_hex)?;
        serde_json::to_string(&response)
            .map_err(|error| partial_serialize_error(&error.to_string()))
    }

    /// Prepare a serializable partial-navigation response with projected state.
    ///
    /// Moves compiler-selected values from the caller's owned state without
    /// cloning the state tree. Unknown component surfaces retain full state for
    /// correctness; reserved host injection state is excluded in either case.
    /// The response includes [`PartialNavigation::is_match`] so hosts can decide
    /// their HTTP status before serializing directly to their output buffer.
    ///
    /// # Errors
    ///
    /// Returns an error for invalid compiled style metadata or client inventory.
    #[must_use = "handle preparation errors before serializing the navigation response"]
    pub fn prepare_partial(
        &self,
        state: Value,
        entry_id: &str,
        request_path: &str,
        inventory_hex: &str,
    ) -> Result<PartialNavigation, HandlerError> {
        self.ensure_style_metadata()?;
        let mut index = self.request_index();
        let (response, state_selection, matched) = render_partial_indexed_with_state(
            self.protocol(),
            entry_id,
            request_path,
            inventory_hex,
            &mut index,
        )?;
        let state = select_owned_state(state, &state_selection);
        let response = PartialResponseWithState::new(response, state)?;
        Ok(PartialNavigation { response, matched })
    }

    /// Test route existence using the compiled route matcher, without rendering
    /// component assets or serializing state.
    #[must_use]
    pub fn matches_route(&self, entry_id: &str, request_path: &str) -> bool {
        let chain =
            collect_route_chain_plan(self.protocol(), entry_id, request_path, self.route_index());
        route_chain_matches(&chain.entries, request_path)
    }

    /// Render component template payloads for requested component tags.
    pub fn render_component_templates(
        &self,
        component_tags: &[&str],
        inventory_hex: &str,
    ) -> Result<Value, HandlerError> {
        self.ensure_style_metadata()?;
        let mut index = self.request_index();
        render_component_templates_indexed(
            self.protocol(),
            component_tags,
            inventory_hex,
            &mut index,
        )
    }

    fn validate_component_style_metadata(protocol: &WebUIProtocol) -> Option<String> {
        if protocol.style_closures.is_empty() {
            let requires_closures = protocol.components.iter().any(|(tag, component)| {
                protocol.component_style_resource(tag).is_some() || component.uses_shadow_dom
            });
            if requires_closures {
                return Some(
                    "component style closure metadata is required by this protocol".to_string(),
                );
            }
            return None;
        }
        let mut seen_resources = HashSet::new();
        for (root, closure) in &protocol.style_closures {
            seen_resources.clear();
            seen_resources.reserve(closure.component_tags.len());
            for tag in &closure.component_tags {
                if !seen_resources.insert(tag.as_str()) {
                    return Some(format!(
                        "component style closure `{root}` contains duplicate resource `{tag}`"
                    ));
                }
                if protocol.component_style_resource(tag).is_none() {
                    return Some(format!(
                        "component style closure `{root}` references missing resource `{tag}`"
                    ));
                }
            }
        }
        for (fragment_id, fragments) in &protocol.fragments {
            for fragment in &fragments.fragments {
                let Some(Fragment::Signal(signal)) = fragment.fragment.as_ref() else {
                    continue;
                };
                let Some(root) = crate::structural_signal_value(signal)
                    .and_then(|value| value.strip_prefix("shadow_styles:"))
                else {
                    continue;
                };
                let Some(component) = protocol.components.get(fragment_id) else {
                    return Some(format!(
                        "Shadow style hook `{root}` references unknown component `{fragment_id}`"
                    ));
                };
                if root != fragment_id.as_str() || !component.uses_shadow_dom {
                    return Some(format!(
                        "Shadow style hook `{root}` does not match component fragment `{fragment_id}`"
                    ));
                }
            }
        }
        for (tag, component) in &protocol.components {
            if !component.uses_shadow_dom {
                continue;
            }
            let Some(fragments) = protocol.fragments.get(tag) else {
                continue;
            };
            if !protocol.style_closures.contains_key(tag) {
                return Some(format!(
                    "component style closure metadata is missing Shadow root `{tag}`"
                ));
            }
            let hook_count = fragments
                .fragments
                .iter()
                .filter(|fragment| {
                    matches!(
                        fragment.fragment.as_ref(),
                        Some(Fragment::Signal(signal))
                            if crate::structural_signal_value(signal)
                                .and_then(|value| value.strip_prefix("shadow_styles:"))
                                == Some(tag.as_str())
                    )
                })
                .count();
            if hook_count == 0 {
                return Some(format!(
                    "Shadow component `{tag}` is missing its compiler style insertion hook"
                ));
            }
            if hook_count > 1 {
                return Some(format!(
                    "Shadow component `{tag}` emitted more than one style insertion hook"
                ));
            }
        }
        None
    }

    #[cfg(test)]
    fn render_partial_metadata(
        &self,
        entry_id: &str,
        request_path: &str,
        inventory_hex: &str,
    ) -> Result<Value, HandlerError> {
        self.ensure_style_metadata()?;
        let mut index = self.request_index();
        render_partial_indexed(
            self.protocol(),
            entry_id,
            request_path,
            inventory_hex,
            &mut index,
        )
    }

    fn request_index(&self) -> RequestProtocolIndex<'_> {
        RequestProtocolIndex {
            component_index: &self.component_index,
            route_index: &self.route_index,
            template_metadata_cache: TemplateMetadataCache::Shared(&self.template_metadata_cache),
        }
    }
}

/// Pre-computed index for a protocol, caching expensive lookups.
///
/// The component bit-index map is deterministic for a given protocol. The
/// route index and template metadata cache support test callers that create and
/// reuse a standalone index directly.
#[cfg(test)]
struct ProtocolIndex {
    /// Component name → bit index for inventory tracking.
    pub component_index: HashMap<String, u32>,
    /// Authored route template patterns compiled once.
    pub route_index: CompiledRouteIndex,
    /// Parsed WebUI template metadata keyed by component tag.
    template_metadata_cache: HashMap<String, Value>,
}

struct ComponentAssets {
    component_styles: Value,
    templates: serde_json::Map<String, Value>,
    functions: serde_json::Map<String, Value>,
}

/// Build the versioned, tree-local component style metadata for the requested
/// roots.
pub(crate) fn collect_component_styles<'a>(
    protocol: &WebUIProtocol,
    roots: impl IntoIterator<Item = &'a str>,
) -> Result<Value, HandlerError> {
    collect_component_styles_inner(protocol, roots, None)
}

#[derive(Clone, Copy)]
struct StyleInventoryView<'a> {
    bits: &'a [u8],
    index: &'a HashMap<String, u32>,
    chunks_are_indexed: bool,
}

impl StyleInventoryView<'_> {
    fn contains_component(self, tag: &str) -> bool {
        self.index
            .get(tag)
            .is_some_and(|&index| has_component(self.bits, index))
    }

    fn contains_chunk(self, name: &str) -> bool {
        self.chunks_are_indexed && self.contains_component(name)
    }
}

#[cfg(test)]
pub(crate) fn collect_component_style_delta<'a>(
    protocol: &WebUIProtocol,
    roots: impl IntoIterator<Item = &'a str>,
    style_inventory: &[u8],
    style_resource_index: &HashMap<String, u32>,
) -> Result<Value, HandlerError> {
    collect_component_styles_inner(
        protocol,
        roots,
        Some(StyleInventoryView {
            bits: style_inventory,
            index: style_resource_index,
            chunks_are_indexed: true,
        }),
    )
}

pub(crate) struct BorrowedComponentStyleDelta<'a> {
    strategy: webui_protocol::CssStrategy,
    resources: Vec<BorrowedStyleResource<'a>>,
    closures: Vec<BorrowedStyleClosure<'a>>,
    ordered: Vec<&'a str>,
}

struct BorrowedStyleResource<'a> {
    name: &'a str,
    resource: &'a str,
    members: Option<&'a [String]>,
}

struct BorrowedStyleClosure<'a> {
    root: &'a str,
    start: usize,
    end: usize,
}

impl BorrowedComponentStyleDelta<'_> {
    pub(crate) fn resource_names(&self) -> impl Iterator<Item = &str> {
        self.resources.iter().map(|resource| resource.name)
    }
}

impl Serialize for BorrowedComponentStyleDelta<'_> {
    fn serialize<S>(&self, serializer: S) -> std::result::Result<S::Ok, S::Error>
    where
        S: serde::Serializer,
    {
        let mut payload = serializer.serialize_map(Some(4))?;
        payload.serialize_entry(
            "closures",
            &BorrowedStyleClosures {
                closures: &self.closures,
                ordered: &self.ordered,
            },
        )?;
        payload.serialize_entry(
            "resources",
            &BorrowedStyleResources {
                strategy: self.strategy,
                resources: &self.resources,
            },
        )?;
        payload.serialize_entry("strategy", self.strategy.wire_name())?;
        payload.serialize_entry("version", &1)?;
        payload.end()
    }
}

struct BorrowedStyleResources<'a> {
    strategy: webui_protocol::CssStrategy,
    resources: &'a [BorrowedStyleResource<'a>],
}

impl Serialize for BorrowedStyleResources<'_> {
    fn serialize<S>(&self, serializer: S) -> std::result::Result<S::Ok, S::Error>
    where
        S: serde::Serializer,
    {
        let mut resources = serializer.serialize_map(Some(self.resources.len()))?;
        for resource in self.resources {
            resources.serialize_entry(
                resource.name,
                &BorrowedStyleResourceValue {
                    strategy: self.strategy,
                    resource,
                },
            )?;
        }
        resources.end()
    }
}

struct BorrowedStyleResourceValue<'a> {
    strategy: webui_protocol::CssStrategy,
    resource: &'a BorrowedStyleResource<'a>,
}

impl Serialize for BorrowedStyleResourceValue<'_> {
    fn serialize<S>(&self, serializer: S) -> std::result::Result<S::Ok, S::Error>
    where
        S: serde::Serializer,
    {
        let field_count = match (self.strategy, self.resource.members.is_some()) {
            (webui_protocol::CssStrategy::Module, true) => 4,
            (webui_protocol::CssStrategy::Module, false) | (_, true) => 3,
            (_, false) => 2,
        };
        let mut resource = serializer.serialize_map(Some(field_count))?;
        match self.strategy {
            webui_protocol::CssStrategy::Link => {
                resource.serialize_entry("href", self.resource.resource)?;
                resource.serialize_entry("kind", "link")?;
                if let Some(members) = self.resource.members {
                    resource.serialize_entry("members", members)?;
                }
            }
            webui_protocol::CssStrategy::Style => {
                resource.serialize_entry("css", self.resource.resource)?;
                resource.serialize_entry("kind", "style")?;
                if let Some(members) = self.resource.members {
                    resource.serialize_entry("members", members)?;
                }
            }
            webui_protocol::CssStrategy::Module => {
                resource.serialize_entry("css", self.resource.resource)?;
                resource.serialize_entry("kind", "module")?;
                if let Some(members) = self.resource.members {
                    resource.serialize_entry("members", members)?;
                }
                resource.serialize_entry("specifier", self.resource.name)?;
            }
        }
        resource.end()
    }
}

struct BorrowedStyleClosures<'a> {
    closures: &'a [BorrowedStyleClosure<'a>],
    ordered: &'a [&'a str],
}

impl Serialize for BorrowedStyleClosures<'_> {
    fn serialize<S>(&self, serializer: S) -> std::result::Result<S::Ok, S::Error>
    where
        S: serde::Serializer,
    {
        let mut closures = serializer.serialize_map(Some(self.closures.len()))?;
        for closure in self.closures {
            closures.serialize_entry(closure.root, &self.ordered[closure.start..closure.end])?;
        }
        closures.end()
    }
}

pub(crate) fn collect_borrowed_component_style_delta<'a>(
    protocol: &'a WebUIProtocol,
    roots: impl IntoIterator<Item = &'a str>,
    style_inventory: &[u8],
    style_resource_index: &HashMap<String, u32>,
    chunk_index: &HashMap<&str, u32>,
) -> Result<BorrowedComponentStyleDelta<'a>, HandlerError> {
    if protocol.style_closures.is_empty() {
        if protocol
            .components
            .keys()
            .any(|tag| protocol.component_style_resource(tag).is_some())
        {
            return Err(HandlerError::Invariant(
                "component style closure metadata is required by this protocol".to_string(),
            ));
        }
        return Ok(BorrowedComponentStyleDelta {
            strategy: protocol.css_strategy(),
            resources: Vec::new(),
            closures: Vec::new(),
            ordered: Vec::new(),
        });
    }

    let mut seen_roots = HashSet::new();
    let roots: Vec<&str> = roots
        .into_iter()
        .filter(|root| seen_roots.insert(*root))
        .collect();
    let client_inventory = StyleInventoryView {
        bits: style_inventory,
        index: style_resource_index,
        chunks_are_indexed: true,
    };
    let covered_components = covered_components(protocol, &roots, Some(client_inventory));
    let unit_capacity = roots
        .iter()
        .filter_map(|root| protocol.style_closures.get(*root))
        .map(WebUIProtocol::style_closure_unit_count)
        .sum();
    let mut resources = Vec::with_capacity(unit_capacity);
    let mut closures = Vec::with_capacity(roots.len());
    let mut ordered = Vec::with_capacity(unit_capacity);
    let mut emitted = HashSet::with_capacity(unit_capacity);
    let mut serialized_resources = HashSet::with_capacity(unit_capacity);

    for root in roots {
        let Some(closure) = protocol.style_closures.get(root) else {
            if !protocol.fragments.contains_key(root) && !protocol.components.contains_key(root) {
                continue;
            }
            return Err(HandlerError::Invariant(format!(
                "component style closure metadata is missing root `{root}`"
            )));
        };
        if closure.style_chunks.is_empty()
            && !closure.component_tags.is_empty()
            && closure
                .component_tags
                .iter()
                .all(|tag| covered_components.contains(tag.as_str()))
        {
            continue;
        }

        let start = ordered.len();
        emitted.clear();
        let unit_count = WebUIProtocol::style_closure_unit_count(closure);
        for position in 0..unit_count {
            let Some(unit) = protocol.style_closure_unit(closure, chunk_index, position) else {
                continue;
            };
            let name = unit.name;
            let resource = unit.resource.ok_or_else(|| match unit.chunk {
                Some(index) => HandlerError::Invariant(format!(
                    "component style closure `{root}` references missing style chunk {index}"
                )),
                None => HandlerError::Invariant(format!(
                    "component style closure `{root}` references missing resource `{name}`"
                )),
            })?;
            if !emitted.insert(name) {
                continue;
            }

            let (client_has_it, members) = match unit.chunk {
                Some(index) => (
                    client_inventory.contains_chunk(name),
                    protocol.style_chunk_members(index),
                ),
                None => (client_inventory.contains_component(name), None),
            };
            if !client_has_it && serialized_resources.insert(name) {
                resources.push(BorrowedStyleResource {
                    name,
                    resource,
                    members: members.filter(|members| members.len() > 1),
                });
            }
            ordered.push(name);
        }
        closures.push(BorrowedStyleClosure {
            root,
            start,
            end: ordered.len(),
        });
    }

    resources.sort_unstable_by_key(|resource| resource.name);
    closures.sort_unstable_by_key(|closure| closure.root);
    Ok(BorrowedComponentStyleDelta {
        strategy: protocol.css_strategy(),
        resources,
        closures,
        ordered,
    })
}

fn collect_component_styles_for_inventory<'a>(
    protocol: &WebUIProtocol,
    roots: impl IntoIterator<Item = &'a str>,
    component_inventory: &[u8],
    component_index: &HashMap<String, u32>,
) -> Result<Value, HandlerError> {
    collect_component_styles_inner(
        protocol,
        roots,
        Some(StyleInventoryView {
            bits: component_inventory,
            index: component_index,
            chunks_are_indexed: false,
        }),
    )
}

fn collect_component_styles_inner<'a>(
    protocol: &WebUIProtocol,
    roots: impl IntoIterator<Item = &'a str>,
    client_inventory: Option<StyleInventoryView<'_>>,
) -> Result<Value, HandlerError> {
    if protocol.style_closures.is_empty() {
        if protocol
            .components
            .keys()
            .any(|tag| protocol.component_style_resource(tag).is_some())
        {
            return Err(HandlerError::Invariant(
                "component style closure metadata is required by this protocol".to_string(),
            ));
        }
        return Ok(component_styles_payload(
            protocol.css_strategy(),
            serde_json::Map::new(),
            serde_json::Map::new(),
        ));
    }

    let mut resources = serde_json::Map::new();
    let mut closures = serde_json::Map::new();
    let mut seen_roots = HashSet::new();
    let roots: Vec<&str> = roots
        .into_iter()
        .filter(|root| seen_roots.insert(*root))
        .collect();
    let covered_components = covered_components(protocol, &roots, client_inventory);
    let chunk_index = protocol.style_chunk_index();
    let mut emitted = HashSet::new();

    for root in roots {
        let Some(closure) = protocol.style_closures.get(root) else {
            if !protocol.fragments.contains_key(root) && !protocol.components.contains_key(root) {
                continue;
            }
            return Err(HandlerError::Invariant(format!(
                "component style closure metadata is missing root `{root}`"
            )));
        };
        if closure.style_chunks.is_empty()
            && !closure.component_tags.is_empty()
            && closure
                .component_tags
                .iter()
                .all(|tag| covered_components.contains(tag.as_str()))
        {
            continue;
        }
        let unit_count = WebUIProtocol::style_closure_unit_count(closure);
        let mut ordered = Vec::with_capacity(unit_count);
        emitted.clear();
        for position in 0..unit_count {
            // A bundled build ships one resource per chunk. The client installs
            // resources by name in closure order either way, so only the names
            // and their grouping change. A closure that lists members rather
            // than chunks resolves each member to its covering chunk, so it
            // stays self-sufficient instead of relying on some other closure
            // installing first.
            let Some(unit) = protocol.style_closure_unit(closure, &chunk_index, position) else {
                continue;
            };
            let name = unit.name;
            let resource = unit.resource.ok_or_else(|| match unit.chunk {
                Some(index) => HandlerError::Invariant(format!(
                    "component style closure `{root}` references missing style chunk {index}"
                )),
                None => HandlerError::Invariant(format!(
                    "component style closure `{root}` references missing resource `{name}`"
                )),
            })?;
            let (client_has_it, members) = match unit.chunk {
                Some(index) => (
                    client_inventory.is_some_and(|inventory| inventory.contains_chunk(name)),
                    Some(protocol.style_chunk_members(index).unwrap_or_default()),
                ),
                None => (
                    client_inventory.is_some_and(|inventory| inventory.contains_component(name)),
                    None,
                ),
            };
            // Several members of one closure can resolve to the same chunk.
            if !emitted.insert(name) {
                continue;
            }
            if !client_has_it && !resources.contains_key(name) {
                let mut entry = serde_json::Map::new();
                match protocol.css_strategy() {
                    webui_protocol::CssStrategy::Link => {
                        entry.insert("kind".into(), Value::String("link".into()));
                        entry.insert("href".into(), Value::String(resource.to_owned()));
                    }
                    webui_protocol::CssStrategy::Style => {
                        entry.insert("kind".into(), Value::String("style".into()));
                        entry.insert("css".into(), Value::String(resource.to_owned()));
                    }
                    webui_protocol::CssStrategy::Module => {
                        entry.insert("kind".into(), Value::String("module".into()));
                        entry.insert("specifier".into(), Value::String(name.to_owned()));
                        entry.insert("css".into(), Value::String(resource.to_owned()));
                    }
                }
                if let Some(members) = members.filter(|members| members.len() > 1) {
                    entry.insert(
                        "members".into(),
                        Value::Array(members.iter().cloned().map(Value::String).collect()),
                    );
                }
                resources.insert(name.to_owned(), Value::Object(entry));
            }
            ordered.push(Value::String(name.to_owned()));
        }
        closures.insert(root.to_owned(), Value::Array(ordered));
    }

    Ok(component_styles_payload(
        protocol.css_strategy(),
        resources,
        closures,
    ))
}

fn covered_components<'a>(
    protocol: &'a WebUIProtocol,
    roots: &[&str],
    inventory: Option<StyleInventoryView<'_>>,
) -> HashSet<&'a str> {
    let mut covered = HashSet::with_capacity(protocol.components.len());
    for root in roots {
        let Some(closure) = protocol.style_closures.get(*root) else {
            continue;
        };
        for index in &closure.style_chunks {
            if let Some(chunk) = usize::try_from(*index)
                .ok()
                .and_then(|index| protocol.style_chunks.get(index))
            {
                covered.extend(chunk.component_tags.iter().map(String::as_str));
            }
        }
    }

    if let Some(inventory) = inventory {
        for chunk in &protocol.style_chunks {
            if inventory.contains_chunk(&chunk.name) {
                covered.extend(chunk.component_tags.iter().map(String::as_str));
            }
        }
    }
    covered
}

fn component_styles_payload(
    strategy: webui_protocol::CssStrategy,
    resources: serde_json::Map<String, Value>,
    closures: serde_json::Map<String, Value>,
) -> Value {
    let strategy = strategy.wire_name();
    let mut payload = serde_json::Map::new();
    payload.insert("version".into(), Value::from(1));
    payload.insert("strategy".into(), Value::String(strategy.into()));
    payload.insert("resources".into(), Value::Object(resources));
    payload.insert("closures".into(), Value::Object(closures));
    Value::Object(payload)
}

#[cfg(test)]
impl ProtocolIndex {
    /// Build a protocol index from a compiled protocol.
    #[must_use]
    pub(crate) fn new(protocol: &WebUIProtocol) -> Self {
        Self {
            component_index: build_component_index(protocol),
            route_index: CompiledRouteIndex::new(protocol),
            template_metadata_cache: HashMap::new(),
        }
    }

    fn request_index(&mut self) -> RequestProtocolIndex<'_> {
        RequestProtocolIndex {
            component_index: &self.component_index,
            route_index: &self.route_index,
            template_metadata_cache: TemplateMetadataCache::Exclusive(
                &mut self.template_metadata_cache,
            ),
        }
    }
}

enum TemplateMetadataCache<'a> {
    #[cfg(test)]
    Exclusive(&'a mut HashMap<String, Value>),
    Shared(&'a RwLock<HashMap<String, Value>>),
}

struct RequestProtocolIndex<'a> {
    component_index: &'a HashMap<String, u32>,
    route_index: &'a CompiledRouteIndex,
    template_metadata_cache: TemplateMetadataCache<'a>,
}

// ── Component Inventory ─────────────────────────────────────────────────

/// Intern the owner and authored name of every boundary declaration.
///
/// Only start markers carry identity; end markers repeat the declaration ID.
fn build_boundary_declarations(protocol: &WebUIProtocol) -> HashMap<u32, BoundaryDeclaration> {
    let mut declarations = HashMap::new();
    for list in protocol.fragments.values() {
        for fragment in &list.fragments {
            let Some(Fragment::Boundary(boundary)) = fragment.fragment.as_ref() else {
                continue;
            };
            if boundary.phase() != webui_protocol::BoundaryPhase::Start {
                continue;
            }
            declarations.insert(
                boundary.declaration_id,
                BoundaryDeclaration {
                    owner: Arc::from(boundary.owner_fragment_id.as_str()),
                    name: Arc::from(boundary.name.as_str()),
                },
            );
        }
    }
    declarations
}

/// Build a deterministic component-name → bit-index map from the protocol.
///
/// Derives names from fragment keys (hyphenated = custom element) since that
/// is the source of truth regardless of whether a plugin populated
/// `protocol.components`. Components are sorted alphabetically; index =
/// position in that order.
pub(crate) fn build_component_index(protocol: &WebUIProtocol) -> HashMap<String, u32> {
    let mut sorted: Vec<&String> = protocol
        .fragments
        .keys()
        .filter(|key| key.contains('-'))
        .collect();
    sorted.sort_unstable();
    let mut index = HashMap::with_capacity(sorted.len());
    for (i, name) in sorted.into_iter().enumerate() {
        // Index count bounded by component registry size, well within u32 range
        #[allow(clippy::cast_possible_truncation)]
        let idx = i as u32;
        index.insert(name.clone(), idx);
    }
    index
}

/// Build the exact resource-ID index used by streaming style deduplication.
fn build_style_resource_index(protocol: &WebUIProtocol) -> HashMap<String, u32> {
    if protocol.style_chunks.is_empty() {
        return HashMap::new();
    }
    let mut sorted: Vec<&str> = protocol
        .components
        .keys()
        .filter(|tag| protocol.component_style_resource(tag).is_some())
        .map(String::as_str)
        .chain(
            protocol
                .style_chunks
                .iter()
                .map(|chunk| chunk.name.as_str()),
        )
        .collect();
    sorted.sort_unstable();
    sorted.dedup();
    let mut index = HashMap::with_capacity(sorted.len());
    for (position, name) in sorted.into_iter().enumerate() {
        // The protocol cannot hold enough resource records for this to truncate.
        #[allow(clippy::cast_possible_truncation)]
        let position = position as u32;
        index.insert(name.to_string(), position);
    }
    index
}

fn build_style_escape_resources(protocol: &WebUIProtocol) -> HashSet<String> {
    if protocol.css_strategy() == CssStrategy::Link {
        return HashSet::new();
    }

    let mut resources = HashSet::new();
    for (name, component) in &protocol.components {
        if crate::html_encode::style_text_needs_escape(&component.css) {
            resources.insert(name.clone());
        }
    }
    for chunk in &protocol.style_chunks {
        if crate::html_encode::style_text_needs_escape(&chunk.css) {
            resources.insert(chunk.name.clone());
        }
    }
    resources
}

/// Startup-built direct component dependency graph used by streaming
/// checkpoints. Route-free component surfaces walk integer indexes on the
/// request path; only route-dependent surfaces need the more expensive
/// request-aware fragment traversal.
///
/// The same table interns each component's compiled hydration projection as a
/// run of key IDs. IDs are assigned in lexicographic order, so a checkpoint
/// collects its projection by concatenating integer runs and sorting integers —
/// no per-checkpoint component-name hash, no string sort, and no borrowed-string
/// scratch that would have to be rebuilt on every semantic step.
pub(crate) struct ComponentReachabilityIndex {
    names: Vec<String>,
    dependencies: Vec<Box<[u32]>>,
    route_dependent: Vec<bool>,
    hydration_keys: Vec<Box<str>>,
    hydration_key_ids: Vec<u32>,
    hydration_runs: Vec<HydrationRun>,
}

/// One component's interned hydration projection.
///
/// `len == FULL_STATE_RUN` marks a compiled surface that is not expressible as
/// a key allowlist, which forces the whole record to full state exactly as the
/// name-based collector did.
#[derive(Clone, Copy)]
struct HydrationRun {
    start: u32,
    len: u32,
}

impl HydrationRun {
    const FULL_STATE: Self = Self {
        start: 0,
        len: u32::MAX,
    };

    const fn requires_full_state(self) -> bool {
        self.len == u32::MAX
    }
}

impl ComponentReachabilityIndex {
    fn new(protocol: &WebUIProtocol, component_index: &HashMap<String, u32>) -> Self {
        let mut names: Vec<String> = component_index.keys().cloned().collect();
        names.sort_unstable();

        let mut dependencies = Vec::with_capacity(names.len());
        let mut route_dependent = Vec::with_capacity(names.len());
        for name in &names {
            let (direct, has_route) =
                collect_direct_component_dependencies(protocol, name, component_index);
            dependencies.push(direct.into_boxed_slice());
            route_dependent.push(has_route);
        }
        propagate_route_dependencies(&dependencies, &mut route_dependent);
        let (hydration_keys, hydration_key_ids, hydration_runs) =
            intern_hydration_projections(protocol, &names);

        Self {
            names,
            dependencies,
            route_dependent,
            hydration_keys,
            hydration_key_ids,
            hydration_runs,
        }
    }

    pub(crate) fn name(&self, index: u32) -> Option<&str> {
        self.names.get(index as usize).map(String::as_str)
    }

    pub(crate) fn dependencies(&self, index: u32) -> Option<&[u32]> {
        self.dependencies.get(index as usize).map(Box::as_ref)
    }

    pub(crate) fn is_route_dependent(&self, index: u32) -> Option<bool> {
        self.route_dependent.get(index as usize).copied()
    }

    pub(crate) fn requires_expansion(&self, index: u32) -> Option<bool> {
        Some(self.is_route_dependent(index)? || !self.dependencies.get(index as usize)?.is_empty())
    }

    /// Resolve one interned hydration key ID.
    pub(crate) fn hydration_key(&self, id: u32) -> Option<&str> {
        self.hydration_keys.get(id as usize).map(Box::as_ref)
    }

    /// Append one component's hydration key IDs to `ids`.
    ///
    /// Returns `true` when the component's compiled surface requires full
    /// state, in which case `ids` is meaningless for this record.
    pub(crate) fn extend_hydration_keys(&self, index: u32, ids: &mut Vec<u32>) -> bool {
        let Some(run) = self.hydration_runs.get(index as usize).copied() else {
            return true;
        };
        if run.requires_full_state() {
            return true;
        }
        let start = run.start as usize;
        let end = start.saturating_add(run.len as usize);
        match self.hydration_key_ids.get(start..end) {
            Some(run) => ids.extend_from_slice(run),
            None => return true,
        }
        false
    }
}

/// Intern every component's compiled hydration projection into lexicographic
/// key IDs plus one flat run per component.
fn intern_hydration_projections(
    protocol: &WebUIProtocol,
    names: &[String],
) -> (Vec<Box<str>>, Vec<u32>, Vec<HydrationRun>) {
    let mut distinct: Vec<&str> = Vec::new();
    for name in names {
        if let Some(component) = protocol.components.get(name) {
            distinct.extend(component.hydration_keys.iter().map(String::as_str));
        }
    }
    distinct.sort_unstable();
    distinct.dedup();
    let keys: Vec<Box<str>> = distinct.iter().map(|key| Box::from(*key)).collect();

    let mut key_ids = Vec::new();
    let mut runs = Vec::with_capacity(names.len());
    for name in names {
        let Some(component) = protocol.components.get(name) else {
            // A component with no compiled surface cannot be projected, exactly
            // as the name-based collector treated a missing entry.
            runs.push(HydrationRun::FULL_STATE);
            continue;
        };
        let mode = component.hydration_mode;
        let component_keys = &component.hydration_keys;
        let projects_keys = mode == StateProjectionMode::Keys as i32
            || (mode == StateProjectionMode::None as i32 && !component_keys.is_empty());
        if mode == StateProjectionMode::All as i32
            || (!projects_keys && mode != StateProjectionMode::None as i32)
        {
            runs.push(HydrationRun::FULL_STATE);
            continue;
        }
        let start = key_ids.len();
        if projects_keys {
            for key in component_keys {
                if let Ok(position) = distinct.binary_search(&key.as_str()) {
                    if let Ok(id) = u32::try_from(position) {
                        key_ids.push(id);
                    }
                }
            }
        }
        match (u32::try_from(start), u32::try_from(key_ids.len() - start)) {
            (Ok(start), Ok(len)) if len != u32::MAX => runs.push(HydrationRun { start, len }),
            _ => runs.push(HydrationRun::FULL_STATE),
        }
    }
    (keys, key_ids, runs)
}

enum ComponentDependencyWork<'a> {
    Fragment(&'a str),
    Component(u32),
}

fn collect_direct_component_dependencies(
    protocol: &WebUIProtocol,
    root: &str,
    component_index: &HashMap<String, u32>,
) -> (Vec<u32>, bool) {
    let mut work = vec![ComponentDependencyWork::Fragment(root)];
    let mut visited_fragments = HashSet::new();
    let mut seen_components = HashSet::new();
    let mut dependencies = Vec::new();
    let mut has_route = false;

    while let Some(item) = work.pop() {
        match item {
            ComponentDependencyWork::Component(index) => {
                if seen_components.insert(index) {
                    dependencies.push(index);
                }
            }
            ComponentDependencyWork::Fragment(id) => {
                if !visited_fragments.insert(id) {
                    continue;
                }
                let Some(list) = protocol.fragments.get(id) else {
                    continue;
                };
                for fragment in list.fragments.iter().rev() {
                    match fragment.fragment.as_ref() {
                        Some(Fragment::Component(component)) => {
                            if let Some(&index) = component_index.get(&component.fragment_id) {
                                work.push(ComponentDependencyWork::Component(index));
                            }
                        }
                        Some(Fragment::ForLoop(for_loop)) => work.push(
                            ComponentDependencyWork::Fragment(for_loop.fragment_id.as_str()),
                        ),
                        Some(Fragment::IfCond(if_cond)) => work.push(
                            ComponentDependencyWork::Fragment(if_cond.fragment_id.as_str()),
                        ),
                        Some(Fragment::Attribute(attribute)) if !attribute.template.is_empty() => {
                            work.push(ComponentDependencyWork::Fragment(
                                attribute.template.as_str(),
                            ));
                        }
                        Some(Fragment::Route(_)) => has_route = true,
                        _ => {}
                    }
                }
            }
        }
    }

    (dependencies, has_route)
}

fn propagate_route_dependencies(dependencies: &[Box<[u32]>], route_dependent: &mut [bool]) {
    let mut reverse = vec![Vec::new(); dependencies.len()];
    for (parent, children) in dependencies.iter().enumerate() {
        for &child in children.iter() {
            if let Some(parents) = reverse.get_mut(child as usize) {
                #[allow(clippy::cast_possible_truncation)]
                parents.push(parent as u32);
            }
        }
    }

    let mut pending = Vec::new();
    for (index, &depends_on_route) in route_dependent.iter().enumerate() {
        if depends_on_route {
            #[allow(clippy::cast_possible_truncation)]
            pending.push(index as u32);
        }
    }
    while let Some(index) = pending.pop() {
        let Some(parents) = reverse.get(index as usize) else {
            continue;
        };
        for &parent in parents {
            let Some(depends_on_route) = route_dependent.get_mut(parent as usize) else {
                continue;
            };
            if !*depends_on_route {
                *depends_on_route = true;
                pending.push(parent);
            }
        }
    }
}

/// Check if a component's bit is set in the inventory bitfield.
fn has_component(inventory: &[u8], index: u32) -> bool {
    let byte_idx = (index / 8) as usize;
    let bit_idx = index % 8;
    byte_idx < inventory.len() && inventory[byte_idx] & (1 << bit_idx) != 0
}

/// Set a component's bit in the inventory bitfield.
fn set_component(inventory: &mut Vec<u8>, index: u32) {
    let byte_idx = (index / 8) as usize;
    let bit_idx = index % 8;
    if byte_idx >= inventory.len() {
        inventory.resize(byte_idx + 1, 0);
    }
    inventory[byte_idx] |= 1 << bit_idx;
}

/// Parse a hex-encoded inventory string into bytes.
///
/// Returns an error if the hex string has odd length or contains non-hex characters.
pub fn parse_inventory(hex: &str) -> Result<Vec<u8>, HandlerError> {
    if hex.is_empty() {
        return Ok(Vec::new());
    }
    if !hex.len().is_multiple_of(2) {
        return Err(HandlerError::Protocol(
            webui_protocol::ProtocolError::Validation(format!(
                "inventory hex has odd length: {}",
                hex.len()
            )),
        ));
    }
    let mut bytes = Vec::with_capacity(hex.len() / 2);
    let mut chars = hex.bytes();
    while let (Some(hi), Some(lo)) = (chars.next(), chars.next()) {
        let h = route_matcher::hex_val(hi).ok_or_else(|| {
            HandlerError::Protocol(webui_protocol::ProtocolError::Validation(format!(
                "invalid hex digit in inventory: {:#04x}",
                hi
            )))
        })?;
        let l = route_matcher::hex_val(lo).ok_or_else(|| {
            HandlerError::Protocol(webui_protocol::ProtocolError::Validation(format!(
                "invalid hex digit in inventory: {:#04x}",
                lo
            )))
        })?;
        bytes.push((h << 4) | l);
    }
    Ok(bytes)
}

/// Encode an inventory bitfield as a hex string.
pub fn encode_inventory(inv: &[u8]) -> String {
    const HEX: &[u8; 16] = b"0123456789abcdef";
    let mut encoded = String::with_capacity(inv.len() * 2);
    for byte in inv {
        encoded.push(char::from(HEX[usize::from(byte >> 4)]));
        encoded.push(char::from(HEX[usize::from(byte & 0x0f)]));
    }
    encoded
}

/// Encode the inventory bitfield for a known set of rendered components.
pub(crate) fn encode_component_inventory(
    component_names: &HashSet<String>,
    index: &HashMap<String, u32>,
) -> String {
    let mut inventory = Vec::new();
    for name in component_names {
        if let Some(&idx) = index.get(name.as_str()) {
            set_component(&mut inventory, idx);
        }
    }
    encode_inventory(&inventory)
}

/// Walk the protocol fragment graph from `entry_id` and return the names of
/// all components the route needs that are NOT in the client's inventory.
///
/// Returns `(needed_names, updated_inventory_hex)`.
pub fn get_needed_components(
    protocol: &WebUIProtocol,
    entry_id: &str,
    inventory_hex: &str,
    component_index: &HashMap<String, u32>,
) -> Result<(Vec<String>, String), HandlerError> {
    let route_index = CompiledRouteIndex::new(protocol);
    let component_names =
        collect_inventoryable_components(protocol, entry_id, None, true, &route_index);
    filter_needed_components(&component_names, inventory_hex, component_index)
}

/// Walk the protocol from the persistent `entry_id` and return the component
/// templates needed for the current `request_path`.
///
/// Returns `(needed_names, updated_inventory_hex)`.
#[cfg(test)]
pub(crate) fn get_needed_components_for_request(
    protocol: &WebUIProtocol,
    entry_id: &str,
    request_path: &str,
    inventory_hex: &str,
    indexes: (&HashMap<String, u32>, &CompiledRouteIndex),
) -> Result<(Vec<String>, String), HandlerError> {
    let (component_index, route_index) = indexes;
    let component_names = collect_inventoryable_components(
        protocol,
        entry_id,
        Some(request_path),
        false,
        route_index,
    );
    filter_needed_components(&component_names, inventory_hex, component_index)
}

fn serialize_partial_response(
    response: Value,
    state_json: &str,
    state_selection: &StateSelection<'_>,
) -> Result<String, HandlerError> {
    let state = select_raw_state(state_json, state_selection)?;
    let response = PartialResponseWithState::new(response, state)?;
    serde_json::to_string(&response).map_err(|error| partial_serialize_error(&error.to_string()))
}

fn validate_json(json: &str) -> Result<(), HandlerError> {
    validate_json_inner(json).map_err(|error| invalid_state_json(&error.to_string()))
}

fn validate_json_inner(json: &str) -> serde_json::Result<()> {
    let mut deserializer = serde_json::Deserializer::from_str(json);
    ValidJson
        .deserialize(&mut deserializer)
        .and_then(|_| deserializer.end())
}

struct ValidJson;

impl<'de> DeserializeSeed<'de> for ValidJson {
    type Value = ();

    fn deserialize<D>(self, deserializer: D) -> std::result::Result<(), D::Error>
    where
        D: serde::Deserializer<'de>,
    {
        deserializer.deserialize_any(ValidJsonVisitor)
    }
}

struct ValidJsonVisitor;

impl<'de> Visitor<'de> for ValidJsonVisitor {
    type Value = ();

    fn expecting(&self, formatter: &mut fmt::Formatter<'_>) -> fmt::Result {
        formatter.write_str("valid JSON")
    }

    fn visit_bool<E>(self, _value: bool) -> std::result::Result<(), E> {
        Ok(())
    }

    fn visit_i64<E>(self, _value: i64) -> std::result::Result<(), E> {
        Ok(())
    }

    fn visit_u64<E>(self, _value: u64) -> std::result::Result<(), E> {
        Ok(())
    }

    fn visit_f64<E>(self, value: f64) -> std::result::Result<(), E>
    where
        E: serde::de::Error,
    {
        if value.is_finite() {
            Ok(())
        } else {
            Err(E::custom("number out of range"))
        }
    }

    fn visit_str<E>(self, _value: &str) -> std::result::Result<(), E> {
        Ok(())
    }

    fn visit_borrowed_str<E>(self, _value: &'de str) -> std::result::Result<(), E> {
        Ok(())
    }

    fn visit_string<E>(self, _value: String) -> std::result::Result<(), E> {
        Ok(())
    }

    fn visit_unit<E>(self) -> std::result::Result<(), E> {
        Ok(())
    }

    fn visit_none<E>(self) -> std::result::Result<(), E> {
        Ok(())
    }

    fn visit_some<D>(self, deserializer: D) -> std::result::Result<(), D::Error>
    where
        D: serde::Deserializer<'de>,
    {
        ValidJson.deserialize(deserializer)
    }

    fn visit_seq<A>(self, mut sequence: A) -> std::result::Result<(), A::Error>
    where
        A: SeqAccess<'de>,
    {
        while sequence.next_element_seed(ValidJson)?.is_some() {}
        Ok(())
    }

    fn visit_map<A>(self, mut map: A) -> std::result::Result<(), A::Error>
    where
        A: MapAccess<'de>,
    {
        while map.next_key::<IgnoredAny>()?.is_some() {
            map.next_value_seed(ValidJson)?;
        }
        Ok(())
    }
}

struct PartialResponseWithState<State> {
    response: Map<String, Value>,
    state: State,
}

impl<State> PartialResponseWithState<State> {
    fn new(response: Value, state: State) -> Result<Self, HandlerError> {
        let Value::Object(response) = response else {
            return Err(partial_response_not_object());
        };
        Ok(Self { response, state })
    }
}

impl<State: Serialize> Serialize for PartialResponseWithState<State> {
    fn serialize<S>(&self, serializer: S) -> std::result::Result<S::Ok, S::Error>
    where
        S: serde::Serializer,
    {
        let mut map = serializer.serialize_map(Some(self.response.len().saturating_add(1)))?;
        for (key, value) in &self.response {
            map.serialize_entry(key, value)?;
        }
        map.serialize_entry("state", &self.state)?;
        map.end()
    }
}

struct ProjectedRawState<'de> {
    entries: Vec<(Cow<'de, str>, &'de RawValue)>,
}

enum SelectedRawState<'de> {
    Full(&'de RawValue),
    Keys(ProjectedRawState<'de>),
}
impl Serialize for SelectedRawState<'_> {
    fn serialize<S>(&self, serializer: S) -> std::result::Result<S::Ok, S::Error>
    where
        S: serde::Serializer,
    {
        match self {
            Self::Full(state) => state.serialize(serializer),
            Self::Keys(state) => state.serialize(serializer),
        }
    }
}

impl Serialize for ProjectedRawState<'_> {
    fn serialize<S>(&self, serializer: S) -> std::result::Result<S::Ok, S::Error>
    where
        S: serde::Serializer,
    {
        let mut map = serializer.serialize_map(Some(self.entries.len()))?;
        for (key, value) in &self.entries {
            map.serialize_entry(key.as_ref(), value)?;
        }
        map.end()
    }
}

fn project_raw_state<'de>(
    state_json: &'de str,
    state_keys: &[&str],
) -> Result<ProjectedRawState<'de>, HandlerError> {
    let is_object = state_json
        .as_bytes()
        .iter()
        .find(|byte| !byte.is_ascii_whitespace())
        .is_some_and(|byte| *byte == b'{');
    if !is_object {
        validate_json(state_json)?;
        return Ok(ProjectedRawState {
            entries: Vec::new(),
        });
    }

    let mut deserializer = serde_json::Deserializer::from_str(state_json);
    let mut state = ProjectedRawStateSeed { state_keys }
        .deserialize(&mut deserializer)
        .and_then(|state| {
            deserializer.end()?;
            Ok(state)
        })
        .map_err(|error| invalid_state_json(&error.to_string()))?;
    state.entries.sort_unstable_by(|left, right| {
        left.0.as_ref().as_bytes().cmp(right.0.as_ref().as_bytes())
    });
    Ok(state)
}

fn select_raw_state<'de>(
    state_json: &'de str,
    selection: &StateSelection<'_>,
) -> Result<SelectedRawState<'de>, HandlerError> {
    let state_keys = match selection {
        StateSelection::Full => {
            // The reserved inject key carries host HTML, never application
            // state, so it must not reach the client here either. The
            // candidate probe keeps the overwhelmingly common case - no
            // reserved key - on the zero-copy passthrough.
            if contains_reserved_state_key(state_json) {
                return strip_reserved_raw_state(state_json).map(SelectedRawState::Keys);
            }
            return serde_json::from_str::<&RawValue>(state_json)
                .map(SelectedRawState::Full)
                .map_err(|error| invalid_state_json(&error.to_string()));
        }
        StateSelection::Keys(keys) => keys.as_slice(),
        // Key-ID projections are produced only by the streaming continuation,
        // which serializes through `write_selected_state` and never reaches
        // partial navigation's raw-JSON projection.
        StateSelection::KeyIds(_) | StateSelection::FullExceptKeyIds(_) => {
            return Err(unexpected_key_id_selection());
        }
    };
    project_raw_state(state_json, state_keys).map(SelectedRawState::Keys)
}

/// Detect literal or Unicode-escaped spellings of the top-level reserved key.
///
/// The fast candidate scan preserves the common no-match path. Structural
/// depth is checked only when a candidate exists, so nested application keys
/// do not force full-state reserialization.
fn contains_reserved_state_key(state_json: &str) -> bool {
    let bytes = state_json.as_bytes();
    let mut search_start = 0;
    while let Some(relative_index) = memchr2(b'$', b'\\', &bytes[search_start..]) {
        let candidate = search_start + relative_index;
        if candidate > 0
            && bytes[candidate - 1] == b'"'
            && matches_reserved_state_key(bytes, candidate)
        {
            return contains_top_level_reserved_state_key(bytes);
        }
        search_start = candidate + 1;
    }
    false
}

fn contains_top_level_reserved_state_key(bytes: &[u8]) -> bool {
    let Some(mut cursor) = bytes.iter().position(|byte| !byte.is_ascii_whitespace()) else {
        return false;
    };
    if bytes[cursor] != b'{' {
        return false;
    }

    cursor += 1;
    let mut depth = 1;
    while cursor < bytes.len() {
        match bytes[cursor] {
            b'"' => {
                if depth == 1 && matches_reserved_state_key(bytes, cursor + 1) {
                    return true;
                }
                cursor = skip_json_string(bytes, cursor + 1);
            }
            b'{' | b'[' => {
                depth += 1;
                cursor += 1;
            }
            b'}' | b']' => {
                depth -= 1;
                if depth == 0 {
                    return false;
                }
                cursor += 1;
            }
            _ => cursor += 1,
        }
    }
    false
}

fn skip_json_string(bytes: &[u8], mut cursor: usize) -> usize {
    while let Some(relative_index) = memchr2(b'"', b'\\', &bytes[cursor..]) {
        cursor += relative_index;
        if bytes[cursor] == b'"' {
            return cursor + 1;
        }
        cursor = (cursor + 2).min(bytes.len());
    }
    bytes.len()
}

fn matches_reserved_state_key(bytes: &[u8], mut cursor: usize) -> bool {
    for expected in crate::STATE_INJECT_KEY.bytes() {
        if bytes.get(cursor).is_some_and(|byte| *byte == expected) {
            cursor += 1;
        } else if matches_unicode_escape(bytes, cursor, expected) {
            cursor += 6;
        } else {
            return false;
        }
    }

    if bytes.get(cursor) != Some(&b'"') {
        return false;
    }
    cursor += 1;
    while bytes.get(cursor).is_some_and(u8::is_ascii_whitespace) {
        cursor += 1;
    }
    bytes.get(cursor) == Some(&b':')
}

fn matches_unicode_escape(bytes: &[u8], cursor: usize, expected: u8) -> bool {
    let Some(escape) = bytes.get(cursor..cursor.saturating_add(6)) else {
        return false;
    };
    escape[..4] == *b"\\u00"
        && decode_hex_nibble(escape[4]).is_some_and(|high| {
            decode_hex_nibble(escape[5]).is_some_and(|low| (high << 4) | low == expected)
        })
}

fn decode_hex_nibble(byte: u8) -> Option<u8> {
    match byte {
        b'0'..=b'9' => Some(byte - b'0'),
        b'a'..=b'f' => Some(byte - b'a' + 10),
        b'A'..=b'F' => Some(byte - b'A' + 10),
        _ => None,
    }
}

/// Re-emit a raw state object with the reserved inject key removed.
fn strip_reserved_raw_state(state_json: &str) -> Result<ProjectedRawState<'_>, HandlerError> {
    let mut deserializer = serde_json::Deserializer::from_str(state_json);
    let projected = ReservedFilteredRawStateSeed
        .deserialize(&mut deserializer)
        .map_err(|error| invalid_state_json(&error.to_string()))?;
    deserializer
        .end()
        .map_err(|error| invalid_state_json(&error.to_string()))?;
    Ok(projected)
}

struct ReservedFilteredRawStateSeed;

impl<'de> DeserializeSeed<'de> for ReservedFilteredRawStateSeed {
    type Value = ProjectedRawState<'de>;

    fn deserialize<D>(self, deserializer: D) -> std::result::Result<Self::Value, D::Error>
    where
        D: serde::Deserializer<'de>,
    {
        deserializer.deserialize_map(ReservedFilteredRawStateVisitor)
    }
}

struct ReservedFilteredRawStateVisitor;

impl<'de> Visitor<'de> for ReservedFilteredRawStateVisitor {
    type Value = ProjectedRawState<'de>;

    fn expecting(&self, formatter: &mut fmt::Formatter<'_>) -> fmt::Result {
        formatter.write_str("a JSON object")
    }

    fn visit_map<A>(self, mut map: A) -> std::result::Result<Self::Value, A::Error>
    where
        A: MapAccess<'de>,
    {
        let mut entries: Vec<(Cow<'de, str>, &'de RawValue)> = Vec::new();
        while let Some(key) = map.next_key_seed(BorrowedString)? {
            if key.as_ref() == crate::STATE_INJECT_KEY {
                map.next_value_seed(ValidJson)?;
                continue;
            }
            let value: &'de RawValue = map.next_value()?;
            validate_json_inner(value.get()).map_err(serde::de::Error::custom)?;
            entries.push((key, value));
        }
        Ok(ProjectedRawState { entries })
    }
}

struct ProjectedRawStateSeed<'a> {
    state_keys: &'a [&'a str],
}

impl<'de> DeserializeSeed<'de> for ProjectedRawStateSeed<'_> {
    type Value = ProjectedRawState<'de>;

    fn deserialize<D>(self, deserializer: D) -> std::result::Result<Self::Value, D::Error>
    where
        D: serde::Deserializer<'de>,
    {
        deserializer.deserialize_map(ProjectedRawStateVisitor {
            state_keys: self.state_keys,
        })
    }
}

struct ProjectedRawStateVisitor<'a> {
    state_keys: &'a [&'a str],
}

impl<'de> Visitor<'de> for ProjectedRawStateVisitor<'_> {
    type Value = ProjectedRawState<'de>;

    fn expecting(&self, formatter: &mut fmt::Formatter<'_>) -> fmt::Result {
        formatter.write_str("a JSON object")
    }

    fn visit_map<A>(self, mut map: A) -> std::result::Result<Self::Value, A::Error>
    where
        A: MapAccess<'de>,
    {
        let mut entries: Vec<(Cow<'de, str>, &'de RawValue)> =
            Vec::with_capacity(self.state_keys.len());
        while let Some(key) = map.next_key_seed(BorrowedString)? {
            if key.as_ref() == crate::STATE_INJECT_KEY
                || self.state_keys.binary_search(&key.as_ref()).is_err()
            {
                map.next_value_seed(ValidJson)?;
                continue;
            }

            let value: &'de RawValue = map.next_value()?;
            validate_json_inner(value.get()).map_err(serde::de::Error::custom)?;
            if let Some(entry) = entries
                .iter_mut()
                .find(|(existing, _)| existing.as_ref() == key.as_ref())
            {
                *entry = (key, value);
            } else {
                entries.push((key, value));
            }
        }
        Ok(ProjectedRawState { entries })
    }
}

struct BorrowedString;

impl<'de> DeserializeSeed<'de> for BorrowedString {
    type Value = Cow<'de, str>;

    fn deserialize<D>(self, deserializer: D) -> std::result::Result<Self::Value, D::Error>
    where
        D: serde::Deserializer<'de>,
    {
        deserializer.deserialize_str(BorrowedStringVisitor)
    }
}

struct BorrowedStringVisitor;

impl<'de> Visitor<'de> for BorrowedStringVisitor {
    type Value = Cow<'de, str>;

    fn expecting(&self, formatter: &mut fmt::Formatter<'_>) -> fmt::Result {
        formatter.write_str("a string")
    }

    fn visit_borrowed_str<E>(self, value: &'de str) -> std::result::Result<Self::Value, E> {
        Ok(Cow::Borrowed(value))
    }

    fn visit_str<E>(self, value: &str) -> std::result::Result<Self::Value, E> {
        Ok(Cow::Owned(value.to_owned()))
    }

    fn visit_string<E>(self, value: String) -> std::result::Result<Self::Value, E> {
        Ok(Cow::Owned(value))
    }
}

#[cold]
#[inline(never)]
fn invalid_state_json(message: &str) -> HandlerError {
    HandlerError::InvalidState(message.to_string())
}

#[cold]
#[inline(never)]
fn unexpected_key_id_selection() -> HandlerError {
    HandlerError::Invariant(
        "streaming hydration key-ID projection reached partial navigation".to_string(),
    )
}

#[cold]
#[inline(never)]
fn partial_serialize_error(message: &str) -> HandlerError {
    HandlerError::Rendering(format!("failed to serialize partial response: {message}"))
}

#[cold]
#[inline(never)]
fn partial_response_not_object() -> HandlerError {
    HandlerError::Invariant("partial response must serialize as a JSON object".to_string())
}

/// Collect request-reachable components in deterministic first-discovery order.
pub(crate) fn collect_reachable_component_order_for_request(
    protocol: &WebUIProtocol,
    entry_id: &str,
    request_path: &str,
    route_index: &CompiledRouteIndex,
) -> Vec<String> {
    collect_inventoryable_components(protocol, entry_id, Some(request_path), false, route_index)
}

/// Filter components against the client's inventory bitfield using sequential indices.
/// Zero collisions — each component has a unique bit.
///
/// Expects `component_names` to already be unique. Input order is preserved
/// in the returned `needed` vector (no alphabetical re-sort), so downstream
/// `<head>` CSS `<link>` emission follows document/traversal order. The
/// updated inventory hex is order-independent (bits are keyed by `index`).
///
/// Returns the missing component names and the updated inventory hex string.
pub fn filter_needed_components(
    component_names: &[String],
    inventory_hex: &str,
    index: &HashMap<String, u32>,
) -> Result<(Vec<String>, String), HandlerError> {
    let filtered = filter_components_with_inventory(component_names, inventory_hex, index)?;
    Ok((filtered.needed, filtered.updated_inventory))
}

struct FilteredComponents {
    needed: Vec<String>,
    updated_inventory: String,
    client_inventory: Vec<u8>,
}

fn filter_components_with_inventory(
    component_names: &[String],
    inventory_hex: &str,
    index: &HashMap<String, u32>,
) -> Result<FilteredComponents, HandlerError> {
    let client_inv = parse_inventory(inventory_hex)?;
    let mut updated_inv = client_inv.clone();

    let mut needed = Vec::with_capacity(component_names.len());
    for name in component_names {
        if let Some(&idx) = index.get(name.as_str()) {
            if !has_component(&client_inv, idx) {
                needed.push(name.clone());
            }
            set_component(&mut updated_inv, idx);
        } else {
            // Component exists in the fragment graph but has no index entry
            // (no protocol.components record). It can't be tracked in the
            // bitfield, so we must always send it.
            needed.push(name.clone());
        }
    }

    Ok(FilteredComponents {
        needed,
        updated_inventory: encode_inventory(&updated_inv),
        client_inventory: client_inv,
    })
}

fn has_template_payload(component: &webui_protocol::ComponentData) -> bool {
    !component.template_json.is_empty() || !component.template.is_empty()
}

#[derive(Debug)]
/// Interning arena for the route-base paths produced during a graph walk.
///
/// A walk queues one entry per graph edge but descends through only a handful
/// of nested route levels, so every queued fragment used to carry its own
/// `String` copy of a path shared by many siblings. Storing each distinct base
/// once and referencing it by index makes [`QueuedFragment`] `Copy` and removes
/// a heap allocation per queued edge.
struct RouteBaseArena {
    bases: Vec<String>,
}

impl RouteBaseArena {
    /// Index of the implicit `/` root base, present in every arena.
    const ROOT: u32 = 0;

    fn new() -> Self {
        Self {
            bases: vec!["/".to_string()],
        }
    }

    /// Position of `base` when it has already been interned.
    ///
    /// The linear scan is deliberate: route nesting is shallow (a handful of
    /// levels), so scanning beats hashing and keeps the arena allocation-free
    /// after the first sighting of each level.
    fn find(&self, base: &str) -> Option<u32> {
        // Arena length is bounded by route nesting depth.
        #[allow(clippy::cast_possible_truncation)]
        self.bases
            .iter()
            .position(|known| known == base)
            .map(|position| position as u32)
    }

    #[allow(clippy::cast_possible_truncation)]
    fn push(&mut self, base: String) -> u32 {
        let id = self.bases.len() as u32;
        self.bases.push(base);
        id
    }

    /// Intern a borrowed `base`, reusing an existing slot when already known.
    ///
    /// Use [`Self::intern_owned`] when the caller already owns the path, so a
    /// first sighting moves it instead of copying it.
    fn intern(&mut self, base: &str) -> u32 {
        match self.find(base) {
            Some(id) => id,
            None => self.push(base.to_string()),
        }
    }

    /// Intern an owned `base`, moving it in on first sighting.
    ///
    /// `route_matcher::compute_route_base` already returns an owned `String`,
    /// so taking it by value keeps a newly discovered level to the one
    /// allocation the caller had to make anyway.
    fn intern_owned(&mut self, base: String) -> u32 {
        match self.find(&base) {
            Some(id) => id,
            None => self.push(base),
        }
    }

    fn get(&self, id: u32) -> &str {
        self.bases.get(id as usize).map_or("/", String::as_str)
    }
}

/// One pending node in a fragment-graph walk.
///
/// `id` borrows the protocol's fragment name and `route_base` indexes a
/// [`RouteBaseArena`], so queueing an edge copies 16 bytes instead of
/// allocating two `String`s.
#[derive(Clone, Copy)]
struct QueuedFragment<'protocol> {
    id: &'protocol str,
    inventoryable: bool,
    /// Base path for resolving relative route paths at this level.
    route_base: u32,
}

/// Key identifying an already-walked fragment.
///
/// Route-insensitive walks collapse every base into `None` so a fragment is
/// visited once regardless of the path that reached it.
type VisitedKey<'protocol> = (&'protocol str, Option<u32>);

#[inline]
fn mark_fragment_visited<'protocol>(
    visited: &mut HashSet<VisitedKey<'protocol>>,
    queued: &QueuedFragment<'protocol>,
    route_sensitive: bool,
) -> bool {
    visited.insert((queued.id, route_sensitive.then_some(queued.route_base)))
}

/// Shared context for route child walkers, bundling common parameters
/// to stay within the 5-argument clippy limit.
struct ChildWalkCtx<'a> {
    request_path: &'a str,
    protocol: &'a WebUIProtocol,
    route_index: &'a CompiledRouteIndex,
}

/// Walk the fragment graph from `entry_id` and collect all inventoryable
/// component names in document/traversal (first-discovery) order.
///
/// Uses an iterative stack-based traversal. When `request_path` is provided,
/// the walk follows only the best-matching route at each nesting level (route-aware).
/// Without a request path, all route branches are followed conservatively.
///
/// Components are marked `inventoryable` when they have a corresponding entry
/// in `protocol.components` with a non-empty template payload — these are the
/// components whose client metadata the browser may need during navigation.
fn collect_inventoryable_components<'protocol>(
    protocol: &'protocol WebUIProtocol,
    entry_id: &'protocol str,
    request_path: Option<&str>,
    root_inventoryable: bool,
    route_index: &CompiledRouteIndex,
) -> Vec<String> {
    let mut arena = RouteBaseArena::new();
    let stack = vec![QueuedFragment {
        id: entry_id,
        inventoryable: root_inventoryable,
        route_base: RouteBaseArena::ROOT,
    }];
    collect_inventoryable_components_from_stack(
        protocol,
        request_path,
        route_index,
        stack,
        &mut arena,
    )
}

/// Collect the transitive client component surface rooted in this checkpoint's
/// rendered tags. Conditional and empty-repeat branches are followed
/// conservatively so a later client-side state change already has its metadata.
///
/// Roots arrive as startup-built component indexes so the caller's capture stays
/// free of any protocol borrow; names are resolved here, on the uncommon
/// request-aware path that already converts every root to an owned string.
pub(crate) fn collect_reachable_components_from_roots<'protocol>(
    protocol: &'protocol WebUIProtocol,
    roots: &[(u32, Option<Box<str>>)],
    reachability: &'protocol ComponentReachabilityIndex,
    request_path: &str,
    route_index: &CompiledRouteIndex,
) -> Vec<String> {
    let mut arena = RouteBaseArena::new();
    let mut stack = Vec::with_capacity(roots.len());
    for (root, route_base) in roots.iter().rev() {
        let Some(name) = reachability.name(*root) else {
            continue;
        };
        let route_base = match route_base.as_deref() {
            Some(base) => arena.intern(base),
            None => RouteBaseArena::ROOT,
        };
        stack.push(QueuedFragment {
            id: name,
            inventoryable: true,
            route_base,
        });
    }
    collect_inventoryable_components_from_stack(
        protocol,
        Some(request_path),
        route_index,
        stack,
        &mut arena,
    )
}

fn collect_inventoryable_components_from_stack<'protocol>(
    protocol: &'protocol WebUIProtocol,
    request_path: Option<&str>,
    route_index: &CompiledRouteIndex,
    mut stack: Vec<QueuedFragment<'protocol>>,
    arena: &mut RouteBaseArena,
) -> Vec<String> {
    let mut visited_fragments = HashSet::new();
    let route_sensitive = request_path.is_some();
    // Preserve first-discovery (document/traversal) order so Link-strategy
    // CSS `<link>` tags are emitted in source order, not alphabetically.
    // `seen_components` dedups; `component_ids` keeps order (a plain
    // `HashSet` would lose it).
    let mut seen_components = HashSet::new();
    let mut component_ids: Vec<String> = Vec::new();
    while let Some(queued) = stack.pop() {
        if queued.id.is_empty() {
            continue;
        }

        if queued.inventoryable && seen_components.insert(queued.id) {
            component_ids.push(queued.id.to_string());
        }

        if !mark_fragment_visited(&mut visited_fragments, &queued, route_sensitive) {
            continue;
        }

        let Some(frag_list) = protocol.fragments.get(queued.id) else {
            continue;
        };

        let matched_route = request_path.and_then(|path| {
            route_renderer::find_best_route_match(
                &frag_list.fragments,
                path,
                arena.get(queued.route_base),
                route_index,
            )
        });

        // Reversed iteration so this LIFO stack pops children in document
        // order, giving deterministic, source-ordered component discovery.
        for frag in frag_list.fragments.iter().rev() {
            match frag.fragment.as_ref() {
                Some(Fragment::Component(component)) => {
                    stack.push(QueuedFragment {
                        id: &component.fragment_id,
                        inventoryable: true,
                        route_base: queued.route_base,
                    });
                }
                Some(Fragment::ForLoop(for_loop)) => {
                    stack.push(QueuedFragment {
                        id: &for_loop.fragment_id,
                        inventoryable: false,
                        route_base: queued.route_base,
                    });
                }
                Some(Fragment::IfCond(if_cond)) => {
                    stack.push(QueuedFragment {
                        id: &if_cond.fragment_id,
                        inventoryable: false,
                        route_base: queued.route_base,
                    });
                }

                Some(Fragment::Attribute(attr)) if !attr.template.is_empty() => {
                    stack.push(QueuedFragment {
                        id: &attr.template,
                        inventoryable: false,
                        route_base: queued.route_base,
                    });
                }
                Some(Fragment::Route(route_frag)) => {
                    let is_selected = matched_route
                        .as_ref()
                        .is_some_and(|(best_key, _)| best_key == route_frag.fragment_id.as_str());
                    if is_selected && !route_frag.content_fragment_id.is_empty() {
                        stack.push(QueuedFragment {
                            id: &route_frag.content_fragment_id,
                            inventoryable: false,
                            route_base: queued.route_base,
                        });
                    }
                    if is_selected && !route_frag.fragment_id.is_empty() {
                        // Compute new route base from consumed segments
                        let child_route_base = match (&matched_route, request_path) {
                            (Some((_, rm)), Some(path)) => arena.intern_owned(
                                route_matcher::compute_route_base(path, rm.consumed_segments),
                            ),
                            _ => queued.route_base,
                        };

                        stack.push(QueuedFragment {
                            id: &route_frag.fragment_id,
                            inventoryable: protocol
                                .components
                                .get(&route_frag.fragment_id)
                                .is_some_and(has_template_payload),
                            route_base: child_route_base,
                        });

                        // Inventory pending/error components for the entire
                        // route subtree, not just the matched chain. Pending UI
                        // renders while a (possibly unmatched) sibling route's
                        // partial is in flight, and error UI renders if that
                        // fetch fails, so the client must already hold these
                        // templates before — or without — a successful fetch for
                        // the target route.
                        collect_route_boundary_components(
                            std::slice::from_ref(route_frag),
                            child_route_base,
                            protocol,
                            &mut stack,
                        );

                        // Walk nested child routes to find the next matched level.
                        // This mirrors the handler's outlet rendering: match children
                        // against the request path and follow the matched chain.
                        if !route_frag.children.is_empty() {
                            if let Some(path) = request_path {
                                walk_route_children(
                                    &route_frag.children,
                                    child_route_base,
                                    &mut stack,
                                    arena,
                                    &ChildWalkCtx {
                                        request_path: path,
                                        protocol,
                                        route_index,
                                    },
                                );
                            }
                        }
                    }
                }
                _ => {}
            }
        }
    }

    component_ids
}

/// Select the best-matching child route among siblings by specificity.
///
/// Returns the index and match result of the highest-specificity match,
/// preserving first-match-wins for equal specificity (declaration order).
fn select_best_child_route(
    children: &[WebUIFragmentRoute],
    request_path: &str,
    route_base: &str,
    route_index: &CompiledRouteIndex,
) -> Option<(usize, route_matcher::RouteMatch)> {
    let request_segments = route_matcher::split_request_path(request_path);
    let mut best: Option<(usize, route_matcher::RouteMatch)> = None;
    for (idx, child) in children.iter().enumerate() {
        if let Some(m) = route_matcher::match_route_indexed_with_segments(
            route_index,
            &child.path,
            route_base,
            &request_segments,
            child.exact,
        ) {
            let is_better = best
                .as_ref()
                .is_none_or(|(_, prev)| m.specificity > prev.specificity);
            if is_better {
                best = Some((idx, m));
            }
        }
    }
    best
}

/// Walk nested route children to find matched routes and add their
/// components to the inventory stack. Mirrors the handler's outlet rendering.
fn walk_route_children<'protocol>(
    children: &'protocol [WebUIFragmentRoute],
    route_base: u32,
    stack: &mut Vec<QueuedFragment<'protocol>>,
    arena: &mut RouteBaseArena,
    ctx: &ChildWalkCtx<'_>,
) {
    let mut current = children;
    let mut base = route_base;

    loop {
        // Resolve the base before interning below so the arena's immutable
        // borrow ends before the mutable one begins.
        let matched =
            select_best_child_route(current, ctx.request_path, arena.get(base), ctx.route_index);
        let Some((idx, rm)) = matched else {
            break;
        };
        let Some(matched) = current.get(idx) else {
            break;
        };
        if matched.fragment_id.is_empty() {
            break;
        }

        let child_base = arena.intern_owned(route_matcher::compute_route_base(
            ctx.request_path,
            rm.consumed_segments,
        ));

        stack.push(QueuedFragment {
            id: &matched.fragment_id,
            inventoryable: ctx
                .protocol
                .components
                .get(&matched.fragment_id)
                .is_some_and(has_template_payload),
            route_base: child_base,
        });

        if !matched.pending_component.is_empty() {
            stack.push(QueuedFragment {
                id: &matched.pending_component,
                inventoryable: ctx
                    .protocol
                    .components
                    .get(&matched.pending_component)
                    .is_some_and(has_template_payload),
                route_base: child_base,
            });
        }
        if !matched.error_component.is_empty() {
            stack.push(QueuedFragment {
                id: &matched.error_component,
                inventoryable: ctx
                    .protocol
                    .components
                    .get(&matched.error_component)
                    .is_some_and(has_template_payload),
                route_base: child_base,
            });
        }

        if matched.children.is_empty() {
            break;
        }
        current = &matched.children;
        base = child_base;
    }
}

/// Inventory the pending/error boundary components for an entire route subtree.
///
/// Unlike [`walk_route_children`], which follows only the best-matching chain,
/// this collects boundary components for *every* route reachable from `routes`.
/// Pending UI renders while a route's partial fetch is in flight and error UI
/// renders if that fetch fails, so the client must already hold these templates
/// for any navigable sibling — not only the currently active route. The walk is
/// iterative because the framework forbids recursion in core paths.
fn collect_route_boundary_components<'protocol>(
    routes: &'protocol [WebUIFragmentRoute],
    route_base: u32,
    protocol: &WebUIProtocol,
    stack: &mut Vec<QueuedFragment<'protocol>>,
) {
    let mut remaining: Vec<&'protocol WebUIFragmentRoute> = routes.iter().collect();
    while let Some(route) = remaining.pop() {
        for component in [&route.pending_component, &route.error_component] {
            if component.is_empty() {
                continue;
            }
            stack.push(QueuedFragment {
                id: component,
                inventoryable: protocol
                    .components
                    .get(component)
                    .is_some_and(has_template_payload),
                route_base,
            });
        }
        remaining.extend(route.children.iter());
    }
}

/// Walk the fragment graph following matched routes and collect all route
/// parameters from every level of the active route chain.
///
/// This is used by the dev server to inject nested route params into state.
pub fn collect_nested_route_params(
    protocol: &Protocol,
    entry_id: &str,
    request_path: &str,
) -> HashMap<String, String> {
    let route_index = protocol.route_index();
    let protocol = protocol.protocol();
    let mut all_params = HashMap::new();
    let mut visited_fragments = HashSet::new();
    let mut arena = RouteBaseArena::new();
    let mut stack = vec![QueuedFragment {
        id: entry_id,
        inventoryable: false,
        route_base: RouteBaseArena::ROOT,
    }];

    while let Some(queued) = stack.pop() {
        if queued.id.is_empty() || !mark_fragment_visited(&mut visited_fragments, &queued, true) {
            continue;
        }

        let Some(frag_list) = protocol.fragments.get(queued.id) else {
            continue;
        };

        let matched_route = route_renderer::find_best_route_match(
            &frag_list.fragments,
            request_path,
            arena.get(queued.route_base),
            route_index,
        );

        for frag in &frag_list.fragments {
            match frag.fragment.as_ref() {
                Some(Fragment::Component(component)) => {
                    stack.push(QueuedFragment {
                        id: &component.fragment_id,
                        inventoryable: false,
                        route_base: queued.route_base,
                    });
                }
                Some(Fragment::ForLoop(for_loop)) => {
                    stack.push(QueuedFragment {
                        id: &for_loop.fragment_id,
                        inventoryable: false,
                        route_base: queued.route_base,
                    });
                }
                Some(Fragment::IfCond(if_cond)) => {
                    stack.push(QueuedFragment {
                        id: &if_cond.fragment_id,
                        inventoryable: false,
                        route_base: queued.route_base,
                    });
                }

                Some(Fragment::Route(route_frag)) => {
                    let is_selected = matched_route
                        .as_ref()
                        .is_some_and(|(best_key, _)| best_key == route_frag.fragment_id.as_str());
                    if is_selected && !route_frag.fragment_id.is_empty() {
                        if let Some((_, ref rm)) = matched_route {
                            // Collect params from this route level. Cloning
                            // entry-wise avoids allocating a throwaway map to
                            // move them out of.
                            for (name, value) in &rm.params {
                                all_params.insert(name.clone(), value.clone());
                            }

                            let child_route_base =
                                arena.intern_owned(route_matcher::compute_route_base(
                                    request_path,
                                    rm.consumed_segments,
                                ));

                            stack.push(QueuedFragment {
                                id: &route_frag.fragment_id,
                                inventoryable: false,
                                route_base: child_route_base,
                            });

                            // Walk nested children to collect params from deeper levels
                            collect_params_from_children(
                                &route_frag.children,
                                request_path,
                                arena.get(child_route_base),
                                &mut all_params,
                                route_index,
                            );
                        }
                    }
                }
                _ => {}
            }
        }
    }

    all_params
}

/// Iteratively collect route params from nested route children.
fn collect_params_from_children(
    children: &[WebUIFragmentRoute],
    request_path: &str,
    route_base: &str,
    all_params: &mut HashMap<String, String>,
    route_index: &CompiledRouteIndex,
) {
    let mut current = children;
    let mut base = route_base.to_string();

    while let Some((idx, rm)) = select_best_child_route(current, request_path, &base, route_index) {
        all_params.extend(rm.params);
        let matched = &current[idx];
        if matched.children.is_empty() {
            break;
        }
        let child_base = route_matcher::compute_route_base(request_path, rm.consumed_segments);
        current = &matched.children;
        base = child_base;
    }
}

// ── Partial Response ────────────────────────────────────────────────

/// Resolve `{param}` placeholders in a list of tag templates.
///
/// Replaces `{paramName}` with the actual value from `params`.
/// Tags without placeholders are returned as-is. Missing params
/// result in the placeholder being left unresolved (defensive).
fn resolve_tag_templates(templates: &[String], params: &HashMap<String, String>) -> Vec<String> {
    let mut resolved = Vec::with_capacity(templates.len());
    for template in templates {
        if !template.contains('{') {
            resolved.push(template.clone());
            continue;
        }
        let mut result = String::with_capacity(template.len());
        let mut rest = template.as_str();
        while let Some(open) = rest.find('{') {
            result.push_str(&rest[..open]);
            rest = &rest[open + 1..];
            if let Some(close) = rest.find('}') {
                let name = &rest[..close];
                if let Some(value) = params.get(name) {
                    result.push_str(value);
                } else {
                    result.push('{');
                    result.push_str(name);
                    result.push('}');
                }
                rest = &rest[close + 1..];
            } else {
                result.push('{');
            }
        }
        result.push_str(rest);
        resolved.push(result);
    }
    resolved
}

/// Single-pass graph walk that collects both inventoryable component names
/// and the matched route chain. Eliminates the duplicate graph traversal
/// that previously existed in `render_partial`.
fn collect_inventory_and_chain<'protocol>(
    protocol: &'protocol WebUIProtocol,
    entry_id: &'protocol str,
    request_path: &str,
    index: &mut RequestProtocolIndex<'_>,
) -> (Vec<String>, Vec<RouteChainEntry>) {
    let mut visited_fragments = HashSet::new();
    // Deduped ordered collection: `filter_needed_components` now takes a
    // slice of unique names. Order is irrelevant for this consumer
    // (`render_partial` re-sorts in `collect_component_assets`), but the
    // list must stay duplicate-free.
    let mut seen_components = HashSet::new();
    let mut component_ids: Vec<String> = Vec::new();
    let mut chain = Vec::new();
    let mut arena = RouteBaseArena::new();
    let mut stack = vec![QueuedFragment {
        id: entry_id,
        inventoryable: false,
        route_base: RouteBaseArena::ROOT,
    }];

    while let Some(queued) = stack.pop() {
        if queued.id.is_empty() {
            continue;
        }

        if queued.inventoryable && seen_components.insert(queued.id) {
            component_ids.push(queued.id.to_string());
        }

        if !mark_fragment_visited(&mut visited_fragments, &queued, true) {
            continue;
        }

        let Some(frag_list) = protocol.fragments.get(queued.id) else {
            continue;
        };

        let matched_route = route_renderer::find_best_route_match(
            &frag_list.fragments,
            request_path,
            arena.get(queued.route_base),
            index.route_index,
        );

        for frag in &frag_list.fragments {
            match frag.fragment.as_ref() {
                Some(Fragment::Component(component)) => {
                    // Inventory: components are inventoryable
                    stack.push(QueuedFragment {
                        id: &component.fragment_id,
                        inventoryable: true,
                        route_base: queued.route_base,
                    });
                }
                Some(Fragment::ForLoop(for_loop)) => {
                    // Inventory: follow control-flow edges conservatively
                    stack.push(QueuedFragment {
                        id: &for_loop.fragment_id,
                        inventoryable: false,
                        route_base: queued.route_base,
                    });
                }
                Some(Fragment::IfCond(if_cond)) => {
                    stack.push(QueuedFragment {
                        id: &if_cond.fragment_id,
                        inventoryable: false,
                        route_base: queued.route_base,
                    });
                }

                Some(Fragment::Attribute(attr)) if !attr.template.is_empty() => {
                    stack.push(QueuedFragment {
                        id: &attr.template,
                        inventoryable: false,
                        route_base: queued.route_base,
                    });
                }
                Some(Fragment::Route(route_frag)) => {
                    let is_selected = matched_route
                        .as_ref()
                        .is_some_and(|(best_key, _)| best_key == route_frag.fragment_id.as_str());
                    if is_selected && !route_frag.content_fragment_id.is_empty() {
                        stack.push(QueuedFragment {
                            id: &route_frag.content_fragment_id,
                            inventoryable: false,
                            route_base: queued.route_base,
                        });
                    }
                    if is_selected && !route_frag.fragment_id.is_empty() {
                        if let Some((_, ref rm)) = matched_route {
                            // Chain: record matched route entry
                            chain.push(RouteChainEntry {
                                component: route_frag.fragment_id.clone(),
                                path: route_frag.path.clone(),
                                params: rm.params.clone(),
                                exact: route_frag.exact,
                                allowed_query: route_frag.allowed_query.clone(),
                                keep_alive: route_frag.keep_alive,
                                cache_tags: route_frag.cache_tags.clone(),
                                invalidates: route_frag.invalidates.clone(),
                                pending_component: route_frag.pending_component.clone(),
                                error_component: route_frag.error_component.clone(),
                            });

                            let child_route_base =
                                arena.intern_owned(route_matcher::compute_route_base(
                                    request_path,
                                    rm.consumed_segments,
                                ));

                            // Inventory: follow matched route component
                            let is_inventoryable = protocol
                                .components
                                .get(&route_frag.fragment_id)
                                .is_some_and(has_template_payload);
                            stack.push(QueuedFragment {
                                id: &route_frag.fragment_id,
                                inventoryable: is_inventoryable,
                                route_base: child_route_base,
                            });

                            collect_route_boundary_components(
                                std::slice::from_ref(route_frag),
                                child_route_base,
                                protocol,
                                &mut stack,
                            );

                            // Both: walk nested child routes
                            if !route_frag.children.is_empty() {
                                walk_children_for_inventory_and_chain(
                                    &route_frag.children,
                                    child_route_base,
                                    ChainWalkSinks {
                                        stack: &mut stack,
                                        chain: &mut chain,
                                        arena: &mut arena,
                                    },
                                    &ChildWalkCtx {
                                        request_path,
                                        protocol,
                                        route_index: index.route_index,
                                    },
                                );
                            }
                        }
                    }
                }
                _ => {}
            }
        }
    }

    (component_ids, chain)
}

/// Mutable sinks threaded through the inventory + chain child walk.
///
/// Bundled so the walk stays within the workspace's five-argument limit.
struct ChainWalkSinks<'walk, 'protocol> {
    stack: &'walk mut Vec<QueuedFragment<'protocol>>,
    chain: &'walk mut Vec<RouteChainEntry>,
    arena: &'walk mut RouteBaseArena,
}

/// Walk nested route children, collecting both inventory and chain entries.
fn walk_children_for_inventory_and_chain<'protocol>(
    children: &'protocol [WebUIFragmentRoute],
    route_base: u32,
    sinks: ChainWalkSinks<'_, 'protocol>,
    ctx: &ChildWalkCtx<'_>,
) {
    let ChainWalkSinks {
        stack,
        chain,
        arena,
    } = sinks;
    let mut current = children;
    let mut base = route_base;

    loop {
        // Resolve the base before interning below so the arena's immutable
        // borrow ends before the mutable one begins.
        let matched =
            select_best_child_route(current, ctx.request_path, arena.get(base), ctx.route_index);
        let Some((idx, rm)) = matched else {
            break;
        };
        let Some(matched) = current.get(idx) else {
            break;
        };
        if matched.fragment_id.is_empty() {
            break;
        }

        let child_base = arena.intern_owned(route_matcher::compute_route_base(
            ctx.request_path,
            rm.consumed_segments,
        ));

        chain.push(RouteChainEntry {
            component: matched.fragment_id.clone(),
            path: matched.path.clone(),
            params: rm.params,
            exact: matched.exact,
            allowed_query: matched.allowed_query.clone(),
            keep_alive: matched.keep_alive,
            cache_tags: matched.cache_tags.clone(),
            invalidates: matched.invalidates.clone(),
            pending_component: matched.pending_component.clone(),
            error_component: matched.error_component.clone(),
        });

        stack.push(QueuedFragment {
            id: &matched.fragment_id,
            inventoryable: ctx
                .protocol
                .components
                .get(&matched.fragment_id)
                .is_some_and(has_template_payload),
            route_base: child_base,
        });

        if matched.children.is_empty() {
            break;
        }
        current = &matched.children;
        base = child_base;
    }
}

/// Produce state-free partial-navigation metadata for NDJSON chunk 1.
///
/// Returns the matched route chain, templates, inventory, and cache tags.
/// State is intentionally excluded so a streaming host can send it later.
/// Use [`render_partial`] for a complete JSON response.
///
/// Returns a `serde_json::Value` object with fields:
/// - `componentStyles`: versioned tree-local resources and ordered closures
/// - `templates`: client template metadata keyed by component tag (inventory-filtered)
/// - `templateFunctions`: component-local condition closure arrays keyed by component tag
/// - `inventory`: updated hex bitmask
/// - `path`: the request path
/// - `chain`: matched route chain array
/// - `cacheTags`: resolved cache tags from the full route chain (union of all levels)
#[cfg(test)]
fn render_partial_metadata(
    protocol: &WebUIProtocol,
    entry_id: &str,
    request_path: &str,
    inventory_hex: &str,
    index: &mut ProtocolIndex,
) -> Result<Value, HandlerError> {
    let mut request_index = index.request_index();
    render_partial_indexed(
        protocol,
        entry_id,
        request_path,
        inventory_hex,
        &mut request_index,
    )
}

/// Produce a complete partial-navigation response with projected parsed state.
///
/// Only keys required to create or update client components reachable on the
/// active route are retained. Authored components use their explicit
/// navigation surface (`@observable + @attr + template roots`); scriptless
/// templates use compiled template roots.
#[cfg(test)]
fn render_partial(
    protocol: &WebUIProtocol,
    state: Value,
    entry_id: &str,
    request_path: &str,
    inventory_hex: &str,
) -> Result<Value, HandlerError> {
    let mut index = ProtocolIndex::new(protocol);
    let mut request_index = index.request_index();
    let (mut response, state_selection, _) = render_partial_indexed_with_state(
        protocol,
        entry_id,
        request_path,
        inventory_hex,
        &mut request_index,
    )?;
    let response = response
        .as_object_mut()
        .ok_or_else(partial_response_not_object)?;
    response.insert("state".into(), select_owned_state(state, &state_selection));
    Ok(Value::Object(std::mem::take(response)))
}

#[cfg(test)]
fn render_partial_indexed(
    protocol: &WebUIProtocol,
    entry_id: &str,
    request_path: &str,
    inventory_hex: &str,
    index: &mut RequestProtocolIndex<'_>,
) -> Result<Value, HandlerError> {
    render_partial_indexed_with_state(protocol, entry_id, request_path, inventory_hex, index)
        .map(|(response, _, _)| response)
}

fn render_partial_indexed_with_state<'a>(
    protocol: &'a WebUIProtocol,
    entry_id: &str,
    request_path: &str,
    inventory_hex: &str,
    index: &mut RequestProtocolIndex<'_>,
) -> Result<(Value, StateSelection<'a>, bool), HandlerError> {
    // Single-pass walk: collect both inventory components and route chain.
    let (component_ids, mut chain) =
        collect_inventory_and_chain(protocol, entry_id, request_path, index);
    let matched = route_chain_matches(&chain, request_path);
    let state_selection =
        crate::collect_navigation_state(protocol, component_ids.iter().map(String::as_str));

    let filtered =
        filter_components_with_inventory(&component_ids, inventory_hex, index.component_index)?;

    // Resolve cache tags and invalidation templates with accumulated params.
    let mut accumulated_params: HashMap<String, String> = HashMap::new();
    let mut all_resolved_tags: Vec<String> = Vec::new();

    for entry in &mut chain {
        for (k, v) in &entry.params {
            accumulated_params.insert(k.clone(), v.clone());
        }
        entry.cache_tags = resolve_tag_templates(&entry.cache_tags, &accumulated_params);
        entry.invalidates = resolve_tag_templates(&entry.invalidates, &accumulated_params);
        all_resolved_tags.extend(entry.cache_tags.iter().cloned());
    }

    let tag_refs: Vec<&str> = filtered.needed.iter().map(String::as_str).collect();
    let assets = collect_component_assets(protocol, &tag_refs, &filtered.client_inventory, index)?;

    let chain_array = Value::Array(chain.iter().map(RouteChainEntry::to_json).collect());

    let mut result = serde_json::Map::with_capacity(7);
    result.insert("componentStyles".into(), assets.component_styles);
    result.insert("templates".into(), Value::Object(assets.templates));
    result.insert("templateFunctions".into(), Value::Object(assets.functions));
    result.insert(
        "inventory".into(),
        Value::String(filtered.updated_inventory),
    );
    result.insert("path".into(), Value::String(request_path.to_string()));
    result.insert("chain".into(), chain_array);
    if !all_resolved_tags.is_empty() {
        let mut seen = HashSet::new();
        let deduped: Vec<Value> = all_resolved_tags
            .into_iter()
            .filter(|t| seen.insert(t.clone()))
            .map(Value::String)
            .collect();
        result.insert("cacheTags".into(), Value::Array(deduped));
    }
    Ok((Value::Object(result), state_selection, matched))
}

/// A serializable navigation response with projected state and route-match status.
///
/// Returned by [`Protocol::prepare_partial`]. Its JSON representation preserves
/// the complete partial-navigation schema; the match status is not serialized.
#[derive(serde::Serialize)]
#[serde(transparent)]
#[must_use]
pub struct PartialNavigation {
    response: PartialResponseWithState<Value>,
    #[serde(skip)]
    matched: bool,
}

impl PartialNavigation {
    /// Whether the request matched an application route rather than only its shell.
    #[must_use]
    pub fn is_match(&self) -> bool {
        self.matched
    }
}

fn route_chain_matches(chain: &[RouteChainEntry], request_path: &str) -> bool {
    if request_path
        .split_once('?')
        .map_or(request_path, |(path, _)| path)
        == "/"
    {
        return !chain.is_empty();
    }
    match chain {
        [] => false,
        [only] => only.path != "/",
        _ => true,
    }
}

fn select_owned_state(state: Value, selection: &StateSelection<'_>) -> Value {
    let state_keys = match selection {
        StateSelection::Full => {
            let mut state = state;
            if let Value::Object(state) = &mut state {
                state.remove(crate::STATE_INJECT_KEY);
            }
            return state;
        }
        StateSelection::Keys(keys) => keys.as_slice(),
        // Streaming's key-ID projection never reaches partial navigation.
        StateSelection::KeyIds(_) | StateSelection::FullExceptKeyIds(_) => {
            return Value::Object(Map::new());
        }
    };
    let Value::Object(mut source) = state else {
        return Value::Object(Map::new());
    };
    let mut projected = Map::with_capacity(state_keys.len().min(source.len()));
    for &key in state_keys {
        if key == crate::STATE_INJECT_KEY {
            continue;
        }
        if let Some(value) = source.remove(key) {
            projected.insert(key.to_owned(), value);
        }
    }
    Value::Object(projected)
}

/// Produce a JSON response for a POST mutation action.
///
/// Walks the matched route chain, resolves `invalidates` tag templates
/// with actual param values, and returns them alongside the application
/// state. Host servers call this for `POST` requests to route paths.
///
/// Returns a `serde_json::Value` object with fields:
/// - `state`: the application state passed through
/// - `invalidateTags`: resolved invalidation tags from the matched leaf route
/// - `path`: the request path
#[cfg(test)]
fn render_action_response(
    protocol: &WebUIProtocol,
    state: Value,
    entry_id: &str,
    request_path: &str,
    index: &mut ProtocolIndex,
) -> Value {
    let mut request_index = index.request_index();
    render_action_response_indexed(protocol, state, entry_id, request_path, &mut request_index)
}

#[cfg(test)]
fn render_action_response_indexed(
    protocol: &WebUIProtocol,
    state: Value,
    entry_id: &str,
    request_path: &str,
    index: &mut RequestProtocolIndex<'_>,
) -> Value {
    let chain = collect_route_chain(protocol, entry_id, request_path, index.route_index);

    // Accumulate params across the chain for tag resolution
    let mut accumulated_params: HashMap<String, String> = HashMap::new();
    let mut all_invalidates: Vec<String> = Vec::new();

    for entry in &chain {
        for (k, v) in &entry.params {
            accumulated_params.insert(k.clone(), v.clone());
        }
        let resolved = resolve_tag_templates(&entry.invalidates, &accumulated_params);
        all_invalidates.extend(resolved);
    }

    // Deduplicate while preserving order
    let mut seen = HashSet::new();
    let deduped: Vec<Value> = all_invalidates
        .into_iter()
        .filter(|t| seen.insert(t.clone()))
        .map(Value::String)
        .collect();

    let mut result = serde_json::Map::with_capacity(3);
    result.insert("state".into(), state);
    result.insert("invalidateTags".into(), Value::Array(deduped));
    result.insert("path".into(), Value::String(request_path.to_string()));
    Value::Object(result)
}

/// Return compiled templates and CSS for specific components by tag name.
///
/// This supports on-demand loading of components that aren't part of the
/// route tree (e.g., dialogs, popovers) — the client calls this before
/// creating the element so templates + styles are registered without FOUC.
///
/// Uses the same inventory bitfield as partial navigation to avoid sending
/// templates the client already has.
#[cfg(test)]
fn render_component_templates(
    protocol: &WebUIProtocol,
    component_tags: &[&str],
    inventory_hex: &str,
    index: &mut ProtocolIndex,
) -> Result<Value, HandlerError> {
    let mut request_index = index.request_index();
    render_component_templates_indexed(protocol, component_tags, inventory_hex, &mut request_index)
}

fn render_component_templates_indexed(
    protocol: &WebUIProtocol,
    component_tags: &[&str],
    inventory_hex: &str,
    index: &mut RequestProtocolIndex<'_>,
) -> Result<Value, HandlerError> {
    // Deduplicate preserving caller order; filter expects unique names.
    let mut seen: HashSet<&str> = HashSet::new();
    let requested: Vec<String> = component_tags
        .iter()
        .filter(|s| seen.insert(**s))
        .map(|s| (*s).to_string())
        .collect();
    let filtered =
        filter_components_with_inventory(&requested, inventory_hex, index.component_index)?;

    let tag_refs: Vec<&str> = filtered.needed.iter().map(String::as_str).collect();
    let assets = collect_component_assets(protocol, &tag_refs, &filtered.client_inventory, index)?;

    let mut result = serde_json::Map::with_capacity(4);
    result.insert("componentStyles".into(), assets.component_styles);
    result.insert("templates".into(), Value::Object(assets.templates));
    result.insert("templateFunctions".into(), Value::Object(assets.functions));
    result.insert(
        "inventory".into(),
        Value::String(filtered.updated_inventory),
    );
    Ok(Value::Object(result))
}

/// Shared helper: collect templates and style metadata for component tags.
fn collect_component_assets(
    protocol: &WebUIProtocol,
    tags: &[&str],
    client_inventory: &[u8],
    index: &mut RequestProtocolIndex<'_>,
) -> Result<ComponentAssets, HandlerError> {
    let component_styles = collect_component_styles_for_inventory(
        protocol,
        tags.iter().copied(),
        client_inventory,
        index.component_index,
    )?;
    let mut tmpl_map = serde_json::Map::new();
    let mut function_map = serde_json::Map::new();

    // Sort for deterministic output (reproducible responses, cache keys)
    let mut sorted_tags: Vec<&str> = tags.to_vec();
    sorted_tags.sort_unstable();

    for tag in sorted_tags {
        let Some(component) = protocol.components.get(tag) else {
            continue;
        };
        if !has_template_payload(component) {
            continue;
        }
        if !component.template_json.is_empty() {
            let template_value = cached_template_metadata(
                &mut index.template_metadata_cache,
                tag,
                &component.template_json,
            )?;
            tmpl_map.insert(tag.to_string(), template_value);
            if !component.template_functions.is_empty() {
                function_map.insert(
                    tag.to_string(),
                    Value::String(component.template_functions.clone()),
                );
            }
        } else {
            tmpl_map.insert(tag.to_string(), Value::String(component.template.clone()));
        }
    }

    Ok(ComponentAssets {
        component_styles,
        templates: tmpl_map,
        functions: function_map,
    })
}

fn cached_template_metadata(
    cache: &mut TemplateMetadataCache<'_>,
    tag: &str,
    template_json: &str,
) -> Result<Value, HandlerError> {
    match cache {
        #[cfg(test)]
        TemplateMetadataCache::Exclusive(cache) => {
            cached_template_metadata_exclusive(cache, tag, template_json)
        }
        TemplateMetadataCache::Shared(cache) => {
            if let Some(value) = cache
                .read()
                .map_err(|_| protocol_metadata_cache_poisoned())?
                .get(tag)
                .cloned()
            {
                return Ok(value);
            }

            let value = parse_template_metadata(tag, template_json)?;
            let mut cache = cache
                .write()
                .map_err(|_| protocol_metadata_cache_poisoned())?;
            Ok(cache.entry(tag.to_string()).or_insert(value).clone())
        }
    }
}

#[cfg(test)]
fn cached_template_metadata_exclusive(
    cache: &mut HashMap<String, Value>,
    tag: &str,
    template_json: &str,
) -> Result<Value, HandlerError> {
    if let Some(value) = cache.get(tag) {
        return Ok(value.clone());
    }

    let value = parse_template_metadata(tag, template_json)?;
    cache.insert(tag.to_string(), value.clone());
    Ok(value)
}

fn parse_template_metadata(tag: &str, template_json: &str) -> Result<Value, HandlerError> {
    serde_json::from_str(template_json).map_err(|error| {
        HandlerError::Rendering(format!(
            "failed to parse template metadata for {tag}: {error}"
        ))
    })
}

#[cold]
#[inline(never)]
fn protocol_metadata_cache_poisoned() -> HandlerError {
    HandlerError::Invariant(
        "protocol metadata cache is unavailable after a previous panic".to_string(),
    )
}

// ── Route Chain ─────────────────────────────────────────────────────

/// A single entry in the matched route chain, one per nesting level.
#[derive(Debug, Clone)]
pub struct RouteChainEntry {
    /// Component tag name for this route level.
    pub component: String,
    /// The route path pattern (as declared in the template).
    pub path: String,
    /// Bound route parameters at this level.
    pub params: HashMap<String, String>,
    /// Whether this route requires an exact match.
    pub exact: bool,
    /// Comma-separated allowlist of query parameters forwarded as attributes.
    pub allowed_query: String,
    /// When true, the router keeps the component alive across navigations.
    pub keep_alive: bool,
    /// Cache tag templates from the proto (e.g. `["thread:{threadId}", "inbox"]`).
    pub cache_tags: Vec<String>,
    /// Invalidation tag templates from the proto.
    pub invalidates: Vec<String>,
    /// Component tag name for pending/loading UI.
    pub pending_component: String,
    /// Component tag name for error boundary UI.
    pub error_component: String,
}

pub(crate) struct RouteChainPlan {
    pub(crate) entries: Vec<RouteChainEntry>,
    pub(crate) document_style_targets: Vec<bool>,
}

impl RouteChainEntry {
    /// Serialize this entry to a JSON value ready for inclusion in a partial response.
    #[must_use]
    pub fn to_json(&self) -> Value {
        let mut obj = serde_json::Map::with_capacity(9);
        obj.insert("component".into(), Value::String(self.component.clone()));
        obj.insert("path".into(), Value::String(self.path.clone()));
        if !self.params.is_empty() {
            let params_obj: serde_json::Map<String, Value> = self
                .params
                .iter()
                .map(|(k, v)| (k.clone(), Value::String(v.clone())))
                .collect();
            obj.insert("params".into(), Value::Object(params_obj));
        }
        if self.exact {
            obj.insert("exact".into(), Value::Bool(true));
        }
        if !self.allowed_query.is_empty() {
            obj.insert(
                "allowedQuery".into(),
                Value::String(self.allowed_query.clone()),
            );
        }
        if self.keep_alive {
            obj.insert("keepAlive".into(), Value::Bool(true));
        }
        if !self.pending_component.is_empty() {
            obj.insert(
                "pendingComponent".into(),
                Value::String(self.pending_component.clone()),
            );
        }
        if !self.error_component.is_empty() {
            obj.insert(
                "errorComponent".into(),
                Value::String(self.error_component.clone()),
            );
        }
        if !self.invalidates.is_empty() {
            obj.insert(
                "invalidates".into(),
                Value::Array(
                    self.invalidates
                        .iter()
                        .map(|s| Value::String(s.clone()))
                        .collect(),
                ),
            );
        }
        Value::Object(obj)
    }
}

/// Collect the matched route chain for a request path.
///
/// Walks the fragment graph from `entry_id`, follows the matched route at
/// each nesting level, and returns a chain entry per matched level.
#[cfg(test)]
pub(crate) fn collect_route_chain(
    protocol: &WebUIProtocol,
    entry_id: &str,
    request_path: &str,
    route_index: &CompiledRouteIndex,
) -> Vec<RouteChainEntry> {
    collect_route_chain_plan(protocol, entry_id, request_path, route_index).entries
}

struct RouteChainWork {
    id: String,
    route_base: String,
    targets_document: bool,
}

pub(crate) fn collect_route_chain_plan(
    protocol: &WebUIProtocol,
    entry_id: &str,
    request_path: &str,
    route_index: &CompiledRouteIndex,
) -> RouteChainPlan {
    let mut chain = Vec::new();
    let mut document_style_targets = Vec::new();
    let mut visited_fragments = HashSet::new();
    let mut stack = vec![RouteChainWork {
        id: entry_id.to_string(),
        route_base: "/".to_string(),
        targets_document: !protocol.component_uses_shadow_dom(entry_id),
    }];

    while let Some(queued) = stack.pop() {
        if queued.id.is_empty()
            || !visited_fragments.insert((queued.id.clone(), queued.route_base.clone()))
        {
            continue;
        }

        let Some(frag_list) = protocol.fragments.get(&queued.id) else {
            continue;
        };

        let matched_route = route_renderer::find_best_route_match(
            &frag_list.fragments,
            request_path,
            &queued.route_base,
            route_index,
        );

        for frag in &frag_list.fragments {
            match frag.fragment.as_ref() {
                Some(Fragment::Component(component)) => {
                    stack.push(RouteChainWork {
                        id: component.fragment_id.clone(),
                        route_base: queued.route_base.clone(),
                        targets_document: queued.targets_document
                            && !protocol.component_uses_shadow_dom(&component.fragment_id),
                    });
                }
                Some(Fragment::ForLoop(for_loop)) => {
                    stack.push(RouteChainWork {
                        id: for_loop.fragment_id.clone(),
                        route_base: queued.route_base.clone(),
                        targets_document: queued.targets_document,
                    });
                }
                Some(Fragment::IfCond(if_cond)) => {
                    stack.push(RouteChainWork {
                        id: if_cond.fragment_id.clone(),
                        route_base: queued.route_base.clone(),
                        targets_document: queued.targets_document,
                    });
                }

                Some(Fragment::Route(route_frag)) => {
                    let is_selected = matched_route
                        .as_ref()
                        .is_some_and(|(best_key, _)| best_key == route_frag.fragment_id.as_str());
                    if is_selected && !route_frag.fragment_id.is_empty() {
                        if let Some((_, ref rm)) = matched_route {
                            let targets_document = queued.targets_document
                                && !protocol.component_uses_shadow_dom(&route_frag.fragment_id);
                            chain.push(RouteChainEntry {
                                component: route_frag.fragment_id.clone(),
                                path: route_frag.path.clone(),
                                params: rm.params.clone(),
                                exact: route_frag.exact,
                                allowed_query: route_frag.allowed_query.clone(),
                                keep_alive: route_frag.keep_alive,
                                cache_tags: route_frag.cache_tags.clone(),
                                invalidates: route_frag.invalidates.clone(),
                                pending_component: route_frag.pending_component.clone(),
                                error_component: route_frag.error_component.clone(),
                            });
                            document_style_targets.push(targets_document);

                            let child_route_base = route_matcher::compute_route_base(
                                request_path,
                                rm.consumed_segments,
                            );

                            stack.push(RouteChainWork {
                                id: route_frag.fragment_id.clone(),
                                route_base: child_route_base.clone(),
                                targets_document,
                            });

                            // Walk nested children iteratively
                            let mut output = RouteChainOutput {
                                entries: &mut chain,
                                document_style_targets: &mut document_style_targets,
                            };
                            collect_chain_from_children(
                                &route_frag.children,
                                &child_route_base,
                                targets_document,
                                &mut output,
                                &mut ChildWalkCtx {
                                    request_path,
                                    protocol,
                                    route_index,
                                },
                            );
                        }
                    }
                }
                _ => {}
            }
        }
    }

    RouteChainPlan {
        entries: chain,
        document_style_targets,
    }
}

struct RouteChainOutput<'a> {
    entries: &'a mut Vec<RouteChainEntry>,
    document_style_targets: &'a mut Vec<bool>,
}

/// Iteratively collect chain entries from nested route children.
fn collect_chain_from_children(
    children: &[WebUIFragmentRoute],
    route_base: &str,
    targets_document: bool,
    output: &mut RouteChainOutput<'_>,
    ctx: &mut ChildWalkCtx<'_>,
) {
    let mut pending: Vec<(&[WebUIFragmentRoute], String, bool)> =
        vec![(children, route_base.to_string(), targets_document)];

    while let Some((current, base, current_targets_document)) = pending.pop() {
        if let Some((idx, rm)) =
            select_best_child_route(current, ctx.request_path, &base, ctx.route_index)
        {
            let matched = &current[idx];
            let matched_targets_document = current_targets_document
                && !ctx.protocol.component_uses_shadow_dom(&matched.fragment_id);
            output.entries.push(RouteChainEntry {
                component: matched.fragment_id.clone(),
                path: matched.path.clone(),
                params: rm.params,
                exact: matched.exact,
                allowed_query: matched.allowed_query.clone(),
                keep_alive: matched.keep_alive,
                cache_tags: matched.cache_tags.clone(),
                invalidates: matched.invalidates.clone(),
                pending_component: matched.pending_component.clone(),
                error_component: matched.error_component.clone(),
            });
            output.document_style_targets.push(matched_targets_document);
            if !matched.children.is_empty() {
                let child_base =
                    route_matcher::compute_route_base(ctx.request_path, rm.consumed_segments);
                pending.push((&matched.children, child_base, matched_targets_document));
            }
        }
    }
}

#[cfg(test)]
mod tests {
    use super::*;
    use std::collections::HashMap;
    use std::sync::{Arc, Barrier};
    use std::thread;
    use webui_protocol::{FragmentList, WebUIFragment, WebUiFragmentRoute};

    #[test]
    fn protocol_caches_inline_style_resources_requiring_escape() {
        let mut protocol = WebUIProtocol::new(HashMap::new());
        protocol.set_css_strategy(CssStrategy::Style);
        protocol.components.insert(
            "safe-card".to_string(),
            webui_protocol::ComponentData {
                css: ".safe{color:green}".to_string(),
                ..Default::default()
            },
        );
        protocol.components.insert(
            "unsafe-card".to_string(),
            webui_protocol::ComponentData {
                css: ".unsafe{content:'</StYlE>'}".to_string(),
                ..Default::default()
            },
        );
        protocol.style_chunks.push(webui_protocol::StyleChunk {
            name: "_chunk-safe-card-2".to_string(),
            css: ".safe{color:green}.other{color:blue}".to_string(),
            ..Default::default()
        });
        protocol.style_chunks.push(webui_protocol::StyleChunk {
            name: "_chunk-unsafe-card-2".to_string(),
            css: ".unsafe{content:'</style>'}.other{color:blue}".to_string(),
            ..Default::default()
        });

        let prepared = Protocol::new(protocol);
        let resources = prepared.style_resources_requiring_escape();

        assert_eq!(resources.len(), 2);
        assert!(resources.contains("unsafe-card"));
        assert!(resources.contains("_chunk-unsafe-card-2"));
    }

    #[test]
    fn protocol_decodes_once_and_exposes_tokens() {
        let mut fragments = HashMap::new();
        fragments.insert(
            "index.html".to_string(),
            FragmentList {
                fragments: vec![WebUIFragment::raw("<p>Prepared</p>")],
                contains_boundary: false,
            },
        );
        let protocol = WebUIProtocol::with_tokens(fragments, vec!["colorBrand".to_string()]);
        let bytes = protocol.to_protobuf().unwrap();
        let prepared = Protocol::from_protobuf(&bytes).unwrap();

        assert!(prepared.protocol().fragments.contains_key("index.html"));
        assert_eq!(prepared.tokens(), ["colorBrand"]);
    }

    #[test]
    fn continuation_state_plans_memoize_per_entry_without_locking() {
        // Every response for an entry must read the same prepared plan through
        // the slot table: no lock, no hash, and no per-response rebuild.
        let mut fragments = HashMap::new();
        fragments.insert(
            "index.html".to_string(),
            FragmentList {
                fragments: vec![WebUIFragment::raw("<p>plan</p>")],
                contains_boundary: false,
            },
        );
        let prepared = Protocol::new(WebUIProtocol::new(fragments));

        let first = prepared.continuation_state_plan("index.html").unwrap();
        let second = prepared.continuation_state_plan("index.html").unwrap();
        assert!(
            std::ptr::eq(first, second),
            "a memoized plan must be borrowed, not rebuilt or cloned"
        );
        // The table reserves one cell per compiled record, so the cell must stay
        // small enough that a large protocol's lazy table is a rounding error.
        let cell = std::mem::size_of::<OnceLock<PreparedContinuationStatePlan>>();
        assert!(
            cell <= 40,
            "continuation plan memo cell grew to {cell} bytes"
        );

        let barrier = Arc::new(Barrier::new(4));
        let address = std::ptr::from_ref(first).addr();
        thread::scope(|scope| {
            for _ in 0..4 {
                let barrier = Arc::clone(&barrier);
                let prepared = &prepared;
                scope.spawn(move || {
                    barrier.wait();
                    let plan = prepared.continuation_state_plan("index.html").unwrap();
                    assert_eq!(
                        std::ptr::from_ref(plan).addr(),
                        address,
                        "concurrent responses must share one initialization"
                    );
                    assert!(plan.resolve().is_ok());
                });
            }
        });
    }

    #[test]
    fn continuation_state_plans_replay_captured_failures() {
        // A malformed entry is diagnosed identically on every response, and an
        // unknown entry still reports the missing record rather than a slot.
        let mut fragments = HashMap::new();
        fragments.insert(
            "index.html".to_string(),
            FragmentList {
                fragments: vec![WebUIFragment::component("missing-card")],
                contains_boundary: false,
            },
        );
        let prepared = Protocol::new(WebUIProtocol::new(fragments));

        for _ in 0..2 {
            match prepared
                .continuation_state_plan("index.html")
                .and_then(|plan| plan.resolve())
                .err()
            {
                Some(HandlerError::MissingFragment(id)) => assert_eq!(id, "missing-card"),
                other => panic!("expected a replayable missing-record failure, got {other:?}"),
            }
        }
        match prepared.continuation_state_plan("absent.html").err() {
            Some(HandlerError::MissingFragment(id)) => assert_eq!(id, "absent.html"),
            other => panic!("expected a missing-entry diagnostic, got {other:?}"),
        }
    }

    #[test]
    fn component_reachability_interns_hydration_projections() {
        // Streaming records collect their projection from component indexes, so
        // the interned runs must reproduce the compiled per-component surface
        // in lexicographic ID order.
        let mut fragments = HashMap::new();
        fragments.insert("keyed-card".to_string(), FragmentList::default());
        fragments.insert("all-card".to_string(), FragmentList::default());
        fragments.insert("bare-card".to_string(), FragmentList::default());
        let mut protocol = WebUIProtocol::new(fragments);
        protocol.components.insert(
            "keyed-card".to_string(),
            webui_protocol::ComponentData {
                hydration_mode: StateProjectionMode::Keys as i32,
                hydration_keys: vec!["zebra".to_string(), "alpha".to_string()],
                ..Default::default()
            },
        );
        protocol.components.insert(
            "all-card".to_string(),
            webui_protocol::ComponentData {
                hydration_mode: StateProjectionMode::All as i32,
                ..Default::default()
            },
        );
        let prepared = Protocol::new(protocol);
        let index = prepared.component_reachability();
        let component = prepared.component_index();

        let mut ids = Vec::new();
        assert!(
            !index.extend_hydration_keys(component["keyed-card"], &mut ids),
            "a keyed surface projects keys"
        );
        ids.sort_unstable();
        let keys: Vec<&str> = ids
            .iter()
            .filter_map(|id| index.hydration_key(*id))
            .collect();
        assert_eq!(
            keys,
            ["alpha", "zebra"],
            "sorted IDs must be lexicographically sorted keys"
        );

        let mut ids = Vec::new();
        assert!(
            index.extend_hydration_keys(component["all-card"], &mut ids),
            "an ALL surface forces full state"
        );
        assert!(
            index.extend_hydration_keys(component["bare-card"], &mut ids),
            "a component without compiled metadata forces full state"
        );
    }

    #[test]
    fn protocol_retains_only_serialized_component_asset_styles() {
        let mut protocol = WebUIProtocol::default();
        protocol.component_asset_style_preloads =
            vec![webui_protocol::ComponentAssetStylePreload {
                root: "lazy-panel".to_string(),
                style_hrefs: vec!["/lazy-panel.css".to_string()],
            }];

        let prepared = Protocol::new(protocol);

        assert!(prepared
            .protocol()
            .component_asset_style_preloads
            .is_empty());
        assert_eq!(
            prepared.component_asset_style_manifest().unwrap(),
            r#"{"lazy-panel":["/lazy-panel.css"]}"#
        );
        assert!(prepared.component_asset_style_links().is_empty());
    }

    #[test]
    fn protocol_precomputes_deduplicated_light_component_asset_styles() {
        let mut protocol = WebUIProtocol::default();
        protocol.set_css_strategy(webui_protocol::CssStrategy::Link);
        for root in ["lazy-panel", "secondary-panel"] {
            protocol.components.insert(
                root.to_string(),
                webui_protocol::ComponentData {
                    uses_shadow_dom: false,
                    ..Default::default()
                },
            );
        }
        protocol.component_asset_style_preloads = vec![
            webui_protocol::ComponentAssetStylePreload {
                root: "lazy-panel".to_string(),
                style_hrefs: vec![
                    "/lazy-panel.css".to_string(),
                    "/shared.css?theme=a&mode=\"dark\"".to_string(),
                ],
            },
            webui_protocol::ComponentAssetStylePreload {
                root: "secondary-panel".to_string(),
                style_hrefs: vec![
                    "/secondary-panel.css".to_string(),
                    "/shared.css?theme=a&mode=\"dark\"".to_string(),
                ],
            },
        ];

        let prepared = Protocol::new(protocol);

        assert!(prepared
            .protocol()
            .component_asset_style_preloads
            .is_empty());
        assert!(prepared
            .component_asset_style_manifest()
            .unwrap()
            .is_empty());
        assert_eq!(
            prepared.component_asset_style_links(),
            concat!(
                r#"<link rel="stylesheet" href="/lazy-panel.css">"#,
                r#"<link rel="stylesheet" href="/shared.css?theme=a&amp;mode=&quot;dark&quot;">"#,
                r#"<link rel="stylesheet" href="/secondary-panel.css">"#,
            )
        );
    }

    #[test]
    fn protocol_partial_matches_direct_index_path() {
        let mut fragments = HashMap::new();
        fragments.insert(
            "index.html".to_string(),
            FragmentList {
                fragments: vec![WebUIFragment::route("/", "home-page")],
                contains_boundary: false,
            },
        );
        fragments.insert(
            "home-page".to_string(),
            FragmentList {
                fragments: vec![WebUIFragment::raw("<p>Home</p>")],
                contains_boundary: false,
            },
        );
        let protocol = WebUIProtocol::new(fragments);
        let mut direct_index = ProtocolIndex::new(&protocol);
        let direct =
            render_partial_metadata(&protocol, "index.html", "/", "", &mut direct_index).unwrap();
        let prepared = Protocol::new(protocol);
        let cached = prepared
            .render_partial_metadata("index.html", "/", "")
            .unwrap();

        assert_eq!(cached, direct);
    }

    #[test]
    fn protocol_partial_supports_concurrent_metadata_reads() {
        let mut fragments = HashMap::new();
        fragments.insert(
            "index.html".to_string(),
            FragmentList {
                fragments: vec![WebUIFragment::route("/", "home-page")],
                contains_boundary: false,
            },
        );
        fragments.insert(
            "home-page".to_string(),
            FragmentList {
                fragments: vec![WebUIFragment::raw("<p>Home</p>")],
                contains_boundary: false,
            },
        );
        let mut protocol = WebUIProtocol::new(fragments);
        protocol.components.insert(
            "home-page".to_string(),
            webui_protocol::ComponentData {
                template_json: r#"{"h":"<p>Home</p>"}"#.to_string(),
                ..Default::default()
            },
        );

        let prepared = Arc::new(Protocol::new(protocol));
        let barrier = Arc::new(Barrier::new(4));
        let handles: Vec<_> = (0..4)
            .map(|_| {
                let prepared = Arc::clone(&prepared);
                let barrier = Arc::clone(&barrier);
                thread::spawn(move || {
                    barrier.wait();
                    for _ in 0..50 {
                        let response = prepared
                            .render_partial_metadata("index.html", "/", "")
                            .unwrap();
                        assert_eq!(response["templates"]["home-page"]["h"], "<p>Home</p>");
                    }
                })
            })
            .collect();

        for handle in handles {
            handle.join().unwrap();
        }
    }

    fn prepared_partial_protocol(hydration_keys: &[&str]) -> Protocol {
        let mut fragments = HashMap::new();
        fragments.insert(
            "index.html".to_string(),
            FragmentList {
                fragments: vec![WebUIFragment::route("/", "home-page")],
                contains_boundary: false,
            },
        );
        fragments.insert(
            "home-page".to_string(),
            FragmentList {
                fragments: vec![WebUIFragment::raw("<p>Home</p>")],
                contains_boundary: false,
            },
        );
        let mut protocol = WebUIProtocol::new(fragments);
        protocol.components.insert(
            "home-page".to_string(),
            webui_protocol::ComponentData {
                template_json: r#"{"h":"<p>Home</p>"}"#.to_string(),
                hydration_mode: webui_protocol::StateProjectionMode::Keys as i32,
                hydration_keys: hydration_keys
                    .iter()
                    .map(|key| (*key).to_string())
                    .collect(),
                navigation_mode: Some(webui_protocol::StateProjectionMode::Keys as i32),
                navigation_keys: hydration_keys
                    .iter()
                    .map(|key| (*key).to_string())
                    .collect(),
                ..Default::default()
            },
        );
        Protocol::new(protocol)
    }

    fn prepared_full_state_partial_protocol() -> Protocol {
        let mut prepared = prepared_partial_protocol(&[]);
        let protocol = &mut prepared.protocol;
        if let Some(component) = protocol.components.get_mut("home-page") {
            component.navigation_mode = Some(webui_protocol::StateProjectionMode::All as i32);
            component.navigation_keys.clear();
        }
        prepared
    }

    #[test]
    fn partial_state_serialization_preserves_validated_raw_json() {
        let prepared = prepared_partial_protocol(&["value"]);
        let output = prepared
            .render_partial_json(
                r#"{"serverOnly":"drop","value":1e2}"#,
                "index.html",
                "/",
                "",
            )
            .unwrap();
        assert!(output.contains(r#""state":{"value":1e2}"#));
        assert!(!output.contains("serverOnly"));

        let parsed: Value = serde_json::from_str(&output).unwrap();
        assert_eq!(parsed["state"]["value"], 100.0);
    }

    #[test]
    fn partial_state_projection_strips_reserved_inject_key() {
        let prepared = prepared_partial_protocol(&[crate::STATE_INJECT_KEY, "value"]);
        let output = prepared
            .render_partial_json(
                r#"{"$webui":{"bodyEnd":"<script>secret</script>"},"serverOnly":"drop","value":1}"#,
                "index.html",
                "/",
                "",
            )
            .unwrap();
        let parsed: Value = serde_json::from_str(&output).unwrap();

        assert_eq!(parsed["state"], serde_json::json!({"value": 1}));
        assert!(!output.contains("<script>secret</script>"), "{output}");
    }

    #[test]
    fn parsed_partial_state_moves_selected_values_into_response() {
        let prepared = prepared_partial_protocol(&[crate::STATE_INJECT_KEY, "value"]);
        let output = prepared
            .render_partial(
                serde_json::json!({
                    "$webui": {"bodyEnd": "<script>secret</script>"},
                    "serverOnly": ["large", "discarded", "value"],
                    "value": {"nested": "kept"}
                }),
                "index.html",
                "/",
                "",
            )
            .unwrap();
        let parsed: Value = serde_json::from_str(&output).unwrap();

        assert_eq!(
            parsed["state"],
            serde_json::json!({"value": {"nested": "kept"}})
        );
        assert!(!output.contains("serverOnly"));
        assert!(!output.contains("<script>secret</script>"), "{output}");
    }

    #[test]
    fn uncertain_partial_surface_preserves_complete_raw_state() {
        let prepared = prepared_full_state_partial_protocol();
        let output = prepared
            .render_partial_json(
                r#"{"serverOnly":"keep","value":1e2}"#,
                "index.html",
                "/",
                "",
            )
            .unwrap();
        assert!(output.contains(r#""state":{"serverOnly":"keep","value":1e2}"#));
    }

    #[test]
    fn uncertain_partial_surface_strips_escaped_reserved_inject_key() {
        let prepared = prepared_full_state_partial_protocol();
        for state in [
            r#"{"\u0024webui":{"bodyEnd":"<script>secret</script>"},"serverOnly":"keep","value":1}"#,
            r#"{"$\u0077\u0065\u0062\u0075\u0069":{"bodyEnd":"<script>secret</script>"},"serverOnly":"keep","value":1}"#,
        ] {
            let output = prepared
                .render_partial_json(state, "index.html", "/", "")
                .unwrap();
            let parsed: Value = serde_json::from_str(&output).unwrap();

            assert_eq!(
                parsed["state"],
                serde_json::json!({"serverOnly": "keep", "value": 1})
            );
            assert!(!output.contains("<script>secret</script>"), "{output}");
        }
    }

    #[test]
    fn parsed_full_partial_state_strips_reserved_inject_key() {
        let prepared = prepared_full_state_partial_protocol();
        let output = prepared
            .render_partial(
                serde_json::json!({
                    "$webui": {"bodyEnd": "<script>secret</script>"},
                    "serverOnly": "keep",
                    "value": 1
                }),
                "index.html",
                "/",
                "",
            )
            .unwrap();
        let parsed: Value = serde_json::from_str(&output).unwrap();

        assert_eq!(
            parsed["state"],
            serde_json::json!({"serverOnly": "keep", "value": 1})
        );
        assert!(!output.contains("<script>secret</script>"), "{output}");
    }

    #[test]
    fn uncertain_partial_surface_preserves_nested_reserved_key_bytes() {
        let prepared = prepared_full_state_partial_protocol();
        let output = prepared
            .render_partial_json(
                r#"{"outer": { "$webui": {"bodyEnd": "application data"} }, "value": 1e2}"#,
                "index.html",
                "/",
                "",
            )
            .unwrap();

        assert!(
            output.contains(
                r#""state":{"outer": { "$webui": {"bodyEnd": "application data"} }, "value": 1e2}"#
            ),
            "{output}"
        );
    }

    #[test]
    fn partial_state_serialization_rejects_invalid_json() {
        let prepared = prepared_partial_protocol(&[]);
        let error = prepared
            .render_partial_json(r#"{"broken":"#, "index.html", "/", "")
            .expect_err("invalid state JSON must fail");
        assert!(
            matches!(error, HandlerError::InvalidState(_)),
            "host bindings classify caller state errors by variant, got {error:?}"
        );
        assert!(error.to_string().contains("invalid state JSON"));
    }

    #[test]
    fn partial_state_serialization_emits_empty_state_without_client_components() {
        let prepared = Protocol::new(WebUIProtocol::default());
        let output = prepared
            .render_partial_json(r#"{"serverOnly":"drop"}"#, "index.html", "/", "")
            .unwrap();
        let parsed: Value = serde_json::from_str(&output).unwrap();
        assert_eq!(parsed["state"], serde_json::json!({}));
    }

    #[test]
    fn partial_state_serialization_validates_selected_and_skipped_numbers() {
        let prepared = prepared_partial_protocol(&["value"]);
        for state in [r#"{"value":1e9999}"#, r#"{"serverOnly":1e9999,"value":1}"#] {
            let error = prepared
                .render_partial_json(state, "index.html", "/", "")
                .expect_err("out-of-range state numbers must fail");
            assert!(
                matches!(error, HandlerError::InvalidState(_)),
                "host bindings classify caller state errors by variant, got {error:?}"
            );
            assert!(error.to_string().contains("invalid state JSON"));
        }
    }

    #[test]
    fn partial_state_serialization_uses_last_duplicate_and_decodes_keys() {
        let prepared = prepared_partial_protocol(&["value"]);
        let output = prepared
            .render_partial_json(r#"{"value":1,"va\u006cue":2}"#, "index.html", "/", "")
            .unwrap();
        let parsed: Value = serde_json::from_str(&output).unwrap();
        assert_eq!(parsed["state"], serde_json::json!({"value": 2}));
    }

    #[test]
    fn parsed_partial_state_projects_without_cloning_server_only_values() {
        let prepared = prepared_partial_protocol(&["value"]);
        let response = render_partial(
            prepared.protocol(),
            serde_json::json!({"serverOnly": [1, 2, 3], "value": "kept"}),
            "index.html",
            "/",
            "",
        )
        .unwrap();
        assert_eq!(response["state"], serde_json::json!({"value": "kept"}));
    }

    #[test]
    fn uncertain_partial_surface_preserves_complete_parsed_state() {
        let prepared = prepared_full_state_partial_protocol();
        let state = serde_json::json!({"serverOnly": [1, 2, 3], "value": "kept"});
        let response =
            render_partial(prepared.protocol(), state.clone(), "index.html", "/", "").unwrap();
        assert_eq!(response["state"], state);
    }

    #[test]
    fn partial_state_validation_matches_value_number_limits() {
        for json in [
            r#"{"value":1e9999}"#,
            r#"{"value":-1e9999}"#,
            r#"{"value":1e308}"#,
            r#"{"value":18446744073709551615}"#,
            r#"{"value":18446744073709551616}"#,
        ] {
            assert_eq!(
                validate_json(json).is_ok(),
                serde_json::from_str::<Value>(json).is_ok(),
                "validation mismatch for {json}"
            );
        }
    }

    #[test]
    fn test_parse_encode_inventory_roundtrip() {
        let original = vec![0xABu8, 0xCD, 0xEF, 0x01];
        let hex = encode_inventory(&original);
        let decoded = parse_inventory(&hex).unwrap();
        assert_eq!(original, decoded);
    }

    #[test]
    fn test_parse_inventory_empty() {
        let result = parse_inventory("").unwrap();
        assert!(result.is_empty());
    }

    #[test]
    fn test_parse_inventory_rejects_odd_length() {
        let result = parse_inventory("abc");
        assert!(result.is_err());
    }

    #[test]
    fn test_parse_inventory_rejects_invalid_hex() {
        let result = parse_inventory("zz");
        assert!(result.is_err());
    }

    #[test]
    fn test_bitfield_set_and_check() {
        let mut inv = vec![0u8; 4];
        set_component(&mut inv, 0);
        set_component(&mut inv, 7);
        set_component(&mut inv, 8);
        set_component(&mut inv, 15);
        assert!(has_component(&inv, 0));
        assert!(has_component(&inv, 7));
        assert!(has_component(&inv, 8));
        assert!(has_component(&inv, 15));
        assert!(!has_component(&inv, 1));
        assert!(!has_component(&inv, 9));
    }

    #[test]
    fn test_filter_needed_components_no_false_positives() {
        // With sequential indices, no two components share a bit
        let mut index = HashMap::new();
        index.insert("email-message".to_string(), 0);
        index.insert("o-button".to_string(), 1);
        index.insert("o-avatar".to_string(), 2);

        let names = vec!["email-message".to_string(), "o-button".to_string()];

        // Only o-button (index 1) is loaded — bit 1 set
        let mut inv = vec![0u8; 1];
        set_component(&mut inv, 1); // o-button
        let inv_hex = encode_inventory(&inv);

        let (needed, _) = filter_needed_components(&names, &inv_hex, &index).unwrap();
        assert_eq!(needed.len(), 1);
        assert!(
            needed.contains(&"email-message".to_string()),
            "email-message must be needed: {needed:?}"
        );
    }

    #[test]
    fn test_get_needed_components_empty_inventory() {
        let mut fragments = HashMap::new();
        fragments.insert(
            "app-shell".to_string(),
            FragmentList {
                fragments: vec![WebUIFragment::component("my-card")],
                contains_boundary: false,
            },
        );
        fragments.insert(
            "my-card".to_string(),
            FragmentList {
                fragments: vec![WebUIFragment::raw("card")],
                contains_boundary: false,
            },
        );

        let protocol = WebUIProtocol::with_tokens(fragments, Vec::new());
        let comp_index = build_component_index(&protocol);
        let (needed, _inv) =
            get_needed_components(&protocol, "app-shell", "", &comp_index).unwrap();
        assert!(needed.contains(&"app-shell".to_string()));
        assert!(needed.contains(&"my-card".to_string()));
    }

    #[test]
    fn test_get_needed_components_skips_inventory() {
        let mut fragments = HashMap::new();
        fragments.insert(
            "app-shell".to_string(),
            FragmentList {
                fragments: vec![WebUIFragment::component("my-card")],
                contains_boundary: false,
            },
        );
        fragments.insert(
            "my-card".to_string(),
            FragmentList {
                fragments: vec![WebUIFragment::raw("card")],
                contains_boundary: false,
            },
        );

        let mut protocol = WebUIProtocol::with_tokens(fragments, Vec::new());
        protocol
            .components
            .entry("app-shell".to_string())
            .or_default()
            .template = "<t></t>".to_string();
        protocol
            .components
            .entry("my-card".to_string())
            .or_default()
            .template = "<t></t>".to_string();

        let comp_index = build_component_index(&protocol);
        let (_needed, inv_hex) =
            get_needed_components(&protocol, "app-shell", "", &comp_index).unwrap();
        let (needed2, _) =
            get_needed_components(&protocol, "app-shell", &inv_hex, &comp_index).unwrap();
        assert!(needed2.is_empty());
    }

    #[test]
    fn test_get_needed_components_skips_control_fragments() {
        let mut fragments = HashMap::new();
        fragments.insert(
            "app-shell".to_string(),
            FragmentList {
                fragments: vec![
                    WebUIFragment::if_cond(
                        webui_protocol::ConditionExpr::identifier("showNav"),
                        "if-shell",
                    ),
                    WebUIFragment::for_loop("item", "items", "for-items"),
                    WebUIFragment::attribute_template("title", "attr-title"),
                ],
                contains_boundary: false,
            },
        );
        fragments.insert(
            "if-shell".to_string(),
            FragmentList {
                fragments: vec![WebUIFragment::component("mp-category-nav")],
                contains_boundary: false,
            },
        );
        fragments.insert(
            "for-items".to_string(),
            FragmentList {
                fragments: vec![WebUIFragment::component("mp-product-card")],
                contains_boundary: false,
            },
        );
        fragments.insert(
            "attr-title".to_string(),
            FragmentList {
                fragments: vec![WebUIFragment::raw("Products")],
                contains_boundary: false,
            },
        );
        fragments.insert(
            "mp-category-nav".to_string(),
            FragmentList {
                fragments: vec![WebUIFragment::raw("<nav></nav>")],
                contains_boundary: false,
            },
        );
        fragments.insert(
            "mp-product-card".to_string(),
            FragmentList {
                fragments: vec![WebUIFragment::raw("<article></article>")],
                contains_boundary: false,
            },
        );

        let protocol = WebUIProtocol::with_tokens(fragments, Vec::new());
        let comp_index = build_component_index(&protocol);
        let needed: HashSet<String> =
            get_needed_components(&protocol, "app-shell", "", &comp_index)
                .unwrap()
                .0
                .into_iter()
                .collect();

        assert!(needed.contains("app-shell"));
        assert!(needed.contains("mp-category-nav"));
        assert!(needed.contains("mp-product-card"));
        assert!(!needed.contains("if-shell"));
        assert!(!needed.contains("for-items"));
        assert!(!needed.contains("attr-title"));
    }

    #[test]
    fn test_get_needed_components_for_request_includes_shell_and_matched_route_chain() {
        let mut fragments = HashMap::new();
        fragments.insert(
            "index.html".to_string(),
            FragmentList {
                fragments: vec![WebUIFragment::component("mp-app")],
                contains_boundary: false,
            },
        );
        fragments.insert(
            "mp-app".to_string(),
            FragmentList {
                fragments: vec![
                    WebUIFragment::component("mp-category-nav"),
                    WebUIFragment::route_from(WebUiFragmentRoute {
                        path: "/search/:category".into(),
                        fragment_id: "mp-search-page".into(),
                        exact: true,
                        keep_alive: false,
                        ..Default::default()
                    }),
                    WebUIFragment::route_from(WebUiFragmentRoute {
                        path: "/product/:handle".into(),
                        fragment_id: "mp-product-page".into(),
                        exact: true,
                        keep_alive: false,
                        ..Default::default()
                    }),
                ],

                contains_boundary: false,
            },
        );
        fragments.insert(
            "mp-category-nav".to_string(),
            FragmentList {
                fragments: vec![WebUIFragment::raw("<nav></nav>")],
                contains_boundary: false,
            },
        );
        fragments.insert(
            "mp-search-page".to_string(),
            FragmentList {
                fragments: vec![WebUIFragment::component("mp-product-grid")],
                contains_boundary: false,
            },
        );
        fragments.insert(
            "mp-product-grid".to_string(),
            FragmentList {
                fragments: vec![WebUIFragment::raw("<div>grid</div>")],
                contains_boundary: false,
            },
        );
        fragments.insert(
            "mp-product-page".to_string(),
            FragmentList {
                fragments: vec![WebUIFragment::component("mp-product-detail")],
                contains_boundary: false,
            },
        );
        fragments.insert(
            "mp-product-detail".to_string(),
            FragmentList {
                fragments: vec![WebUIFragment::raw("<div>detail</div>")],
                contains_boundary: false,
            },
        );

        let mut protocol = WebUIProtocol::with_tokens(fragments, Vec::new());
        protocol
            .components
            .entry("mp-search-page".to_string())
            .or_default()
            .template = "<mp-search-page></mp-search-page>".to_string();
        protocol
            .components
            .entry("mp-product-page".to_string())
            .or_default()
            .template = "<mp-product-page></mp-product-page>".to_string();

        let comp_index = build_component_index(&protocol);
        let (needed, _inv) = get_needed_components_for_request(
            &protocol,
            "index.html",
            "/search/shirts",
            "",
            (&comp_index, &CompiledRouteIndex::new(&protocol)),
        )
        .unwrap();
        let needed: HashSet<String> = needed.into_iter().collect();

        assert!(needed.contains("mp-app"));
        assert!(needed.contains("mp-category-nav"));
        assert!(needed.contains("mp-search-page"));
        assert!(needed.contains("mp-product-grid"));
        assert!(!needed.contains("mp-product-page"));
        assert!(!needed.contains("mp-product-detail"));
    }

    #[test]
    fn test_get_needed_components_for_request_follows_nested_route_chain() {
        let mut fragments = HashMap::new();
        fragments.insert(
            "index.html".to_string(),
            FragmentList {
                fragments: vec![WebUIFragment::component("mp-app")],
                contains_boundary: false,
            },
        );
        fragments.insert(
            "mp-app".to_string(),
            FragmentList {
                fragments: vec![WebUIFragment::route_from(WebUiFragmentRoute {
                    path: "/account/*rest".into(),
                    fragment_id: "mp-account-shell".into(),
                    exact: false,
                    keep_alive: false,
                    ..Default::default()
                })],

                contains_boundary: false,
            },
        );
        fragments.insert(
            "mp-account-shell".to_string(),
            FragmentList {
                fragments: vec![
                    WebUIFragment::component("mp-account-nav"),
                    WebUIFragment::route_from(WebUiFragmentRoute {
                        path: "/account/profile".into(),
                        fragment_id: "mp-profile-page".into(),
                        exact: true,
                        keep_alive: false,
                        ..Default::default()
                    }),
                    WebUIFragment::route_from(WebUiFragmentRoute {
                        path: "/account/orders/:id".into(),
                        fragment_id: "mp-order-page".into(),
                        exact: true,
                        keep_alive: false,
                        ..Default::default()
                    }),
                ],

                contains_boundary: false,
            },
        );
        fragments.insert(
            "mp-account-nav".to_string(),
            FragmentList {
                fragments: vec![WebUIFragment::raw("<nav></nav>")],
                contains_boundary: false,
            },
        );
        fragments.insert(
            "mp-profile-page".to_string(),
            FragmentList {
                fragments: vec![WebUIFragment::raw("<profile></profile>")],
                contains_boundary: false,
            },
        );
        fragments.insert(
            "mp-order-page".to_string(),
            FragmentList {
                fragments: vec![WebUIFragment::component("mp-order-detail")],
                contains_boundary: false,
            },
        );
        fragments.insert(
            "mp-order-detail".to_string(),
            FragmentList {
                fragments: vec![WebUIFragment::raw("<detail></detail>")],
                contains_boundary: false,
            },
        );

        let mut protocol = WebUIProtocol::with_tokens(fragments, Vec::new());
        protocol
            .components
            .entry("mp-account-shell".to_string())
            .or_default()
            .template = "<mp-account-shell></mp-account-shell>".to_string();
        protocol
            .components
            .entry("mp-profile-page".to_string())
            .or_default()
            .template = "<mp-profile-page></mp-profile-page>".to_string();
        protocol
            .components
            .entry("mp-order-page".to_string())
            .or_default()
            .template = "<mp-order-page></mp-order-page>".to_string();

        let comp_index = build_component_index(&protocol);
        let (needed, _inv) = get_needed_components_for_request(
            &protocol,
            "index.html",
            "/account/orders/42",
            "",
            (&comp_index, &CompiledRouteIndex::new(&protocol)),
        )
        .unwrap();
        let needed: HashSet<String> = needed.into_iter().collect();

        assert!(needed.contains("mp-app"));
        assert!(needed.contains("mp-account-shell"));
        assert!(needed.contains("mp-account-nav"));
        assert!(needed.contains("mp-order-page"));
        assert!(needed.contains("mp-order-detail"));
        assert!(!needed.contains("mp-profile-page"));
    }

    #[test]
    fn test_get_needed_components_for_request_over_ships_if_and_loop_within_matched_route() {
        let mut fragments = HashMap::new();
        fragments.insert(
            "index.html".to_string(),
            FragmentList {
                fragments: vec![WebUIFragment::component("mp-app")],
                contains_boundary: false,
            },
        );
        fragments.insert(
            "mp-app".to_string(),
            FragmentList {
                fragments: vec![WebUIFragment::route_from(WebUiFragmentRoute {
                    path: "/search".into(),
                    fragment_id: "mp-search-page".into(),
                    exact: true,
                    keep_alive: false,
                    ..Default::default()
                })],

                contains_boundary: false,
            },
        );
        fragments.insert(
            "mp-search-page".to_string(),
            FragmentList {
                fragments: vec![
                    WebUIFragment::if_cond(
                        webui_protocol::ConditionExpr::identifier("showFilters"),
                        "if-filters",
                    ),
                    WebUIFragment::for_loop("item", "items", "item-loop"),
                ],
                contains_boundary: false,
            },
        );
        fragments.insert(
            "if-filters".to_string(),
            FragmentList {
                fragments: vec![WebUIFragment::component("mp-filter-panel")],
                contains_boundary: false,
            },
        );
        fragments.insert(
            "item-loop".to_string(),
            FragmentList {
                fragments: vec![WebUIFragment::component("mp-item-card")],
                contains_boundary: false,
            },
        );
        fragments.insert(
            "mp-filter-panel".to_string(),
            FragmentList {
                fragments: vec![WebUIFragment::raw("<filters></filters>")],
                contains_boundary: false,
            },
        );
        fragments.insert(
            "mp-item-card".to_string(),
            FragmentList {
                fragments: vec![WebUIFragment::raw("<item></item>")],
                contains_boundary: false,
            },
        );

        let mut protocol = WebUIProtocol::with_tokens(fragments, Vec::new());
        protocol
            .components
            .entry("mp-search-page".to_string())
            .or_default()
            .template = "<mp-search-page></mp-search-page>".to_string();

        let comp_index = build_component_index(&protocol);
        let (needed, _inv) = get_needed_components_for_request(
            &protocol,
            "index.html",
            "/search",
            "",
            (&comp_index, &CompiledRouteIndex::new(&protocol)),
        )
        .unwrap();
        let needed: HashSet<String> = needed.into_iter().collect();

        assert!(needed.contains("mp-app"));
        assert!(needed.contains("mp-search-page"));
        assert!(needed.contains("mp-filter-panel"));
        assert!(needed.contains("mp-item-card"));
    }

    #[test]
    fn test_get_needed_components_for_request_respects_inventory() {
        let mut fragments = HashMap::new();
        fragments.insert(
            "index.html".to_string(),
            FragmentList {
                fragments: vec![WebUIFragment::component("mp-app")],
                contains_boundary: false,
            },
        );
        fragments.insert(
            "mp-app".to_string(),
            FragmentList {
                fragments: vec![WebUIFragment::route_from(WebUiFragmentRoute {
                    path: "/search".into(),
                    fragment_id: "mp-search-page".into(),
                    exact: true,
                    keep_alive: false,
                    ..Default::default()
                })],

                contains_boundary: false,
            },
        );
        fragments.insert(
            "mp-search-page".to_string(),
            FragmentList {
                fragments: vec![WebUIFragment::component("mp-product-grid")],
                contains_boundary: false,
            },
        );
        fragments.insert(
            "mp-product-grid".to_string(),
            FragmentList {
                fragments: vec![WebUIFragment::raw("<grid></grid>")],
                contains_boundary: false,
            },
        );

        let mut protocol = WebUIProtocol::with_tokens(fragments, Vec::new());
        for name in ["mp-app", "mp-search-page", "mp-product-grid"] {
            protocol
                .components
                .entry(name.to_string())
                .or_default()
                .template = format!("<f-template id=\"{name}\"></f-template>");
        }

        let comp_index = build_component_index(&protocol);
        let route_index = CompiledRouteIndex::new(&protocol);
        let (_needed, inventory) = get_needed_components_for_request(
            &protocol,
            "index.html",
            "/search",
            "",
            (&comp_index, &route_index),
        )
        .unwrap();
        let (needed_again, _) = get_needed_components_for_request(
            &protocol,
            "index.html",
            "/search",
            &inventory,
            (&comp_index, &route_index),
        )
        .unwrap();
        assert!(needed_again.is_empty());
    }

    #[test]
    fn test_inventory_includes_boundary_components_for_unmatched_sibling_routes() {
        // Regression: pending/error components for routes that are NOT in the
        // matched chain at the current request path must still be inventoried.
        // The client renders pending UI before a sibling route's partial
        // resolves and error UI when it fails, so neither can be delivered by
        // the target route's own fetch — both must already be on the client.
        let mut fragments = HashMap::new();
        fragments.insert(
            "index.html".to_string(),
            FragmentList {
                fragments: vec![WebUIFragment::route_from(WebUiFragmentRoute {
                    path: "/".into(),
                    fragment_id: "route-shell".into(),
                    children: vec![
                        WebUiFragmentRoute {
                            path: "slow".into(),
                            fragment_id: "page-slow".into(),
                            exact: true,
                            pending_component: "loading-skeleton".into(),
                            ..Default::default()
                        },
                        WebUiFragmentRoute {
                            path: "failing".into(),
                            fragment_id: "page-failing".into(),
                            exact: true,
                            error_component: "error-display".into(),
                            ..Default::default()
                        },
                    ],
                    ..Default::default()
                })],

                contains_boundary: false,
            },
        );
        for id in [
            "route-shell",
            "page-slow",
            "page-failing",
            "loading-skeleton",
            "error-display",
        ] {
            fragments.insert(
                id.to_string(),
                FragmentList {
                    fragments: vec![WebUIFragment::raw("<x></x>")],
                    contains_boundary: false,
                },
            );
        }

        let mut protocol = WebUIProtocol::with_tokens(fragments, Vec::new());
        for id in [
            "route-shell",
            "page-slow",
            "page-failing",
            "loading-skeleton",
            "error-display",
        ] {
            protocol
                .components
                .entry(id.to_string())
                .or_default()
                .template = format!("<f-template id=\"{id}\"></f-template>");
        }

        // Request the root path: neither "slow" nor "failing" is in the matched chain.
        let reachable = collect_reachable_component_order_for_request(
            &protocol,
            "index.html",
            "/",
            &CompiledRouteIndex::new(&protocol),
        );
        assert!(
            reachable.iter().any(|name| name == "loading-skeleton"),
            "pending component of an unmatched sibling route must be inventoried: {reachable:?}"
        );
        assert!(
            reachable.iter().any(|name| name == "error-display"),
            "error component of an unmatched sibling route must be inventoried: {reachable:?}"
        );
    }

    #[test]
    fn component_reachability_propagates_route_dependency_to_parent() {
        let protocol = WebUIProtocol::new(HashMap::from([
            (
                "comp-a".to_string(),
                FragmentList {
                    fragments: vec![WebUIFragment::component("comp-b")],
                    contains_boundary: false,
                },
            ),
            (
                "comp-b".to_string(),
                FragmentList {
                    fragments: vec![WebUIFragment::route("/", "page-a")],
                    contains_boundary: false,
                },
            ),
            (
                "page-a".to_string(),
                FragmentList {
                    fragments: vec![WebUIFragment::raw("<p>page</p>")],
                    contains_boundary: false,
                },
            ),
        ]));
        let component_index = build_component_index(&protocol);
        let reachability = ComponentReachabilityIndex::new(&protocol, &component_index);

        assert_eq!(
            reachability.is_route_dependent(component_index["comp-a"]),
            Some(true)
        );
        assert_eq!(
            reachability.is_route_dependent(component_index["comp-b"]),
            Some(true)
        );
        assert_eq!(
            reachability.is_route_dependent(component_index["page-a"]),
            Some(false)
        );
    }

    #[test]
    fn request_reachability_visits_reused_route_component_at_each_base() {
        let mut protocol = WebUIProtocol::new(HashMap::from([
            (
                "shared-shell".to_string(),
                FragmentList {
                    fragments: vec![WebUIFragment::route("details", "detail-page")],
                    contains_boundary: false,
                },
            ),
            (
                "detail-page".to_string(),
                FragmentList {
                    fragments: vec![WebUIFragment::raw("<p>Detail</p>")],
                    contains_boundary: false,
                },
            ),
        ]));
        for tag in ["shared-shell", "detail-page"] {
            protocol
                .components
                .entry(tag.to_string())
                .or_default()
                .template = "<template></template>".to_string();
        }
        let route_index = CompiledRouteIndex::new(&protocol);
        let handler_protocol = Protocol::new(protocol.clone());
        let reachability = handler_protocol.component_reachability();
        let shell = handler_protocol.component_index()["shared-shell"];
        let roots = [
            (shell, Some(Box::from("/other"))),
            (shell, Some(Box::from("/account"))),
        ];

        let reachable = collect_reachable_components_from_roots(
            &protocol,
            &roots,
            reachability,
            "/account/details",
            &route_index,
        );

        assert!(
            reachable.iter().any(|tag| tag == "detail-page"),
            "the second route base must not be hidden by fragment-id deduplication: {reachable:?}"
        );
    }

    #[test]
    fn component_reachability_index_is_lazy() {
        let protocol = Protocol::new(WebUIProtocol::new(HashMap::from([(
            "comp-a".to_string(),
            FragmentList {
                fragments: vec![WebUIFragment::raw("<p>leaf</p>")],
                contains_boundary: false,
            },
        )])));

        assert!(protocol.component_reachability.get().is_none());
        assert_eq!(
            protocol
                .component_reachability()
                .is_route_dependent(protocol.component_index["comp-a"]),
            Some(false)
        );
        assert!(protocol.component_reachability.get().is_some());
    }

    #[test]
    fn test_render_partial_carries_module_css_in_component_styles() {
        let mut fragments = HashMap::new();
        fragments.insert(
            "index.html".to_string(),
            FragmentList {
                fragments: vec![WebUIFragment::component("my-page")],
                contains_boundary: false,
            },
        );
        fragments.insert(
            "my-page".to_string(),
            FragmentList {
                fragments: vec![WebUIFragment::raw("<p>page</p>")],
                contains_boundary: false,
            },
        );

        let mut protocol = WebUIProtocol::with_tokens(fragments, Vec::new());
        protocol.set_css_strategy(webui_protocol::CssStrategy::Module);
        let component = protocol
            .components
            .entry("my-page".to_string())
            .or_default();
        component.template_json = r#"{"h":"<p>page</p>"}"#.to_string();
        component.css = ".page{color:red}".to_string();
        protocol.populate_style_closures(&["index.html"]);

        let mut index = ProtocolIndex::new(&protocol);
        let partial =
            render_partial_metadata(&protocol, "index.html", "/", "", &mut index).unwrap();
        assert_eq!(partial["componentStyles"]["version"], 1);
        assert_eq!(partial["componentStyles"]["strategy"], "module");
        assert_eq!(
            partial["componentStyles"]["resources"]["my-page"],
            serde_json::json!({
                "kind": "module",
                "specifier": "my-page",
                "css": ".page{color:red}"
            })
        );
        assert_eq!(
            partial["componentStyles"]["closures"]["my-page"],
            serde_json::json!(["my-page"])
        );

        // templates should contain only JSON-safe metadata
        let templates = partial["templates"]
            .as_object()
            .expect("templates should be an object");
        assert_eq!(templates.len(), 1);
        let template = templates.get("my-page").expect("my-page template");
        assert_eq!(template["h"], "<p>page</p>");

        let inventory = partial["inventory"].as_str().expect("inventory");
        let repeated =
            render_partial_metadata(&protocol, "index.html", "/", inventory, &mut index).unwrap();
        assert!(repeated["templates"].as_object().unwrap().is_empty());
        assert_eq!(
            repeated["componentStyles"]["resources"],
            serde_json::json!({}),
            "inventoried style definitions must not be retransmitted"
        );
        assert_eq!(
            repeated["componentStyles"]["closures"],
            serde_json::json!({}),
            "inventoried style closures must not be retransmitted"
        );
    }

    #[test]
    fn styled_protocol_without_closures_is_rejected() {
        let mut protocol = WebUIProtocol::default();
        protocol.fragments = HashMap::from([
            (
                "index.html".to_string(),
                FragmentList {
                    fragments: vec![WebUIFragment::component("legacy-page")],
                    contains_boundary: false,
                },
            ),
            (
                "legacy-page".to_string(),
                FragmentList {
                    fragments: vec![WebUIFragment::raw("<p>Legacy</p>")],
                    contains_boundary: false,
                },
            ),
        ]);
        protocol.components.insert(
            "legacy-page".to_string(),
            webui_protocol::ComponentData {
                template_json: r#"{"h":"<p>Legacy</p>"}"#.to_string(),
                css: ".legacy{display:block}".to_string(),
                ..Default::default()
            },
        );
        protocol.set_css_strategy(webui_protocol::CssStrategy::Module);

        let mut index = ProtocolIndex::new(&protocol);
        let error = render_partial_metadata(&protocol, "index.html", "/", "", &mut index)
            .expect_err("styled protocols require closure metadata");
        assert!(error
            .to_string()
            .contains("component style closure metadata is required"));
    }

    #[test]
    fn test_render_partial_link_strategy_uses_component_styles() {
        let mut fragments = HashMap::new();
        fragments.insert(
            "index.html".to_string(),
            FragmentList {
                fragments: vec![WebUIFragment::component("my-page")],
                contains_boundary: false,
            },
        );
        fragments.insert(
            "my-page".to_string(),
            FragmentList {
                fragments: vec![WebUIFragment::raw("<p>page</p>")],
                contains_boundary: false,
            },
        );

        let mut protocol = WebUIProtocol::with_tokens(fragments, Vec::new());
        protocol.set_css_strategy(webui_protocol::CssStrategy::Link);
        let component = protocol
            .components
            .entry("my-page".to_string())
            .or_default();
        component.template_json = r#"{"h":"<p>page</p>"}"#.to_string();
        component.css_href = "my-page.css".to_string();
        // css is empty — Link strategy stores href, not content
        protocol.populate_style_closures(&["index.html"]);

        let mut index = ProtocolIndex::new(&protocol);
        let partial =
            render_partial_metadata(&protocol, "index.html", "/", "", &mut index).unwrap();
        let templates = partial["templates"]
            .as_object()
            .expect("templates should be an object");

        assert_eq!(templates.len(), 1, "should include template metadata");
        assert_eq!(
            partial["componentStyles"]["resources"]["my-page"],
            serde_json::json!({"kind": "link", "href": "my-page.css"})
        );
    }

    #[test]
    fn test_render_partial_style_strategy_uses_component_styles() {
        let mut fragments = HashMap::new();
        fragments.insert(
            "index.html".to_string(),
            FragmentList {
                fragments: vec![WebUIFragment::component("my-page")],
                contains_boundary: false,
            },
        );
        fragments.insert(
            "my-page".to_string(),
            FragmentList {
                fragments: vec![WebUIFragment::raw("<p>page</p>")],
                contains_boundary: false,
            },
        );

        let mut protocol = WebUIProtocol::with_tokens(fragments, Vec::new());
        protocol.set_css_strategy(webui_protocol::CssStrategy::Style);
        let component = protocol
            .components
            .entry("my-page".to_string())
            .or_default();
        component.template_json = r#"{"h":"<p>page</p>"}"#.to_string();
        component.css = ".p{color:red}".to_string();
        protocol.populate_style_closures(&["index.html"]);

        let mut index = ProtocolIndex::new(&protocol);
        let partial =
            render_partial_metadata(&protocol, "index.html", "/", "", &mut index).unwrap();
        let templates = partial["templates"]
            .as_object()
            .expect("templates should be an object");

        assert_eq!(templates.len(), 1, "should include template metadata");
        assert_eq!(
            partial["componentStyles"]["resources"]["my-page"],
            serde_json::json!({"kind": "style", "css": ".p{color:red}"})
        );
    }

    #[test]
    fn test_render_partial_emits_empty_component_styles_for_no_css_components() {
        let mut fragments = HashMap::new();
        fragments.insert(
            "index.html".to_string(),
            FragmentList {
                fragments: vec![WebUIFragment::component("my-page")],
                contains_boundary: false,
            },
        );
        fragments.insert(
            "my-page".to_string(),
            FragmentList {
                fragments: vec![WebUIFragment::raw("<p>page</p>")],
                contains_boundary: false,
            },
        );

        let mut protocol = WebUIProtocol::with_tokens(fragments, Vec::new());
        let component = protocol
            .components
            .entry("my-page".to_string())
            .or_default();
        component.template_json = r#"{"h":"<p>page</p>"}"#.to_string();
        // No CSS — simulates Link or Style mode

        let mut index = ProtocolIndex::new(&protocol);
        let partial =
            render_partial_metadata(&protocol, "index.html", "/", "", &mut index).unwrap();
        assert_eq!(
            partial["componentStyles"]["resources"],
            serde_json::json!({})
        );
        assert_eq!(
            partial["componentStyles"]["closures"],
            serde_json::json!({})
        );
    }

    #[test]
    fn test_render_partial_filters_styles_with_template_inventory() {
        let mut fragments = HashMap::new();
        fragments.insert(
            "index.html".to_string(),
            FragmentList {
                fragments: vec![WebUIFragment::component("my-page")],
                contains_boundary: false,
            },
        );
        fragments.insert(
            "my-page".to_string(),
            FragmentList {
                fragments: vec![WebUIFragment::raw("<p>page</p>")],
                contains_boundary: false,
            },
        );

        let mut protocol = WebUIProtocol::with_tokens(fragments, Vec::new());
        protocol.set_css_strategy(webui_protocol::CssStrategy::Module);
        let component = protocol
            .components
            .entry("my-page".to_string())
            .or_default();
        component.template_json = r#"{"h":"<p>page</p>"}"#.to_string();
        component.css = ".page{color:red}".to_string();
        protocol.populate_style_closures(&["index.html"]);

        let mut index = ProtocolIndex::new(&protocol);
        // First call to establish inventory
        let partial1 =
            render_partial_metadata(&protocol, "index.html", "/", "", &mut index).unwrap();
        let inv = partial1["inventory"].as_str().unwrap_or_default();
        assert!(!inv.is_empty());

        let partial2 =
            render_partial_metadata(&protocol, "index.html", "/", inv, &mut index).unwrap();
        let templates = partial2["templates"]
            .as_object()
            .expect("templates should be an object");

        assert!(
            templates.is_empty(),
            "templates should be empty when inventory is full"
        );
        assert_eq!(
            partial2["componentStyles"]["resources"],
            serde_json::json!({})
        );
        assert_eq!(
            partial2["componentStyles"]["closures"],
            serde_json::json!({})
        );
    }

    #[test]
    fn component_style_delta_sends_missing_and_reuses_registered_closure_resources() {
        let mut protocol = WebUIProtocol::default();
        protocol.set_css_strategy(webui_protocol::CssStrategy::Style);
        for tag in ["page-b", "shared-card"] {
            protocol.fragments.insert(
                tag.to_string(),
                FragmentList {
                    fragments: Vec::new(),
                    contains_boundary: false,
                },
            );
            protocol.components.insert(
                tag.to_string(),
                webui_protocol::ComponentData {
                    css: format!(".{tag}{{display:block}}"),
                    ..Default::default()
                },
            );
        }
        protocol.style_closures.insert(
            "page-b".to_string(),
            webui_protocol::ComponentStyleClosure {
                component_tags: vec!["page-b".to_string(), "shared-card".to_string()],
                style_chunks: Vec::new(),
            },
        );
        protocol.style_closures.insert(
            "shared-card".to_string(),
            webui_protocol::ComponentStyleClosure {
                component_tags: vec!["shared-card".to_string()],
                style_chunks: Vec::new(),
            },
        );
        let mut index = ProtocolIndex::new(&protocol);

        let first_page =
            render_component_templates(&protocol, &["page-b"], "", &mut index).unwrap();
        assert!(first_page["componentStyles"]["resources"]["page-b"].is_object());
        assert!(
            first_page["componentStyles"]["resources"]["shared-card"].is_object(),
            "a missing closure dependency must be sent with its new root"
        );

        let shared =
            render_component_templates(&protocol, &["shared-card"], "", &mut index).unwrap();
        let shared_inventory = shared["inventory"].as_str().unwrap_or_default();
        let page = render_component_templates(&protocol, &["page-b"], shared_inventory, &mut index)
            .unwrap();
        assert_eq!(
            page["componentStyles"]["closures"]["page-b"],
            serde_json::json!(["page-b", "shared-card"])
        );
        assert!(page["componentStyles"]["resources"]["page-b"].is_object());
        assert!(
            page["componentStyles"]["resources"]
                .get("shared-card")
                .is_none(),
            "a resource already covered by inventory must not be retransmitted"
        );
    }

    #[test]
    fn bundled_style_metadata_tracks_chunks_independently_and_covers_members() {
        let mut protocol = WebUIProtocol::default();
        protocol.set_css_strategy(webui_protocol::CssStrategy::Style);
        for tag in ["a-card", "b-card"] {
            protocol
                .fragments
                .insert(tag.to_string(), FragmentList::default());
            protocol.components.insert(
                tag.to_string(),
                webui_protocol::ComponentData {
                    css: format!(".{tag}{{display:block}}"),
                    ..Default::default()
                },
            );
            protocol.style_closures.insert(
                tag.to_string(),
                webui_protocol::ComponentStyleClosure {
                    component_tags: vec![tag.to_string()],
                    style_chunks: Vec::new(),
                },
            );
        }
        protocol
            .fragments
            .insert("index.html".to_string(), FragmentList::default());
        protocol.style_closures.insert(
            "index.html".to_string(),
            webui_protocol::ComponentStyleClosure {
                component_tags: vec!["a-card".to_string(), "b-card".to_string()],
                style_chunks: vec![0],
            },
        );
        protocol.style_chunks.push(webui_protocol::StyleChunk {
            name: "_chunk-a-card-2".to_string(),
            css: ".a-card{display:block}\n.b-card{display:block}".to_string(),
            css_href: String::new(),
            component_tags: vec!["a-card".to_string(), "b-card".to_string()],
        });

        let initial =
            collect_component_styles(&protocol, ["index.html", "a-card", "b-card"]).unwrap();
        assert_eq!(
            initial["resources"]["_chunk-a-card-2"]["members"],
            serde_json::json!(["a-card", "b-card"])
        );
        assert_eq!(
            initial["closures"],
            serde_json::json!({ "index.html": ["_chunk-a-card-2"] }),
            "member closures already covered by the requested tree must not duplicate CSS"
        );
        assert_eq!(
            initial["resources"].as_object().map(serde_json::Map::len),
            Some(1)
        );

        let component_index = build_component_index(&protocol);
        let mut component_inventory = vec![0u8; component_index.len().div_ceil(8)];
        for index in component_index.values() {
            set_component(&mut component_inventory, *index);
        }
        let from_component_inventory = collect_component_styles_for_inventory(
            &protocol,
            ["index.html"],
            &component_inventory,
            &component_index,
        )
        .unwrap();
        assert!(
            from_component_inventory["resources"]["_chunk-a-card-2"].is_object(),
            "component-template bits do not prove that the client registered a chunk"
        );

        let style_index = build_style_resource_index(&protocol);
        let mut style_inventory = vec![0u8; style_index.len().div_ceil(8)];
        set_component(&mut style_inventory, style_index["_chunk-a-card-2"]);
        let from_style_inventory = collect_component_style_delta(
            &protocol,
            ["index.html"],
            &style_inventory,
            &style_index,
        )
        .unwrap();
        assert_eq!(
            from_style_inventory["resources"],
            serde_json::json!({}),
            "the exact style-resource inventory should suppress a registered chunk"
        );
        let chunk_index = protocol.style_chunk_index();
        let borrowed = collect_borrowed_component_style_delta(
            &protocol,
            ["index.html"],
            &style_inventory,
            &style_index,
            &chunk_index,
        )
        .unwrap();
        assert_eq!(
            serde_json::to_string(&borrowed).unwrap(),
            serde_json::to_string(&from_style_inventory).unwrap(),
            "the borrowed streaming serializer must preserve the canonical style payload bytes"
        );
    }

    #[test]
    fn borrowed_streaming_style_payload_matches_owned_for_every_strategy() {
        for strategy in [
            webui_protocol::CssStrategy::Link,
            webui_protocol::CssStrategy::Style,
            webui_protocol::CssStrategy::Module,
        ] {
            let mut protocol = WebUIProtocol::default();
            protocol.set_css_strategy(strategy);
            protocol
                .fragments
                .insert("index.html".to_string(), FragmentList::default());
            protocol.components.insert(
                "a-card".to_string(),
                webui_protocol::ComponentData {
                    css: ".a-card{display:block}".to_string(),
                    css_href: "/a-card.css".to_string(),
                    ..Default::default()
                },
            );
            protocol.style_closures.insert(
                "index.html".to_string(),
                webui_protocol::ComponentStyleClosure {
                    component_tags: vec!["a-card".to_string()],
                    style_chunks: Vec::new(),
                },
            );

            let style_index = build_component_index(&protocol);
            let style_inventory = vec![0u8; style_index.len().div_ceil(8)];
            let owned = collect_component_style_delta(
                &protocol,
                ["index.html"],
                &style_inventory,
                &style_index,
            )
            .unwrap();
            let chunk_index = protocol.style_chunk_index();
            let borrowed = collect_borrowed_component_style_delta(
                &protocol,
                ["index.html"],
                &style_inventory,
                &style_index,
                &chunk_index,
            )
            .unwrap();

            assert_eq!(
                serde_json::to_string(&borrowed).unwrap(),
                serde_json::to_string(&owned).unwrap(),
                "borrowed payload differs for {strategy:?}"
            );
        }
    }

    /// A closure that lists members must still deliver the chunk that ships
    /// them.
    ///
    /// Only closures the bundler treated as roots carry `style_chunks`; a plain
    /// Light component keeps its member list. Delivering those members verbatim
    /// re-ships bytes the covering chunk already contains, and leaves the
    /// closure correct only if some other closure installs the chunk first.
    /// Resolving each member through the chunk index removes both problems.
    #[test]
    fn member_closures_deliver_the_chunk_that_covers_them() {
        let mut protocol = WebUIProtocol::default();
        protocol.set_css_strategy(webui_protocol::CssStrategy::Style);
        for tag in ["a-card", "b-card"] {
            protocol
                .fragments
                .insert(tag.to_string(), FragmentList::default());
            protocol.components.insert(
                tag.to_string(),
                webui_protocol::ComponentData {
                    css: format!(".{tag}{{display:block}}"),
                    ..Default::default()
                },
            );
        }
        protocol
            .fragments
            .insert("lazy-panel".to_string(), FragmentList::default());
        // Not a bundler root, so it keeps its member list.
        protocol.style_closures.insert(
            "lazy-panel".to_string(),
            webui_protocol::ComponentStyleClosure {
                component_tags: vec!["a-card".to_string(), "b-card".to_string()],
                style_chunks: Vec::new(),
            },
        );
        protocol.style_chunks.push(webui_protocol::StyleChunk {
            name: "_chunk-a-card-2".to_string(),
            css: ".a-card{display:block}\n.b-card{display:block}".to_string(),
            css_href: String::new(),
            component_tags: vec!["a-card".to_string(), "b-card".to_string()],
        });

        let styles = collect_component_styles(&protocol, ["lazy-panel"]).unwrap();
        assert_eq!(
            styles["closures"],
            serde_json::json!({ "lazy-panel": ["_chunk-a-card-2"] }),
            "both members resolve to one chunk, named once"
        );
        assert_eq!(
            styles["resources"].as_object().map(serde_json::Map::len),
            Some(1),
            "the per-member stylesheets the chunk already contains are not re-shipped"
        );
        assert!(
            styles["resources"]["_chunk-a-card-2"].is_object(),
            "the closure carries the chunk itself, not a dependency on another closure"
        );
    }

    /// A member with no covering chunk still delivers its own stylesheet.
    #[test]
    fn member_closures_fall_back_when_no_chunk_covers_them() {
        let mut protocol = WebUIProtocol::default();
        protocol.set_css_strategy(webui_protocol::CssStrategy::Style);
        for tag in ["a-card", "solo-card"] {
            protocol
                .fragments
                .insert(tag.to_string(), FragmentList::default());
            protocol.components.insert(
                tag.to_string(),
                webui_protocol::ComponentData {
                    css: format!(".{tag}{{display:block}}"),
                    ..Default::default()
                },
            );
        }
        protocol
            .fragments
            .insert("lazy-panel".to_string(), FragmentList::default());
        protocol.style_closures.insert(
            "lazy-panel".to_string(),
            webui_protocol::ComponentStyleClosure {
                component_tags: vec!["a-card".to_string(), "solo-card".to_string()],
                style_chunks: Vec::new(),
            },
        );
        protocol.style_chunks.push(webui_protocol::StyleChunk {
            name: "_chunk-a-card-1".to_string(),
            css: ".a-card{display:block}".to_string(),
            css_href: String::new(),
            component_tags: vec!["a-card".to_string()],
        });

        let styles = collect_component_styles(&protocol, ["lazy-panel"]).unwrap();
        assert_eq!(
            styles["closures"],
            serde_json::json!({ "lazy-panel": ["_chunk-a-card-1", "solo-card"] }),
            "cascade order is preserved across the chunked and unchunked members"
        );
        assert!(styles["resources"]["solo-card"].is_object());
    }

    #[test]
    fn test_non_route_siblings_included_in_needed_components() {
        // Reproduces the commerce app layout: mp-app has both route children
        // (via outlet) AND non-route sibling components (mp-cart-panel, mp-footer).
        // All siblings must be in the needed set so their module CSS definitions
        // are emitted in <head> during SSR.
        let mut fragments = HashMap::new();

        // Entry → app-shell component
        fragments.insert(
            "index.html".to_string(),
            FragmentList {
                fragments: vec![WebUIFragment::component("app-shell")],
                contains_boundary: false,
            },
        );

        // app-shell has: navbar (component), route (outlet), cart-panel (component)
        fragments.insert(
            "app-shell".to_string(),
            FragmentList {
                fragments: vec![
                    WebUIFragment::component("my-navbar"),
                    WebUIFragment::route_from(WebUiFragmentRoute {
                        path: "/about".into(),
                        fragment_id: "page-about".into(),
                        exact: true,
                        keep_alive: false,
                        ..Default::default()
                    }),
                    WebUIFragment::component("cart-panel"),
                ],

                contains_boundary: false,
            },
        );

        // Leaf fragments
        fragments.insert(
            "my-navbar".to_string(),
            FragmentList {
                fragments: vec![WebUIFragment::raw("<nav/>")],
                contains_boundary: false,
            },
        );
        fragments.insert(
            "page-about".to_string(),
            FragmentList {
                fragments: vec![WebUIFragment::raw("<h1>About</h1>")],
                contains_boundary: false,
            },
        );
        fragments.insert(
            "cart-panel".to_string(),
            FragmentList {
                fragments: vec![WebUIFragment::raw("<aside>Cart</aside>")],
                contains_boundary: false,
            },
        );

        let mut protocol = WebUIProtocol::with_tokens(fragments, Vec::new());
        for name in ["app-shell", "my-navbar", "page-about", "cart-panel"] {
            let comp = protocol.components.entry(name.to_string()).or_default();
            comp.template_json = format!(r#"{{"h":"<div class=\"{name}\"></div>"}}"#);
            comp.css = format!(".{name}{{display:block}}");
        }

        let comp_index = build_component_index(&protocol);
        let (needed, _inv) = get_needed_components_for_request(
            &protocol,
            "index.html",
            "/about",
            "",
            (&comp_index, &CompiledRouteIndex::new(&protocol)),
        )
        .unwrap();

        assert!(
            needed.contains(&"app-shell".to_string()),
            "app-shell should be needed: {needed:?}"
        );
        assert!(
            needed.contains(&"my-navbar".to_string()),
            "my-navbar (non-route sibling) should be needed: {needed:?}"
        );
        assert!(
            needed.contains(&"page-about".to_string()),
            "page-about (active route) should be needed: {needed:?}"
        );
        assert!(
            needed.contains(&"cart-panel".to_string()),
            "cart-panel (non-route sibling) should be needed: {needed:?}"
        );
    }

    // ── RouteChainEntry.to_json + allowed_query tests ────────────────

    #[test]
    fn test_chain_entry_to_json_includes_allowed_query() {
        let entry = RouteChainEntry {
            component: "compose-page".into(),
            path: "compose".into(),
            params: HashMap::new(),
            exact: true,
            allowed_query: "action,to,subject".into(),
            keep_alive: false,
            cache_tags: Vec::new(),
            invalidates: Vec::new(),
            pending_component: String::new(),
            error_component: String::new(),
        };
        let json = entry.to_json();
        assert_eq!(json["allowedQuery"], "action,to,subject");
    }

    #[test]
    fn test_chain_entry_to_json_omits_empty_allowed_query() {
        let entry = RouteChainEntry {
            component: "home-page".into(),
            path: "/".into(),
            params: HashMap::new(),
            exact: true,
            allowed_query: String::new(),
            keep_alive: false,
            cache_tags: Vec::new(),
            invalidates: Vec::new(),
            pending_component: String::new(),
            error_component: String::new(),
        };
        let json = entry.to_json();
        assert!(
            json.get("allowedQuery").is_none(),
            "empty allowed_query should not appear in JSON"
        );
    }

    #[test]
    fn test_collect_route_chain_carries_allowed_query() {
        let mut fragments = HashMap::new();
        fragments.insert(
            "index.html".to_string(),
            FragmentList {
                fragments: vec![WebUIFragment::route_from(WebUiFragmentRoute {
                    path: "/".into(),
                    fragment_id: "app-shell".into(),
                    exact: false,
                    children: vec![WebUiFragmentRoute {
                        path: "compose".into(),
                        fragment_id: "compose-page".into(),
                        exact: true,
                        allowed_query: "action,to".into(),
                        keep_alive: false,
                        ..Default::default()
                    }],
                    keep_alive: false,
                    ..Default::default()
                })],

                contains_boundary: false,
            },
        );
        fragments.insert(
            "app-shell".to_string(),
            FragmentList {
                fragments: vec![WebUIFragment::raw("<h1>App</h1>"), WebUIFragment::outlet()],
                contains_boundary: false,
            },
        );
        fragments.insert(
            "compose-page".to_string(),
            FragmentList {
                fragments: vec![WebUIFragment::raw("<p>Compose</p>")],
                contains_boundary: false,
            },
        );
        let mut protocol = WebUIProtocol::new(fragments);
        protocol
            .components
            .entry("app-shell".into())
            .or_default()
            .css_href = "/app-shell.css".into();
        protocol
            .components
            .entry("compose-page".into())
            .or_default()
            .template_json = r#"{"h":"<p>Compose</p>"}"#.into();

        let chain = collect_route_chain(
            &protocol,
            "index.html",
            "/compose",
            &CompiledRouteIndex::new(&protocol),
        );
        assert_eq!(chain.len(), 2);
        assert_eq!(chain[0].component, "app-shell");
        assert!(chain[0].allowed_query.is_empty());
        assert_eq!(chain[1].component, "compose-page");
        assert_eq!(chain[1].allowed_query, "action,to");
    }

    #[test]
    fn scriptless_partial_uses_navigation_keys_without_bootstrap_keys() {
        let mut fragments = HashMap::new();
        fragments.insert(
            "index.html".to_string(),
            FragmentList {
                fragments: vec![WebUIFragment::route_from(WebUiFragmentRoute {
                    path: "/items".into(),
                    fragment_id: "items-page".into(),
                    exact: true,
                    ..Default::default()
                })],

                contains_boundary: false,
            },
        );
        fragments.insert(
            "items-page".to_string(),
            FragmentList {
                fragments: vec![WebUIFragment::raw("<p>Items</p>")],
                contains_boundary: false,
            },
        );
        let mut protocol = WebUIProtocol::new(fragments);
        protocol.components.insert(
            "items-page".to_string(),
            webui_protocol::ComponentData {
                template_json: r#"{"h":"<p>Items</p>","th":1}"#.into(),
                navigation_mode: Some(webui_protocol::StateProjectionMode::Keys as i32),
                navigation_keys: vec!["items".into(), "title".into()],
                ..Default::default()
            },
        );

        let partial = render_partial(
            &protocol,
            serde_json::json!({
                "items": [1, 2],
                "serverOnly": "secret",
                "title": "Catalog",
            }),
            "index.html",
            "/items",
            "",
        )
        .unwrap();

        assert_eq!(
            partial["state"],
            serde_json::json!({
                "items": [1, 2],
                "title": "Catalog",
            })
        );
    }

    #[test]
    fn partial_requires_explicit_navigation_keys() {
        let mut fragments = HashMap::new();
        fragments.insert(
            "index.html".to_string(),
            FragmentList {
                fragments: vec![WebUIFragment::component("authored-card")],
                contains_boundary: false,
            },
        );
        fragments.insert(
            "authored-card".to_string(),
            FragmentList {
                fragments: vec![WebUIFragment::raw("<p>Card</p>")],
                contains_boundary: false,
            },
        );
        let mut protocol = WebUIProtocol::new(fragments);
        protocol.components.insert(
            "authored-card".to_string(),
            webui_protocol::ComponentData {
                hydration_mode: webui_protocol::StateProjectionMode::Keys as i32,
                hydration_keys: vec!["title".into()],
                navigation_mode: Some(webui_protocol::StateProjectionMode::None as i32),
                ..Default::default()
            },
        );

        let partial = render_partial(
            &protocol,
            serde_json::json!({
                "serverOnly": "secret",
                "title": "Authored",
            }),
            "index.html",
            "/",
            "",
        )
        .unwrap();

        assert_eq!(partial["state"], serde_json::json!({}));
    }

    #[test]
    fn prepared_navigation_projects_owned_state_and_reports_matches() {
        let mut protocol = WebUIProtocol::new(HashMap::from([
            (
                "index.html".into(),
                FragmentList {
                    fragments: vec![WebUIFragment::route_from(WebUiFragmentRoute {
                        path: "/items".into(),
                        fragment_id: "items-page".into(),
                        exact: true,
                        ..Default::default()
                    })],
                    ..Default::default()
                },
            ),
            (
                "items-page".into(),
                FragmentList {
                    fragments: vec![WebUIFragment::raw("<p>Items</p>")],
                    ..Default::default()
                },
            ),
        ]));
        protocol.components.insert(
            "items-page".into(),
            webui_protocol::ComponentData {
                template_json: r#"{"h":"<p>Items</p>","th":1}"#.into(),
                navigation_mode: Some(StateProjectionMode::Keys as i32),
                navigation_keys: vec!["serverDerived".into(), "title".into()],
                ..Default::default()
            },
        );
        let protocol = Protocol::new(protocol);
        let state = serde_json::json!({
            "serverDerived": [1, 2],
            "title": "Catalog",
            "serverOnly": [3, 4],
            "$webui": {"bodyEnd": "<script>host only</script>"}
        });
        let pointer = state["serverDerived"].as_array().unwrap().as_ptr();
        assert!(protocol.matches_route("index.html", "/items"));
        assert!(!protocol.matches_route("index.html", "/missing"));
        let partial = protocol
            .prepare_partial(state, "index.html", "/items", "")
            .unwrap();
        assert!(partial.is_match());
        assert_eq!(
            partial.response.state["serverDerived"]
                .as_array()
                .unwrap()
                .as_ptr(),
            pointer
        );
        let wire = serde_json::to_value(partial).unwrap();
        assert_eq!(
            wire["state"],
            serde_json::json!({"serverDerived": [1, 2], "title": "Catalog"})
        );
        assert_eq!(wire["path"], "/items");
        assert_eq!(wire["chain"][0]["component"], "items-page");
        assert!(wire.get("matched").is_none());
        let missing = protocol
            .prepare_partial(Value::Null, "index.html", "/missing", "")
            .unwrap();
        assert!(!missing.is_match());
    }

    #[test]
    fn prepared_navigation_matches_owned_and_raw_string_responses() {
        let protocol = prepared_partial_protocol(&["value"]);
        let state = serde_json::json!({
            "value": {"label": "片", "count": 42},
            "unused": ["discarded"],
            "$webui": {"headEnd": "<meta name=\"host-only\">"}
        });
        let prepared = protocol
            .prepare_partial(state.clone(), "index.html", "/", "")
            .unwrap();
        let bytes = serde_json::to_vec(&prepared).unwrap();
        assert_eq!(
            bytes,
            protocol
                .render_partial(state.clone(), "index.html", "/", "")
                .unwrap()
                .into_bytes()
        );
        assert_eq!(
            bytes,
            protocol
                .render_partial_json(&state.to_string(), "index.html", "/", "")
                .unwrap()
                .into_bytes()
        );
    }

    #[test]
    fn prepared_navigation_filters_reserved_state_when_projection_is_unknown() {
        let protocol = prepared_full_state_partial_protocol();
        let response = protocol
            .prepare_partial(
                serde_json::json!({
                    "value": 1,
                    "dynamicField": [2, 3],
                    "$webui": {"bodyEnd": "<script>host only</script>"}
                }),
                "index.html",
                "/",
                "",
            )
            .unwrap();
        let wire = serde_json::to_value(response).unwrap();
        assert_eq!(
            wire["state"],
            serde_json::json!({"value": 1, "dynamicField": [2, 3]})
        );
    }

    #[test]
    fn prepared_navigation_keeps_state_for_resident_templates() {
        let protocol = prepared_partial_protocol(&["value"]);
        let first = protocol
            .prepare_partial(Value::Null, "index.html", "/", "")
            .unwrap();
        let first = serde_json::to_value(first).unwrap();
        let response = protocol
            .prepare_partial(
                serde_json::json!({"value": "updated", "unused": "drop"}),
                "index.html",
                "/",
                first["inventory"].as_str().unwrap(),
            )
            .unwrap();
        let wire = serde_json::to_value(response).unwrap();
        assert!(wire["templates"].as_object().unwrap().is_empty());
        assert_eq!(wire["state"], serde_json::json!({"value": "updated"}));
    }

    #[test]
    fn fully_static_scriptless_partial_emits_empty_state() {
        let mut fragments = HashMap::new();
        fragments.insert(
            "index.html".to_string(),
            FragmentList {
                fragments: vec![WebUIFragment::component("static-card")],
                contains_boundary: false,
            },
        );
        fragments.insert(
            "static-card".to_string(),
            FragmentList {
                fragments: vec![WebUIFragment::raw("<p>Static</p>")],
                contains_boundary: false,
            },
        );
        let mut protocol = WebUIProtocol::new(fragments);
        protocol.components.insert(
            "static-card".to_string(),
            webui_protocol::ComponentData {
                template_json: r#"{"h":"<p>Static</p>","th":1}"#.into(),
                navigation_mode: Some(webui_protocol::StateProjectionMode::None as i32),
                ..Default::default()
            },
        );

        let partial = render_partial(
            &protocol,
            serde_json::json!({ "serverOnly": "secret" }),
            "index.html",
            "/",
            "",
        )
        .unwrap();

        assert_eq!(partial["state"], serde_json::json!({}));
    }

    #[test]
    fn test_render_component_templates_returns_template_and_css() {
        let mut fragments = HashMap::new();
        fragments.insert(
            "settings-dialog".to_string(),
            FragmentList {
                fragments: vec![WebUIFragment::raw("<div class='dialog'>Settings</div>")],
                contains_boundary: false,
            },
        );
        let mut protocol = WebUIProtocol::with_tokens(fragments, Vec::new());
        protocol.set_css_strategy(webui_protocol::CssStrategy::Module);
        let comp = protocol
            .components
            .entry("settings-dialog".to_string())
            .or_default();
        comp.template_json = r#"{"h":"<div>Settings</div>"}"#.to_string();
        comp.css = ".dialog{position:fixed}".to_string();
        protocol.populate_style_closures(&["settings-dialog"]);

        let mut index = ProtocolIndex::new(&protocol);
        let result =
            render_component_templates(&protocol, &["settings-dialog"], "", &mut index).unwrap();
        let templates = result["templates"].as_object().expect("templates object");
        assert_eq!(templates.len(), 1);
        assert_eq!(templates["settings-dialog"]["h"], "<div>Settings</div>");
        assert_eq!(
            result["componentStyles"]["resources"]["settings-dialog"],
            serde_json::json!({
                "kind": "module",
                "specifier": "settings-dialog",
                "css": ".dialog{position:fixed}"
            })
        );
        assert!(
            index
                .template_metadata_cache
                .contains_key("settings-dialog"),
            "parsed static template metadata should be cached in ProtocolIndex"
        );
    }

    #[test]
    fn test_render_component_templates_respects_inventory() {
        let mut fragments = HashMap::new();
        fragments.insert(
            "my-dialog".to_string(),
            FragmentList {
                fragments: vec![WebUIFragment::raw("<div>Dialog</div>")],
                contains_boundary: false,
            },
        );
        let mut protocol = WebUIProtocol::with_tokens(fragments, Vec::new());
        protocol.set_css_strategy(webui_protocol::CssStrategy::Module);
        let comp = protocol
            .components
            .entry("my-dialog".to_string())
            .or_default();
        comp.template_json = r#"{"h":"<div>Dialog</div>"}"#.to_string();
        comp.css = ".d{color:red}".to_string();
        protocol.populate_style_closures(&["my-dialog"]);

        let mut index = ProtocolIndex::new(&protocol);
        // First call: no inventory → should return the component
        let result1 =
            render_component_templates(&protocol, &["my-dialog"], "", &mut index).unwrap();
        let inv = result1["inventory"].as_str().expect("inventory string");
        assert_eq!(result1["templates"].as_object().unwrap().len(), 1);

        // Second call with inventory → component already loaded, should skip
        let result2 =
            render_component_templates(&protocol, &["my-dialog"], inv, &mut index).unwrap();
        assert_eq!(result2["templates"].as_object().unwrap().len(), 0);
        assert_eq!(
            result2["componentStyles"]["closures"],
            serde_json::json!({})
        );
        assert_eq!(
            result2["componentStyles"]["resources"],
            serde_json::json!({})
        );
    }

    #[test]
    fn test_render_component_templates_unknown_component_returns_empty() {
        let fragments = HashMap::new();
        let protocol = WebUIProtocol::with_tokens(fragments, Vec::new());

        let mut index = ProtocolIndex::new(&protocol);
        let result =
            render_component_templates(&protocol, &["nonexistent-widget"], "", &mut index).unwrap();
        assert_eq!(result["templates"].as_object().unwrap().len(), 0);
        assert_eq!(
            result["componentStyles"]["resources"],
            serde_json::json!({})
        );
    }

    #[test]
    fn test_render_partial_includes_sibling_boundary_templates() {
        let mut fragments = HashMap::new();
        fragments.insert(
            "index.html".to_string(),
            FragmentList {
                fragments: vec![WebUIFragment::route_from(WebUiFragmentRoute {
                    path: "/".into(),
                    fragment_id: "app-shell".into(),
                    exact: false,
                    children: vec![
                        WebUiFragmentRoute {
                            path: "inbox".into(),
                            fragment_id: "inbox-page".into(),
                            exact: true,
                            pending_component: "inbox-loading".into(),
                            ..Default::default()
                        },
                        WebUiFragmentRoute {
                            path: "settings".into(),
                            fragment_id: "settings-page".into(),
                            exact: true,
                            pending_component: "settings-loading".into(),
                            error_component: "settings-error".into(),
                            ..Default::default()
                        },
                    ],
                    ..Default::default()
                })],

                contains_boundary: false,
            },
        );

        for name in [
            "app-shell",
            "inbox-page",
            "inbox-loading",
            "settings-page",
            "settings-loading",
            "settings-error",
        ] {
            fragments.insert(
                name.to_string(),
                FragmentList {
                    fragments: vec![WebUIFragment::raw(format!("<p>{name}</p>"))],
                    contains_boundary: false,
                },
            );
        }

        let mut protocol = WebUIProtocol::new(fragments);
        for name in [
            "app-shell",
            "inbox-page",
            "inbox-loading",
            "settings-page",
            "settings-loading",
            "settings-error",
        ] {
            protocol
                .components
                .entry(name.to_string())
                .or_default()
                .template_json = format!(r#"{{"h":"<p>{name}</p>"}}"#);
        }

        let mut index = ProtocolIndex::new(&protocol);
        let partial =
            render_partial_metadata(&protocol, "index.html", "/inbox", "", &mut index).unwrap();
        let templates = partial["templates"].as_object().unwrap();

        assert!(
            templates.contains_key("settings-loading"),
            "sibling pending template should be preloaded for route transitions: {partial}"
        );
        assert!(
            templates.contains_key("settings-error"),
            "sibling error template should be preloaded for failed route transitions: {partial}"
        );
        let chain = partial["chain"].as_array().unwrap();
        assert_eq!(chain.len(), 2);
        assert_eq!(chain[0]["component"], "app-shell");
        assert_eq!(chain[1]["component"], "inbox-page");
    }

    // ── resolve_tag_templates tests ──────────────────────────────────

    #[test]
    fn test_resolve_tag_templates_no_placeholders() {
        let tags = vec!["inbox".to_string(), "counts".to_string()];
        let params = HashMap::new();
        let resolved = resolve_tag_templates(&tags, &params);
        assert_eq!(resolved, vec!["inbox", "counts"]);
    }

    #[test]
    fn test_resolve_tag_templates_with_params() {
        let tags = vec!["thread:{threadId}".to_string(), "inbox".to_string()];
        let mut params = HashMap::new();
        params.insert("threadId".to_string(), "42".to_string());
        let resolved = resolve_tag_templates(&tags, &params);
        assert_eq!(resolved, vec!["thread:42", "inbox"]);
    }

    #[test]
    fn test_resolve_tag_templates_multiple_params() {
        let tags = vec!["folder:{folderId}:user:{userId}".to_string()];
        let mut params = HashMap::new();
        params.insert("folderId".to_string(), "drafts".to_string());
        params.insert("userId".to_string(), "abc".to_string());
        let resolved = resolve_tag_templates(&tags, &params);
        assert_eq!(resolved, vec!["folder:drafts:user:abc"]);
    }

    #[test]
    fn test_resolve_tag_templates_missing_param_left_unresolved() {
        let tags = vec!["thread:{threadId}".to_string()];
        let params = HashMap::new();
        let resolved = resolve_tag_templates(&tags, &params);
        assert_eq!(resolved, vec!["thread:{threadId}"]);
    }

    // ── Chain entry to_json with new fields ───────────────────────

    #[test]
    fn test_chain_entry_to_json_includes_new_fields() {
        let entry = RouteChainEntry {
            component: "mail-thread".into(),
            path: "email/:threadId".into(),
            params: {
                let mut p = HashMap::new();
                p.insert("threadId".to_string(), "42".to_string());
                p
            },
            exact: true,
            allowed_query: String::new(),
            keep_alive: false,
            cache_tags: vec!["thread:42".to_string()],
            invalidates: vec!["inbox".to_string(), "counts".to_string()],
            pending_component: "mail-skeleton".into(),
            error_component: "error-page".into(),
        };
        let json = entry.to_json();
        assert_eq!(json["pendingComponent"], "mail-skeleton");
        assert_eq!(json["errorComponent"], "error-page");
        let inv = json["invalidates"].as_array().unwrap();
        assert_eq!(inv.len(), 2);
        assert_eq!(inv[0], "inbox");
        assert_eq!(inv[1], "counts");
    }

    #[test]
    fn test_chain_entry_to_json_omits_empty_new_fields() {
        let entry = RouteChainEntry {
            component: "home-page".into(),
            path: "/".into(),
            params: HashMap::new(),
            exact: true,
            allowed_query: String::new(),
            keep_alive: false,
            cache_tags: Vec::new(),
            invalidates: Vec::new(),
            pending_component: String::new(),
            error_component: String::new(),
        };
        let json = entry.to_json();
        assert!(json.get("pendingComponent").is_none());
        assert!(json.get("errorComponent").is_none());
        assert!(json.get("invalidates").is_none());
    }

    // ── render_partial with cache tags ────────────────────────────

    #[test]
    fn test_render_partial_includes_resolved_cache_tags() {
        let mut fragments = HashMap::new();
        fragments.insert(
            "index.html".to_string(),
            FragmentList {
                fragments: vec![WebUIFragment::route_from(WebUiFragmentRoute {
                    path: "/".into(),
                    fragment_id: "app-shell".into(),
                    exact: false,
                    children: vec![WebUiFragmentRoute {
                        path: "email/:threadId".into(),
                        fragment_id: "mail-thread".into(),
                        exact: true,
                        cache_tags: vec!["thread:{threadId}".to_string(), "inbox".to_string()],
                        ..Default::default()
                    }],
                    cache_tags: vec!["folders".to_string()],
                    ..Default::default()
                })],

                contains_boundary: false,
            },
        );
        fragments.insert(
            "app-shell".to_string(),
            FragmentList {
                fragments: vec![WebUIFragment::raw("<h1>App</h1>"), WebUIFragment::outlet()],
                contains_boundary: false,
            },
        );
        fragments.insert(
            "mail-thread".to_string(),
            FragmentList {
                fragments: vec![WebUIFragment::raw("<p>Thread</p>")],
                contains_boundary: false,
            },
        );
        let protocol = WebUIProtocol::new(fragments);

        let mut index = ProtocolIndex::new(&protocol);
        let partial =
            render_partial_metadata(&protocol, "index.html", "/email/42", "", &mut index).unwrap();
        let tags = partial["cacheTags"].as_array().unwrap();
        let tag_strings: Vec<&str> = tags.iter().map(|v| v.as_str().unwrap()).collect();
        assert!(
            tag_strings.contains(&"folders"),
            "should contain parent tags"
        );
        assert!(
            tag_strings.contains(&"thread:42"),
            "should resolve threadId param to 42"
        );
        assert!(tag_strings.contains(&"inbox"), "should contain static tags");
    }

    // ── render_action_response tests ─────────────────────────────

    #[test]
    fn test_render_action_response_returns_resolved_invalidation_tags() {
        let mut fragments = HashMap::new();
        fragments.insert(
            "index.html".to_string(),
            FragmentList {
                fragments: vec![WebUIFragment::route_from(WebUiFragmentRoute {
                    path: "/".into(),
                    fragment_id: "app-shell".into(),
                    exact: false,
                    children: vec![WebUiFragmentRoute {
                        path: "compose".into(),
                        fragment_id: "compose-page".into(),
                        exact: true,
                        invalidates: vec![
                            "inbox".to_string(),
                            "sent".to_string(),
                            "counts".to_string(),
                        ],
                        ..Default::default()
                    }],
                    ..Default::default()
                })],

                contains_boundary: false,
            },
        );
        fragments.insert(
            "app-shell".to_string(),
            FragmentList {
                fragments: vec![WebUIFragment::raw("<h1>App</h1>"), WebUIFragment::outlet()],
                contains_boundary: false,
            },
        );
        fragments.insert(
            "compose-page".to_string(),
            FragmentList {
                fragments: vec![WebUIFragment::raw("<p>Compose</p>")],
                contains_boundary: false,
            },
        );
        let protocol = WebUIProtocol::new(fragments);

        let mut index = ProtocolIndex::new(&protocol);
        let result = render_action_response(
            &protocol,
            serde_json::json!({"ok": true}),
            "index.html",
            "/compose",
            &mut index,
        );

        let tags = result["invalidateTags"].as_array().unwrap();
        let tag_strings: Vec<&str> = tags.iter().map(|v| v.as_str().unwrap()).collect();
        assert_eq!(tag_strings, vec!["inbox", "sent", "counts"]);
        assert_eq!(result["state"]["ok"], true);
    }

    #[test]
    fn test_render_action_response_resolves_param_placeholders() {
        let mut fragments = HashMap::new();
        fragments.insert(
            "index.html".to_string(),
            FragmentList {
                fragments: vec![WebUIFragment::route_from(WebUiFragmentRoute {
                    path: "/".into(),
                    fragment_id: "app-shell".into(),
                    exact: false,
                    children: vec![WebUiFragmentRoute {
                        path: "email/:threadId/reply".into(),
                        fragment_id: "reply-page".into(),
                        exact: true,
                        invalidates: vec!["thread:{threadId}".to_string(), "inbox".to_string()],
                        ..Default::default()
                    }],
                    ..Default::default()
                })],

                contains_boundary: false,
            },
        );
        fragments.insert(
            "app-shell".to_string(),
            FragmentList {
                fragments: vec![WebUIFragment::raw("<h1>App</h1>"), WebUIFragment::outlet()],
                contains_boundary: false,
            },
        );
        fragments.insert(
            "reply-page".to_string(),
            FragmentList {
                fragments: vec![WebUIFragment::raw("<p>Reply</p>")],
                contains_boundary: false,
            },
        );
        let protocol = WebUIProtocol::new(fragments);

        let mut index = ProtocolIndex::new(&protocol);
        let result = render_action_response(
            &protocol,
            serde_json::json!({}),
            "index.html",
            "/email/42/reply",
            &mut index,
        );

        let tags = result["invalidateTags"].as_array().unwrap();
        let tag_strings: Vec<&str> = tags.iter().map(|v| v.as_str().unwrap()).collect();
        assert!(tag_strings.contains(&"thread:42"));
        assert!(tag_strings.contains(&"inbox"));
    }
}