everruns_core/capabilities/

mod.rs

//! Capabilities Module for Agent Loop
//!
//! This module provides the capabilities abstraction that allows composing
//! agent functionality through modular units. Each capability can contribute:
//! - System prompt additions
//! - Tools for the agent
//! - Behavior modifications (future)
//!
//! Design decisions:
//! - Capabilities are defined via the Capability trait for flexibility
//! - CapabilityRegistry holds all available capability implementations
//! - apply_capabilities() merges capability contributions into RuntimeAgent
//! - The agent-loop remains execution-focused; capabilities are applied before execution
//! - System prompt sections use XML tags for clear boundaries between components.
//!   This follows Anthropic's recommendation for multi-component prompts and reduces
//!   misattribution between capability instructions, user-provided AGENTS.md, and the
//!   agent's base system prompt. See knowledge/project/xml-prompt-formatting.md for rationale.
//!
//! Each capability is in its own file with collocated tools.

use crate::command::{
    CommandDescriptor, CommandExecutionContext, CommandResult, ExecuteCommandRequest,
};
use crate::events::TokenUsage;
use crate::mcp_server::{ScopedMcpServers, merge_scoped_mcp_servers};
use crate::message::Message;
use crate::message_filter::MessageFilterProvider;
use crate::runtime_agent::RuntimeAgent;
use crate::tool_types::{ToolCall, ToolDefinition};
use crate::tools::{Tool, ToolExecutionResult, ToolRegistry};
use crate::typed_id::SessionId;
use crate::{session_files::SessionFileSystem, tool_context::ToolContext};
use async_trait::async_trait;
use everruns_capability::is_plugin_capability;
use serde::{Deserialize, Serialize};
use std::collections::HashMap;
use std::sync::Arc;

// ============================================================================
// Integration Plugin System
// ============================================================================

/// Plugin registration point for external integration crates.
///
/// Integration crates use `inventory::submit!` to register their capabilities
/// without requiring `everruns-core` to know about them at compile time.
/// Host or product composition iterates these descriptors and applies its
/// deployment-grade and feature-selection policy. Core only owns the neutral
/// registration contract.
///
/// # Example
///
/// ```ignore
/// // In integrations/daytona/src/lib.rs:
/// inventory::submit! {
///     everruns_core::capabilities::IntegrationPlugin {
///         experimental_only: false,
///         feature_flag: None,
///         factory: || Box::new(DaytonaCapability),
///     }
/// }
/// ```
pub struct IntegrationPlugin {
    /// If true, product composition registers this only for experimental grades.
    pub experimental_only: bool,
    /// If set, only registered when the named deployment feature flag is enabled.
    /// Resolved at registry build time via `ExecutionFeatureDecisions`: internal
    /// infrastructure flags first, otherwise the explicit `FEATURE_<NAME>` env
    /// var (fail-closed — no grade-based default for registration gates).
    pub feature_flag: Option<&'static str>,
    /// Factory function that creates the capability instance.
    pub factory: fn() -> Box<dyn Capability>,
}

inventory::collect!(IntegrationPlugin);

pub use crate::capability_types::{
    CapabilityStatus, MountAccess, MountDirectoryBuilder, MountEntry, MountPoint, MountSource,
};
use everruns_capability::{CapabilityId, CapabilityRef as AgentCapabilityConfig};

// ============================================================================
// Capability contract modules
// ============================================================================

mod declarative;
pub mod facts;
pub mod skill_contribution;
pub mod util;

// Re-export capabilities
/// Capability ID for outbound A2A agent delegation. Defined ungated so session
/// attachment logic can reference it even when the `a2a` feature (and the
/// delegation implementation) is compiled out.
pub const A2A_AGENT_DELEGATION_CAPABILITY_ID: &str = "a2a_agent_delegation";
/// KV key prefix for A2A delegation run records. Defined ungated so the
/// session-storage internal-prefix reservation (a TM-TOOL/TM-AGENT mitigation
/// against forged attachments) holds even when the `a2a` feature is compiled out.
pub const AGENT_RUN_KEY_PREFIX: &str = "agent_run:";
/// Shared concurrency class for every provider of the model-visible
/// `spawn_agent` tool. Implementations live in host/integration crates, while
/// collection keeps the merged tool serialized through this neutral key.
pub const SPAWN_AGENT_CONCURRENCY_CLASS: &str = "spawn_agent";
pub use declarative::{
    DECLARATIVE_CAPABILITY_PREFIX, DeclarativeCapabilityDefinition, DeclarativeCapabilityFile,
    DeclarativeCapabilitySkill, DeclarativeCapabilitySkillFile, declarative_capability_id,
    declarative_capability_info, hydrate_declarative_capability_config,
    hydrate_plugin_capability_config, is_declarative_capability, parse_declarative_capability_id,
    plugin_capability_info, validate_declarative_capability_definition,
};
pub use facts::{FACTS_DYNAMIC_NOTE, Fact, FactsContext, Volatility, render_facts_block};
pub use skill_contribution::{
    MAX_SKILLS_PER_CAPABILITY, SKILL_CAPABILITY_PREFIX, SKILLS_DISCOVERY_PATH,
    SkillCapabilityIdExt, SkillContribution, SkillInstructions, SkillMeta, SkillSource,
    discover_skills_from_entries, is_skill_capability, parse_skill_capability_id,
    reconstruct_skill_md, skill_capability_id,
};

// ============================================================================
// System Prompt Context
// ============================================================================

/// Context provided to capabilities when resolving dynamic system prompt contributions.
///
/// This gives capabilities access to session-specific resources (filesystem, etc.)
/// so they can generate system prompt content at runtime rather than returning
/// only static text.
pub struct SystemPromptContext {
    /// The current session ID
    pub session_id: SessionId,
    /// Optional locale for localized prompts and tool behavior.
    pub locale: Option<String>,
    /// Optional file store for reading session files (e.g., AGENTS.md)
    pub file_store: Option<Arc<dyn SessionFileSystem>>,
    /// The model the agent will run on, when known at collection time.
    ///
    /// Enables model-adaptive capabilities (see [`Capability::resolve_for_model`],
    /// e.g. `auto_tool_search`). `None` when the model is not yet resolved; such
    /// capabilities then fall back to their provider-agnostic behavior.
    pub model: Option<String>,
    /// Optional session key/value store, for capabilities whose contribution is
    /// persisted session state rather than static text (e.g. `channel_context`
    /// reading the accumulated `ThreadContext`). `None` for callers that do not
    /// provide one; such capabilities then contribute nothing.
    pub session_storage: Option<Arc<dyn crate::session_services::SessionStorageStore>>,
}

impl SystemPromptContext {
    /// Create context with no file store (for callers that don't need filesystem access)
    pub fn without_file_store(session_id: SessionId) -> Self {
        Self {
            session_id,
            locale: None,
            file_store: None,
            model: None,
            session_storage: None,
        }
    }

    /// Set the model the agent will run on (drives model-adaptive capabilities).
    pub fn with_model(mut self, model: impl Into<String>) -> Self {
        self.model = Some(model.into());
        self
    }
}

// ============================================================================
// Capability Trait
// ============================================================================

/// Trait for implementing capabilities that extend agent functionality.
///
/// A capability can contribute:
/// - System prompt additions (appended after the agent's base system prompt)
/// - Tools (added to agent's available tools)
///
/// # System Prompt Contributions
///
/// Capabilities provide system prompt content via `system_prompt_contribution()`.
/// This async method receives a `SystemPromptContext` with access to the session
/// filesystem, allowing capabilities to generate dynamic content (e.g., reading
/// AGENTS.md or scanning for skills).
///
/// The default implementation wraps the static `system_prompt_addition()` text
/// in `<capability id="...">` XML tags. Capabilities that need dynamic content
/// override `system_prompt_contribution()` directly.
///
/// # Example
///
/// ```ignore
/// use everruns_core::capabilities::Capability;
///
/// struct CurrentTimeCapability;
///
/// impl Capability for CurrentTimeCapability {
///     fn id(&self) -> &str {
///         "current_time"
///     }
///
///     fn name(&self) -> &str {
///         "Current Time"
///     }
///
///     fn description(&self) -> &str {
///         "Provides tools to get the current date and time."
///     }
///
///     fn tools(&self) -> Vec<Box<dyn Tool>> {
///         vec![Box::new(GetCurrentTimeTool)]
///     }
/// }
/// ```
/// Localized display strings for one locale.
///
/// Base English strings stay in `name()` / `description()` / `config_schema()`;
/// localizations are additive overlays, so adding a locale never changes the
/// `Capability` trait contract for existing implementations.
#[derive(Debug, Clone)]
pub struct CapabilityLocalization {
    /// Language tag this entry applies to, lowercase (e.g. `"uk"` or `"uk-ua"`).
    pub locale: &'static str,
    /// Localized display name; `None` falls back to `name()`.
    pub name: Option<&'static str>,
    /// Localized description; `None` falls back to `description()`.
    pub description: Option<&'static str>,
    /// One-line summary of what this capability's config controls.
    ///
    /// Provide an `"en"` entry for the base locale; capabilities without
    /// config leave this `None` everywhere.
    pub config_description: Option<&'static str>,
    /// Overlay merged into `config_schema()` by clients before rendering.
    ///
    /// Mirrors JSON Schema structure (`properties` / `items` nesting); nodes
    /// carry `title`, `description`, and `enum_labels` (map from enum value
    /// to localized label, applied to `oneOf` `const`/`title` entries).
    pub config_overlay: Option<serde_json::Value>,
}

impl CapabilityLocalization {
    /// Entry with only display strings (no config).
    pub fn text(locale: &'static str, name: &'static str, description: &'static str) -> Self {
        Self {
            locale,
            name: Some(name),
            description: Some(description),
            config_description: None,
            config_overlay: None,
        }
    }
}

/// Resolve a localized field with the standard fallback chain:
/// exact tag → language family → `"en"`. Returns `None` when no entry
/// provides the field; callers fall back to the unlocalized trait values.
pub fn resolve_localized_field<T>(
    localizations: &[CapabilityLocalization],
    locale: Option<&str>,
    field: impl Fn(&CapabilityLocalization) -> Option<T>,
) -> Option<T> {
    let mut candidates: Vec<String> = Vec::new();
    if let Some(raw) = locale {
        let normalized = raw.trim().replace('_', "-").to_lowercase();
        if !normalized.is_empty() {
            if let Some((language, _)) = normalized.split_once('-') {
                let language = language.to_string();
                candidates.push(normalized);
                candidates.push(language);
            } else {
                candidates.push(normalized);
            }
        }
    }
    candidates.push("en".to_string());

    for candidate in candidates {
        let hit = localizations
            .iter()
            .find(|entry| entry.locale.eq_ignore_ascii_case(&candidate))
            .and_then(&field);
        if hit.is_some() {
            return hit;
        }
    }
    None
}

#[async_trait]
pub trait Capability: Send + Sync {
    /// Explicit native asynchronous tool selection. Providers without support
    /// retain the ordinary synchronous definitions and scheduler.
    fn native_async_tools(
        &self,
        _config: &serde_json::Value,
    ) -> Option<std::collections::BTreeMap<String, Option<serde_json::Value>>> {
        None
    }
    /// Returns the unique capability identifier as a string
    fn id(&self) -> &str;

    /// Returns legacy identifiers that resolve to this capability.
    ///
    /// Aliases exist so a capability can be renamed without breaking persisted
    /// agent configs: registry lookups (`get`, `has`) and dependency resolution
    /// treat an alias exactly like the canonical `id()`. Resolution always
    /// normalizes aliases to the canonical ID, so an alias and its canonical
    /// ID never activate the capability twice. New code must use `id()`;
    /// aliases are a compatibility surface only.
    fn aliases(&self) -> Vec<&'static str> {
        vec![]
    }

    /// Returns the display name
    fn name(&self) -> &str;

    /// Returns a description of what this capability provides
    fn description(&self) -> &str;

    /// Returns localization overlays for this capability's display strings.
    ///
    /// Include an `"en"` entry when providing `config_description` for the
    /// base locale. Lookup follows `resolve_localized_field` fallback rules.
    fn localizations(&self) -> Vec<CapabilityLocalization> {
        vec![]
    }

    /// Display name resolved for `locale`; `None` or unknown locales fall
    /// back to `name()`.
    fn localized_name(&self, locale: Option<&str>) -> String {
        resolve_localized_field(&self.localizations(), locale, |entry| entry.name)
            .unwrap_or_else(|| self.name())
            .to_string()
    }

    /// Description resolved for `locale`; falls back to `description()`.
    fn localized_description(&self, locale: Option<&str>) -> String {
        resolve_localized_field(&self.localizations(), locale, |entry| entry.description)
            .unwrap_or_else(|| self.description())
            .to_string()
    }

    /// One-line human-readable summary of what this capability's config
    /// controls, resolved for `locale`. `None` when the capability exposes
    /// no per-agent config.
    fn describe_schema(&self, locale: Option<&str>) -> Option<String> {
        resolve_localized_field(&self.localizations(), locale, |entry| {
            entry.config_description
        })
        .map(str::to_string)
    }

    /// Returns the current status of this capability
    fn status(&self) -> CapabilityStatus {
        CapabilityStatus::Available
    }

    /// Returns the icon name for UI rendering (optional)
    fn icon(&self) -> Option<&str> {
        None
    }

    /// Returns the category for grouping in UI (optional)
    fn category(&self) -> Option<&str> {
        None
    }

    /// Host-owned annotations that core does not interpret.
    ///
    /// The typed accessors above (`category`, `status`, `is_guardrail`, …) are
    /// the vocabulary core itself reasons about. This is the escape hatch for
    /// everything a *host* wants to carry alongside a capability — a UI icon,
    /// an embedder's grouping key, deployment provenance — without adding a
    /// field to core for each one. Core reads nothing here.
    ///
    /// The schema belongs to whoever writes it. Never put credentials or other
    /// sensitive payload here: it is surfaced to clients alongside the rest of
    /// the capability descriptor.
    fn metadata(&self) -> Option<serde_json::Value> {
        None
    }

    /// Whether this capability is a guardrail — a constraint on agent
    /// behavior (content checks, tool restrictions) rather than a grant of
    /// new abilities. Structural marker for UI sections and catalog
    /// filtering; carries no runtime semantics. See knowledge/execution/guardrails.md.
    fn is_guardrail(&self) -> bool {
        false
    }

    /// Model-adaptive dispatch: delegate this capability's contributions to a
    /// different underlying capability based on the agent's model.
    ///
    /// Capability collection (which knows the model via
    /// [`SystemPromptContext::model`]) calls this and, when it returns `Some`,
    /// collects the returned capability's contributions in place of this one's.
    /// The default returns `None` (no delegation). `auto_tool_search` overrides
    /// it to pick hosted vs client-side tool search. `model` is `None` when not
    /// yet resolved; implementations should choose a safe provider-agnostic
    /// default in that case.
    fn resolve_for_model(&self, _model: Option<&str>) -> Option<&dyn Capability> {
        None
    }

    /// Returns static text to include in the agent's system prompt (optional).
    ///
    /// This is the simple sync path for capabilities with static prompts.
    /// For dynamic content that requires filesystem access, override
    /// `system_prompt_contribution()` instead.
    ///
    /// **Contract: no duplication with tool definitions.** System prompt
    /// additions must NOT repeat information already present in tool names,
    /// descriptions, or parameter schemas. Only include content that cannot
    /// be inferred from tool definitions alone:
    ///
    /// - High-level semantics (when to use which tool, behavioral guidance)
    /// - Constraints the model cannot discover from schemas (row limits,
    ///   naming rules, workspace root paths, scheduling limits)
    /// - Data layout (filesystem paths for state files)
    /// - Cross-tool relationships or ordering not evident from descriptions
    ///
    /// If every piece of information in the prompt is already covered by the
    /// tool definitions, return `None` instead.
    fn system_prompt_addition(&self) -> Option<&str> {
        None
    }

    /// Returns the system prompt contribution for this capability, with access
    /// to session context (filesystem, etc.).
    ///
    /// This is the primary method for contributing to the system prompt.
    /// The returned string is included as-is in the final prompt (the capability
    /// is responsible for its own XML wrapping).
    ///
    /// The default implementation wraps `system_prompt_addition()` in
    /// `<capability id="...">` XML tags. Capabilities with dynamic content
    /// (e.g., `agent_instructions`, `skills`) override this to read from the
    /// session filesystem.
    async fn system_prompt_contribution(&self, _ctx: &SystemPromptContext) -> Option<String> {
        self.system_prompt_addition().map(|addition| {
            format!(
                "<capability id=\"{}\">\n{}\n</capability>",
                self.id(),
                addition
            )
        })
    }

    /// Returns a preview of the system prompt addition for UI display.
    ///
    /// For most capabilities this is identical to `system_prompt_addition()`.
    /// Capabilities with dynamic content (e.g. `agent_instructions` which reads
    /// AGENTS.md at runtime) override this to return a representative preview.
    fn system_prompt_preview(&self) -> Option<String> {
        self.system_prompt_addition().map(|s| s.to_string())
    }

    /// Returns tool implementations provided by this capability
    fn tools(&self) -> Vec<Box<dyn Tool>> {
        vec![]
    }

    /// Returns tool implementations configured by per-capability config.
    ///
    /// Called during capability collection with the per-agent config for this
    /// capability (from `AgentCapabilityConfig.config`). Capabilities that adapt
    /// their tools based on config override this method.
    ///
    /// Default delegates to `tools()`.
    fn tools_with_config(&self, _config: &serde_json::Value) -> Vec<Box<dyn Tool>> {
        self.tools()
    }

    /// Returns a provider for one target of the neutral `spawn_agent` router.
    ///
    /// Hosted delegation implementations use this seam so core can assemble a
    /// single model-facing tool without knowing capability IDs or product
    /// configuration. The provider tool receives the original call unchanged.
    fn delegation_target_with_config(
        &self,
        _config: &serde_json::Value,
    ) -> Option<DelegationTargetProvider> {
        None
    }

    /// Whether this capability should be activated from the tools collected so
    /// far. This generic hook supports cross-cutting adapters without teaching
    /// core their IDs or deployment ownership.
    fn auto_activates_for(&self, _tool_definitions: &[ToolDefinition]) -> bool {
        false
    }

    /// Returns system prompt contribution adapted to per-capability config.
    ///
    /// Called during capability collection. Capabilities whose system prompt
    /// content depends on config override this method.
    ///
    /// Default delegates to `system_prompt_contribution(ctx)`.
    async fn system_prompt_contribution_with_config(
        &self,
        ctx: &SystemPromptContext,
        _config: &serde_json::Value,
    ) -> Option<String> {
        self.system_prompt_contribution(ctx).await
    }

    /// User-visible conversation context contributed by this capability.
    ///
    /// Content returned here renders as the leading user-role message of every
    /// turn: model-visible and re-resolved alongside the system prompt, but
    /// never folded into the cached system prompt. This is the correct sink
    /// for untrusted workspace content (e.g. AGENTS.md hierarchies): it keeps
    /// file instructions below harness safety instructions in the instruction
    /// hierarchy and out of the cache-stable prefix.
    ///
    /// Default returns `None` (no conversation context).
    async fn conversation_context_contribution(
        &self,
        _ctx: &SystemPromptContext,
    ) -> Option<String> {
        None
    }

    /// Called during capability collection. Capabilities whose conversation
    /// context depends on config override this method.
    ///
    /// Default delegates to `conversation_context_contribution(ctx)`.
    async fn conversation_context_contribution_with_config(
        &self,
        ctx: &SystemPromptContext,
        _config: &serde_json::Value,
    ) -> Option<String> {
        self.conversation_context_contribution(ctx).await
    }

    /// Returns tool definitions for the agent config
    /// By default, converts tools() to definitions
    fn tool_definitions(&self) -> Vec<ToolDefinition> {
        self.tools().iter().map(|t| t.to_definition()).collect()
    }

    /// Returns mount points to populate in the session filesystem
    ///
    /// Mount points allow capabilities to provide files and directories
    /// that are automatically created when a session starts. This is useful
    /// for providing sample data, documentation, or configuration files.
    ///
    /// By default, returns an empty vector (no mounts).
    fn mounts(&self) -> Vec<MountPoint> {
        vec![]
    }

    /// Returns capability IDs that this capability depends on.
    ///
    /// Dependencies are automatically resolved at runtime when applying
    /// capabilities. If capability A depends on capability B, then B's
    /// contributions (tools, system prompt, mounts) will be included
    /// when A is selected, even if B is not explicitly selected.
    ///
    /// By default, returns an empty vector (no dependencies).
    fn dependencies(&self) -> Vec<&'static str> {
        vec![]
    }

    /// Returns UI feature strings that this capability contributes to.
    ///
    /// Features are open-ended strings indicating what user-facing functionality
    /// this capability enables. Multiple capabilities can contribute the same
    /// feature (e.g., both `session_schedule` and a future `signals` capability
    /// might contribute `"schedules"`).
    ///
    /// The UI uses the aggregated set of features from all active capabilities
    /// to decide which tabs/sections to render.
    ///
    /// Known features: `"file_system"`, `"schedules"`, `"secrets"`,
    /// `"key_value"`, `"sql_database"`, `"leased_resources"`.
    ///
    /// By default, returns an empty vector (no features).
    fn features(&self) -> Vec<&'static str> {
        vec![]
    }

    /// Returns the JSON Schema for this capability's per-agent config.
    ///
    /// The schema is exposed through `CapabilityInfo` so clients can render a
    /// generic settings editor for capabilities without hard-coding capability
    /// IDs. Capabilities without configurable settings return `None`.
    fn config_schema(&self) -> Option<serde_json::Value> {
        None
    }

    /// Returns UI hints for rendering `config_schema`.
    ///
    /// This follows the react-jsonschema-form `uiSchema` shape. The server owns
    /// durable config semantics; clients own the generic component implementation.
    fn config_ui_schema(&self) -> Option<serde_json::Value> {
        None
    }

    /// Validates per-capability config before it is persisted.
    ///
    /// Default accepts any config for backward compatibility. Capabilities with
    /// a `config_schema()` should reject invalid values here so HTTP, CLI, and
    /// MCP write paths share the same server-side guardrail.
    fn validate_config(&self, _config: &serde_json::Value) -> Result<(), String> {
        Ok(())
    }

    /// Returns remote MCP servers contributed by this capability.
    ///
    /// These are merged into harness/agent/session scoped MCP config at runtime.
    /// Explicit scoped MCP config overrides capability-contributed defaults by
    /// logical server name.
    fn mcp_servers(&self) -> ScopedMcpServers {
        ScopedMcpServers::default()
    }

    /// Returns config-aware remote MCP server contributions.
    fn mcp_servers_with_config(&self, _config: &serde_json::Value) -> ScopedMcpServers {
        self.mcp_servers()
    }

    /// Returns a message filter provider if this capability modifies message retrieval.
    ///
    /// Capabilities can contribute filters that modify how messages are loaded
    /// from the database. This enables features like:
    /// - Time-based filtering (recent messages only)
    /// - Event type filtering
    /// - Tool result filtering by tool name
    /// - Ephemeral message injection (summaries, reminders)
    ///
    /// Filters are applied in capability priority order (by `MessageFilterProvider::priority()`).
    ///
    /// By default, returns None (no message filtering).
    fn message_filter_provider(&self) -> Option<Arc<dyn MessageFilterProvider>> {
        None
    }

    /// Derive the config passed to this capability's message filter.
    ///
    /// `compaction_enabled` lets a filter coordinate with a separately selected
    /// compaction policy without core matching on either capability's ID.
    fn message_filter_config(
        &self,
        config: &serde_json::Value,
        _compaction_enabled: bool,
    ) -> serde_json::Value {
        config.clone()
    }

    /// Returns a provider that can build a prompt-facing model view from
    /// lossless stored messages before provider serialization.
    ///
    /// This is for capability-owned context transformations such as compaction
    /// cost-control masking. Storage messages remain unchanged.
    ///
    /// By default, returns None (no model-view transformation).
    fn model_view_provider(&self) -> Option<Arc<dyn ModelViewProvider>> {
        None
    }

    /// Returns an in-process hook invoked when a turn fails with a *terminal*
    /// LLM error (one that will not be retried), before the user-facing error
    /// message is emitted. The hook may perform a side effect (e.g. schedule a
    /// continuation) and/or return extra fields to augment the user-facing error
    /// copy. This is the platform seam for capability-owned error recovery — the
    /// same in-process hook family as [`Self::tool_call_hooks`] and
    /// [`Self::message_filter_provider`]; the reason atom invokes it generically
    /// and knows nothing about any specific capability's behavior. See
    /// [`crate::llm_error_hook`].
    ///
    /// By default, returns None (no error hook).
    fn llm_error_hook(&self) -> Option<Arc<dyn crate::llm_error_hook::LlmErrorHook>> {
        None
    }

    /// Provider-facing deferred tool-loading configuration contributed by
    /// this capability. The execution engine consumes this generically and
    /// does not match on implementation-owned capability IDs.
    fn tool_search_config(
        &self,
        _config: &serde_json::Value,
    ) -> Option<crate::driver_registry::ToolSearchConfig> {
        None
    }

    /// Provider-facing prompt-cache configuration contributed by this
    /// capability.
    fn prompt_cache_config(
        &self,
        _config: &serde_json::Value,
    ) -> Option<crate::driver_registry::PromptCacheConfig> {
        None
    }

    /// Driver-namespaced opaque per-call options (`"<driver-id>/<option>"`)
    /// requested by this capability. Each entry's shape is owned by the driver
    /// crate named in the key; core transports the values untouched.
    fn driver_options(&self, _config: &serde_json::Value) -> Vec<(String, serde_json::Value)> {
        Vec::new()
    }

    /// Request-level parallel tool-call preference contributed by this
    /// capability. `None` leaves the runtime/provider default unchanged.
    fn parallel_tool_calls_preference(&self, _config: &serde_json::Value) -> Option<bool> {
        None
    }

    /// User-facing terminal-error disclosure selected by this capability.
    fn error_disclosure(
        &self,
        _config: &serde_json::Value,
    ) -> Option<crate::user_facing_error::ErrorDisclosure> {
        None
    }

    /// Filter assistant text before it is persisted or returned. This is a
    /// deterministic, config-aware seam for capability-owned annotations.
    fn filter_response_text(&self, text: String, _config: &serde_json::Value) -> String {
        text
    }

    /// Context-compaction policy configured by this capability. The reason
    /// atom owns orchestration and invokes the returned implementation without
    /// matching on a capability ID.
    fn compaction_policy(
        &self,
        _config: &serde_json::Value,
    ) -> Option<Arc<dyn crate::compaction_policy::CompactionPolicy>> {
        None
    }

    /// Returns key/value [`Fact`]s this capability contributes to the model.
    ///
    /// Facts are routed by their [`Volatility`] so prompt caching is preserved:
    /// [`Volatility::Static`] facts fold into the cached system-prompt prefix at
    /// build time; [`Volatility::Dynamic`] facts are appended at the
    /// conversation tail on every turn (outside the cached prefix). This is the
    /// generic seam for "changing facts" such as the current time — see
    /// [`crate::capabilities::facts`].
    ///
    /// Called both at prompt-assembly time (to fold static facts and detect
    /// whether any dynamic facts exist) and per request (to render the live
    /// tail block), so implementations must be cheap and side-effect free.
    ///
    /// By default, returns an empty vector (no facts).
    fn facts(&self, _config: &serde_json::Value, _ctx: &FactsContext) -> Vec<Fact> {
        vec![]
    }

    /// Returns pre-tool execution hooks provided by this capability.
    ///
    /// These hooks run before each individual tool is executed — for *every*
    /// tool the agent calls (built-in, MCP, or client-side), not just this
    /// capability's own tools. A hook can mutate the tool call or block it
    /// outright (returning [`crate::tool_hooks::PreToolUseDecision::Block`]), which
    /// makes this the seam for cross-cutting policy such as approval gating.
    /// The first hook to block wins.
    ///
    /// By default, returns an empty vector (no hooks).
    fn pre_tool_use_hooks(&self) -> Vec<Arc<dyn crate::tool_hooks::PreToolUseHook>> {
        vec![]
    }

    /// Returns pre-tool execution hooks adapted to per-capability config.
    ///
    /// Default delegates to `pre_tool_use_hooks()`. Capabilities whose hook
    /// behavior depends on config (e.g. `guardrails`) override this.
    fn pre_tool_use_hooks_with_config(
        &self,
        _config: &serde_json::Value,
    ) -> Vec<Arc<dyn crate::tool_hooks::PreToolUseHook>> {
        self.pre_tool_use_hooks()
    }

    /// Returns post-tool execution hooks provided by this capability.
    ///
    /// These hooks run after each individual tool completes execution.
    /// They can persist output, inject metadata, or transform results.
    /// Capability-contributed hooks run before infrastructure (final) hooks.
    ///
    /// By default, returns an empty vector (no hooks).
    fn post_tool_exec_hooks(&self) -> Vec<Arc<dyn crate::tool_hooks::PostToolExecHook>> {
        vec![]
    }

    /// Returns post-tool execution hooks adapted to per-capability config.
    ///
    /// Default delegates to `post_tool_exec_hooks()`. Capabilities whose hook
    /// behavior depends on config (e.g. `guardrails`) override this.
    fn post_tool_exec_hooks_with_config(
        &self,
        _config: &serde_json::Value,
    ) -> Vec<Arc<dyn crate::tool_hooks::PostToolExecHook>> {
        self.post_tool_exec_hooks()
    }

    /// Returns tool definition hooks provided by this capability.
    ///
    /// These hooks run after the runtime agent has merged and deduplicated its
    /// final tool list, before the tool schemas are sent to the LLM. They let
    /// capabilities apply cross-cutting schema changes to all active tools,
    /// including tools contributed by other capabilities, MCP, or clients.
    ///
    /// By default, returns an empty vector (no tool definition transforms).
    fn tool_definition_hooks(&self) -> Vec<Arc<dyn ToolDefinitionHook>> {
        vec![]
    }

    /// Returns tool definition hooks adapted to per-capability config.
    ///
    /// Default delegates to `tool_definition_hooks()`. Capabilities whose
    /// schema transforms depend on config override this method.
    fn tool_definition_hooks_with_config(
        &self,
        _config: &serde_json::Value,
    ) -> Vec<Arc<dyn ToolDefinitionHook>> {
        self.tool_definition_hooks()
    }

    /// Returns tool definition hooks adapted to per-capability config and the
    /// collection context (session id, model, ...).
    ///
    /// Default delegates to [`Self::tool_definition_hooks_with_config`], which
    /// ignores the context. Capabilities whose hooks carry session-scoped state
    /// override this to capture `ctx` — e.g. `tool_search` keys its
    /// progressive-disclosure reveal set by `ctx.session_id`, since the
    /// capability is a process-global singleton shared across sessions and a
    /// `ToolDefinitionHook::transform` has no session context of its own.
    fn tool_definition_hooks_with_context(
        &self,
        _ctx: &SystemPromptContext,
        config: &serde_json::Value,
    ) -> Vec<Arc<dyn ToolDefinitionHook>> {
        self.tool_definition_hooks_with_config(config)
    }

    /// Returns tool call hooks provided by this capability.
    ///
    /// These hooks run after the model has produced a tool call. They can read
    /// model-authored metadata for UI display and transform the tool call used
    /// for actual execution.
    ///
    /// By default, returns an empty vector (no tool call handling).
    fn tool_call_hooks(&self) -> Vec<Arc<dyn ToolCallHook>> {
        vec![]
    }

    /// Returns a configured hook over the finalized model tool-call batch.
    /// This later seam is suitable for policy that needs all calls plus their
    /// final schemas before the assistant message is persisted.
    fn finalized_tool_calls_hook(
        &self,
        _config: &serde_json::Value,
    ) -> Option<Arc<dyn crate::finalized_tool_calls::FinalizedToolCallsHook>> {
        None
    }

    /// Contribute human-readable narration for one of *this capability's* tool
    /// calls (e.g. "Read AGENTS.md", "Searched tools: router").
    ///
    /// The **default** dispatches to the matching tool's
    /// [`crate::tools::Tool::narrate`], so a capability narrates its tools for
    /// free — narration lives on the tool that owns it. Override this only when
    /// narration is config-driven or spans tools, or when the tools are dynamic
    /// (e.g. proxied MCP tools that have no local `Tool` struct).
    ///
    /// Returns `None` for tool names this capability does not provide, so other
    /// capabilities — or the generic fallback in [`crate::tool_narration`] —
    /// can handle them. The framework consults this for every applied
    /// capability (see `assemble`/`CapabilityNarrationHook`) on the act path.
    fn narrate(
        &self,
        _tool_def: Option<&ToolDefinition>,
        tool_call: &ToolCall,
        phase: crate::tool_narration::ToolNarrationPhase,
        locale: Option<&str>,
        ctx: crate::tool_narration::ToolNarrationContext<'_>,
    ) -> Option<String> {
        self.tools()
            .iter()
            .find(|tool| tool.name() == tool_call.name)
            .and_then(|tool| tool.narrate(tool_call, phase, locale, ctx))
    }

    /// Returns user-defined hook specifications contributed by this capability.
    ///
    /// User hooks are JSON-serializable specs (see
    /// `crate::user_hook_types::UserHookSpec` and `knowledge/runtime-resources/user-hooks.md`) that
    /// the `HookAdapterBuilder` validates and turns into per-event
    /// `Arc<dyn …Hook>` adapters during capability collection. Capabilities
    /// that ship reusable hook bundles (formatters, security guards, audit
    /// commands) override this; the user-facing `user_hooks` capability also
    /// uses this hook to surface user-config-authored entries.
    ///
    /// Contributors return *data only* — the executor is constructed
    /// centrally by the core so global timeout/output/sandbox limits cannot
    /// be bypassed.
    ///
    /// By default, returns an empty vector (no contributed hooks).
    fn user_hooks(&self) -> Vec<crate::user_hook_types::UserHookSpec> {
        vec![]
    }

    /// Returns user-defined hook specifications adapted to per-capability
    /// config.
    ///
    /// Default delegates to `user_hooks()`. The `user_hooks` capability
    /// overrides this to parse hook entries out of its config.
    fn user_hooks_with_config(
        &self,
        _config: &serde_json::Value,
    ) -> Vec<crate::user_hook_types::UserHookSpec> {
        self.user_hooks()
    }

    /// Returns the risk level of this capability.
    ///
    /// TM-AGENT-005: High-risk capabilities (code execution, network access)
    /// require admin approval when assigned to agents/harnesses. Capabilities
    /// that combine execution + network access enable data exfiltration.
    ///
    /// By default, returns `RiskLevel::Low`.
    fn risk_level(&self) -> RiskLevel {
        RiskLevel::Low
    }

    /// Returns system commands this capability provides.
    ///
    /// System commands are user-invocable /slash commands that execute directly
    /// without involving the LLM. They are surfaced in the UI command palette
    /// alongside invocable skills.
    ///
    /// By default, returns an empty vector (no commands).
    fn commands(&self) -> Vec<CommandDescriptor> {
        vec![]
    }

    /// Execute a system command declared by [`Self::commands`].
    ///
    /// Capabilities that declare commands MUST override this. The default
    /// implementation returns an error so that misconfigurations surface at
    /// invocation time rather than silently succeeding. Capabilities should
    /// match on `request.name`, validate `request.arguments`, and use the
    /// references they captured at construction time to mutate any external
    /// state (provider store, file system, etc.).
    ///
    /// Commands that need the session's assembled context or an out-of-band
    /// LLM call (e.g. `/btw`) use the host facilities on
    /// [`CommandExecutionContext::host`] — see
    /// [`crate::command_host::CommandHost`] and knowledge/project/commands.md.
    async fn execute_command(
        &self,
        request: &ExecuteCommandRequest,
        _ctx: &CommandExecutionContext,
    ) -> crate::error::Result<CommandResult> {
        Err(crate::error::AgentLoopError::config(format!(
            "capability {} declared command /{} but does not implement execute_command",
            self.id(),
            request.name,
        )))
    }

    /// Returns agent blueprints contributed by this capability.
    ///
    /// Blueprints are pre-built agent definitions with private tools, baked-in prompts,
    /// and fixed/default models. They are spawned via `spawn_agent` with a subagent target
    /// and `blueprint`.
    /// Blueprint tools never appear in the host agent's tool list.
    ///
    /// By default, returns an empty vector (no blueprints).
    fn agent_blueprints(&self) -> Vec<AgentBlueprint> {
        vec![]
    }

    /// Returns skills contributed by this capability in code.
    ///
    /// Contributions are normalized during capability collection into read-only
    /// mount points at `/.agents/skills/{name}/` so the built-in `skills`
    /// capability discovers them alongside user-uploaded and registry-based
    /// skills. This keeps discovery, prompt listing, and activation in one
    /// place rather than adding a parallel skill pipeline.
    ///
    /// By default, returns an empty vector (no contributed skills).
    fn contribute_skills(&self) -> Vec<SkillContribution> {
        vec![]
    }

    /// Returns streaming output guardrails contributed by this capability.
    ///
    /// Each provider is armed once per assistant message stream with the
    /// fully assembled system prompt and per-capability config; the returned
    /// per-stream `OutputGuardrailRun` is invoked after every batched delta
    /// in the streaming hot path. Returning `Block` aborts the stream and
    /// the client is told to replace the accumulated text with a canned
    /// message. See [`crate::output_guardrail`].
    ///
    /// Default: no guardrails.
    fn output_guardrails(&self) -> Vec<Arc<dyn crate::output_guardrail::OutputGuardrail>> {
        vec![]
    }

    /// Async, end-of-message output guardrails (EVE-573).
    ///
    /// Unlike [`Self::output_guardrails`] (synchronous, per-delta, hot path),
    /// these providers run **once** on the fully assembled assistant message
    /// after streaming completes and before the message is finalized into
    /// context. They receive an LLM-capable context and may perform I/O (e.g.
    /// a moderation classifier). The per-agent capability config is passed so a
    /// capability contributes nothing unless it has an applicable check
    /// configured — keeping the common (no-output-check) case free of work.
    ///
    /// Default: no guardrails.
    fn post_output_guardrails_with_config(
        &self,
        _config: &serde_json::Value,
    ) -> Vec<Arc<dyn crate::output_guardrail::PostGenerationOutputGuardrail>> {
        vec![]
    }

    /// Returns end-of-message citation annotation hooks contributed by this
    /// capability, adapted to per-agent config.
    ///
    /// Like [`Self::post_output_guardrails_with_config`], these run once on the
    /// fully assembled assistant message after streaming completes. But instead
    /// of a block/allow decision they attach citation [`crate::message::TextAnnotation`]s
    /// to the message text (optionally rewriting it first, e.g. to strip inline
    /// citation markers). This is the seam citation capabilities use to turn
    /// retrieved sources into claim-level provenance. See
    /// [`crate::annotation_hook`] and `knowledge/runtime-resources/citations.md`.
    ///
    /// A capability contributes nothing unless a citation feed is configured,
    /// keeping the common (no-citations) case free of work.
    ///
    /// Default: no annotation hooks.
    fn post_output_annotation_hooks_with_config(
        &self,
        _config: &serde_json::Value,
    ) -> Vec<Arc<dyn crate::annotation_hook::PostGenerationAnnotationHook>> {
        vec![]
    }

    /// Returns a citation verifier contributed by this capability, if any.
    ///
    /// Runs once after all citation feeds have attached annotations, over the
    /// collected set, stamping a [`crate::message::VerificationVerdict`] on each
    /// citation. Decoupled from the feeds so any feed can be paired with any
    /// verifier. The `citation_verification` capability implements this. See
    /// [`crate::annotation_hook::CitationVerifier`] and `knowledge/runtime-resources/citations.md`.
    ///
    /// Default: no verifier.
    fn citation_verifier_with_config(
        &self,
        _config: &serde_json::Value,
    ) -> Option<Arc<dyn crate::annotation_hook::CitationVerifier>> {
        None
    }
}

pub trait ToolDefinitionHook: Send + Sync {
    fn transform(&self, tools: Vec<ToolDefinition>) -> Vec<ToolDefinition>;

    /// Whether this hook should still run when the agent's model uses native
    /// (hosted) tool_search. Client-side deferral hooks return `false` so they
    /// don't strip schemas the hosted tool_search index needs (the two are
    /// mutually exclusive). Defaults to `true`.
    fn applies_with_native_tool_search(&self) -> bool {
        true
    }
}

pub trait ToolCallHook: Send + Sync {
    fn narration(
        &self,
        _tool_def: Option<&ToolDefinition>,
        _tool_call: &ToolCall,
        _phase: crate::tool_narration::ToolNarrationPhase,
        _locale: Option<&str>,
        _ctx: crate::tool_narration::ToolNarrationContext<'_>,
    ) -> Option<String> {
        None
    }

    fn transform_for_execution(&self, tool_call: ToolCall) -> ToolCall {
        tool_call
    }
}

/// Adapts a [`Capability`]'s [`Capability::narrate`] into a [`ToolCallHook`] so
/// capability-owned narration flows through the same hook channel the act atom
/// already consults. One is registered per applied capability during
/// `assemble`, after every explicit tool-call hook, so model-authored
/// narration (e.g. `human_intent`) still takes precedence.
pub struct CapabilityNarrationHook(pub Arc<dyn Capability>);

impl ToolCallHook for CapabilityNarrationHook {
    fn narration(
        &self,
        tool_def: Option<&ToolDefinition>,
        tool_call: &ToolCall,
        phase: crate::tool_narration::ToolNarrationPhase,
        locale: Option<&str>,
        ctx: crate::tool_narration::ToolNarrationContext<'_>,
    ) -> Option<String> {
        self.0.narrate(tool_def, tool_call, phase, locale, ctx)
    }
}

/// Risk classification for capabilities (TM-AGENT-005).
///
/// Used to enforce approval requirements when assigning capabilities.
#[derive(
    Debug, Clone, Copy, PartialEq, Eq, PartialOrd, Ord, serde::Serialize, serde::Deserialize,
)]
#[cfg_attr(feature = "openapi", derive(utoipa::ToSchema))]
#[cfg_attr(feature = "openapi", schema(example = "low"))]
#[serde(rename_all = "lowercase")]
pub enum RiskLevel {
    /// No special approval needed
    Low,
    /// Logged but allowed for org members
    Medium,
    /// Requires org admin role to assign
    High,
}

// ============================================================================
// Agent Blueprints
// ============================================================================

/// Model selection strategy for agent blueprints.
#[derive(Debug, Clone, Serialize, Deserialize)]
#[serde(rename_all = "snake_case")]
pub enum BlueprintModel {
    /// Always use this model. Host cannot override.
    Fixed(String),
    /// Use this model unless host provides override via config.
    Default(String),
    /// Use whatever model the host agent uses.
    Inherit,
}

/// Pre-built agent definition with private tools, baked-in prompt, and model selection.
///
/// Contributed by capabilities via `agent_blueprints()`. Spawned via
/// `spawn_agent` with a subagent target and `blueprint`. Blueprint tools never appear in the
/// host agent's tool list — they exist only inside the spawned child session.
pub struct AgentBlueprint {
    /// Unique identifier (e.g. `"github_scout"`)
    pub id: &'static str,
    /// Human-readable display name
    pub name: &'static str,
    /// When to use this blueprint (LLM reads this for delegation decisions)
    pub description: &'static str,
    /// Model selection strategy
    pub model: BlueprintModel,
    /// Baked-in system prompt for the child agent
    pub system_prompt: &'static str,
    /// Private tools — only available inside the blueprint's session
    pub tools: Vec<Box<dyn Tool>>,
    /// Iteration limit (default: 20)
    pub max_turns: Option<usize>,
    /// JSON Schema for allowed host-provided config. `None` = no config accepted.
    pub config_schema: Option<serde_json::Value>,
}

impl AgentBlueprint {
    /// Convert blueprint tools to tool definitions (for RuntimeAgent building).
    pub fn tool_definitions(&self) -> Vec<ToolDefinition> {
        self.tools.iter().map(|t| t.to_definition()).collect()
    }
}

impl std::fmt::Debug for AgentBlueprint {
    fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
        f.debug_struct("AgentBlueprint")
            .field("id", &self.id)
            .field("name", &self.name)
            .field("model", &self.model)
            .field("tool_count", &self.tools.len())
            .field("max_turns", &self.max_turns)
            .finish()
    }
}

// ============================================================================
// Capability Registry
// ============================================================================

/// Registry that holds all available capability implementations.
///
/// The registry provides access to capabilities by ID and allows
/// applying multiple capabilities to build a RuntimeAgent.
///
/// # Example
///
/// ```
/// use everruns_core::capabilities::CapabilityRegistry;
///
/// let registry = CapabilityRegistry::new();
/// assert!(registry.is_empty());
/// ```
#[derive(Clone)]
pub struct CapabilityRegistry {
    capabilities: HashMap<String, Arc<dyn Capability>>,
    /// Canonical-id/alias bookkeeping delegated to the neutral capability
    /// contract so the Framework and product resolve identity identically
    /// (see [`Capability::aliases`]).
    index: everruns_capability::CapabilityIdIndex,
}

impl CapabilityRegistry {
    /// Create a new empty registry
    pub fn new() -> Self {
        Self {
            capabilities: HashMap::new(),
            index: everruns_capability::CapabilityIdIndex::new(),
        }
    }

    /// Register a capability
    pub fn register(&mut self, capability: impl Capability + 'static) {
        self.register_arc(Arc::new(capability));
    }

    /// Register a boxed capability
    pub fn register_boxed(&mut self, capability: Box<dyn Capability>) {
        self.register_arc(Arc::from(capability));
    }

    /// Register an Arc-wrapped capability.
    ///
    /// Re-registering the same canonical ID replaces the previous
    /// implementation (legacy override semantics); use
    /// [`CapabilityRegistry::try_register_arc`] to reject collisions instead.
    pub fn register_arc(&mut self, capability: Arc<dyn Capability>) {
        let canonical = capability.id().to_string();
        self.index
            .insert_or_replace(canonical.clone(), &capability.aliases());
        self.capabilities.insert(canonical, capability);
    }

    /// Register an Arc-wrapped capability, rejecting duplicate IDs and alias
    /// collisions via the neutral contract's registry rules.
    pub fn try_register_arc(
        &mut self,
        capability: Arc<dyn Capability>,
    ) -> Result<(), everruns_capability::CapabilityError> {
        let canonical = capability.id().to_string();
        self.index
            .insert(canonical.clone(), &capability.aliases())?;
        self.capabilities.insert(canonical, capability);
        Ok(())
    }

    /// Register inventory-submitted integrations accepted by a caller-owned policy.
    ///
    /// Core owns the registry mutation algorithm; host and product composition
    /// own every deployment-grade and feature decision supplied by `include`.
    pub fn register_inventory_plugins(
        &mut self,
        mut include: impl FnMut(&IntegrationPlugin) -> bool,
    ) {
        for plugin in inventory::iter::<IntegrationPlugin>() {
            if include(plugin) {
                self.register_boxed((plugin.factory)());
            }
        }
    }

    /// Get a capability by ID or alias
    pub fn get(&self, id: &str) -> Option<&Arc<dyn Capability>> {
        self.capabilities.get(self.index.canonical_of(id)?)
    }

    /// Resolve an ID or alias to the canonical capability ID.
    ///
    /// Returns `None` for IDs that are neither registered nor an alias of a
    /// registered capability (e.g. declarative or MCP refs).
    pub fn canonical_id<'a>(&'a self, id: &'a str) -> Option<&'a str> {
        self.index.canonical_of(id)
    }

    /// Remove a capability from the registry by ID or alias.
    pub fn unregister(&mut self, id: &str) -> Option<Arc<dyn Capability>> {
        let canonical = self.index.remove(id)?;
        self.capabilities.remove(&canonical)
    }

    /// Check if a capability is registered (by ID or alias)
    pub fn has(&self, id: &str) -> bool {
        self.get(id).is_some()
    }

    /// Get all registered capabilities
    pub fn list(&self) -> Vec<&Arc<dyn Capability>> {
        self.capabilities.values().collect()
    }

    /// Get the number of registered capabilities
    pub fn len(&self) -> usize {
        self.capabilities.len()
    }

    /// Check if the registry is empty
    pub fn is_empty(&self) -> bool {
        self.capabilities.is_empty()
    }

    /// Create a builder for fluent capability registration
    pub fn builder() -> CapabilityRegistryBuilder {
        CapabilityRegistryBuilder::new()
    }

    /// Find a blueprint by ID across all registered capabilities.
    ///
    /// Returns a fresh `AgentBlueprint` (with new tool instances) each time.
    pub fn blueprint(&self, id: &str) -> Option<AgentBlueprint> {
        for cap in self.capabilities.values() {
            for bp in cap.agent_blueprints() {
                if bp.id == id {
                    return Some(bp);
                }
            }
        }
        None
    }

    /// Find a blueprint and the capability that registered it.
    ///
    /// Returns `(capability_id, blueprint)` with fresh tool instances.
    pub fn blueprint_with_capability(&self, id: &str) -> Option<(String, AgentBlueprint)> {
        for (capability_id, cap) in &self.capabilities {
            for bp in cap.agent_blueprints() {
                if bp.id == id {
                    return Some((capability_id.clone(), bp));
                }
            }
        }
        None
    }

    /// Collect all blueprints from all registered capabilities.
    pub fn all_blueprints(&self) -> Vec<AgentBlueprint> {
        self.capabilities
            .values()
            .flat_map(|cap| cap.agent_blueprints())
            .collect()
    }
}

impl Default for CapabilityRegistry {
    fn default() -> Self {
        Self::new()
    }
}

impl std::fmt::Debug for CapabilityRegistry {
    fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
        let ids: Vec<_> = self.capabilities.keys().collect();
        f.debug_struct("CapabilityRegistry")
            .field("capabilities", &ids)
            .finish()
    }
}

/// Builder for creating a CapabilityRegistry with a fluent API
pub struct CapabilityRegistryBuilder {
    registry: CapabilityRegistry,
}

impl CapabilityRegistryBuilder {
    /// Create a new builder with an empty registry
    pub fn new() -> Self {
        Self {
            registry: CapabilityRegistry::new(),
        }
    }

    /// Add a capability
    pub fn capability(mut self, capability: impl Capability + 'static) -> Self {
        self.registry.register(capability);
        self
    }

    /// Build the registry
    pub fn build(self) -> CapabilityRegistry {
        self.registry
    }
}

impl Default for CapabilityRegistryBuilder {
    fn default() -> Self {
        Self::new()
    }
}

// ============================================================================
// Collect Capabilities Helper
// ============================================================================

/// Context available to capability-owned model-view transforms.
pub struct ModelViewContext<'a> {
    pub session_id: SessionId,
    pub prior_usage: Option<&'a TokenUsage>,
}

/// Provider-side hook for building prompt-facing model views.
///
/// Providers receive the output of earlier providers and return the messages
/// that should be sent into provider serialization. Lower priority providers
/// run earlier.
pub trait ModelViewProvider: Send + Sync {
    fn apply_model_view(
        &self,
        messages: Vec<Message>,
        config: &serde_json::Value,
        context: &ModelViewContext<'_>,
    ) -> Vec<Message>;

    fn priority(&self) -> i32 {
        0
    }
}

/// Collected data from capabilities before applying to config.
///
/// This intermediate struct allows sharing the capability collection logic
/// between `apply_capabilities` and `apply_capabilities_to_builder`.
pub struct CollectedCapabilities {
    /// System prompt additions (in order)
    pub system_prompt_parts: Vec<String>,
    /// Source attribution for each system prompt addition.
    pub system_prompt_attributions: Vec<SystemPromptAttribution>,
    /// Conversation-context additions (in order). Unlike system prompt parts,
    /// these render as the leading user-role message of every turn:
    /// model-visible and re-resolved alongside the system prompt, but never
    /// folded into the cached system prompt. Untrusted workspace content
    /// (e.g. AGENTS.md hierarchies) belongs here, below harness safety
    /// instructions in the instruction hierarchy.
    pub conversation_context_parts: Vec<String>,
    /// Source attribution for each conversation-context addition.
    pub conversation_context_attributions: Vec<SystemPromptAttribution>,
    /// Tool implementations for the registry
    pub tools: Vec<Box<dyn Tool>>,
    /// Tool definitions for config
    pub tool_definitions: Vec<ToolDefinition>,
    /// Mount points from capabilities
    pub mounts: Vec<MountPoint>,
    /// Message filter providers with their configs (in priority order)
    pub message_filter_providers: Vec<(Arc<dyn MessageFilterProvider>, serde_json::Value)>,
    /// IDs of capabilities that were collected
    pub applied_ids: Vec<String>,
    /// Tool search configuration (set when openai_tool_search capability is present)
    pub tool_search: Option<crate::driver_registry::ToolSearchConfig>,
    /// Prompt caching configuration (set when prompt_caching capability is present)
    pub prompt_cache: Option<crate::driver_registry::PromptCacheConfig>,
    /// Driver-namespaced opaque per-call options (e.g. provider-executed
    /// server tools contributed by the `openrouter_server_tools` capability).
    /// First contributor wins per key.
    pub driver_options: HashMap<String, serde_json::Value>,
    /// Request-level parallel tool calls preference (set when the
    /// `parallel_tool_calls` capability is present with mode `prefer`/`avoid`).
    /// `None` when absent or mode `none`.
    pub parallel_tool_calls: Option<bool>,
    /// Hooks that transform the final runtime tool definition list.
    pub tool_definition_hooks: Vec<Arc<dyn ToolDefinitionHook>>,
    /// Hooks that inspect or transform model-produced tool calls.
    pub tool_call_hooks: Vec<Arc<dyn ToolCallHook>>,
    /// Scoped remote MCP servers contributed by capabilities.
    pub mcp_servers: ScopedMcpServers,
    // NOTE: output guardrails are intentionally NOT collected here. They are
    // re-derived per turn in `ReasonAtom` directly from the resolved capability
    // configs + registry, because they need the assembled system prompt at
    // arming time (which only exists once the runtime agent is built). Storing
    // them here would duplicate that work for callers that don't run a stream.
}

#[derive(Debug, Clone, PartialEq, Eq)]
pub struct SystemPromptAttribution {
    pub capability_id: String,
    pub content: String,
}

impl CollectedCapabilities {
    /// Returns the combined system prompt prefix from all capabilities.
    /// Returns None if no capabilities contributed system prompt additions.
    pub fn system_prompt_prefix(&self) -> Option<String> {
        if self.system_prompt_parts.is_empty() {
            None
        } else {
            Some(self.system_prompt_parts.join("\n\n"))
        }
    }

    /// Combined conversation context from all capabilities (joined with blank
    /// lines), or `None` when no capability contributed any. Renders as the
    /// leading user-role message of every turn, never as system prompt.
    pub fn conversation_context(&self) -> Option<String> {
        if self.conversation_context_parts.is_empty() {
            None
        } else {
            Some(self.conversation_context_parts.join("\n\n"))
        }
    }

    /// Apply all collected message filter providers to a query.
    ///
    /// Providers are applied in priority order (lower priority first).
    pub fn apply_message_filters(&self, query: &mut crate::message_filter::MessageQuery) {
        // Providers are already sorted by priority during collection
        for (provider, config) in &self.message_filter_providers {
            provider.apply_filters(query, config);
        }
    }

    /// Apply post-load transforms from all message filter providers.
    /// Called after messages are loaded, filtered, and injected.
    pub fn apply_post_load_filters(&self, messages: &mut Vec<crate::message::Message>) {
        for (provider, config) in &self.message_filter_providers {
            provider.post_load(messages, config);
        }
    }

    /// Check if any capabilities contribute message filters.
    pub fn has_message_filters(&self) -> bool {
        !self.message_filter_providers.is_empty()
    }
}

pub struct DelegationTargetProvider {
    pub target_type: &'static str,
    pub tool: Box<dyn Tool>,
}

/// Shared execution mode accepted natively by every `spawn_agent` provider.
#[derive(Debug, Clone, Copy, PartialEq, Eq, serde::Serialize, serde::Deserialize)]
#[serde(rename_all = "snake_case")]
pub enum SpawnMode {
    Background,
    Foreground,
}

impl SpawnMode {
    pub fn parse(value: &str) -> Option<Self> {
        match value {
            "background" => Some(Self::Background),
            "foreground" => Some(Self::Foreground),
            _ => None,
        }
    }

    pub fn as_str(self) -> &'static str {
        match self {
            Self::Background => "background",
            Self::Foreground => "foreground",
        }
    }
}

struct UnifiedSpawnAgentTool {
    providers: Vec<DelegationTargetProvider>,
}

fn validate_spawn_agent_target_fields(
    arguments: &serde_json::Value,
    target_type: &str,
) -> Result<(), String> {
    for field in ["blueprint", "config"] {
        if target_type != "subagent" && arguments.get(field).is_some_and(|value| !value.is_null()) {
            return Err(format!(
                "{field} is only valid for subagent targets, not {target_type}."
            ));
        }
    }
    Ok(())
}

impl UnifiedSpawnAgentTool {
    fn new(providers: Vec<DelegationTargetProvider>) -> Self {
        Self { providers }
    }

    fn provider_for(&self, target_type: &str) -> Option<&dyn Tool> {
        self.providers
            .iter()
            .find(|provider| provider.target_type == target_type)
            .map(|provider| provider.tool.as_ref())
    }

    fn target_types(&self) -> Vec<&'static str> {
        ["subagent", "agent", "external_a2a"]
            .into_iter()
            .filter(|target_type| {
                self.providers
                    .iter()
                    .any(|provider| provider.target_type == *target_type)
            })
            .collect()
    }

    /// Per-`target.type` constraint branches, nested inside the `target`
    /// property. Anthropic rejects `oneOf`/`allOf`/`anyOf` at the top level
    /// of a tool `input_schema`, so provider-specific requirements must live
    /// below the root (nested composition is accepted).
    fn target_constraint_branches(&self) -> Vec<serde_json::Value> {
        self.target_types()
            .into_iter()
            .filter_map(|target_type| match target_type {
                "subagent" => Some(serde_json::json!({
                    "properties": {
                        "type": {"const": "subagent"}
                    }
                })),
                "agent" => Some(serde_json::json!({
                    "properties": {
                        "type": {"const": "agent"}
                    },
                    "required": ["type", "id"]
                })),
                "external_a2a" => Some(serde_json::json!({
                    "properties": {
                        "type": {"const": "external_a2a"}
                    },
                    "anyOf": [
                        {"required": ["id"]},
                        {"required": ["external_agent_id"]}
                    ]
                })),
                _ => None,
            })
            .collect()
    }

    // NOTE: subagent and agent providers require `name` at execution
    // (`require_str`), while external_a2a ignores it. A schema that required
    // `name` only for the local targets would need a top-level
    // `oneOf`/`if`/`allOf`, which Anthropic rejects in a tool `input_schema`.
    // `name` is therefore required at the root unconditionally: requiring a
    // field external_a2a merely ignores is safe (the schema never permits a
    // call execution would reject), whereas omitting it would let a
    // `name`-less subagent call pass validation and then fail at dispatch —
    // exactly the mismatch #2787 set out to close.
}

#[async_trait]
impl Tool for UnifiedSpawnAgentTool {
    fn narrate(
        &self,
        tool_call: &ToolCall,
        phase: crate::tool_narration::ToolNarrationPhase,
        locale: Option<&str>,
        ctx: crate::tool_narration::ToolNarrationContext<'_>,
    ) -> Option<String> {
        // A call still streaming its arguments, or one naming an unknown
        // target, must not fall back to "Running Spawn Agent": narrate the
        // delegation directly so the line always names the agent being spawned.
        let from_provider = tool_call
            .arguments
            .get("target")
            .and_then(|target| target.get("type"))
            .and_then(serde_json::Value::as_str)
            .and_then(|target_type| self.provider_for(target_type))
            .and_then(|tool| tool.narrate(tool_call, phase, locale, ctx));
        Some(from_provider.unwrap_or_else(|| {
            crate::tool_narration::narrate_subagent_spawn(&tool_call.arguments, phase, locale)
        }))
    }

    fn name(&self) -> &str {
        "spawn_agent"
    }

    fn display_name(&self) -> Option<&str> {
        Some("Spawn Agent")
    }

    fn description(&self) -> &str {
        "Delegate work to another agent target. Set target.type to one of the advertised target types; background returns a task_id for generic task tools, and foreground waits for the result."
    }

    fn parameters_schema(&self) -> serde_json::Value {
        serde_json::json!({
            "type": "object",
            "properties": {
                "name": {
                    "type": "string",
                    "description": "Human-readable name for the delegated run (subagent, first-party handoff, or external delegation). Used as the task label."
                },
                "instructions": {
                    "type": "string",
                    "description": "Instructions for the delegated agent. Do not include credentials or bearer tokens."
                },
                "goal": {
                    "type": "string",
                    "description": "Optional objective stored on the spawned session and made visible at system-prompt level."
                },
                "lifetime": {
                    "type": "string",
                    "enum": ["linked", "detached"],
                    "default": "linked",
                    "description": "linked creates a lifecycle child; detached creates an independent top-level peer session. Not valid for external_a2a."
                },
                "seed": {
                    "type": "string",
                    "enum": ["fresh", "fork", "workspace"],
                    "default": "fresh",
                    "description": "Detached-session seed mode: fresh starts blank, fork copies history/workspace/session storage, workspace copies workspace files only."
                },
                "target": {
                    "type": "object",
                    "properties": {
                        "type": {
                            "type": "string",
                            "enum": self.target_types(),
                            "description": "Delegation target type. Use subagent for same-agent child sessions, agent for configured first-party handoffs, or external_a2a for configured remote A2A agents."
                        },
                        "id": {
                            "type": "string",
                            "description": "Configured target id for first-party handoffs or external A2A agents."
                        },
                        "external_agent_id": {
                            "type": "string",
                            "description": "Configured external A2A agent id."
                        }
                    },
                    "required": ["type"],
                    "oneOf": self.target_constraint_branches(),
                    "additionalProperties": false
                },
                "mode": {
                    "type": "string",
                    "enum": ["background", "foreground"],
                    "description": "Execution mode. Use background to return immediately with a task_id, or foreground to block until the delegated work reaches a terminal state or timeout."
                },
                "blueprint": {
                    "type": "string",
                    "description": "Subagent-only blueprint ID to spawn a specialist agent with its own tools and model."
                },
                "config": {
                    "type": "object",
                    "description": "Subagent-only blueprint configuration. Only valid when blueprint is set."
                },
                "result_schema": {
                    "type": "object",
                    "description": "JSON Schema for a required final structured result. Local child agents must call report_result; external A2A agents must return a structured data artifact."
                },
                "message_schema": {
                    "type": "object",
                    "description": "JSON Schema for structured progress messages from local child agents. When set, the child receives report_task_progress. External A2A targets reject this option explicitly."
                },
                "public_context": {
                    "type": "object",
                    "description": "Agent-handoff-only non-secret structured context to include with the instructions."
                },
                "wait_timeout_secs": {
                    "type": "integer",
                    "minimum": 1,
                    "maximum": 86400,
                    "description": "External-A2A-only foreground timeout."
                },
                "wake_on_completion": {
                    "type": "boolean",
                    "description": "External-A2A-only control for background completion wake-ups."
                }
            },
            "required": ["name", "instructions", "target"],
            "additionalProperties": false
        })
    }

    fn hints(&self) -> crate::tool_types::ToolHints {
        let mut hints = crate::tool_types::ToolHints::default()
            .with_long_running(true)
            .with_concurrency_class(SPAWN_AGENT_CONCURRENCY_CLASS);
        if self.provider_for("external_a2a").is_some() {
            hints = hints.with_open_world(true);
        }
        hints
    }

    async fn execute(&self, _arguments: serde_json::Value) -> ToolExecutionResult {
        ToolExecutionResult::tool_error(
            "spawn_agent requires context. This tool must be executed with session context.",
        )
    }

    async fn execute_with_context(
        &self,
        arguments: serde_json::Value,
        context: &ToolContext,
    ) -> ToolExecutionResult {
        let target_type = match arguments
            .get("target")
            .and_then(|target| target.get("type"))
            .and_then(serde_json::Value::as_str)
        {
            Some(target_type) => target_type,
            None => {
                return ToolExecutionResult::tool_error("Missing required parameter: target.type");
            }
        };

        let Some(provider) = self.provider_for(target_type) else {
            let supported = self.target_types().join(", ");
            return ToolExecutionResult::tool_error(format!(
                "Unsupported spawn_agent target.type: \"{target_type}\". Supported target types: {supported}"
            ));
        };
        if let Err(error) = validate_spawn_agent_target_fields(&arguments, target_type) {
            return ToolExecutionResult::tool_error(error);
        }
        if target_type == "external_a2a"
            && arguments
                .get("lifetime")
                .and_then(serde_json::Value::as_str)
                .is_some_and(|value| value == "detached")
        {
            return ToolExecutionResult::tool_error(
                "lifetime=\"detached\" is only valid for local session targets (subagent or agent), not external_a2a.",
            );
        }
        if target_type == "external_a2a"
            && arguments
                .get("message_schema")
                .is_some_and(|schema| !schema.is_null())
        {
            return ToolExecutionResult::tool_error(
                "message_schema is not supported for external_a2a targets because remote agents cannot receive report_task_progress.",
            );
        }

        provider.execute_with_context(arguments, context).await
    }

    fn requires_context(&self) -> bool {
        true
    }
}

/// Compose the model-visible system prompt from the stable base prompt and
/// collected capability contributions. Keep the base prompt first so changes in
/// dynamic capabilities (for example AGENTS.md reads or environment context)
/// do not invalidate provider prefix caches for the agent's core instructions.
pub fn compose_system_prompt(base_system_prompt: &str, additions: Option<&str>) -> String {
    let Some(additions) = additions.filter(|value| !value.is_empty()) else {
        return base_system_prompt.to_string();
    };

    if base_system_prompt.is_empty() {
        return additions.to_string();
    }

    if base_system_prompt.contains("<system-prompt>") {
        format!("{base_system_prompt}\n\n{additions}")
    } else {
        format!("<system-prompt>\n{base_system_prompt}\n</system-prompt>\n\n{additions}")
    }
}

/// Lightweight result containing only message filter providers.
///
/// Used when callers only need message filtering (e.g., message loading in
/// ReasonAtom) without paying the cost of system prompt contribution or tool
/// collection. This avoids unnecessary filesystem reads (AGENTS.md) and tool
/// instantiation on the message-filter-only path.
pub struct CollectedMessageFilters {
    /// Message filter providers with their configs (in priority order)
    pub message_filter_providers: Vec<(Arc<dyn MessageFilterProvider>, serde_json::Value)>,
}

/// Lightweight result containing only model-view providers.
pub struct CollectedModelViewProviders {
    /// Model-view providers with their configs (in priority order).
    pub model_view_providers: Vec<(Arc<dyn ModelViewProvider>, serde_json::Value)>,
}

// Note: apply_message_filters/apply_post_load_filters mirror the same methods
// on CollectedCapabilities. The duplication is intentional — extracting a trait
// would add indirection for 3 lines of loop body, and the two structs serve
// different purposes (lightweight vs full collection).

impl CollectedMessageFilters {
    /// Apply all collected message filter providers to a query.
    pub fn apply_message_filters(&self, query: &mut crate::message_filter::MessageQuery) {
        for (provider, config) in &self.message_filter_providers {
            provider.apply_filters(query, config);
        }
    }

    /// Apply post-load transforms from all message filter providers.
    pub fn apply_post_load_filters(&self, messages: &mut Vec<crate::message::Message>) {
        for (provider, config) in &self.message_filter_providers {
            provider.post_load(messages, config);
        }
    }
}

impl CollectedModelViewProviders {
    /// Apply all collected model-view providers in priority order.
    pub fn apply_model_view(
        &self,
        mut messages: Vec<Message>,
        context: &ModelViewContext<'_>,
    ) -> Vec<Message> {
        for (provider, config) in &self.model_view_providers {
            messages = provider.apply_model_view(messages, config, context);
        }
        messages
    }
}

/// True when an available capability contributes compaction policy in this set.
///
/// Infinity context defers token-budget eviction to compaction when both are
/// enabled (see knowledge/runtime-resources/infinity-context.md) so that compaction's summary — not a
/// bare "hidden" notice — covers trimmed history.
fn compaction_is_enabled(
    capability_configs: &[AgentCapabilityConfig],
    registry: &CapabilityRegistry,
) -> bool {
    capability_configs.iter().any(|cap_config| {
        registry.get(cap_config.capability_id()).is_some_and(|cap| {
            cap.status().is_active() && cap.compaction_policy(cap_config.config_value()).is_some()
        })
    })
}

/// Collect only message filter providers from capabilities, skipping system
/// prompt contributions, tools, mounts, and other expensive work.
///
/// This is a fast path for callers that only need message filtering (e.g.,
/// the message-loading step in ReasonAtom before RuntimeAgent is built).
pub fn collect_message_filters_only(
    capability_configs: &[AgentCapabilityConfig],
    registry: &CapabilityRegistry,
) -> CollectedMessageFilters {
    let mut message_filter_providers: Vec<(Arc<dyn MessageFilterProvider>, serde_json::Value)> =
        Vec::new();
    let compaction_on = compaction_is_enabled(capability_configs, registry);

    for cap_config in capability_configs {
        let cap_id = cap_config.capability_id();
        if let Some(capability) = registry.get(cap_id) {
            if !capability.status().is_active() {
                continue;
            }
            // Resolve against None: no model is known at message-filter collection
            // time, so fall back to the model-agnostic variant if present.
            let effective: &dyn Capability = capability
                .resolve_for_model(None)
                .unwrap_or_else(|| capability.as_ref());
            if let Some(provider) = effective.message_filter_provider() {
                let config =
                    effective.message_filter_config(cap_config.config_value(), compaction_on);
                message_filter_providers.push((provider, config));
            }
        }
    }

    message_filter_providers.sort_by_key(|(p, _)| p.priority());

    CollectedMessageFilters {
        message_filter_providers,
    }
}

/// Collect only model-view providers from capabilities.
///
/// `model` should be the LLM model name when it is known at call time (e.g. the
/// ReasonAtom already holds a resolved model execution). Pass `None` only when the
/// model is genuinely unavailable so capabilities fall back to the model-agnostic
/// variant.
pub fn collect_model_view_providers(
    capability_configs: &[AgentCapabilityConfig],
    registry: &CapabilityRegistry,
    model: Option<&str>,
) -> CollectedModelViewProviders {
    let mut model_view_providers: Vec<(Arc<dyn ModelViewProvider>, serde_json::Value)> = Vec::new();

    for cap_config in capability_configs {
        let cap_id = cap_config.capability_id();
        if let Some(capability) = registry.get(cap_id) {
            if !capability.status().is_active() {
                continue;
            }
            let effective: &dyn Capability = capability
                .resolve_for_model(model)
                .unwrap_or_else(|| capability.as_ref());
            if let Some(provider) = effective.model_view_provider() {
                model_view_providers.push((provider, cap_config.config_value().clone()));
            }
        }
    }

    model_view_providers.sort_by_key(|(p, _)| p.priority());

    CollectedModelViewProviders {
        model_view_providers,
    }
}

/// Collect [`Volatility::Dynamic`] facts from every active capability, in
/// configured order. Called by `ReasonAtom` once per request so live values
/// (e.g. the current time) are fresh, then rendered into the trailing `<facts>`
/// block. Static facts are ignored here — they already live in the cached
/// system prompt.
pub fn collect_dynamic_facts(
    capability_configs: &[AgentCapabilityConfig],
    registry: &CapabilityRegistry,
    model: Option<&str>,
    ctx: &FactsContext,
) -> Vec<Fact> {
    let mut dynamic = Vec::new();
    for cap_config in capability_configs {
        let cap_id = cap_config.capability_id();
        if let Some(capability) = registry.get(cap_id) {
            if !capability.status().is_active() {
                continue;
            }
            let effective: &dyn Capability = capability
                .resolve_for_model(model)
                .unwrap_or_else(|| capability.as_ref());
            for fact in effective.facts(cap_config.config_value(), ctx) {
                if fact.volatility == Volatility::Dynamic {
                    dynamic.push(fact);
                }
            }
        }
    }
    dynamic
}

pub fn collect_capability_mcp_servers(
    capability_configs: &[AgentCapabilityConfig],
    registry: &CapabilityRegistry,
) -> ScopedMcpServers {
    let mut servers = ScopedMcpServers::default();

    for cap_config in capability_configs {
        let cap_id = cap_config.capability_id();
        // Both `declarative:` and `plugin:` carry a serialized
        // `DeclarativeCapabilityDefinition`; handle them the same way.
        if is_declarative_capability(cap_id) || is_plugin_capability(cap_id) {
            if let Ok(definition) = serde_json::from_value::<DeclarativeCapabilityDefinition>(
                cap_config.config_value().clone(),
            ) {
                if !definition.status.is_active() {
                    continue;
                }
                if let Some(contributed) = definition.mcp_servers {
                    servers = merge_scoped_mcp_servers(&servers, &contributed);
                }
            }
            continue;
        }
        if let Some(capability) = registry.get(cap_id) {
            if !capability.status().is_active() {
                continue;
            }
            servers = merge_scoped_mcp_servers(
                &servers,
                &capability.mcp_servers_with_config(cap_config.config_value()),
            );
        }
    }

    servers
}

// ============================================================================
// Dependency Resolution
// ============================================================================

/// Maximum number of capabilities after dependency resolution.
/// This prevents runaway dependency chains and resource exhaustion.
pub const MAX_RESOLVED_CAPABILITIES: usize = 100;

/// Error type for dependency resolution failures
#[derive(Debug, Clone, PartialEq, Eq)]
pub enum DependencyError {
    /// Circular dependency detected in the capability graph
    CircularDependency {
        /// The capability where the cycle was detected
        capability_id: String,
        /// The dependency chain leading to the cycle
        chain: Vec<String>,
    },
    /// Too many capabilities after resolution
    TooManyCapabilities {
        /// Number of capabilities requested
        count: usize,
        /// Maximum allowed
        max: usize,
    },
}

impl std::fmt::Display for DependencyError {
    fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
        match self {
            DependencyError::CircularDependency {
                capability_id,
                chain,
            } => {
                write!(
                    f,
                    "Circular dependency detected: {} depends on itself via chain: {} -> {}",
                    capability_id,
                    chain.join(" -> "),
                    capability_id
                )
            }
            DependencyError::TooManyCapabilities { count, max } => {
                write!(
                    f,
                    "Too many capabilities after resolution: {} (max: {})",
                    count, max
                )
            }
        }
    }
}

impl std::error::Error for DependencyError {}

/// Result of resolving capability dependencies
#[derive(Debug, Clone)]
pub struct ResolvedCapabilities {
    /// All capability IDs after resolving dependencies (in topological order)
    /// Dependencies come before dependents.
    pub resolved_ids: Vec<String>,
    /// IDs that were added as dependencies (not in the original selection)
    pub added_as_dependencies: Vec<String>,
    /// Original user-selected capability IDs
    pub user_selected: Vec<String>,
}

/// Resolve capability dependencies, returning all required capability IDs.
///
/// This function:
/// 1. Takes the user-selected capability IDs
/// 2. Recursively collects all dependencies
/// 3. Returns them in topological order (dependencies before dependents)
/// 4. Detects circular dependencies and returns an error
/// 5. Enforces a maximum capability limit
///
/// # Arguments
///
/// * `selected_ids` - User-selected capability IDs
/// * `registry` - The capability registry to look up dependencies
///
/// # Returns
///
/// `Ok(ResolvedCapabilities)` with all required capabilities in order,
/// or `Err(DependencyError)` if circular dependencies are detected or
/// the limit is exceeded.
pub fn resolve_dependencies(
    selected_ids: &[String],
    registry: &CapabilityRegistry,
) -> Result<ResolvedCapabilities, DependencyError> {
    use std::collections::HashSet;

    // Canonicalize so capabilities selected via alias match their resolved IDs.
    let user_selected: HashSet<String> = selected_ids
        .iter()
        .map(|id| registry.canonical_id(id).unwrap_or(id).to_string())
        .collect();
    let mut resolved: Vec<String> = Vec::new();
    let mut resolved_set: HashSet<String> = HashSet::new();
    let mut added_as_dependencies: Vec<String> = Vec::new();

    // Process each selected capability and its dependencies using DFS
    for cap_id in selected_ids {
        resolve_single_capability(
            cap_id,
            registry,
            &mut resolved,
            &mut resolved_set,
            &mut added_as_dependencies,
            &user_selected,
            &mut Vec::new(), // visiting chain for cycle detection
        )?;
    }

    // Check max limit
    if resolved.len() > MAX_RESOLVED_CAPABILITIES {
        return Err(DependencyError::TooManyCapabilities {
            count: resolved.len(),
            max: MAX_RESOLVED_CAPABILITIES,
        });
    }

    Ok(ResolvedCapabilities {
        resolved_ids: resolved,
        added_as_dependencies,
        user_selected: selected_ids.to_vec(),
    })
}

/// Resolve dependency-expanded capability configs, preserving explicit config on selected IDs.
///
/// Dependencies are inserted with empty configs. If the same capability is provided more than
/// once, the last explicit config wins.
pub fn resolve_capability_configs(
    selected_configs: &[AgentCapabilityConfig],
    registry: &CapabilityRegistry,
) -> Result<Vec<AgentCapabilityConfig>, DependencyError> {
    let mut selected_ids: Vec<String> = Vec::new();
    for config in selected_configs {
        // Both `declarative:` and `plugin:` carry a `DeclarativeCapabilityDefinition`
        // config that may declare dependencies.
        if (is_declarative_capability(config.capability_id())
            || is_plugin_capability(config.capability_id()))
            && let Ok(definition) = serde_json::from_value::<DeclarativeCapabilityDefinition>(
                config.config_value().clone(),
            )
        {
            selected_ids.extend(definition.dependencies);
        }
        selected_ids.push(config.capability_id().to_string());
    }
    let resolved = resolve_dependencies(&selected_ids, registry)?;

    // Key explicit configs by canonical ID so config supplied under an alias
    // still attaches to the (canonical) resolved capability ID.
    let explicit_configs: std::collections::HashMap<String, serde_json::Value> = selected_configs
        .iter()
        .map(|config| {
            let id = config.capability_id();
            let id = registry.canonical_id(id).unwrap_or(id);
            (id.to_string(), config.config_value().clone())
        })
        .collect();

    Ok(resolved
        .resolved_ids
        .into_iter()
        .map(|capability_id| {
            explicit_configs
                .get(&capability_id)
                .cloned()
                .map(|config| AgentCapabilityConfig::with_config(capability_id.clone(), config))
                .unwrap_or_else(|| AgentCapabilityConfig::new(capability_id))
        })
        .collect())
}

/// Helper function to resolve a single capability and its dependencies recursively.
fn resolve_single_capability(
    cap_id: &str,
    registry: &CapabilityRegistry,
    resolved: &mut Vec<String>,
    resolved_set: &mut std::collections::HashSet<String>,
    added_as_dependencies: &mut Vec<String>,
    user_selected: &std::collections::HashSet<String>,
    visiting: &mut Vec<String>,
) -> Result<(), DependencyError> {
    // Normalize aliases to the canonical ID so an alias and its canonical ID
    // resolve (and dedupe) to the same capability. Unknown IDs (declarative,
    // MCP, skill refs) pass through unchanged.
    let cap_id = registry.canonical_id(cap_id).unwrap_or(cap_id);

    // Already resolved
    if resolved_set.contains(cap_id) {
        return Ok(());
    }

    // Check for circular dependency
    if visiting.contains(&cap_id.to_string()) {
        return Err(DependencyError::CircularDependency {
            capability_id: cap_id.to_string(),
            chain: visiting.clone(),
        });
    }

    // Get capability from registry
    let capability = match registry.get(cap_id) {
        Some(cap) => cap,
        None => {
            // `declarative:` and `plugin:` refs carry their full definition in
            // the config payload — they don't need a registry entry. Pass them
            // through so `collect_capabilities_with_configs` can process them.
            if (is_declarative_capability(cap_id) || is_plugin_capability(cap_id))
                && !resolved_set.contains(cap_id)
            {
                resolved.push(cap_id.to_string());
                resolved_set.insert(cap_id.to_string());
                if !user_selected.contains(cap_id) {
                    added_as_dependencies.push(cap_id.to_string());
                }
            }
            return Ok(());
        }
    };

    // Mark as visiting
    visiting.push(cap_id.to_string());

    // Resolve dependencies first (depth-first)
    for dep_id in capability.dependencies() {
        resolve_single_capability(
            dep_id,
            registry,
            resolved,
            resolved_set,
            added_as_dependencies,
            user_selected,
            visiting,
        )?;
    }

    // Remove from visiting
    visiting.pop();

    // Add to resolved
    if !resolved_set.contains(cap_id) {
        resolved.push(cap_id.to_string());
        resolved_set.insert(cap_id.to_string());

        // Track if this was added as a dependency (not user-selected)
        if !user_selected.contains(cap_id) {
            added_as_dependencies.push(cap_id.to_string());
        }
    }

    Ok(())
}

/// Compute the aggregated set of UI features from a list of capability IDs.
///
/// Resolves dependencies, collects features from all resolved capabilities,
/// and returns deduplicated feature strings.
pub fn compute_features(capability_ids: &[String], registry: &CapabilityRegistry) -> Vec<String> {
    use std::collections::HashSet;

    let resolved_ids = match resolve_dependencies(capability_ids, registry) {
        Ok(resolved) => resolved.resolved_ids,
        Err(_) => capability_ids.to_vec(),
    };

    let mut seen = HashSet::new();
    let mut features = Vec::new();
    for cap_id in &resolved_ids {
        if let Some(cap) = registry.get(cap_id) {
            for feature in cap.features() {
                if seen.insert(feature) {
                    features.push(feature.to_string());
                }
            }
        }
    }
    features
}

/// Get direct dependencies for a capability ID.
/// Returns empty vec if capability not found.
pub fn get_dependencies(cap_id: &str, registry: &CapabilityRegistry) -> Vec<String> {
    registry
        .get(cap_id)
        .map(|cap| cap.dependencies().iter().map(|s| s.to_string()).collect())
        .unwrap_or_default()
}

/// Collect contributions from capabilities without applying them.
///
/// Resolves dependencies first, then calls `system_prompt_contribution()` (async)
/// on each capability, enabling dynamic content generation based on session context
/// (e.g., reading AGENTS.md, discovering skills).
///
/// Note: This function does not collect message filter providers since it doesn't
/// have access to per-agent capability configs. Use `collect_capabilities_with_configs`
/// if you need message filter providers.
///
/// # Arguments
///
/// * `capability_ids` - Ordered list of capability IDs to collect
/// * `registry` - The capability registry containing implementations
/// * `ctx` - Session context for dynamic prompt resolution
pub async fn collect_capabilities(
    capability_ids: &[String],
    registry: &CapabilityRegistry,
    ctx: &SystemPromptContext,
) -> CollectedCapabilities {
    // Resolve dependencies so that transitive capabilities (e.g. session_storage
    // via browserless) are included automatically.
    let resolved_ids = match resolve_dependencies(capability_ids, registry) {
        Ok(resolved) => resolved.resolved_ids,
        Err(e) => {
            tracing::warn!("Failed to resolve capability dependencies: {}", e);
            capability_ids.to_vec()
        }
    };

    // Convert to AgentCapabilityConfig with empty configs
    let configs: Vec<AgentCapabilityConfig> = resolved_ids
        .iter()
        .map(|id| {
            AgentCapabilityConfig::with_config(
                CapabilityId::new(id),
                serde_json::Value::Object(serde_json::Map::new()),
            )
        })
        .collect();

    collect_capabilities_with_configs(&configs, registry, ctx).await
}

/// Collect contributions from capabilities with their per-agent configurations.
///
/// Calls `system_prompt_contribution()` (async) on each capability, enabling
/// dynamic content generation based on session context.
///
/// # Arguments
///
/// * `capability_configs` - Ordered list of capability configs (ID + per-agent config)
/// * `registry` - The capability registry containing implementations
/// * `ctx` - Session context for dynamic prompt resolution
pub async fn collect_capabilities_with_configs(
    capability_configs: &[AgentCapabilityConfig],
    registry: &CapabilityRegistry,
    ctx: &SystemPromptContext,
) -> CollectedCapabilities {
    let mut system_prompt_parts: Vec<String> = Vec::new();
    let mut system_prompt_attributions: Vec<SystemPromptAttribution> = Vec::new();
    let mut conversation_context_parts: Vec<String> = Vec::new();
    let mut conversation_context_attributions: Vec<SystemPromptAttribution> = Vec::new();
    let mut tools: Vec<Box<dyn Tool>> = Vec::new();
    let mut tool_definitions: Vec<ToolDefinition> = Vec::new();
    let mut mounts: Vec<MountPoint> = Vec::new();
    let mut message_filter_providers: Vec<(Arc<dyn MessageFilterProvider>, serde_json::Value)> =
        Vec::new();
    let mut applied_ids: Vec<String> = Vec::new();
    let mut tool_search: Option<crate::driver_registry::ToolSearchConfig> = None;
    let mut prompt_cache: Option<crate::driver_registry::PromptCacheConfig> = None;
    let mut driver_options: HashMap<String, serde_json::Value> = HashMap::new();
    let mut parallel_tool_calls: Option<bool> = None;
    let mut tool_definition_hooks: Vec<Arc<dyn ToolDefinitionHook>> = Vec::new();
    let mut tool_call_hooks: Vec<Arc<dyn ToolCallHook>> = Vec::new();
    // Per-capability narration adapters, appended after explicit tool-call
    // hooks so model-authored narration (human_intent) keeps precedence.
    let mut narration_hooks: Vec<Arc<dyn ToolCallHook>> = Vec::new();
    let mut mcp_servers = ScopedMcpServers::default();
    // Facts contributed by capabilities. Static facts fold into the cached
    // system prompt below; a single note is added when any dynamic fact exists,
    // explaining the live `<facts>` block that `ReasonAtom` appends per turn.
    let mut static_facts: Vec<Fact> = Vec::new();
    let mut has_dynamic_facts = false;
    let facts_ctx = FactsContext::new(ctx.session_id);
    let compaction_on = compaction_is_enabled(capability_configs, registry);
    let mut delegation_targets: Vec<DelegationTargetProvider> = Vec::new();

    for cap_config in capability_configs {
        let cap_id = cap_config.capability_id();
        // `declarative:` and `plugin:` refs both carry a serialized
        // `DeclarativeCapabilityDefinition` in their config and execute through
        // the same runtime path. `plugin:` is handled first (more specific
        // prefix), then `declarative:`, then the registry lookup.
        if is_declarative_capability(cap_id) || is_plugin_capability(cap_id) {
            match serde_json::from_value::<DeclarativeCapabilityDefinition>(
                cap_config.config_value().clone(),
            ) {
                Ok(definition) => {
                    if !definition.status.is_active() {
                        continue;
                    }

                    if let Some(prompt) = definition.system_prompt.as_deref() {
                        let contribution =
                            format!("<capability id=\"{}\">\n{}\n</capability>", cap_id, prompt);
                        system_prompt_attributions.push(SystemPromptAttribution {
                            capability_id: cap_id.to_string(),
                            content: contribution.clone(),
                        });
                        system_prompt_parts.push(contribution);
                    }

                    mounts.extend(definition.mounts(cap_id));
                    if let Some(ref servers) = definition.mcp_servers {
                        mcp_servers = merge_scoped_mcp_servers(&mcp_servers, servers);
                    }
                    for skill in definition.skill_contributions() {
                        mounts.push(skill.to_mount(cap_id));
                    }

                    applied_ids.push(cap_id.to_string());
                }
                Err(error) => {
                    tracing::warn!(
                        capability_id = %cap_id,
                        error = %error,
                        "Skipping invalid declarative/plugin capability config"
                    );
                }
            }
            continue;
        }
        if let Some(capability) = registry.get(cap_id) {
            // Skip inert capabilities: `ComingSoon` is not implemented yet and
            // `Retired` has been removed. Both resolve to a no-op rather than an
            // error so an agent that still references one keeps running.
            if !capability.status().is_active() {
                continue;
            }

            // Model-adaptive dispatch: a capability may delegate its contributions
            // to a different underlying capability based on the agent's model
            // (e.g. `auto_tool_search` picks hosted vs client-side tool search).
            // Every contribution below is collected from `effective` (system prompt,
            // tools, hooks, tool definitions, mounts, MCP servers, skills, message
            // filters); for the common non-delegating case `effective` is just
            // `capability`. Driver preferences are also contributed through the
            // effective implementation's neutral trait methods, so a resolved
            // `auto_tool_search` behaves as whichever mechanism it became.
            // Attribution stays on the configured `cap_id`/`capability` so tools
            // surface under the capability the user actually configured.
            let effective: &dyn Capability =
                match capability.resolve_for_model(ctx.model.as_deref()) {
                    Some(inner) => inner,
                    None => capability.as_ref(),
                };
            let delegation_target =
                effective.delegation_target_with_config(cap_config.config_value());

            // Collect dynamic system prompt contribution (config-aware, may read from filesystem)
            if let Some(contribution) = effective
                .system_prompt_contribution_with_config(ctx, cap_config.config_value())
                .await
            {
                system_prompt_attributions.push(SystemPromptAttribution {
                    capability_id: cap_id.to_string(),
                    content: contribution.clone(),
                });
                system_prompt_parts.push(contribution);
            }

            // Collect conversation-context contribution (config-aware, may read
            // from filesystem). Renders as the leading user-role message of
            // every turn, never as system prompt, so untrusted workspace
            // content cannot share privilege with harness safety instructions.
            if let Some(contribution) = effective
                .conversation_context_contribution_with_config(ctx, cap_config.config_value())
                .await
            {
                conversation_context_attributions.push(SystemPromptAttribution {
                    capability_id: cap_id.to_string(),
                    content: contribution.clone(),
                });
                conversation_context_parts.push(contribution);
            }

            // Collect declared facts. Static facts fold into the cached prompt
            // below; dynamic facts are re-collected per request by `ReasonAtom`
            // and appended at the conversation tail, so here we only note their
            // presence to add the explanatory system-prompt line.
            for fact in effective.facts(cap_config.config_value(), &facts_ctx) {
                match fact.volatility {
                    Volatility::Static => static_facts.push(fact),
                    Volatility::Dynamic => has_dynamic_facts = true,
                }
            }

            // Collect tools and hooks (config-aware: capabilities can adapt based on per-agent config)
            tools.extend(effective.tools_with_config(cap_config.config_value()));
            if let Some(target) = delegation_target {
                delegation_targets.push(target);
            }
            tool_definition_hooks.extend(
                effective.tool_definition_hooks_with_context(ctx, cap_config.config_value()),
            );
            tool_call_hooks.extend(effective.tool_call_hooks());
            // Route this capability's `narrate()` through the hook channel.
            narration_hooks.push(Arc::new(CapabilityNarrationHook(capability.clone())));
            // Output guardrails are NOT collected here — see CollectedCapabilities
            // for rationale. ReasonAtom re-derives them at stream-arming time.

            // Collect tool definitions, propagating capability category if not already set
            let cap_category = effective.category();
            for def in effective.tool_definitions() {
                let def = match (def.category(), cap_category) {
                    (None, Some(cat)) => def.with_category(cat),
                    _ => def,
                }
                .with_capability_attribution(cap_id, Some(capability.name()));
                tool_definitions.push(def);
            }

            tool_search = effective
                .tool_search_config(cap_config.config_value())
                .or(tool_search);
            prompt_cache = effective
                .prompt_cache_config(cap_config.config_value())
                .or(prompt_cache);
            parallel_tool_calls = effective
                .parallel_tool_calls_preference(cap_config.config_value())
                .or(parallel_tool_calls);

            for (key, value) in effective.driver_options(cap_config.config_value()) {
                driver_options.entry(key).or_insert(value);
            }

            // Collect mount points
            mounts.extend(effective.mounts());

            mcp_servers = merge_scoped_mcp_servers(
                &mcp_servers,
                &effective.mcp_servers_with_config(cap_config.config_value()),
            );

            // Normalize capability-contributed skills into mount points under
            // `/.agents/skills/{name}/`. Discovery/activation stays with the
            // built-in `skills` capability — see knowledge/project/skills-registry.md.
            for skill in effective.contribute_skills() {
                mounts.push(skill.to_mount(cap_id));
            }

            // Collect message filter provider
            if let Some(provider) = effective.message_filter_provider() {
                let config =
                    effective.message_filter_config(cap_config.config_value(), compaction_on);
                message_filter_providers.push((provider, config));
            }

            applied_ids.push(cap_id.to_string());
        }
    }

    // Delegation providers share one model-facing `spawn_agent` dispatcher.
    // Unknown tools with that name still win to preserve their contract.
    if !tools.iter().any(|tool| tool.name() == "spawn_agent") && !delegation_targets.is_empty() {
        let tool = UnifiedSpawnAgentTool::new(delegation_targets);
        let def = tool
            .to_definition()
            .with_category("Orchestration")
            .with_capability_attribution("agent_delegation", Some("Agent Delegation"));
        tools.push(Box::new(tool));
        tool_definitions.push(def);
    }

    // Auto-activated adapters are selected through a neutral capability hook;
    // core does not name or own the hosted implementation.
    let auto_activated: Vec<_> = registry
        .list()
        .into_iter()
        .filter(|cap| {
            !applied_ids.iter().any(|id| id == cap.id())
                && cap.status().is_active()
                && cap.auto_activates_for(&tool_definitions)
        })
        .cloned()
        .collect();
    for cap in auto_activated {
        tools.extend(cap.tools());
        let cap_category = cap.category();
        for def in cap.tool_definitions() {
            let def = match (def.category(), cap_category) {
                (None, Some(cat)) => def.with_category(cat),
                _ => def,
            }
            .with_capability_attribution(cap.id(), Some(cap.name()));
            tool_definitions.push(def);
        }
        narration_hooks.push(Arc::new(CapabilityNarrationHook(cap.clone())));
        applied_ids.push(cap.id().to_string());
    }

    // Fold static facts into the cached system-prompt prefix, and add the
    // dynamic-facts note once when any capability declared a dynamic fact. Both
    // are stable across turns, so they stay in the cached prefix; the live
    // dynamic values are appended at the conversation tail per request.
    if let Some(block) = facts::render_facts_block(&static_facts) {
        system_prompt_attributions.push(SystemPromptAttribution {
            capability_id: "facts".to_string(),
            content: block.clone(),
        });
        system_prompt_parts.push(block);
    }
    if has_dynamic_facts {
        system_prompt_attributions.push(SystemPromptAttribution {
            capability_id: "facts".to_string(),
            content: FACTS_DYNAMIC_NOTE.to_string(),
        });
        system_prompt_parts.push(FACTS_DYNAMIC_NOTE.to_string());
    }

    // Append per-capability narration adapters after every explicit tool-call
    // hook so capability-owned narration is consulted only once model-authored
    // hooks (human_intent) have had their say.
    tool_call_hooks.extend(narration_hooks);

    // Sort message filter providers by priority (lower = earlier)
    message_filter_providers.sort_by_key(|(p, _)| p.priority());

    CollectedCapabilities {
        system_prompt_parts,
        system_prompt_attributions,
        conversation_context_parts,
        conversation_context_attributions,
        tools,
        tool_definitions,
        mounts,
        message_filter_providers,
        applied_ids,
        tool_search,
        prompt_cache,
        driver_options,
        parallel_tool_calls,
        tool_definition_hooks,
        tool_call_hooks,
        mcp_servers,
    }
}

// ============================================================================
// Apply Capabilities to RuntimeAgent
// ============================================================================

/// Result of applying capabilities to a base runtime agent
pub struct AppliedCapabilities {
    /// The modified runtime agent with capability contributions merged
    pub runtime_agent: RuntimeAgent,
    /// Tool registry containing all capability tools
    pub tool_registry: ToolRegistry,
    /// IDs of capabilities that were applied
    pub applied_ids: Vec<String>,
}

/// Apply capabilities to a base runtime agent configuration.
///
/// This function:
/// 1. Collects system prompt contributions from capabilities (in order)
/// 2. Appends them after the agent's base system prompt
/// 3. Collects all tools from capabilities
/// 4. Returns the modified runtime agent and a tool registry
///
/// # Arguments
///
/// * `base_runtime_agent` - The agent's base runtime configuration
/// * `capability_ids` - Ordered list of capability IDs to apply
/// * `registry` - The capability registry containing implementations
/// * `ctx` - Session context for dynamic prompt resolution
///
/// # Returns
///
/// An `AppliedCapabilities` struct containing the modified runtime agent,
/// tool registry, and list of applied capability IDs.
///
/// # Example
///
/// ```ignore
/// use everruns_core::capabilities::{apply_capabilities, CapabilityRegistry, SystemPromptContext};
/// use everruns_core::runtime_agent::RuntimeAgent;
///
/// let registry = CapabilityRegistry::new();
/// let base_runtime_agent = RuntimeAgent::new("You are a helpful assistant.", "gpt-5.2");
/// let ctx = SystemPromptContext::without_file_store(SessionId::new());
///
/// let capability_ids = Vec::new();
/// let applied = apply_capabilities(base_runtime_agent, &capability_ids, &registry, &ctx).await;
///
/// assert!(applied.applied_ids.is_empty());
/// ```
pub async fn apply_capabilities(
    base_runtime_agent: RuntimeAgent,
    capability_ids: &[String],
    registry: &CapabilityRegistry,
    ctx: &SystemPromptContext,
) -> AppliedCapabilities {
    let collected = collect_capabilities(capability_ids, registry, ctx).await;

    // Build final system prompt: base prompt first, then capability additions.
    let final_system_prompt = compose_system_prompt(
        &base_runtime_agent.system_prompt,
        collected.system_prompt_prefix().as_deref(),
    );

    // Conversation context (e.g. hierarchical AGENTS.md) renders as the
    // leading user-role message, never as system prompt. Bound before fields
    // move out of `collected` below.
    let conversation_context = collected.conversation_context();
    // Build tool registry from collected tools
    let mut tool_registry = ToolRegistry::new();
    for tool in collected.tools {
        tool_registry.register_boxed(tool);
    }

    // Create modified runtime agent
    let mut tools = collected.tool_definitions;
    for hook in &collected.tool_definition_hooks {
        tools = hook.transform(tools);
    }

    let runtime_agent = RuntimeAgent {
        system_prompt: final_system_prompt,
        model: base_runtime_agent.model,
        tools,
        max_iterations: base_runtime_agent.max_iterations,
        temperature: base_runtime_agent.temperature,
        max_tokens: base_runtime_agent.max_tokens,
        tool_search: collected.tool_search,
        prompt_cache: collected.prompt_cache,
        driver_options: collected.driver_options,
        network_access: base_runtime_agent.network_access,
        // Explicit request-level preference (escape hatch) wins; otherwise the
        // `parallel_tool_calls` capability supplies the preference.
        parallel_tool_calls: base_runtime_agent
            .parallel_tool_calls
            .or(collected.parallel_tool_calls),
        // Conversation context (e.g. hierarchical AGENTS.md) renders as the
        // leading user-role message, never as system prompt.
        conversation_context,
    };

    AppliedCapabilities {
        runtime_agent,
        tool_registry,
        applied_ids: collected.applied_ids,
    }
}

// ============================================================================
// Tests
// ============================================================================

#[cfg(test)]
mod tests {
    use super::*;
    use crate::typed_id::SessionId;
    use uuid::Uuid;

    /// Test helper: dummy context with no file store
    fn test_ctx() -> SystemPromptContext {
        SystemPromptContext::without_file_store(SessionId::new())
    }

    // -------------------------------------------------------------------------
    // Local stand-ins for the fixture capabilities that moved to the
    // `everruns-test-support` crate (EVE-875). The registry/apply/dependency
    // mechanics tested here only need capabilities with these shapes: one
    // that contributes nothing, one that contributes plain tools, and one
    // that carries mounts plus a dependency.
    // -------------------------------------------------------------------------

    struct StubSubagentSpawnTool;

    #[async_trait]
    impl Tool for StubSubagentSpawnTool {
        fn name(&self) -> &str {
            "spawn_agent"
        }
        fn description(&self) -> &str {
            "stub subagent delegation"
        }
        fn parameters_schema(&self) -> serde_json::Value {
            serde_json::json!({ "type": "object" })
        }
        fn narrate(
            &self,
            tool_call: &ToolCall,
            phase: crate::tool_narration::ToolNarrationPhase,
            locale: Option<&str>,
            _ctx: crate::tool_narration::ToolNarrationContext<'_>,
        ) -> Option<String> {
            Some(crate::tool_narration::narrate_subagent_spawn(
                &tool_call.arguments,
                phase,
                locale,
            ))
        }
        async fn execute(&self, _arguments: serde_json::Value) -> crate::ToolExecutionResult {
            crate::ToolExecutionResult::success(serde_json::json!({}))
        }
    }

    fn spawn_agent_call(arguments: serde_json::Value) -> ToolCall {
        ToolCall {
            id: "call-1".to_string(),
            name: "spawn_agent".to_string(),
            arguments,
        }
    }

    /// The dispatcher always names the agent being spawned, including when the
    /// call carries no usable `target.type` yet.
    #[test]
    fn unified_spawn_agent_narration_names_the_agent() {
        let tool = UnifiedSpawnAgentTool::new(vec![DelegationTargetProvider {
            target_type: "subagent",
            tool: Box::new(StubSubagentSpawnTool),
        }]);
        let ctx = crate::tool_narration::ToolNarrationContext::default();

        assert_eq!(
            tool.narrate(
                &spawn_agent_call(serde_json::json!({
                    "name": "Orbit Scout",
                    "target": { "type": "subagent" },
                    "blueprint": "github_scout"
                })),
                crate::tool_narration::ToolNarrationPhase::Started,
                None,
                ctx,
            )
            .as_deref(),
            Some("Launching Orbit Scout subagent (github_scout)")
        );

        assert_eq!(
            tool.narrate(
                &spawn_agent_call(serde_json::json!({ "name": "Orbit Scout" })),
                crate::tool_narration::ToolNarrationPhase::Started,
                None,
                ctx,
            )
            .as_deref(),
            Some("Launching Orbit Scout subagent")
        );
    }

    #[test]
    fn unified_spawn_agent_rejects_subagent_fields_for_configured_targets() {
        for target_type in ["agent", "external_a2a"] {
            let arguments = serde_json::json!({
                "target": { "type": target_type, "id": "actual-target" },
                "blueprint": "decoy-target"
            });
            assert_eq!(
                validate_spawn_agent_target_fields(&arguments, target_type),
                Err(format!(
                    "blueprint is only valid for subagent targets, not {target_type}."
                ))
            );

            let arguments = serde_json::json!({
                "target": { "type": target_type, "id": "actual-target" },
                "config": { "model": "decoy" }
            });
            assert_eq!(
                validate_spawn_agent_target_fields(&arguments, target_type),
                Err(format!(
                    "config is only valid for subagent targets, not {target_type}."
                ))
            );
        }
    }

    /// Contributes nothing: no tools, no prompt, no dependencies.
    struct NoopFixture;

    impl Capability for NoopFixture {
        fn id(&self) -> &str {
            "noop"
        }
        fn name(&self) -> &str {
            "No-Op"
        }
        fn description(&self) -> &str {
            "Contributes nothing."
        }
    }

    /// Declares one arbitrary feature to exercise core's neutral projection.
    struct FeatureFixture;

    impl Capability for FeatureFixture {
        fn id(&self) -> &str {
            "feature_fixture"
        }
        fn name(&self) -> &str {
            "Feature Fixture"
        }
        fn description(&self) -> &str {
            "Declares one test-only feature."
        }
        fn features(&self) -> Vec<&'static str> {
            vec!["fixture_feature"]
        }
    }

    struct FixtureTool(&'static str);

    #[async_trait]
    impl Tool for FixtureTool {
        fn name(&self) -> &str {
            self.0
        }
        fn description(&self) -> &str {
            "Fixture tool."
        }
        fn parameters_schema(&self) -> serde_json::Value {
            serde_json::json!({
                "type": "object",
                "properties": {},
                "additionalProperties": false
            })
        }
        async fn execute(&self, _arguments: serde_json::Value) -> ToolExecutionResult {
            ToolExecutionResult::success(serde_json::json!({ "ok": true }))
        }
    }

    struct BackgroundFixtureTool;

    #[async_trait]
    impl Tool for BackgroundFixtureTool {
        fn name(&self) -> &str {
            "bash"
        }
        fn description(&self) -> &str {
            "Fixture background-capable shell tool."
        }
        fn parameters_schema(&self) -> serde_json::Value {
            serde_json::json!({"type": "object"})
        }
        async fn execute(&self, _arguments: serde_json::Value) -> ToolExecutionResult {
            ToolExecutionResult::success(serde_json::json!({"ok": true}))
        }
        fn hints(&self) -> crate::tool_types::ToolHints {
            crate::tool_types::ToolHints {
                supports_background: Some(true),
                ..Default::default()
            }
        }
    }

    struct FileSystemFixture;

    impl Capability for FileSystemFixture {
        fn id(&self) -> &str {
            "session_file_system"
        }
        fn name(&self) -> &str {
            "Fixture Filesystem"
        }
        fn description(&self) -> &str {
            "Fixture filesystem capability."
        }
        fn tools(&self) -> Vec<Box<dyn Tool>> {
            vec![
                Box::new(FixtureTool("read_file")),
                Box::new(FixtureTool("write_file")),
            ]
        }
        fn features(&self) -> Vec<&'static str> {
            vec!["file_system"]
        }
    }

    /// Stands in for the product `session_storage` capability, which moved to
    /// `everruns-platform` with the other service-backed families (EVE-886).
    /// Feature computation is core's mechanism, so it is exercised here against
    /// a fixture rather than a product implementation.
    struct StorageFixture;

    impl Capability for StorageFixture {
        fn id(&self) -> &str {
            "session_storage"
        }
        fn name(&self) -> &str {
            "Fixture Storage"
        }
        fn description(&self) -> &str {
            "Fixture session storage capability."
        }
        fn features(&self) -> Vec<&'static str> {
            vec!["secrets", "key_value"]
        }
    }

    struct BashFixture;

    impl Capability for BashFixture {
        fn id(&self) -> &str {
            "bashkit_shell"
        }
        fn aliases(&self) -> Vec<&'static str> {
            vec!["virtual_bash"]
        }
        fn name(&self) -> &str {
            "Fixture Bash"
        }
        fn description(&self) -> &str {
            "Fixture shell capability."
        }
        fn tools(&self) -> Vec<Box<dyn Tool>> {
            vec![Box::new(BackgroundFixtureTool)]
        }
        fn dependencies(&self) -> Vec<&'static str> {
            vec!["session_file_system"]
        }
        fn features(&self) -> Vec<&'static str> {
            vec!["file_system"]
        }
        fn risk_level(&self) -> RiskLevel {
            RiskLevel::High
        }
    }

    struct WebFetchFixture;

    impl Capability for WebFetchFixture {
        fn id(&self) -> &str {
            "web_fetch"
        }
        fn name(&self) -> &str {
            "Fixture Web Fetch"
        }
        fn description(&self) -> &str {
            "Fixture web capability."
        }
        fn risk_level(&self) -> RiskLevel {
            RiskLevel::High
        }
    }

    /// Portable-policy-shaped stand-ins used only to exercise neutral core
    /// collection mechanics after policy implementations moved out of core.
    struct DynamicFactFixture;

    impl Capability for DynamicFactFixture {
        fn id(&self) -> &str {
            "current_time"
        }
        fn name(&self) -> &str {
            "Dynamic Fact Fixture"
        }
        fn description(&self) -> &str {
            "Fixture with one dynamic fact and one tool."
        }
        fn icon(&self) -> Option<&str> {
            Some("clock")
        }
        fn category(&self) -> Option<&str> {
            Some("Core")
        }
        fn tools(&self) -> Vec<Box<dyn Tool>> {
            vec![Box::new(FixtureTool("get_current_time"))]
        }
        fn facts(&self, _config: &serde_json::Value, _ctx: &FactsContext) -> Vec<Fact> {
            vec![Fact::dynamic("current_time", "fixture-now")]
        }
    }

    struct PromptToolFixture;

    impl Capability for PromptToolFixture {
        fn id(&self) -> &str {
            "prompt_tool_fixture"
        }
        fn name(&self) -> &str {
            "Prompt Tool Fixture"
        }
        fn description(&self) -> &str {
            "Fixture with a static prompt and tool."
        }
        fn system_prompt_addition(&self) -> Option<&str> {
            Some("Task Management uses the write_todos tool.")
        }
        fn tools(&self) -> Vec<Box<dyn Tool>> {
            vec![Box::new(FixtureTool("write_todos"))]
        }
    }

    struct SecondPromptFixture;

    impl Capability for SecondPromptFixture {
        fn id(&self) -> &str {
            "second_prompt_fixture"
        }
        fn name(&self) -> &str {
            "Second Prompt Fixture"
        }
        fn description(&self) -> &str {
            "Fixture with a second static prompt."
        }
        fn system_prompt_addition(&self) -> Option<&str> {
            Some("A second capability prompt contribution.")
        }
    }

    struct DynamicPreviewFixture;

    impl Capability for DynamicPreviewFixture {
        fn id(&self) -> &str {
            "agent_instructions"
        }
        fn name(&self) -> &str {
            "Dynamic Preview Fixture"
        }
        fn description(&self) -> &str {
            "Fixture whose runtime prompt is dynamic."
        }
        fn system_prompt_preview(&self) -> Option<String> {
            Some("Reads AGENTS.md dynamically.".to_string())
        }
    }

    /// Contributes four plain calculator-style tools and no prompt addition.
    struct MathFixture;

    impl Capability for MathFixture {
        fn id(&self) -> &str {
            "test_math"
        }
        fn name(&self) -> &str {
            "Test Math"
        }
        fn description(&self) -> &str {
            "Fixture: calculator tools."
        }
        fn tools(&self) -> Vec<Box<dyn Tool>> {
            vec![
                Box::new(FixtureTool("add")),
                Box::new(FixtureTool("subtract")),
                Box::new(FixtureTool("multiply")),
                Box::new(FixtureTool("divide")),
            ]
        }
    }

    /// Contributes two plain tools.
    struct WeatherFixture;

    impl Capability for WeatherFixture {
        fn id(&self) -> &str {
            "test_weather"
        }
        fn name(&self) -> &str {
            "Test Weather"
        }
        fn description(&self) -> &str {
            "Fixture: weather tools."
        }
        fn tools(&self) -> Vec<Box<dyn Tool>> {
            vec![
                Box::new(FixtureTool("get_weather")),
                Box::new(FixtureTool("get_forecast")),
            ]
        }
    }

    /// Carries a read-only mount, a prompt addition, a feature, and a
    /// dependency on `session_file_system`.
    struct SampleDataFixture;

    impl Capability for SampleDataFixture {
        fn id(&self) -> &str {
            "sample_data"
        }
        fn name(&self) -> &str {
            "Sample Data"
        }
        fn description(&self) -> &str {
            "Fixture: mounted sample files."
        }
        fn system_prompt_addition(&self) -> Option<&str> {
            Some("Read-only sample files are mounted at `/samples`.")
        }
        fn mounts(&self) -> Vec<MountPoint> {
            let samples_dir = MountDirectoryBuilder::new()
                .file("users.json", "[]")
                .build();
            vec![MountPoint::readonly("/samples", samples_dir, self.id())]
        }
        fn dependencies(&self) -> Vec<&'static str> {
            vec!["session_file_system"]
        }
        fn features(&self) -> Vec<&'static str> {
            vec!["file_system"]
        }
    }

    /// Registry of local contribution fixtures.
    fn fixture_registry() -> CapabilityRegistry {
        let mut registry = CapabilityRegistry::new();
        registry.register(NoopFixture);
        registry.register(FeatureFixture);
        registry.register(MathFixture);
        registry.register(WeatherFixture);
        registry.register(SampleDataFixture);
        registry.register(FileSystemFixture);
        registry.register(StorageFixture);
        registry.register(BashFixture);
        registry.register(WebFetchFixture);
        registry.register(DynamicFactFixture);
        registry.register(PromptToolFixture);
        registry.register(SecondPromptFixture);
        registry.register(DynamicPreviewFixture);
        registry
    }

    /// A host-defined capability carrying annotations core knows nothing about.
    struct HostAnnotatedCapability;

    #[async_trait]
    impl Capability for HostAnnotatedCapability {
        fn id(&self) -> &str {
            "host_annotated"
        }
        fn name(&self) -> &str {
            "Host Annotated"
        }
        fn description(&self) -> &str {
            "Test capability with host-owned metadata."
        }
        fn metadata(&self) -> Option<serde_json::Value> {
            Some(serde_json::json!({"icon": "sparkles", "group": "host"}))
        }
    }

    #[test]
    fn test_capability_registry_get() {
        let mut registry = CapabilityRegistry::new();
        registry.register(NoopFixture);

        let capability = registry.get("noop").unwrap();
        assert_eq!(capability.id(), "noop");
        assert_eq!(capability.status(), CapabilityStatus::Available);
    }

    #[test]
    fn default_registry_is_empty_and_selects_no_product_preset() {
        assert!(CapabilityRegistry::default().is_empty());
        assert!(CapabilityRegistryBuilder::default().build().is_empty());
    }

    #[tokio::test]
    async fn test_capability_registry_blueprint_with_capability() {
        struct BlueprintProviderCapability;

        impl Capability for BlueprintProviderCapability {
            fn id(&self) -> &str {
                "blueprint_provider"
            }
            fn name(&self) -> &str {
                "Blueprint Provider"
            }
            fn description(&self) -> &str {
                "Capability that provides a blueprint for tests"
            }
            fn agent_blueprints(&self) -> Vec<AgentBlueprint> {
                vec![AgentBlueprint {
                    id: "test_blueprint",
                    name: "Test Blueprint",
                    description: "Blueprint for capability registry tests",
                    model: BlueprintModel::Fixed("specialist-model".into()),
                    system_prompt: "Test prompt",
                    tools: vec![Box::new(FixtureTool("private_lookup"))],
                    max_turns: Some(7),
                    config_schema: Some(
                        serde_json::json!({"type":"object", "required":["repository"]}),
                    ),
                }]
            }
        }

        let mut registry = CapabilityRegistry::new();
        registry.register(BlueprintProviderCapability);

        let (capability_id, blueprint) = registry
            .blueprint_with_capability("test_blueprint")
            .expect("blueprint should resolve with capability id");
        assert_eq!(capability_id, "blueprint_provider");
        assert_eq!(blueprint.id, "test_blueprint");
        assert_eq!(blueprint.name, "Test Blueprint");
        assert_eq!(
            blueprint.description,
            "Blueprint for capability registry tests"
        );
        assert_eq!(blueprint.system_prompt, "Test prompt");
        assert!(
            matches!(&blueprint.model, BlueprintModel::Fixed(model) if model == "specialist-model")
        );
        assert_eq!(blueprint.max_turns, Some(7));
        assert_eq!(
            blueprint.config_schema,
            Some(serde_json::json!({"type":"object", "required":["repository"]}))
        );
        let definitions = blueprint.tool_definitions();
        assert_eq!(definitions.len(), 1);
        assert_eq!(definitions[0].name(), "private_lookup");
        assert_eq!(
            registry.blueprint("test_blueprint").unwrap().tools[0].name(),
            "private_lookup"
        );
        assert_eq!(
            registry
                .all_blueprints()
                .iter()
                .map(|b| b.id)
                .collect::<Vec<_>>(),
            ["test_blueprint"]
        );
        assert!(registry.blueprint_with_capability("missing").is_none());
        assert!(registry.blueprint("missing").is_none());
        let host =
            collect_capabilities(&["blueprint_provider".into()], &registry, &test_ctx()).await;
        assert!(host.tools.is_empty());
        assert!(host.tool_definitions.is_empty());
    }

    #[test]
    fn test_capability_registry_builder() {
        let registry = CapabilityRegistry::builder()
            .capability(NoopFixture)
            .build();

        assert!(registry.has("noop"));
        assert_eq!(registry.len(), 1);
    }

    #[test]
    fn test_system_prompt_preview_default_delegates_to_addition() {
        // A capability with a static system_prompt_addition — preview should
        // match the addition by default.
        struct StaticPromptCapability;
        impl Capability for StaticPromptCapability {
            fn id(&self) -> &str {
                "static_prompt"
            }
            fn name(&self) -> &str {
                "Static Prompt"
            }
            fn description(&self) -> &str {
                "Static prompt addition."
            }
            fn system_prompt_addition(&self) -> Option<&str> {
                Some("Use the static prompt.")
            }
        }

        let cap = StaticPromptCapability;
        assert_eq!(
            cap.system_prompt_preview().as_deref(),
            Some("Use the static prompt.")
        );

        // current_time has no system_prompt_addition — preview should be None
        let registry = fixture_registry();
        let current_time = registry.get("current_time").unwrap();
        assert!(current_time.system_prompt_preview().is_none());
        assert!(current_time.system_prompt_addition().is_none());
    }

    // =========================================================================
    // apply_capabilities tests
    // =========================================================================

    #[tokio::test]
    async fn test_apply_capabilities_empty() {
        let registry = CapabilityRegistry::new();
        let base_runtime_agent = RuntimeAgent::new("You are a helpful assistant.", "gpt-5.2");

        let applied =
            apply_capabilities(base_runtime_agent.clone(), &[], &registry, &test_ctx()).await;

        assert_eq!(
            applied.runtime_agent.system_prompt,
            base_runtime_agent.system_prompt
        );
        assert!(applied.tool_registry.is_empty());
        assert!(applied.applied_ids.is_empty());
    }

    #[tokio::test]
    async fn test_apply_capabilities_noop() {
        let registry = fixture_registry();
        let mut base_runtime_agent = RuntimeAgent::new("You are a helpful assistant.", "gpt-5.2");

        base_runtime_agent.max_iterations = 13;
        base_runtime_agent.temperature = Some(0.25);
        base_runtime_agent.max_tokens = Some(1234);
        base_runtime_agent.parallel_tool_calls = Some(false);
        let applied = apply_capabilities(
            base_runtime_agent.clone(),
            &["noop".to_string()],
            &registry,
            &test_ctx(),
        )
        .await;

        // Noop has no system prompt addition or tools
        assert_eq!(
            applied.runtime_agent.system_prompt,
            base_runtime_agent.system_prompt
        );
        assert!(applied.tool_registry.is_empty());
        assert_eq!(applied.applied_ids, vec!["noop"]);
        assert_eq!(
            serde_json::to_value(&applied.runtime_agent).unwrap(),
            serde_json::to_value(&base_runtime_agent).unwrap()
        );
        let collected = collect_capabilities(&["noop".into()], &registry, &test_ctx()).await;
        assert!(collected.mounts.is_empty());
        assert!(collected.message_filter_providers.is_empty());
        assert!(compute_features(&["noop".into()], &registry).is_empty());
    }

    #[tokio::test]
    async fn test_apply_capabilities_current_time() {
        let registry = fixture_registry();
        let base_runtime_agent = RuntimeAgent::new("You are a helpful assistant.", "gpt-5.2");

        let applied = apply_capabilities(
            base_runtime_agent.clone(),
            &["current_time".to_string()],
            &registry,
            &test_ctx(),
        )
        .await;

        // CurrentTime contributes a dynamic `current_time` fact, so the cached
        // prompt gains the explanatory facts note (the live value is appended at
        // the conversation tail per request). It also keeps its tool.
        assert!(
            applied
                .runtime_agent
                .system_prompt
                .contains(FACTS_DYNAMIC_NOTE),
            "current_time should contribute the dynamic-facts note"
        );
        assert!(
            applied
                .runtime_agent
                .system_prompt
                .contains(&base_runtime_agent.system_prompt),
            "base prompt is preserved"
        );
        assert!(applied.tool_registry.has("get_current_time"));
        assert_eq!(applied.tool_registry.len(), 1);
        assert_eq!(applied.applied_ids, vec!["current_time"]);
    }

    #[tokio::test]
    async fn test_apply_capabilities_skips_coming_soon() {
        struct ComingSoonFixture;
        impl Capability for ComingSoonFixture {
            fn id(&self) -> &str {
                "coming_soon_fixture"
            }
            fn name(&self) -> &str {
                "Coming Soon Fixture"
            }
            fn description(&self) -> &str {
                "Test-only capability."
            }
            fn status(&self) -> CapabilityStatus {
                CapabilityStatus::ComingSoon
            }
            fn system_prompt_addition(&self) -> Option<&str> {
                Some("Not yet available.")
            }
        }
        let mut registry = CapabilityRegistry::new();
        registry.register(ComingSoonFixture);
        let base_runtime_agent = RuntimeAgent::new("You are a helpful assistant.", "gpt-5.2");

        let applied = apply_capabilities(
            base_runtime_agent.clone(),
            &["coming_soon_fixture".to_string()],
            &registry,
            &test_ctx(),
        )
        .await;

        assert_eq!(
            applied.runtime_agent.system_prompt,
            base_runtime_agent.system_prompt
        );
        assert!(applied.applied_ids.is_empty());
    }

    /// A deprecated capability has only *announced* its removal, so it must keep
    /// behaving exactly as before. This is the regression guard for the gating
    /// switch from `status() == Available` to `status().is_active()`.
    #[tokio::test]
    async fn test_apply_capabilities_keeps_deprecated_fully_functional() {
        struct DeprecatedFixture;
        impl Capability for DeprecatedFixture {
            fn id(&self) -> &str {
                "deprecated_fixture"
            }
            fn name(&self) -> &str {
                "Deprecated Fixture"
            }
            fn description(&self) -> &str {
                "Test-only capability."
            }
            fn status(&self) -> CapabilityStatus {
                CapabilityStatus::Deprecated
            }
            fn system_prompt_addition(&self) -> Option<&str> {
                Some("Still working.")
            }
        }
        let mut registry = CapabilityRegistry::new();
        registry.register(DeprecatedFixture);
        let base_runtime_agent = RuntimeAgent::new("You are a helpful assistant.", "gpt-5.2");

        let applied = apply_capabilities(
            base_runtime_agent,
            &["deprecated_fixture".to_string()],
            &registry,
            &test_ctx(),
        )
        .await;

        assert!(
            applied
                .runtime_agent
                .system_prompt
                .contains("Still working.")
        );
        assert_eq!(applied.applied_ids, vec!["deprecated_fixture"]);
    }

    /// A retired capability is inert, but an agent that still references one must
    /// keep running: the reference resolves to a no-op and every other capability
    /// in the list still applies.
    #[tokio::test]
    async fn test_apply_capabilities_skips_retired_without_failing() {
        struct RetiredFixture;
        impl Capability for RetiredFixture {
            fn id(&self) -> &str {
                "retired_fixture"
            }
            fn name(&self) -> &str {
                "Retired Fixture"
            }
            fn description(&self) -> &str {
                "Test-only capability."
            }
            fn status(&self) -> CapabilityStatus {
                CapabilityStatus::Retired
            }
            fn system_prompt_addition(&self) -> Option<&str> {
                Some("Should never be applied.")
            }
        }
        let mut registry = fixture_registry();
        registry.register(RetiredFixture);
        let base_runtime_agent = RuntimeAgent::new("You are a helpful assistant.", "gpt-5.2");

        let applied = apply_capabilities(
            base_runtime_agent,
            &["retired_fixture".to_string(), "current_time".to_string()],
            &registry,
            &test_ctx(),
        )
        .await;

        assert!(
            !applied
                .runtime_agent
                .system_prompt
                .contains("Should never be applied.")
        );
        // The surviving capability in the same list is unaffected.
        assert_eq!(applied.applied_ids, vec!["current_time"]);
        assert!(applied.tool_registry.has("get_current_time"));
    }

    #[tokio::test]
    async fn test_apply_capabilities_preserves_order() {
        let registry = fixture_registry();
        let base_runtime_agent = RuntimeAgent::new("Base prompt.", "gpt-5.2");

        // Order should be preserved in applied_ids
        let applied = apply_capabilities(
            base_runtime_agent,
            &["current_time".to_string(), "noop".to_string()],
            &registry,
            &test_ctx(),
        )
        .await;

        assert_eq!(applied.applied_ids, vec!["current_time", "noop"]);
        assert_eq!(applied.tool_registry.len(), 1);
        assert!(applied.tool_registry.has("get_current_time"));
    }

    // =========================================================================
    // XML prompt formatting tests
    // =========================================================================

    // =========================================================================
    // Mount collection tests
    // =========================================================================

    #[tokio::test]
    async fn test_dynamic_facts_add_note_without_static_block() {
        // `current_time` contributes a Dynamic fact, so the cached prompt gets
        // the explanatory note but NOT a static `<facts>` block (the live value
        // is appended at the conversation tail per request instead).
        let registry = fixture_registry();
        let configs = vec![AgentCapabilityConfig::new("current_time".to_string())];
        let collected = collect_capabilities_with_configs(&configs, &registry, &test_ctx()).await;
        let prompt = collected.system_prompt_parts.join("\n");
        assert!(
            prompt.contains(FACTS_DYNAMIC_NOTE),
            "dynamic-facts note should be in the cached prompt"
        );
        assert!(
            !prompt.contains("<facts>\n"),
            "no static <facts> block for a purely-dynamic fact; got: {prompt}"
        );
    }

    #[tokio::test]
    async fn test_static_facts_fold_into_prompt() {
        struct StaticFactCap;
        impl Capability for StaticFactCap {
            fn id(&self) -> &str {
                "test_static_fact"
            }
            fn name(&self) -> &str {
                "Static Fact"
            }
            fn description(&self) -> &str {
                "test"
            }
            fn status(&self) -> CapabilityStatus {
                CapabilityStatus::Available
            }
            fn facts(&self, _config: &serde_json::Value, _ctx: &FactsContext) -> Vec<Fact> {
                vec![Fact::stat("workspace_root", "/workspace")]
            }
        }
        let mut registry = CapabilityRegistry::new();
        registry.register(StaticFactCap);
        let configs = vec![AgentCapabilityConfig::new("test_static_fact".to_string())];
        let collected = collect_capabilities_with_configs(&configs, &registry, &test_ctx()).await;
        let prompt = collected.system_prompt_parts.join("\n");
        assert!(
            prompt.contains("<facts>\n- workspace_root: /workspace\n</facts>"),
            "static fact should fold into the cached prompt; got: {prompt}"
        );
        assert!(
            !prompt.contains(FACTS_DYNAMIC_NOTE),
            "no dynamic note when only static facts exist"
        );
    }

    #[test]
    fn test_collect_dynamic_facts_returns_current_time() {
        let registry = fixture_registry();
        let configs = vec![AgentCapabilityConfig::new("current_time".to_string())];
        let facts = collect_dynamic_facts(
            &configs,
            &registry,
            None,
            &FactsContext::new(SessionId::new()),
        );
        assert_eq!(facts.len(), 1);
        assert_eq!(facts[0].key, "current_time");
        assert_eq!(facts[0].value, "fixture-now");
        assert_eq!(facts[0].volatility, Volatility::Dynamic);
    }

    #[tokio::test]
    async fn test_collect_capabilities_combines_mounts() {
        struct Notes;
        impl Capability for Notes {
            fn id(&self) -> &str {
                "notes"
            }
            fn name(&self) -> &str {
                "Notes"
            }
            fn description(&self) -> &str {
                "Writable notes"
            }
            fn mounts(&self) -> Vec<MountPoint> {
                vec![MountPoint::readwrite(
                    "/notes.txt",
                    MountSource::text_file("Note α"),
                    "notes",
                )]
            }
        }
        let mut registry = fixture_registry();
        registry.register(Notes);
        let collected = collect_capabilities(
            &["sample_data".into(), "notes".into(), "current_time".into()],
            &registry,
            &test_ctx(),
        )
        .await;
        assert_eq!(
            collected.applied_ids,
            [
                "session_file_system",
                "sample_data",
                "notes",
                "current_time"
            ]
        );
        assert_eq!(
            collected.mounts,
            vec![
                MountPoint::readonly(
                    "/samples",
                    MountDirectoryBuilder::new()
                        .file("users.json", "[]")
                        .build(),
                    "sample_data"
                ),
                MountPoint::readwrite("/notes.txt", MountSource::text_file("Note α"), "notes"),
            ]
        );
    }

    // =========================================================================
    // Dependency resolution tests
    // =========================================================================

    #[test]
    fn test_resolve_dependencies_empty() {
        let registry = CapabilityRegistry::new();

        let resolved = resolve_dependencies(&[], &registry).unwrap();

        assert!(resolved.resolved_ids.is_empty());
        assert!(resolved.added_as_dependencies.is_empty());
        assert!(resolved.user_selected.is_empty());
    }

    #[test]
    fn test_resolve_dependencies_no_deps() {
        let registry = fixture_registry();

        // CurrentTime has no dependencies
        let resolved = resolve_dependencies(&["current_time".to_string()], &registry).unwrap();

        assert_eq!(resolved.resolved_ids, vec!["current_time"]);
        assert!(resolved.added_as_dependencies.is_empty());
    }

    #[test]
    fn test_resolve_dependencies_with_deps() {
        let resolved = resolve_dependencies(&["sample_data".into()], &fixture_registry()).unwrap();
        assert_eq!(
            resolved.resolved_ids,
            ["session_file_system", "sample_data"]
        );
        assert_eq!(resolved.added_as_dependencies, ["session_file_system"]);
        assert_eq!(resolved.user_selected, ["sample_data"]);
    }

    #[test]
    fn test_resolve_dependencies_already_selected() {
        let registry = fixture_registry();

        // If dependency is already selected, it shouldn't be duplicated
        let resolved = resolve_dependencies(
            &["session_file_system".to_string(), "sample_data".to_string()],
            &registry,
        )
        .unwrap();

        assert_eq!(resolved.resolved_ids.len(), 2);
        // FileSystem was user-selected, not added as dependency
        assert!(resolved.added_as_dependencies.is_empty());
    }

    #[test]
    fn test_resolve_dependencies_preserves_order() {
        let registry = fixture_registry();

        // Multiple independent capabilities should maintain their relative order
        let resolved =
            resolve_dependencies(&["current_time".to_string(), "noop".to_string()], &registry)
                .unwrap();

        assert_eq!(resolved.resolved_ids, vec!["current_time", "noop"]);
    }

    #[test]
    fn test_resolve_dependencies_unknown_capability() {
        let registry = CapabilityRegistry::new();

        // Unknown capabilities are silently skipped
        let resolved =
            resolve_dependencies(&["unknown_capability".to_string()], &registry).unwrap();

        assert!(resolved.resolved_ids.is_empty());
    }

    #[test]
    fn test_get_dependencies() {
        let registry = fixture_registry();

        // SampleData depends on FileSystem
        let deps = get_dependencies("sample_data", &registry);
        assert_eq!(deps, vec!["session_file_system"]);

        // CurrentTime has no dependencies
        let deps = get_dependencies("current_time", &registry);
        assert!(deps.is_empty());

        // Unknown capability
        let deps = get_dependencies("unknown", &registry);
        assert!(deps.is_empty());
    }

    // Test for circular dependency detection
    // Note: We can't easily test this with built-in capabilities since they don't have cycles.
    // This test uses a custom registry to create a cycle.
    #[test]
    fn test_circular_dependency_error() {
        // Create capabilities that form a cycle: A -> B -> A
        struct CapA;
        struct CapB;

        impl Capability for CapA {
            fn id(&self) -> &str {
                "test_cap_a"
            }
            fn name(&self) -> &str {
                "Test A"
            }
            fn description(&self) -> &str {
                "Test capability A"
            }
            fn dependencies(&self) -> Vec<&'static str> {
                vec!["test_cap_b"]
            }
        }

        impl Capability for CapB {
            fn id(&self) -> &str {
                "test_cap_b"
            }
            fn name(&self) -> &str {
                "Test B"
            }
            fn description(&self) -> &str {
                "Test capability B"
            }
            fn dependencies(&self) -> Vec<&'static str> {
                vec!["test_cap_a"]
            }
        }

        let mut registry = CapabilityRegistry::new();
        registry.register(CapA);
        registry.register(CapB);

        let result = resolve_dependencies(&["test_cap_a".to_string()], &registry);

        assert!(result.is_err());
        match result.unwrap_err() {
            DependencyError::CircularDependency { capability_id, .. } => {
                assert_eq!(capability_id, "test_cap_a");
            }
            _ => panic!("Expected CircularDependency error"),
        }
    }

    // =========================================================================
    // Message filter provider tests
    // =========================================================================

    use crate::message_filter::{MessageFilter, MessageFilterProvider, MessageQuery};

    /// Test capability that provides a message filter
    struct FilterTestCapability {
        priority: i32,
    }

    impl Capability for FilterTestCapability {
        fn id(&self) -> &str {
            "filter_test"
        }
        fn name(&self) -> &str {
            "Filter Test"
        }
        fn description(&self) -> &str {
            "Test capability with message filter"
        }
        fn message_filter_provider(&self) -> Option<Arc<dyn MessageFilterProvider>> {
            Some(Arc::new(FilterTestProvider {
                priority: self.priority,
            }))
        }
    }

    struct FilterTestProvider {
        priority: i32,
    }

    impl MessageFilterProvider for FilterTestProvider {
        fn apply_filters(&self, query: &mut MessageQuery, config: &serde_json::Value) {
            // Add a search filter based on config
            if let Some(search) = config.get("search").and_then(|v| v.as_str()) {
                query
                    .filters
                    .push(MessageFilter::Search(search.to_string()));
            }
        }

        fn priority(&self) -> i32 {
            self.priority
        }
    }

    #[tokio::test]
    async fn test_collect_capabilities_with_configs_no_filter_providers() {
        let registry = fixture_registry();
        let configs = vec![AgentCapabilityConfig::with_config(
            CapabilityId::new("current_time"),
            serde_json::json!({}),
        )];

        let collected = collect_capabilities_with_configs(&configs, &registry, &test_ctx()).await;

        assert!(collected.message_filter_providers.is_empty());
        assert!(!collected.has_message_filters());
    }

    #[tokio::test]
    async fn test_collected_capabilities_apply_message_filters() {
        let mut registry = CapabilityRegistry::new();
        registry.register(FilterTestCapability { priority: 0 });

        let configs = vec![AgentCapabilityConfig::with_config(
            CapabilityId::new("filter_test"),
            serde_json::json!({ "search": "test_query" }),
        )];

        let collected = collect_capabilities_with_configs(&configs, &registry, &test_ctx()).await;

        assert!(collected.has_message_filters());

        // Apply filters to a query
        let session_id: SessionId = Uuid::now_v7().into();
        let mut query = MessageQuery::new(session_id);

        collected.apply_message_filters(&mut query);

        // Should have added the search filter
        assert_eq!(query.filters.len(), 1);
        assert!(matches!(&query.filters[0], MessageFilter::Search(s) if s == "test_query"));
    }

    #[tokio::test]
    async fn test_collected_capabilities_apply_multiple_filters_in_priority_order() {
        struct SearchCapability {
            id: &'static str,
            search_term: &'static str,
            priority: i32,
        }

        struct SearchProvider {
            search_term: &'static str,
            priority: i32,
        }

        impl MessageFilterProvider for SearchProvider {
            fn apply_filters(&self, query: &mut MessageQuery, _config: &serde_json::Value) {
                query
                    .filters
                    .push(MessageFilter::Search(self.search_term.to_string()));
            }

            fn priority(&self) -> i32 {
                self.priority
            }
        }

        impl Capability for SearchCapability {
            fn id(&self) -> &str {
                self.id
            }
            fn name(&self) -> &str {
                "Search"
            }
            fn description(&self) -> &str {
                "Test"
            }
            fn message_filter_provider(&self) -> Option<Arc<dyn MessageFilterProvider>> {
                Some(Arc::new(SearchProvider {
                    search_term: self.search_term,
                    priority: self.priority,
                }))
            }
        }

        let mut registry = CapabilityRegistry::new();
        registry.register(SearchCapability {
            id: "cap_a",
            search_term: "alpha",
            priority: 5,
        });
        registry.register(SearchCapability {
            id: "cap_b",
            search_term: "beta",
            priority: 1,
        });
        registry.register(SearchCapability {
            id: "cap_c",
            search_term: "gamma",
            priority: 10,
        });

        let configs = vec![
            AgentCapabilityConfig::with_config(CapabilityId::new("cap_a"), serde_json::json!({})),
            AgentCapabilityConfig::with_config(CapabilityId::new("cap_b"), serde_json::json!({})),
            AgentCapabilityConfig::with_config(CapabilityId::new("cap_c"), serde_json::json!({})),
        ];

        let collected = collect_capabilities_with_configs(&configs, &registry, &test_ctx()).await;

        let session_id: SessionId = Uuid::now_v7().into();
        let mut query = MessageQuery::new(session_id);

        collected.apply_message_filters(&mut query);

        // Filters should be applied in priority order: beta (1), alpha (5), gamma (10)
        assert_eq!(query.filters.len(), 3);
        assert!(matches!(&query.filters[0], MessageFilter::Search(s) if s == "beta"));
        assert!(matches!(&query.filters[1], MessageFilter::Search(s) if s == "alpha"));
        assert!(matches!(&query.filters[2], MessageFilter::Search(s) if s == "gamma"));
    }

    #[tokio::test]
    async fn test_collect_capabilities_preserves_config_for_filter_provider() {
        let mut registry = CapabilityRegistry::new();
        registry.register(FilterTestCapability { priority: 0 });

        let test_config = serde_json::json!({
            "search": "custom_search",
            "extra_field": 42
        });

        let configs = vec![AgentCapabilityConfig::with_config(
            CapabilityId::new("filter_test"),
            test_config.clone(),
        )];

        let collected = collect_capabilities_with_configs(&configs, &registry, &test_ctx()).await;

        // Verify the config is preserved
        assert_eq!(collected.message_filter_providers.len(), 1);
        let (_, stored_config) = &collected.message_filter_providers[0];
        assert_eq!(*stored_config, test_config);
    }

    // =========================================================================
    // collect_message_filters_only tests
    // =========================================================================

    #[test]
    fn test_collect_message_filters_only_collects_filters() {
        let mut registry = CapabilityRegistry::new();
        registry.register(FilterTestCapability { priority: 0 });

        let configs = vec![AgentCapabilityConfig::with_config(
            CapabilityId::new("filter_test"),
            serde_json::json!({ "search": "test_query" }),
        )];

        let collected = collect_message_filters_only(&configs, &registry);

        let session_id: SessionId = Uuid::now_v7().into();
        let mut query = MessageQuery::new(session_id);
        collected.apply_message_filters(&mut query);

        assert_eq!(query.filters.len(), 1);
        assert!(matches!(&query.filters[0], MessageFilter::Search(s) if s == "test_query"));
    }

    #[test]
    fn test_collect_message_filters_only_skips_unknown_capabilities() {
        let registry = CapabilityRegistry::new();

        let configs = vec![AgentCapabilityConfig::with_config(
            CapabilityId::new("nonexistent"),
            serde_json::json!({}),
        )];

        let collected = collect_message_filters_only(&configs, &registry);
        assert!(collected.message_filter_providers.is_empty());
    }

    #[test]
    fn test_collect_message_filters_only_preserves_priority_order() {
        struct PriorityFilterCap {
            id: &'static str,
            search_term: &'static str,
            priority: i32,
        }

        struct PriorityFilterProvider {
            search_term: &'static str,
            priority: i32,
        }

        impl Capability for PriorityFilterCap {
            fn id(&self) -> &str {
                self.id
            }
            fn name(&self) -> &str {
                self.id
            }
            fn description(&self) -> &str {
                "priority test"
            }
            fn message_filter_provider(&self) -> Option<Arc<dyn MessageFilterProvider>> {
                Some(Arc::new(PriorityFilterProvider {
                    search_term: self.search_term,
                    priority: self.priority,
                }))
            }
        }

        impl MessageFilterProvider for PriorityFilterProvider {
            fn apply_filters(&self, query: &mut MessageQuery, _config: &serde_json::Value) {
                query
                    .filters
                    .push(MessageFilter::Search(self.search_term.to_string()));
            }
            fn priority(&self) -> i32 {
                self.priority
            }
        }

        let mut registry = CapabilityRegistry::new();
        registry.register(PriorityFilterCap {
            id: "gamma",
            search_term: "gamma",
            priority: 10,
        });
        registry.register(PriorityFilterCap {
            id: "alpha",
            search_term: "alpha",
            priority: 5,
        });
        registry.register(PriorityFilterCap {
            id: "beta",
            search_term: "beta",
            priority: 1,
        });

        let configs = vec![
            AgentCapabilityConfig::with_config(CapabilityId::new("gamma"), serde_json::json!({})),
            AgentCapabilityConfig::with_config(CapabilityId::new("alpha"), serde_json::json!({})),
            AgentCapabilityConfig::with_config(CapabilityId::new("beta"), serde_json::json!({})),
        ];

        let collected = collect_message_filters_only(&configs, &registry);

        let session_id: SessionId = Uuid::now_v7().into();
        let mut query = MessageQuery::new(session_id);
        collected.apply_message_filters(&mut query);

        // Filters should be applied in priority order: beta (1), alpha (5), gamma (10)
        assert_eq!(query.filters.len(), 3);
        assert!(matches!(&query.filters[0], MessageFilter::Search(s) if s == "beta"));
        assert!(matches!(&query.filters[1], MessageFilter::Search(s) if s == "alpha"));
        assert!(matches!(&query.filters[2], MessageFilter::Search(s) if s == "gamma"));
    }

    #[test]
    fn test_collect_message_filters_only_post_load_invoked() {
        use crate::message::Message;

        struct PostLoadCap;
        struct PostLoadProvider;

        impl Capability for PostLoadCap {
            fn id(&self) -> &str {
                "post_load_test"
            }
            fn name(&self) -> &str {
                "PostLoad Test"
            }
            fn description(&self) -> &str {
                "test"
            }
            fn message_filter_provider(&self) -> Option<Arc<dyn MessageFilterProvider>> {
                Some(Arc::new(PostLoadProvider))
            }
        }

        impl MessageFilterProvider for PostLoadProvider {
            fn apply_filters(&self, _query: &mut MessageQuery, _config: &serde_json::Value) {}
            fn priority(&self) -> i32 {
                0
            }
            fn post_load(&self, messages: &mut Vec<Message>, _config: &serde_json::Value) {
                // Reverse messages to prove post_load was called
                messages.reverse();
            }
        }

        let mut registry = CapabilityRegistry::new();
        registry.register(PostLoadCap);

        let configs = vec![AgentCapabilityConfig::with_config(
            CapabilityId::new("post_load_test"),
            serde_json::json!({}),
        )];

        let collected = collect_message_filters_only(&configs, &registry);

        let mut messages = vec![Message::user("first"), Message::user("second")];
        collected.apply_post_load_filters(&mut messages);

        // post_load reversed the messages
        assert_eq!(messages[0].text(), Some("second"));
        assert_eq!(messages[1].text(), Some("first"));
    }

    // Tests for resolve_for_model delegation in fast-path collectors

    struct DelegatingFilterCap {
        id: &'static str,
        inner: std::sync::Arc<InnerFilterCap>,
    }
    struct InnerFilterCap;

    impl Capability for InnerFilterCap {
        fn id(&self) -> &str {
            "inner_filter"
        }
        fn tools(&self) -> Vec<Box<dyn Tool>> {
            panic!("fast-path collection must not instantiate tools")
        }
        fn system_prompt_addition(&self) -> Option<&str> {
            panic!("fast-path collection must not collect prompts")
        }
        fn name(&self) -> &str {
            "Inner Filter"
        }
        fn description(&self) -> &str {
            "inner"
        }
        fn message_filter_provider(&self) -> Option<std::sync::Arc<dyn MessageFilterProvider>> {
            Some(std::sync::Arc::new(SentinelFilter))
        }
    }
    struct SentinelFilter;
    impl MessageFilterProvider for SentinelFilter {
        fn apply_filters(&self, query: &mut MessageQuery, config: &serde_json::Value) {
            query.limit = config["limit"].as_i64();
        }
    }
    impl Capability for DelegatingFilterCap {
        fn id(&self) -> &str {
            self.id
        }
        fn name(&self) -> &str {
            "Delegating Filter"
        }
        fn description(&self) -> &str {
            "delegating"
        }
        fn message_filter_provider(&self) -> Option<std::sync::Arc<dyn MessageFilterProvider>> {
            None // outer provides nothing
        }
        fn resolve_for_model(&self, _model: Option<&str>) -> Option<&dyn Capability> {
            Some(&*self.inner)
        }
    }

    #[test]
    fn test_collect_message_filters_only_honors_resolve_for_model_delegation() {
        let inner = std::sync::Arc::new(InnerFilterCap);
        let outer = DelegatingFilterCap {
            id: "delegating_filter",
            inner: inner.clone(),
        };

        let mut registry = CapabilityRegistry::new();
        registry.register(outer);

        let configs = vec![AgentCapabilityConfig::with_config(
            CapabilityId::new("delegating_filter"),
            serde_json::json!({"limit": 17}),
        )];

        // Outer has no message_filter_provider; inner does. resolve_for_model
        // delegates to inner so the provider should be collected.
        let collected = collect_message_filters_only(&configs, &registry);
        assert_eq!(
            collected.message_filter_providers.len(),
            1,
            "provider from resolved inner capability must be collected"
        );
        let mut query = MessageQuery::default();
        collected.apply_message_filters(&mut query);
        assert_eq!(query.limit, Some(17));
    }

    struct DelegatingMvpCap {
        id: &'static str,
        inner: std::sync::Arc<InnerMvpCap>,
    }
    struct InnerMvpCap;

    impl Capability for InnerMvpCap {
        fn id(&self) -> &str {
            "inner_mvp"
        }
        fn tools(&self) -> Vec<Box<dyn Tool>> {
            panic!("fast-path collection must not instantiate tools")
        }
        fn system_prompt_addition(&self) -> Option<&str> {
            panic!("fast-path collection must not collect prompts")
        }
        fn name(&self) -> &str {
            "Inner MVP"
        }
        fn description(&self) -> &str {
            "inner"
        }
        fn model_view_provider(
            &self,
        ) -> Option<std::sync::Arc<dyn crate::capabilities::ModelViewProvider>> {
            // Retain the input and expose the forwarded config and context.
            struct AppendingMvp;
            impl crate::capabilities::ModelViewProvider for AppendingMvp {
                fn apply_model_view(
                    &self,
                    mut messages: Vec<Message>,
                    config: &serde_json::Value,
                    context: &ModelViewContext<'_>,
                ) -> Vec<Message> {
                    messages.push(Message::user(format!(
                        "{}:{}",
                        config["suffix"].as_str().unwrap(),
                        context.session_id
                    )));
                    messages
                }
            }
            Some(std::sync::Arc::new(AppendingMvp))
        }
    }
    impl Capability for DelegatingMvpCap {
        fn id(&self) -> &str {
            self.id
        }
        fn name(&self) -> &str {
            "Delegating MVP"
        }
        fn description(&self) -> &str {
            "delegating"
        }
        fn model_view_provider(
            &self,
        ) -> Option<std::sync::Arc<dyn crate::capabilities::ModelViewProvider>> {
            None // outer provides nothing
        }
        fn resolve_for_model(&self, model: Option<&str>) -> Option<&dyn Capability> {
            (model == Some("selected-model")).then_some(&*self.inner as &dyn Capability)
        }
    }

    #[test]
    fn test_collect_model_view_providers_honors_resolve_for_model_delegation() {
        let inner = std::sync::Arc::new(InnerMvpCap);
        let outer = DelegatingMvpCap {
            id: "delegating_mvp",
            inner: inner.clone(),
        };

        let mut registry = CapabilityRegistry::new();
        registry.register(outer);

        let configs = vec![AgentCapabilityConfig::with_config(
            CapabilityId::new("delegating_mvp"),
            serde_json::json!({"suffix": "delegated"}),
        )];

        // Outer has no model_view_provider; inner does. resolve_for_model
        // delegates to inner so the provider should be collected.
        let collected = collect_model_view_providers(&configs, &registry, Some("selected-model"));
        assert_eq!(
            collected.model_view_providers.len(),
            1,
            "provider from resolved inner capability must be collected"
        );
        assert!(
            collect_model_view_providers(&configs, &registry, Some("other-model"))
                .model_view_providers
                .is_empty()
        );
        let session_id = SessionId::from_seed(42);
        let output = collected.apply_model_view(
            vec![Message::user("original")],
            &ModelViewContext {
                session_id,
                prior_usage: None,
            },
        );
        assert_eq!(
            output.iter().map(Message::text).collect::<Vec<_>>(),
            [
                Some("original"),
                Some(format!("delegated:{session_id}").as_str())
            ]
        );
    }

    // =========================================================================
    // Default selection and alias resolution
    // =========================================================================

    #[test]
    fn test_defaults_do_not_include_bash() {
        // ToolRegistry::with_defaults() must NOT include bash — it comes from
        // capabilities only. This documents the invariant that the bug violated.
        let registry = crate::ToolRegistry::with_defaults();
        assert!(
            !registry.has("bash"),
            "with_defaults() must not include 'bash' — it comes from bashkit_shell capability"
        );
    }

    // =========================================================================
    // Feature tests
    // =========================================================================

    #[test]
    fn test_alias_resolves_to_canonical_capability() {
        let registry = fixture_registry();

        // Legacy `virtual_bash` ID (persisted agent configs) must keep working.
        let via_alias = registry.get("virtual_bash").unwrap();
        assert_eq!(via_alias.id(), "bashkit_shell");
        assert!(registry.has("virtual_bash"));
        assert_eq!(registry.canonical_id("virtual_bash"), Some("bashkit_shell"));
        assert_eq!(
            registry.canonical_id("bashkit_shell"),
            Some("bashkit_shell")
        );
        assert_eq!(registry.canonical_id("nonexistent"), None);
    }

    #[test]
    fn test_alias_dedupes_with_canonical_in_dependency_resolution() {
        let registry = fixture_registry();

        // Selecting both the alias and the canonical ID must resolve to a
        // single activation under the canonical ID.
        let resolved = resolve_dependencies(
            &["virtual_bash".to_string(), "bashkit_shell".to_string()],
            &registry,
        )
        .unwrap();
        let bash_ids: Vec<_> = resolved
            .resolved_ids
            .iter()
            .filter(|id| id.as_str() == "bashkit_shell" || id.as_str() == "virtual_bash")
            .collect();
        assert_eq!(bash_ids, vec!["bashkit_shell"]);
        // Selected via alias => not reported as "added as dependency".
        assert!(
            !resolved
                .added_as_dependencies
                .contains(&"bashkit_shell".to_string())
        );
    }

    #[test]
    fn test_alias_preserves_explicit_config_in_resolution() {
        let registry = fixture_registry();

        let configs = vec![AgentCapabilityConfig::with_config(
            "virtual_bash".to_string(),
            serde_json::json!({"key": "value"}),
        )];
        let resolved = resolve_capability_configs(&configs, &registry).unwrap();
        let bash = resolved
            .iter()
            .find(|c| c.capability_id() == "bashkit_shell")
            .expect("alias must resolve to canonical bashkit_shell config");
        assert_eq!(
            bash.config_value().clone(),
            serde_json::json!({"key": "value"})
        );
    }

    #[test]
    fn test_unregister_by_alias_removes_capability_and_aliases() {
        let mut registry = fixture_registry();

        assert!(registry.unregister("virtual_bash").is_some());
        assert!(!registry.has("bashkit_shell"));
        assert!(!registry.has("virtual_bash"));
    }

    #[test]
    fn test_compute_features_empty() {
        let registry = CapabilityRegistry::new();

        let features = compute_features(&[], &registry);
        assert!(features.is_empty());
    }

    #[test]
    fn test_compute_features_unknown_capability_ignored() {
        let registry = fixture_registry();

        let features = compute_features(
            &["unknown_cap".to_string(), "session_storage".to_string()],
            &registry,
        );
        assert_eq!(features, vec!["secrets", "key_value"]);
    }

    #[test]
    fn test_risk_level_ordering() {
        assert!(RiskLevel::Low < RiskLevel::Medium);
        assert!(RiskLevel::Medium < RiskLevel::High);
    }

    #[test]
    fn test_risk_level_serde_roundtrip() {
        for (level, wire) in [
            (RiskLevel::Low, "\"low\""),
            (RiskLevel::Medium, "\"medium\""),
            (RiskLevel::High, "\"high\""),
        ] {
            assert_eq!(serde_json::to_string(&level).unwrap(), wire);
            assert_eq!(serde_json::from_str::<RiskLevel>(wire).unwrap(), level);
        }
        assert!(serde_json::from_str::<RiskLevel>("\"critical\"").is_err());
    }

    // ========================================================================
    // contribute_skills() collection — EVE-311
    // ========================================================================

    struct SkillContributingCapability;

    impl Capability for SkillContributingCapability {
        fn id(&self) -> &str {
            "contributes_skills"
        }
        fn name(&self) -> &str {
            "Contributes Skills"
        }
        fn description(&self) -> &str {
            "Test capability that contributes skills."
        }
        fn contribute_skills(&self) -> Vec<SkillContribution> {
            vec![
                SkillContribution::new("alpha-skill", "Alpha skill desc", "# Alpha\nDo alpha.")
                    .with_files(vec![(
                        "scripts/a.sh".to_string(),
                        "#!/bin/sh\necho a\n".to_string(),
                    )]),
                SkillContribution::new("beta-skill", "Beta skill desc", "# Beta\nDo beta.")
                    .with_user_invocable(false),
            ]
        }
    }

    fn skill_md_from_entries(entries: &HashMap<String, MountEntry>) -> &str {
        match &entries.get("SKILL.md").expect("SKILL.md missing").source {
            MountSource::InlineFile { content, .. } => content.as_str(),
            _ => panic!("Expected InlineFile for SKILL.md"),
        }
    }

    #[tokio::test]
    async fn test_contribute_skills_normalized_to_mounts() {
        let mut registry = CapabilityRegistry::new();
        registry.register(SkillContributingCapability);

        let configs = vec![AgentCapabilityConfig::with_config(
            CapabilityId::new("contributes_skills"),
            serde_json::json!({}),
        )];

        let collected = collect_capabilities_with_configs(&configs, &registry, &test_ctx()).await;

        let skill_mounts: Vec<_> = collected
            .mounts
            .iter()
            .filter(|m| m.path.starts_with("/.agents/skills/"))
            .collect();
        assert_eq!(skill_mounts.len(), 2);

        // Every contributed skill mount is read-only and owned by the contributing
        // capability so the VFS layer can attribute skill files correctly.
        for m in &skill_mounts {
            assert!(m.is_readonly());
            assert_eq!(m.capability_id, "contributes_skills");
        }

        let alpha = skill_mounts
            .iter()
            .find(|m| m.path == "/.agents/skills/alpha-skill")
            .expect("alpha-skill mount missing");
        match &alpha.source {
            MountSource::InlineDirectory { entries } => {
                assert!(entries.contains_key("SKILL.md"));
                assert!(entries.contains_key("scripts/a.sh"));
                let parsed = crate::skill::parse_skill_md(skill_md_from_entries(entries)).unwrap();
                assert_eq!(parsed.name, "alpha-skill");
                assert_eq!(parsed.description, "Alpha skill desc");
                assert_eq!(parsed.instructions, "# Alpha\nDo alpha.");
                assert!(parsed.user_invocable);
            }
            _ => panic!("Expected InlineDirectory"),
        }

        let beta = skill_mounts
            .iter()
            .find(|m| m.path == "/.agents/skills/beta-skill")
            .expect("beta-skill mount missing");
        match &beta.source {
            MountSource::InlineDirectory { entries } => {
                let parsed = crate::skill::parse_skill_md(skill_md_from_entries(entries)).unwrap();
                assert!(!parsed.user_invocable);
                assert_eq!(parsed.name, "beta-skill");
                assert_eq!(parsed.instructions, "# Beta\nDo beta.");
            }
            _ => panic!("Expected InlineDirectory"),
        }
    }

    #[tokio::test]
    async fn test_contribute_skills_default_empty() {
        // Registry-resident capability without a contribute_skills override
        // must not add skill mounts.
        let mut registry = CapabilityRegistry::new();
        registry.register(FilterTestCapability { priority: 0 });

        let configs = vec![AgentCapabilityConfig::with_config(
            CapabilityId::new("filter_test"),
            serde_json::json!({}),
        )];

        let collected = collect_capabilities_with_configs(&configs, &registry, &test_ctx()).await;
        assert!(
            collected
                .mounts
                .iter()
                .all(|m| !m.path.starts_with("/.agents/skills/"))
        );
    }

    struct LocalizedCapability;

    impl Capability for LocalizedCapability {
        fn id(&self) -> &str {
            "localized"
        }
        fn name(&self) -> &str {
            "Localized"
        }
        fn description(&self) -> &str {
            "English description"
        }
        fn localizations(&self) -> Vec<CapabilityLocalization> {
            vec![
                CapabilityLocalization {
                    locale: "en",
                    name: None,
                    description: None,
                    config_description: Some("Controls things."),
                    config_overlay: None,
                },
                CapabilityLocalization {
                    locale: "uk-UA",
                    name: Some("Регіональна"),
                    description: None,
                    config_description: None,
                    config_overlay: None,
                },
                CapabilityLocalization {
                    locale: "uk",
                    name: Some("Локалізована"),
                    description: Some("Український опис"),
                    config_description: Some("Керує налаштуваннями."),
                    config_overlay: None,
                },
            ]
        }
    }

    #[test]
    fn localized_name_falls_back_exact_language_then_base() {
        let cap = LocalizedCapability;
        // Exact region wins; an absent regional field still falls back by language.
        assert_eq!(cap.localized_name(Some("uk-UA")), "Регіональна");
        assert_eq!(cap.localized_name(Some("uk")), "Локалізована");
        assert_eq!(cap.localized_name(Some("uk-CA")), "Локалізована");
        assert_eq!(cap.localized_name(Some(" UK_ua ")), "Регіональна");
        assert_eq!(cap.localized_description(Some("uk-UA")), "Український опис");
        // Underscore-separated tags are normalized.
        assert_eq!(cap.localized_name(Some("uk_UA")), "Регіональна");
        // Unsupported locales and None fall back to the base name.
        assert_eq!(cap.localized_name(Some("fr-FR")), "Localized");
        assert_eq!(cap.localized_name(None), "Localized");
        assert_eq!(cap.localized_description(Some("uk")), "Український опис");
        assert_eq!(cap.localized_description(Some("de")), "English description");
    }

    #[test]
    fn describe_schema_resolves_config_description_per_locale() {
        let cap = LocalizedCapability;
        assert_eq!(
            cap.describe_schema(Some("uk-UA")).as_deref(),
            Some("Керує налаштуваннями.")
        );
        // Unsupported locales fall back to the "en" entry.
        assert_eq!(
            cap.describe_schema(Some("pl")).as_deref(),
            Some("Controls things.")
        );
        assert_eq!(
            cap.describe_schema(None).as_deref(),
            Some("Controls things.")
        );
        // Capabilities without localizations have no config description.
        assert_eq!(HostAnnotatedCapability.describe_schema(Some("uk")), None);
    }

    #[tokio::test]
    async fn collection_preserves_exact_tool_identity_schema_and_attribution() {
        let registry = fixture_registry();
        for (ids, expected) in [
            (
                vec!["test_math"],
                vec![
                    ("add", "test_math", "Test Math"),
                    ("subtract", "test_math", "Test Math"),
                    ("multiply", "test_math", "Test Math"),
                    ("divide", "test_math", "Test Math"),
                ],
            ),
            (
                vec!["test_weather"],
                vec![
                    ("get_weather", "test_weather", "Test Weather"),
                    ("get_forecast", "test_weather", "Test Weather"),
                ],
            ),
            (
                vec!["sample_data"],
                vec![
                    ("read_file", "session_file_system", "Fixture Filesystem"),
                    ("write_file", "session_file_system", "Fixture Filesystem"),
                ],
            ),
            (
                vec!["bashkit_shell", "test_weather"],
                vec![
                    ("read_file", "session_file_system", "Fixture Filesystem"),
                    ("write_file", "session_file_system", "Fixture Filesystem"),
                    ("bash", "bashkit_shell", "Fixture Bash"),
                    ("get_weather", "test_weather", "Test Weather"),
                    ("get_forecast", "test_weather", "Test Weather"),
                ],
            ),
        ] {
            let ids: Vec<_> = ids.into_iter().map(String::from).collect();
            let collected = collect_capabilities(&ids, &registry, &test_ctx()).await;
            assert_eq!(
                collected.tools.iter().map(|t| t.name()).collect::<Vec<_>>(),
                expected.iter().map(|(n, _, _)| *n).collect::<Vec<_>>()
            );
            assert_eq!(collected.tool_definitions.len(), expected.len());
            for (definition, (name, id, label)) in collected.tool_definitions.iter().zip(expected) {
                assert_eq!(definition.name(), name);
                let hints = definition.hints();
                assert_eq!(hints.capability_id.as_deref(), Some(id));
                assert_eq!(hints.capability_name.as_deref(), Some(label));
                let ToolDefinition::Builtin(tool) = definition else {
                    panic!("expected builtin")
                };
                let schema = if name == "bash" {
                    serde_json::json!({"type":"object"})
                } else {
                    serde_json::json!({"type":"object","properties":{},"additionalProperties":false})
                };
                assert_eq!(tool.parameters, schema);
            }
        }
    }

    #[tokio::test]
    async fn prompt_collection_preserves_exact_sections_attribution_and_base_order() {
        let registry = fixture_registry();
        let ids = vec!["prompt_tool_fixture".into(), "second_prompt_fixture".into()];
        let collected = collect_capabilities(&ids, &registry, &test_ctx()).await;
        let first = "<capability id=\"prompt_tool_fixture\">\nTask Management uses the write_todos tool.\n</capability>";
        let second = "<capability id=\"second_prompt_fixture\">\nA second capability prompt contribution.\n</capability>";
        assert_eq!(collected.system_prompt_parts, vec![first, second]);
        assert_eq!(
            collected.system_prompt_attributions,
            vec![
                SystemPromptAttribution {
                    capability_id: ids[0].clone(),
                    content: first.into()
                },
                SystemPromptAttribution {
                    capability_id: ids[1].clone(),
                    content: second.into()
                }
            ]
        );
        assert_eq!(
            collected.system_prompt_prefix(),
            Some(format!("{first}\n\n{second}"))
        );
        let applied = apply_capabilities(
            RuntimeAgent::new("Base.", "fixture-model"),
            &ids,
            &registry,
            &test_ctx(),
        )
        .await;
        assert_eq!(
            applied.runtime_agent.system_prompt,
            format!("<system-prompt>\nBase.\n</system-prompt>\n\n{first}\n\n{second}")
        );
        assert!(applied.tool_registry.has("write_todos"));
        assert_eq!(applied.tool_registry.len(), 1);
        for (base, addition, expected) in [
            ("Base.", None, "Base."),
            ("Base.", Some(""), "Base."),
            ("", Some("Extra."), "Extra."),
            (
                "<system-prompt>Base.</system-prompt>",
                Some("Extra."),
                "<system-prompt>Base.</system-prompt>\n\nExtra.",
            ),
        ] {
            assert_eq!(compose_system_prompt(base, addition), expected);
        }
    }

    struct DependencyFixture {
        id: String,
        deps: Vec<&'static str>,
        features: Vec<&'static str>,
    }
    impl Capability for DependencyFixture {
        fn id(&self) -> &str {
            &self.id
        }
        fn name(&self) -> &str {
            &self.id
        }
        fn description(&self) -> &str {
            "Dependency fixture"
        }
        fn dependencies(&self) -> Vec<&'static str> {
            self.deps.clone()
        }
        fn features(&self) -> Vec<&'static str> {
            self.features.clone()
        }
    }

    #[test]
    fn feature_projection_preserves_order_and_distinct_dependency_features() {
        let mut registry = CapabilityRegistry::new();
        registry.register(DependencyFixture {
            id: "base".into(),
            deps: vec![],
            features: vec!["base-only", "shared"],
        });
        registry.register(DependencyFixture {
            id: "parent".into(),
            deps: vec!["base"],
            features: vec!["parent-only", "shared"],
        });
        registry.register(DependencyFixture {
            id: "other".into(),
            deps: vec![],
            features: vec!["other-only"],
        });
        assert_eq!(
            compute_features(&["parent".into()], &registry),
            vec!["base-only", "shared", "parent-only"]
        );
        assert_eq!(
            compute_features(
                &[
                    "other".into(),
                    "parent".into(),
                    "base".into(),
                    "parent".into()
                ],
                &registry
            ),
            vec!["other-only", "base-only", "shared", "parent-only"]
        );
    }

    #[test]
    fn dependency_limit_accepts_one_hundred_and_rejects_one_hundred_one() {
        let mut registry = CapabilityRegistry::new();
        let ids: Vec<_> = (0..101).map(|i| format!("cap-{i}")).collect();
        for id in &ids {
            registry.register(DependencyFixture {
                id: id.clone(),
                deps: vec![],
                features: vec![],
            });
        }
        let resolved = resolve_dependencies(&ids[..100], &registry).unwrap();
        assert_eq!(resolved.resolved_ids, ids[..100]);
        assert_eq!(resolved.user_selected, ids[..100]);
        assert!(resolved.added_as_dependencies.is_empty());
        assert_eq!(
            resolve_dependencies(&ids, &registry).unwrap_err(),
            DependencyError::TooManyCapabilities {
                count: 101,
                max: 100
            }
        );
    }
}