toolpath_convo/

derive.rs

//! Shared derivation: [`ConversationView`] → [`toolpath::v1::Path`].
//!
//! Provider-agnostic mapping used by the Pi, Claude, and future conversation
//! providers. Takes a [`ConversationView`] and emits a [`Path`] document with
//! one step per turn and a `conversation.append` structural change carrying
//! the turn's text, thinking, tool uses, and token usage. The emitted path is
//! tagged with `meta.kind = PATH_KIND_AGENT_CODING_SESSION`.

use std::collections::HashMap;

use toolpath::v1::{
    ActorDefinition, ArtifactChange, Base, PATH_KIND_AGENT_CODING_SESSION, Path, PathIdentity,
    PathMeta, Step, StepIdentity, StructuralChange,
};

use crate::{ConversationView, Role, ToolCategory, ToolInvocation, Turn};

/// Configuration for [`derive_path`].
#[derive(Debug, Clone)]
pub struct DeriveConfig {
    /// Override `path.base.uri`. If `None`, fall back to the first turn's
    /// `environment.working_dir`.
    pub base_uri: Option<String>,
    /// Override `path.id`. If `None`, derive as `path-{provider}-{8chars}`.
    pub path_id: Option<String>,
    /// Override `meta.title`. If `None`, default to `"{provider} session: {8chars}"`.
    pub title: Option<String>,
    /// Include `Turn.thinking` in the structural change extras.
    pub include_thinking: bool,
    /// Include `Turn.tool_uses` in the structural change extras.
    pub include_tool_uses: bool,
}

impl Default for DeriveConfig {
    fn default() -> Self {
        Self {
            base_uri: None,
            path_id: None,
            title: None,
            include_thinking: true,
            include_tool_uses: true,
        }
    }
}

/// Derive a [`Path`] from a [`ConversationView`].
pub fn derive_path(view: &ConversationView, config: &DeriveConfig) -> Path {
    let provider = view.provider_id.as_deref().unwrap_or("unknown");
    let id_prefix: String = view.id.chars().take(8).collect();

    let path_id = config
        .path_id
        .clone()
        .unwrap_or_else(|| format!("path-{}-{}", provider, id_prefix));

    // Base resolution order:
    //   1. `config.base_uri` (CLI override): provides the `uri`; ref/branch
    //      come from `view.base` if set.
    //   2. `view.base` (provider-populated): the canonical source.
    //   3. First turn's `environment.working_dir` (legacy fallback).
    let base = config
        .base_uri
        .clone()
        .map(|uri| Base {
            uri,
            ref_str: view.base.as_ref().and_then(|b| b.vcs_revision.clone()),
            branch: view.base.as_ref().and_then(|b| b.vcs_branch.clone()),
        })
        .or_else(|| {
            view.base.as_ref().and_then(|b| {
                let wd = b.working_dir.as_ref()?;
                let uri = if wd.starts_with('/') {
                    format!("file://{}", wd)
                } else {
                    wd.clone()
                };
                Some(Base {
                    uri,
                    ref_str: b.vcs_revision.clone(),
                    branch: b.vcs_branch.clone(),
                })
            })
        })
        .or_else(|| {
            view.turns
                .iter()
                .find_map(|t| t.environment.as_ref()?.working_dir.clone())
                .map(|wd| {
                    let uri = if wd.starts_with('/') {
                        format!("file://{}", wd)
                    } else {
                        wd
                    };
                    Base {
                        uri,
                        ref_str: None,
                        branch: None,
                    }
                })
        });

    let conv_artifact_key = format!("{}://{}", provider, view.id);

    let mut steps: Vec<Step> = Vec::with_capacity(view.turns.len());
    let mut turn_to_step: HashMap<String, String> = HashMap::new();
    let mut actors: HashMap<String, ActorDefinition> = HashMap::new();

    for (idx, turn) in view.turns.iter().enumerate() {
        // Step id: use the turn's native id when set so it round-trips
        // through `extract_conversation`; otherwise synthesize sequentially.
        let step_id = if turn.id.is_empty() {
            format!("step-{:04}", idx + 1)
        } else {
            turn.id.clone()
        };
        turn_to_step.insert(turn.id.clone(), step_id.clone());

        let actor = actor_for_turn(turn, provider);
        record_actor(&mut actors, &actor, turn, provider, view);

        let mut step = Step {
            step: StepIdentity {
                id: step_id,
                parents: Vec::new(),
                actor,
                timestamp: turn.timestamp.clone(),
            },
            change: HashMap::new(),
            meta: None,
        };

        // Parent mapping
        if let Some(parent_id) = &turn.parent_id
            && let Some(parent_step_id) = turn_to_step.get(parent_id)
        {
            step.step.parents.push(parent_step_id.clone());
        }

        // Build conversation.append structural change extras
        let mut extra: HashMap<String, serde_json::Value> = HashMap::new();
        extra.insert(
            "role".to_string(),
            serde_json::Value::String(turn.role.to_string()),
        );
        extra.insert(
            "text".to_string(),
            serde_json::Value::String(turn.text.clone()),
        );

        if config.include_thinking
            && let Some(thinking) = &turn.thinking
        {
            extra.insert(
                "thinking".to_string(),
                serde_json::Value::String(thinking.clone()),
            );
        }

        if config.include_tool_uses && !turn.tool_uses.is_empty() {
            let arr: Vec<serde_json::Value> = turn
                .tool_uses
                .iter()
                .map(|t| {
                    let mut obj = serde_json::json!({
                        "id": t.id,
                        "name": t.name,
                        "input": t.input,
                        "category": t.category,
                    });
                    if let Some(result) = &t.result
                        && let Ok(v) = serde_json::to_value(result)
                    {
                        obj.as_object_mut().unwrap().insert("result".to_string(), v);
                    }
                    obj
                })
                .collect();
            extra.insert("tool_uses".to_string(), serde_json::Value::Array(arr));
        }

        // Message-level accounting lands exactly once per message: when a
        // provider splits one message across several turns (group_id
        // set on each), only the run's last turn carries token_usage, so
        // summing over steps yields session totals. A turn without a
        // group_id is its own accounting unit.
        let last_of_message = match &turn.group_id {
            None => true,
            Some(mid) => view
                .turns
                .get(idx + 1)
                .is_none_or(|next| next.group_id.as_ref() != Some(mid)),
        };
        if last_of_message
            && let Some(usage) = &turn.token_usage
            && let Ok(v) = serde_json::to_value(usage)
        {
            extra.insert("token_usage".to_string(), v);
        }

        // Per-step attributed spend rides its own key on every step that
        // has it (independent of the once-per-message `token_usage`), so
        // summing `token_usage` is unaffected while per-step cost stays
        // readable structurally.
        if let Some(attr) = &turn.attributed_token_usage
            && let Ok(v) = serde_json::to_value(attr)
        {
            extra.insert("attributed_token_usage".to_string(), v);
        }

        if let Some(mid) = &turn.group_id {
            extra.insert(
                "group_id".to_string(),
                serde_json::Value::String(mid.clone()),
            );
        }

        if !turn.delegations.is_empty()
            && let Ok(v) = serde_json::to_value(&turn.delegations)
        {
            extra.insert("delegations".to_string(), v);
        }

        if let Some(stop_reason) = &turn.stop_reason {
            extra.insert(
                "stop_reason".to_string(),
                serde_json::Value::String(stop_reason.clone()),
            );
        }

        if let Some(env) = &turn.environment
            && let Ok(v) = serde_json::to_value(env)
        {
            extra.insert("environment".to_string(), v);
        }

        step.change.insert(
            conv_artifact_key.clone(),
            ArtifactChange {
                raw: None,
                structural: Some(StructuralChange {
                    change_type: "conversation.append".to_string(),
                    extra,
                }),
            },
        );

        // File mutations → sibling `file.write` change entries.
        //
        // Preferred: each `Turn::file_mutations` entry comes from the
        // provider's `to_view` with the resolved diff already in
        // `raw_diff` (claude's git-HEAD lookup, codex's `apply_patch_end`
        // parse, opencode's git2 tree↔tree, etc.). `tool_id` links back
        // to a specific `ToolInvocation` when the provider can attribute.
        //
        // Fallback (un-migrated providers): for any `FileWrite`-category
        // tool with no matching mutation, synthesize from `tool.input`
        // via `file_write_change`.
        let attributed: std::collections::HashSet<String> = turn
            .file_mutations
            .iter()
            .filter_map(|fm| fm.tool_id.clone())
            .collect();
        for fm in &turn.file_mutations {
            let mut t_extra: HashMap<String, serde_json::Value> = HashMap::new();
            if let Some(tid) = &fm.tool_id {
                t_extra.insert(
                    "tool_id".to_string(),
                    serde_json::Value::String(tid.clone()),
                );
                if let Some(tool) = turn.tool_uses.iter().find(|t| &t.id == tid) {
                    t_extra.insert(
                        "tool".to_string(),
                        serde_json::Value::String(tool.name.clone()),
                    );
                }
            }
            if let Some(op) = &fm.operation {
                t_extra.insert(
                    "operation".to_string(),
                    serde_json::Value::String(op.clone()),
                );
            }
            if let Some(b) = &fm.before {
                t_extra.insert("before".to_string(), serde_json::Value::String(b.clone()));
            }
            if let Some(a) = &fm.after {
                t_extra.insert("after".to_string(), serde_json::Value::String(a.clone()));
            }
            if let Some(rt) = &fm.rename_to {
                t_extra.insert(
                    "rename_to".to_string(),
                    serde_json::Value::String(rt.clone()),
                );
            }
            step.change.insert(
                fm.path.clone(),
                ArtifactChange {
                    raw: fm.raw_diff.clone(),
                    structural: Some(StructuralChange {
                        change_type: "file.write".to_string(),
                        extra: t_extra,
                    }),
                },
            );
        }
        for tool in &turn.tool_uses {
            if tool.category != Some(ToolCategory::FileWrite) || attributed.contains(&tool.id) {
                continue;
            }
            let Some(path) = extract_file_path(tool) else {
                continue;
            };
            let (raw, mut t_extra) = file_write_change(tool, &path, None);
            t_extra.insert(
                "tool".to_string(),
                serde_json::Value::String(tool.name.clone()),
            );
            t_extra.insert(
                "tool_id".to_string(),
                serde_json::Value::String(tool.id.clone()),
            );
            step.change.insert(
                path,
                ArtifactChange {
                    raw,
                    structural: Some(StructuralChange {
                        change_type: "file.write".to_string(),
                        extra: t_extra,
                    }),
                },
            );
        }

        steps.push(step);
    }

    // Emit `view.events` as `conversation.event` steps so that attachments,
    // preamble lines (ai-title, last-prompt, queue-operation, permission-mode),
    // and other non-turn entries survive the IR-to-Path-to-IR roundtrip.
    // Without this, derive_path drops everything outside `turns`, so a
    // Claude session loses ~10–25% of its lines on import/export.
    // Track the last emitted step id so events without an explicit
    // `parent_id` can chain off whatever step came before them.
    let mut last_step_id: Option<String> = steps.last().map(|s| s.step.id.clone());
    for (idx, event) in view.events.iter().enumerate() {
        // Event step id: prefer the event's native id so it round-trips.
        let step_id = if event.id.is_empty() {
            format!("event-{:04}", idx + 1)
        } else {
            event.id.clone()
        };
        let actor = format!("tool:{}", provider);
        actors
            .entry(actor.clone())
            .or_insert_with(|| ActorDefinition {
                name: Some(provider.to_string()),
                provider: Some(provider.to_string()),
                ..Default::default()
            });

        // event.data is flattened into StructuralChange.extra. Strip keys
        // that collide with the typed fields on StructuralChange itself —
        // most importantly `type`, which serde renames `change_type` to.
        // A Codex `user_message` event carries `data["type"] = "user_message"`,
        // which would otherwise overwrite our `change_type = "conversation.event"`
        // and break PathOrRef untagged-enum disambiguation on parse.
        let mut extra: HashMap<String, serde_json::Value> = event
            .data
            .iter()
            .filter(|(k, _)| k.as_str() != "type")
            .map(|(k, v)| (k.clone(), v.clone()))
            .collect();
        // Stash the original `type` value under a non-colliding key so
        // round-trip can recover it for providers that need it.
        if let Some(t) = event.data.get("type") {
            extra.insert("event_data_type".to_string(), t.clone());
        }
        extra.insert(
            "entry_type".to_string(),
            serde_json::Value::String(event.event_type.clone()),
        );
        if !event.id.is_empty() {
            extra.insert(
                "event_source_id".to_string(),
                serde_json::Value::String(event.id.clone()),
            );
        }

        let parents: Vec<String> = event
            .parent_id
            .as_ref()
            .and_then(|pid| turn_to_step.get(pid).cloned())
            .or_else(|| last_step_id.clone())
            .into_iter()
            .collect();

        let mut step = Step {
            step: StepIdentity {
                id: step_id.clone(),
                parents,
                actor,
                timestamp: event.timestamp.clone(),
            },
            change: HashMap::new(),
            meta: None,
        };

        step.change.insert(
            conv_artifact_key.clone(),
            ArtifactChange {
                raw: None,
                structural: Some(StructuralChange {
                    change_type: "conversation.event".to_string(),
                    extra,
                }),
            },
        );
        steps.push(step);
        last_step_id = Some(step_id);
    }

    let head = steps.last().map(|s| s.step.id.clone()).unwrap_or_default();

    // Meta
    let title = config
        .title
        .clone()
        .unwrap_or_else(|| format!("{} session: {}", provider, id_prefix));

    let mut meta = PathMeta {
        title: Some(title),
        kind: Some(PATH_KIND_AGENT_CODING_SESSION.to_string()),
        source: view.provider_id.clone(),
        ..Default::default()
    };

    if !actors.is_empty() {
        meta.actors = Some(actors);
    }

    if !view.files_changed.is_empty()
        && let Ok(v) = serde_json::to_value(&view.files_changed)
    {
        meta.extra.insert("files_changed".to_string(), v);
    }

    // Carry `vcs_remote` (not representable on `Base`) under meta.extra.
    if let Some(remote) = view.base.as_ref().and_then(|b| b.vcs_remote.as_ref())
        && !meta.extra.contains_key("vcs_remote")
    {
        meta.extra.insert(
            "vcs_remote".to_string(),
            serde_json::Value::String(remote.clone()),
        );
    }

    // Project canonical session-level fields under well-known keys.
    if let Some(producer) = &view.producer
        && let Ok(v) = serde_json::to_value(producer)
    {
        meta.extra.insert("producer".to_string(), v);
    }

    Path {
        path: PathIdentity {
            id: path_id,
            base,
            head,
            graph_ref: None,
        },
        steps,
        meta: Some(meta),
    }
}

fn actor_for_turn(turn: &Turn, provider: &str) -> String {
    match &turn.role {
        Role::User => "human:user".to_string(),
        Role::Assistant => {
            let model = turn.model.as_deref().unwrap_or("unknown");
            format!("agent:{}", model)
        }
        Role::System => format!("tool:{}", provider),
        Role::Other(_) => format!("tool:{}", provider),
    }
}

fn record_actor(
    actors: &mut HashMap<String, ActorDefinition>,
    actor: &str,
    turn: &Turn,
    provider: &str,
    _view: &ConversationView,
) {
    if actors.contains_key(actor) {
        return;
    }
    let def = if let Some(rest) = actor.strip_prefix("agent:") {
        ActorDefinition {
            name: Some(rest.to_string()),
            provider: Some(provider.to_string()),
            model: turn.model.clone(),
            identities: vec![],
            keys: vec![],
        }
    } else if let Some(rest) = actor.strip_prefix("human:") {
        ActorDefinition {
            name: Some(rest.to_string()),
            ..Default::default()
        }
    } else {
        let name = actor.split_once(':').map(|x| x.1).unwrap_or("").to_string();
        ActorDefinition {
            name: Some(name),
            provider: Some(provider.to_string()),
            ..Default::default()
        }
    };
    actors.insert(actor.to_string(), def);
}

fn extract_file_path(tool: &ToolInvocation) -> Option<String> {
    for field in &["file_path", "path", "filename", "file"] {
        if let Some(v) = tool.input.get(*field)
            && let Some(s) = v.as_str()
        {
            return Some(s.to_string());
        }
    }
    None
}

/// Build `(raw_diff, extra)` for a single FileWrite tool invocation.
///
/// See [`file_write_diff`] for the input shapes handled; this helper
/// additionally captures the structured before/after strings in `extra`.
///
/// `before_state` is threaded through to [`file_write_diff`] for the
/// `Write { content }` shape: when `Some`, it becomes the pre-image and
/// is also recorded in `extra["before"]`. When `None`, the diff falls
/// back to an empty pre-image (addition-only hunk).
fn file_write_change(
    tool: &ToolInvocation,
    path: &str,
    before_state: Option<&str>,
) -> (Option<String>, HashMap<String, serde_json::Value>) {
    let input = &tool.input;
    let str_field = |k: &str| input.get(k).and_then(|v| v.as_str()).map(str::to_string);

    let mut extra: HashMap<String, serde_json::Value> = HashMap::new();

    if let (Some(old), Some(new)) = (str_field("old_string"), str_field("new_string")) {
        extra.insert("before".to_string(), serde_json::Value::String(old.clone()));
        extra.insert("after".to_string(), serde_json::Value::String(new.clone()));
    } else if let Some(content) = str_field("content") {
        if let Some(before) = before_state {
            extra.insert(
                "before".to_string(),
                serde_json::Value::String(before.to_string()),
            );
        }
        extra.insert("after".to_string(), serde_json::Value::String(content));
    } else if let Some(edits) = input.get("edits").and_then(|v| v.as_array()) {
        extra.insert("edits".to_string(), serde_json::Value::Array(edits.clone()));
    }

    (
        file_write_diff(&tool.name, input, path, before_state),
        extra,
    )
}

/// Compute a unified diff string for a file-write tool invocation, given the
/// raw tool input JSON. Handles Claude's Edit / Write / MultiEdit / NotebookEdit
/// shapes; returns `None` for any unrecognised shape or if nothing to diff.
///
/// Exposed so non-Conversation derivers (e.g. `toolpath-claude`'s bespoke
/// Claude-JSONL deriver, which emits its own `tool.invoke` steps) can populate
/// `ArtifactChange.raw` without reimplementing the diff logic.
///
/// Shapes handled:
///   - `Edit    { old_string, new_string, ... }`  → diff old→new
///   - `Write   { content }`                      → diff `before_state`→content
///     (uses `""` when `before_state` is `None`, producing an addition-only hunk)
///   - `MultiEdit { edits: [{old_string, new_string}, ...] }` → hunks joined,
///     each prefixed with `# edit N/total` so consumers can tell them apart.
///
/// # `before_state` for `Write`
///
/// The `Write` tool replaces a file's whole contents but the JSONL log
/// doesn't carry the prior state. Callers that can reconstruct it
/// out-of-band (e.g. by reading `git show HEAD:<path>`) should pass it
/// as `before_state`; the resulting diff shows honest `-`/`+` lines for
/// replaced content. When `None`, we fall back to diffing against the
/// empty string — correct for new files, misleading for overwrites, but
/// the best we can do from the log alone.
///
/// `before_state` is ignored for `Edit` / `MultiEdit` shapes, which
/// already carry their own `old_string`/`new_string` pre-image.
pub fn file_write_diff(
    tool_name: &str,
    input: &serde_json::Value,
    path: &str,
    before_state: Option<&str>,
) -> Option<String> {
    let str_field = |k: &str| input.get(k).and_then(|v| v.as_str());

    // Edit / NotebookEdit / anything else with old/new pair.
    if let (Some(old), Some(new)) = (str_field("old_string"), str_field("new_string")) {
        return Some(unified_diff(path, old, new));
    }

    // Write — whole-file content; diff against the caller-supplied
    // before-state when present, else empty (addition-only hunk).
    if let Some(content) = str_field("content") {
        let before = before_state.unwrap_or("");
        return Some(unified_diff(path, before, content));
    }

    // MultiEdit — multiple sequential edits on one file.
    if let Some(edits) = input.get("edits").and_then(|v| v.as_array()) {
        if edits.is_empty() {
            return None;
        }
        let mut parts: Vec<String> = Vec::new();
        for (idx, edit) in edits.iter().enumerate() {
            let old = edit
                .get("old_string")
                .and_then(|v| v.as_str())
                .unwrap_or("");
            let new = edit
                .get("new_string")
                .and_then(|v| v.as_str())
                .unwrap_or("");
            let header = format!("# edit {}/{}", idx + 1, edits.len());
            parts.push(format!("{header}\n{}", unified_diff(path, old, new)));
        }
        return Some(parts.join("\n"));
    }

    // Unused today, but keeps `tool_name` addressable for future per-tool
    // branches (e.g. NotebookEdit may one day need cell-scoped diffs).
    let _ = tool_name;
    None
}

/// Produce a minimal unified-diff string using `similar::TextDiff`.
///
/// Always emits a `--- a/{path}` / `+++ b/{path}` header even when one side is
/// empty so downstream renderers can anchor the change to the file it touched.
///
/// Any leading `/` on `path` is stripped before splicing into the header —
/// git-style `a/` and `b/` prefixes already denote the repo root, so an
/// absolute path like `/abs/file.rs` would otherwise emit `--- a//abs/file.rs`,
/// which breaks `patch(1)` and other consumers that parse the header.
pub fn unified_diff(path: &str, before: &str, after: &str) -> String {
    use similar::TextDiff;
    let diff = TextDiff::from_lines(before, after);
    let display = path.trim_start_matches('/');
    let mut out = String::new();
    out.push_str(&format!("--- a/{display}\n+++ b/{display}\n"));
    out.push_str(
        &diff
            .unified_diff()
            .context_radius(3)
            .header("", "")
            .to_string(),
    );
    out
}

#[cfg(test)]
mod tests {
    use super::*;
    use crate::{DelegatedWork, EnvironmentSnapshot, TokenUsage, ToolInvocation, ToolResult};

    fn base_turn(id: &str, role: Role) -> Turn {
        Turn {
            id: id.to_string(),
            parent_id: None,
            group_id: None,
            role,
            timestamp: "2026-01-01T00:00:00Z".to_string(),
            text: String::new(),
            thinking: None,
            tool_uses: vec![],
            model: None,
            stop_reason: None,
            token_usage: None,
            attributed_token_usage: None,
            environment: None,
            delegations: vec![],
            file_mutations: Vec::new(),
        }
    }

    fn view_with(turns: Vec<Turn>) -> ConversationView {
        ConversationView {
            id: "abcdef012345".to_string(),
            turns,
            provider_id: Some("pi".to_string()),
            ..Default::default()
        }
    }

    fn conv_change(step: &Step) -> &StructuralChange {
        let key = step
            .change
            .keys()
            .find(|k| k.contains("://"))
            .expect("conversation artifact key present");
        step.change[key].structural.as_ref().unwrap()
    }

    #[test]
    fn test_empty_view() {
        let view = view_with(vec![]);
        let path = derive_path(&view, &DeriveConfig::default());
        assert!(path.steps.is_empty());
        assert_eq!(path.path.head, "");
    }

    #[test]
    fn test_meta_kind_is_convo() {
        let view = view_with(vec![base_turn("t1", Role::User)]);
        let path = derive_path(&view, &DeriveConfig::default());
        assert_eq!(
            path.meta.as_ref().unwrap().kind.as_deref(),
            Some(PATH_KIND_AGENT_CODING_SESSION)
        );
        // ...and survives a JSON round-trip.
        let json = serde_json::to_string(&path).unwrap();
        assert!(
            json.contains(r#""kind":"https://toolpath.net/kinds/agent-coding-session/v1.1.0""#)
        );
    }

    #[test]
    fn test_token_usage_breakdowns_round_trip() {
        use std::collections::BTreeMap;
        // A Turn whose token_usage carries breakdowns should derive into a
        // Path and extract back out with the breakdowns intact.
        let mut breakdowns = BTreeMap::new();
        breakdowns.insert(
            "output".to_string(),
            BTreeMap::from([("reasoning".to_string(), 450u32)]),
        );
        let mut turn = base_turn("t1", Role::Assistant);
        turn.model = Some("claude-opus-4-7".into());
        turn.token_usage = Some(TokenUsage {
            input_tokens: Some(100),
            output_tokens: Some(900),
            breakdowns: breakdowns.clone(),
            ..Default::default()
        });
        let view = view_with(vec![turn]);

        let path = derive_path(&view, &DeriveConfig::default());
        let extracted = crate::extract::extract_conversation(&path);

        let usage = extracted.turns[0]
            .token_usage
            .as_ref()
            .expect("token_usage survives round-trip");
        assert_eq!(usage.input_tokens, Some(100));
        assert_eq!(usage.output_tokens, Some(900));
        assert_eq!(usage.breakdowns, breakdowns);
        assert_eq!(usage.breakdowns["output"]["reasoning"], 450);
    }

    #[test]
    fn test_token_usage_empty_breakdowns_omitted_in_json() {
        // skip_serializing_if guarantees no "breakdowns" key for the empty map,
        // keeping the wire format byte-compatible with pre-breakdowns producers.
        let usage = TokenUsage {
            input_tokens: Some(10),
            output_tokens: Some(20),
            ..Default::default()
        };
        let json = serde_json::to_string(&usage).unwrap();
        assert!(
            !json.contains("breakdowns"),
            "empty breakdowns must be omitted, got: {json}"
        );
    }

    #[test]
    fn test_token_usage_absent_breakdowns_defaults_empty() {
        // Deserializing an old-style token_usage object with no breakdowns key
        // yields an empty map (serde default).
        let usage: TokenUsage =
            serde_json::from_str(r#"{"input_tokens":10,"output_tokens":20}"#).unwrap();
        assert!(usage.breakdowns.is_empty());
    }

    #[test]
    fn test_single_user_turn() {
        let mut turn = base_turn("t1", Role::User);
        turn.text = "hello".into();
        let view = view_with(vec![turn]);
        let path = derive_path(&view, &DeriveConfig::default());
        assert_eq!(path.steps.len(), 1);
        assert_eq!(path.steps[0].step.actor, "human:user");
        assert_eq!(path.steps[0].step.id, "t1");
    }

    #[test]
    fn test_single_assistant_turn() {
        let mut turn = base_turn("t1", Role::Assistant);
        turn.model = Some("claude-opus-4-7".into());
        let view = view_with(vec![turn]);
        let path = derive_path(&view, &DeriveConfig::default());
        assert_eq!(path.steps[0].step.actor, "agent:claude-opus-4-7");
    }

    #[test]
    fn test_assistant_without_model() {
        let turn = base_turn("t1", Role::Assistant);
        let view = view_with(vec![turn]);
        let path = derive_path(&view, &DeriveConfig::default());
        assert_eq!(path.steps[0].step.actor, "agent:unknown");
    }

    #[test]
    fn test_system_role() {
        let turn = base_turn("t1", Role::System);
        let view = view_with(vec![turn]);
        let path = derive_path(&view, &DeriveConfig::default());
        assert_eq!(path.steps[0].step.actor, "tool:pi");
    }

    #[test]
    fn test_other_role() {
        let turn = base_turn("t1", Role::Other("tool".into()));
        let view = view_with(vec![turn]);
        let path = derive_path(&view, &DeriveConfig::default());
        assert_eq!(path.steps[0].step.actor, "tool:pi");
    }

    #[test]
    fn test_parent_id_preserved() {
        let t1 = base_turn("t1", Role::User);
        let mut t2 = base_turn("t2", Role::Assistant);
        t2.parent_id = Some("t1".into());
        t2.model = Some("m".into());
        let view = view_with(vec![t1, t2]);
        let path = derive_path(&view, &DeriveConfig::default());
        assert_eq!(path.steps[1].step.parents, vec!["t1".to_string()]);
    }

    #[test]
    fn derived_path_validates_against_base_schema() {
        let user = base_turn("t1", Role::User);
        let mut assistant = base_turn("t2", Role::Assistant);
        assistant.parent_id = Some("t1".into());
        assistant.model = Some("gpt-5.5".into());
        let system = base_turn("t3", Role::System);
        let other = base_turn("t4", Role::Other("bash".into()));

        let mut view = view_with(vec![user, assistant, system, other]);
        view.events.push(crate::ConversationEvent {
            id: "e1".into(),
            timestamp: "2026-01-01T00:00:00Z".into(),
            parent_id: None,
            event_type: "attachment".into(),
            data: HashMap::new(),
        });

        let path = derive_path(&view, &DeriveConfig::default());
        let graph = serde_json::json!({
            "graph": { "id": "g1" },
            "paths": [serde_json::to_value(&path).unwrap()],
        });

        let schema: serde_json::Value = serde_json::from_str(toolpath::SCHEMA_JSON).unwrap();
        let validator = jsonschema::validator_for(&schema).unwrap();
        let errors: Vec<String> = validator
            .iter_errors(&graph)
            .map(|e| format!("at {}: {e}", e.instance_path()))
            .collect();
        assert!(
            errors.is_empty(),
            "base-schema violations:\n{}",
            errors.join("\n")
        );
    }

    #[test]
    fn derived_path_conforms_to_agent_coding_session_kind() {
        // derive_path stamps meta.kind = agent-coding-session, so its output
        // must satisfy that kind's schema. This view exercises every shape
        // the kind constrains: each turn role, a tool call with a result, a
        // file mutation, a delegation, token usage, environment, and an event.
        let mut user = base_turn("t1", Role::User);
        user.text = "implement the feature".into();

        let mut assistant = base_turn("t2", Role::Assistant);
        assistant.parent_id = Some("t1".into());
        assistant.group_id = Some("msg_t2".into());
        assistant.model = Some("gpt-5.5".into());
        assistant.text = "on it".into();
        assistant.thinking = Some("plan the edit".into());
        assistant.stop_reason = Some("tool_use".into());
        assistant.token_usage = Some(TokenUsage {
            input_tokens: Some(100),
            output_tokens: Some(20),
            cache_read_tokens: Some(50),
            cache_write_tokens: None,
            ..Default::default()
        });
        assistant.attributed_token_usage = Some(TokenUsage {
            output_tokens: Some(20),
            ..Default::default()
        });
        assistant.environment = Some(EnvironmentSnapshot {
            working_dir: Some("/repo".into()),
            vcs_branch: Some("main".into()),
            vcs_revision: None,
        });
        assistant.tool_uses = vec![ToolInvocation {
            id: "call-1".into(),
            name: "write_file".into(),
            input: serde_json::json!({ "file_path": "a.rs", "content": "fn main() {}" }),
            result: Some(ToolResult {
                content: "ok".into(),
                is_error: false,
            }),
            category: Some(crate::ToolCategory::FileWrite),
        }];
        assistant.file_mutations = vec![crate::FileMutation {
            path: "a.rs".into(),
            tool_id: Some("call-1".into()),
            operation: Some("add".into()),
            raw_diff: Some("@@ -0,0 +1 @@\n+fn main() {}".into()),
            before: None,
            after: Some("fn main() {}".into()),
            rename_to: None,
        }];
        assistant.delegations = vec![DelegatedWork {
            agent_id: "sub-1".into(),
            prompt: "do the subtask".into(),
            turns: vec![],
            result: Some("done".into()),
        }];

        let mut system = base_turn("t3", Role::System);
        system.parent_id = Some("t2".into());
        system.text = "system note".into();

        let mut other = base_turn("t4", Role::Other("tool".into()));
        other.parent_id = Some("t3".into());
        other.text = "tool output".into();

        let mut view = view_with(vec![user, assistant, system, other]);
        view.events.push(crate::ConversationEvent {
            id: "e1".into(),
            timestamp: "2026-01-01T00:00:00Z".into(),
            parent_id: None,
            event_type: "attachment".into(),
            data: HashMap::new(),
        });

        let path = derive_path(&view, &DeriveConfig::default());
        assert_eq!(
            path.meta.as_ref().and_then(|m| m.kind.as_deref()),
            Some(toolpath::v1::PATH_KIND_AGENT_CODING_SESSION),
            "derive_path must stamp the agent-coding-session kind"
        );

        let schema_src = std::fs::read_to_string(concat!(
            env!("CARGO_MANIFEST_DIR"),
            "/../path-cli/kinds/agent-coding-session/v1.1.0/schema.json"
        ))
        .expect("read kind schema");
        let schema: serde_json::Value = serde_json::from_str(&schema_src).unwrap();
        let validator = jsonschema::validator_for(&schema).unwrap();
        let value = serde_json::to_value(&path).unwrap();
        let errors: Vec<String> = validator
            .iter_errors(&value)
            .map(|e| format!("at {}: {e}", e.instance_path()))
            .collect();
        assert!(
            errors.is_empty(),
            "kind-schema violations:\n{}",
            errors.join("\n")
        );
    }

    fn fw_tool(name: &str, id: &str, input: serde_json::Value) -> ToolInvocation {
        ToolInvocation {
            id: id.to_string(),
            name: name.to_string(),
            input,
            result: None,
            category: Some(ToolCategory::FileWrite),
        }
    }

    #[test]
    fn test_tool_use_filewrite_with_file_path_field() {
        let mut turn = base_turn("t1", Role::Assistant);
        turn.tool_uses = vec![fw_tool(
            "Write",
            "tu1",
            serde_json::json!({"file_path": "src/main.rs"}),
        )];
        let view = view_with(vec![turn]);
        let path = derive_path(&view, &DeriveConfig::default());
        assert!(path.steps[0].change.contains_key("src/main.rs"));
        let sc = path.steps[0].change["src/main.rs"]
            .structural
            .as_ref()
            .unwrap();
        assert_eq!(sc.change_type, "file.write");
        assert_eq!(sc.extra["tool"], serde_json::json!("Write"));
        assert_eq!(sc.extra["tool_id"], serde_json::json!("tu1"));
    }

    #[test]
    fn test_tool_use_filewrite_with_path_field() {
        let mut turn = base_turn("t1", Role::Assistant);
        turn.tool_uses = vec![fw_tool("Edit", "tu1", serde_json::json!({"path": "a.rs"}))];
        let view = view_with(vec![turn]);
        let path = derive_path(&view, &DeriveConfig::default());
        assert!(path.steps[0].change.contains_key("a.rs"));
    }

    #[test]
    fn test_tool_use_filewrite_with_filename_field() {
        let mut turn = base_turn("t1", Role::Assistant);
        turn.tool_uses = vec![fw_tool("W", "tu1", serde_json::json!({"filename": "b.rs"}))];
        let view = view_with(vec![turn]);
        let path = derive_path(&view, &DeriveConfig::default());
        assert!(path.steps[0].change.contains_key("b.rs"));
    }

    #[test]
    fn test_tool_use_filewrite_with_file_field() {
        let mut turn = base_turn("t1", Role::Assistant);
        turn.tool_uses = vec![fw_tool("W", "tu1", serde_json::json!({"file": "c.rs"}))];
        let view = view_with(vec![turn]);
        let path = derive_path(&view, &DeriveConfig::default());
        assert!(path.steps[0].change.contains_key("c.rs"));
    }

    #[test]
    fn test_tool_use_filewrite_no_recognized_field() {
        let mut turn = base_turn("t1", Role::Assistant);
        turn.tool_uses = vec![fw_tool("W", "tu1", serde_json::json!({"other": "foo"}))];
        let view = view_with(vec![turn]);
        let path = derive_path(&view, &DeriveConfig::default());
        assert_eq!(path.steps[0].change.len(), 1);
        let sc = conv_change(&path.steps[0]);
        assert!(sc.extra.contains_key("tool_uses"));
    }

    #[test]
    fn test_tool_use_non_filewrite_ignored() {
        let mut turn = base_turn("t1", Role::Assistant);
        turn.tool_uses = vec![ToolInvocation {
            id: "tu1".into(),
            name: "Read".into(),
            input: serde_json::json!({"file_path": "x.rs"}),
            result: None,
            category: Some(ToolCategory::FileRead),
        }];
        let view = view_with(vec![turn]);
        let path = derive_path(&view, &DeriveConfig::default());
        assert!(!path.steps[0].change.contains_key("x.rs"));
        assert_eq!(path.steps[0].change.len(), 1);
    }

    #[test]
    fn test_tool_use_edit_emits_unified_diff() {
        let mut turn = base_turn("t1", Role::Assistant);
        turn.tool_uses = vec![fw_tool(
            "Edit",
            "tu1",
            serde_json::json!({
                "file_path": "src/login.rs",
                "old_string": "validate_token()",
                "new_string": "validate_token_v2()",
            }),
        )];
        let view = view_with(vec![turn]);
        let path = derive_path(&view, &DeriveConfig::default());
        let ch = &path.steps[0].change["src/login.rs"];
        let raw = ch.raw.as_deref().expect("edit should emit unified diff");
        assert!(raw.contains("--- a/src/login.rs"));
        assert!(raw.contains("+++ b/src/login.rs"));
        assert!(raw.contains("-validate_token()"));
        assert!(raw.contains("+validate_token_v2()"));
        let sc = ch.structural.as_ref().unwrap();
        assert_eq!(sc.extra["before"], serde_json::json!("validate_token()"));
        assert_eq!(sc.extra["after"], serde_json::json!("validate_token_v2()"));
    }

    #[test]
    fn test_tool_use_write_emits_full_content_diff() {
        let mut turn = base_turn("t1", Role::Assistant);
        turn.tool_uses = vec![fw_tool(
            "Write",
            "tu1",
            serde_json::json!({
                "file_path": "hello.txt",
                "content": "hi\nthere\n",
            }),
        )];
        let view = view_with(vec![turn]);
        let path = derive_path(&view, &DeriveConfig::default());
        let ch = &path.steps[0].change["hello.txt"];
        let raw = ch.raw.as_deref().expect("write should emit diff");
        assert!(raw.contains("+hi"));
        assert!(raw.contains("+there"));
        let sc = ch.structural.as_ref().unwrap();
        assert_eq!(sc.extra["after"], serde_json::json!("hi\nthere\n"));
        assert!(!sc.extra.contains_key("before"));
    }

    #[test]
    fn test_file_write_diff_write_without_before_state_is_addition_only() {
        // Backwards-compatible fallback: `None` → diff against "".
        let input = serde_json::json!({
            "file_path": "hello.txt",
            "content": "hi\nthere\n",
        });
        let raw =
            file_write_diff("Write", &input, "hello.txt", None).expect("write should emit diff");
        assert!(raw.contains("+hi"));
        assert!(raw.contains("+there"));
        // No `-` lines — nothing was there before.
        assert!(
            !raw.lines()
                .any(|l| l.starts_with('-') && !l.starts_with("---"))
        );
    }

    #[test]
    fn test_file_write_diff_write_with_before_state_shows_replacement() {
        let input = serde_json::json!({
            "file_path": "hello.txt",
            "content": "hi\nthere\n",
        });
        let raw = file_write_diff("Write", &input, "hello.txt", Some("bye\nfriend\n"))
            .expect("write should emit diff");
        // Before content should appear as removals.
        assert!(raw.contains("-bye"));
        assert!(raw.contains("-friend"));
        // After content should appear as additions.
        assert!(raw.contains("+hi"));
        assert!(raw.contains("+there"));
    }

    #[test]
    fn test_file_write_diff_before_state_ignored_for_edit_shape() {
        // `Edit` has its own `old_string`; supplied before_state should
        // be ignored.
        let input = serde_json::json!({
            "file_path": "a.rs",
            "old_string": "foo",
            "new_string": "bar",
        });
        let raw = file_write_diff("Edit", &input, "a.rs", Some("something else entirely"))
            .expect("edit should emit diff");
        assert!(raw.contains("-foo"));
        assert!(raw.contains("+bar"));
        assert!(!raw.contains("something else entirely"));
    }

    #[test]
    fn test_unified_diff_strips_leading_slash_on_absolute_path() {
        // Regression for #36: headers for absolute paths must not contain `a//`.
        let raw = unified_diff("/abs/path.rs", "a\n", "b\n");
        assert!(
            raw.contains("--- a/abs/path.rs\n"),
            "missing stripped --- header: {raw}"
        );
        assert!(
            raw.contains("+++ b/abs/path.rs\n"),
            "missing stripped +++ header: {raw}"
        );
        assert!(
            !raw.contains("a//"),
            "header should not contain doubled slash: {raw}"
        );
        assert!(
            !raw.contains("b//"),
            "header should not contain doubled slash: {raw}"
        );
    }

    #[test]
    fn test_unified_diff_preserves_relative_path() {
        // Relative paths (no leading slash) are unchanged — only a single
        // leading `/` is stripped.
        let raw = unified_diff("src/login.rs", "a\n", "b\n");
        assert!(raw.contains("--- a/src/login.rs\n"), "{raw}");
        assert!(raw.contains("+++ b/src/login.rs\n"), "{raw}");
    }

    #[test]
    fn test_tool_use_multiedit_emits_per_hunk_diff() {
        let mut turn = base_turn("t1", Role::Assistant);
        turn.tool_uses = vec![fw_tool(
            "MultiEdit",
            "tu1",
            serde_json::json!({
                "file_path": "m.rs",
                "edits": [
                    {"old_string": "foo", "new_string": "bar"},
                    {"old_string": "baz", "new_string": "qux"},
                ],
            }),
        )];
        let view = view_with(vec![turn]);
        let path = derive_path(&view, &DeriveConfig::default());
        let ch = &path.steps[0].change["m.rs"];
        let raw = ch.raw.as_deref().expect("multiedit should emit diff");
        assert!(raw.contains("# edit 1/2"));
        assert!(raw.contains("# edit 2/2"));
        assert!(raw.contains("-foo"));
        assert!(raw.contains("+bar"));
        assert!(raw.contains("-baz"));
        assert!(raw.contains("+qux"));
    }

    #[test]
    fn test_thinking_included_when_enabled() {
        let mut turn = base_turn("t1", Role::Assistant);
        turn.thinking = Some("hmm".into());
        let view = view_with(vec![turn]);
        let path = derive_path(&view, &DeriveConfig::default());
        let sc = conv_change(&path.steps[0]);
        assert_eq!(sc.extra["thinking"], serde_json::json!("hmm"));
    }

    #[test]
    fn test_thinking_omitted_when_disabled() {
        let mut turn = base_turn("t1", Role::Assistant);
        turn.thinking = Some("hmm".into());
        let view = view_with(vec![turn]);
        let cfg = DeriveConfig {
            include_thinking: false,
            ..Default::default()
        };
        let path = derive_path(&view, &cfg);
        let sc = conv_change(&path.steps[0]);
        assert!(!sc.extra.contains_key("thinking"));
    }

    #[test]
    fn test_tool_uses_included_when_enabled() {
        let mut turn = base_turn("t1", Role::Assistant);
        turn.tool_uses = vec![ToolInvocation {
            id: "tu1".into(),
            name: "Read".into(),
            input: serde_json::json!({}),
            result: Some(ToolResult {
                content: "x".into(),
                is_error: false,
            }),
            category: Some(ToolCategory::FileRead),
        }];
        let view = view_with(vec![turn]);
        let path = derive_path(&view, &DeriveConfig::default());
        let sc = conv_change(&path.steps[0]);
        assert!(sc.extra.contains_key("tool_uses"));
    }

    #[test]
    fn test_tool_uses_omitted_when_disabled() {
        let mut turn = base_turn("t1", Role::Assistant);
        turn.tool_uses = vec![ToolInvocation {
            id: "tu1".into(),
            name: "Read".into(),
            input: serde_json::json!({}),
            result: None,
            category: Some(ToolCategory::FileRead),
        }];
        let view = view_with(vec![turn]);
        let cfg = DeriveConfig {
            include_tool_uses: false,
            ..Default::default()
        };
        let path = derive_path(&view, &cfg);
        let sc = conv_change(&path.steps[0]);
        assert!(!sc.extra.contains_key("tool_uses"));
    }

    #[test]
    fn test_base_uri_from_working_dir() {
        let mut turn = base_turn("t1", Role::User);
        turn.environment = Some(EnvironmentSnapshot {
            working_dir: Some("/Users/alex/proj".into()),
            ..Default::default()
        });
        let view = view_with(vec![turn]);
        let path = derive_path(&view, &DeriveConfig::default());
        assert_eq!(path.path.base.unwrap().uri, "file:///Users/alex/proj");
    }

    #[test]
    fn test_base_uri_from_config_override() {
        let mut turn = base_turn("t1", Role::User);
        turn.environment = Some(EnvironmentSnapshot {
            working_dir: Some("/Users/alex/proj".into()),
            ..Default::default()
        });
        let view = view_with(vec![turn]);
        let cfg = DeriveConfig {
            base_uri: Some("github:org/repo".into()),
            ..Default::default()
        };
        let path = derive_path(&view, &cfg);
        assert_eq!(path.path.base.unwrap().uri, "github:org/repo");
    }

    #[test]
    fn test_base_uri_absent_when_no_source() {
        let turn = base_turn("t1", Role::User);
        let view = view_with(vec![turn]);
        let path = derive_path(&view, &DeriveConfig::default());
        assert!(path.path.base.is_none());
    }

    #[test]
    fn test_path_id_from_config_override() {
        let view = view_with(vec![]);
        let cfg = DeriveConfig {
            path_id: Some("my-custom-id".into()),
            ..Default::default()
        };
        let path = derive_path(&view, &cfg);
        assert_eq!(path.path.id, "my-custom-id");
    }

    #[test]
    fn test_path_id_default_format() {
        let view = view_with(vec![]);
        let path = derive_path(&view, &DeriveConfig::default());
        assert_eq!(path.path.id, "path-pi-abcdef01");
    }

    #[test]
    fn test_files_changed_in_meta() {
        let mut view = view_with(vec![]);
        view.files_changed = vec!["a.rs".into(), "b.rs".into()];
        let path = derive_path(&view, &DeriveConfig::default());
        let meta = path.meta.unwrap();
        assert_eq!(
            meta.extra["files_changed"],
            serde_json::json!(["a.rs", "b.rs"])
        );
    }

    #[test]
    fn test_actors_in_meta() {
        let u = base_turn("t1", Role::User);
        let mut a = base_turn("t2", Role::Assistant);
        a.model = Some("claude-opus-4-7".into());
        let view = view_with(vec![u, a]);
        let path = derive_path(&view, &DeriveConfig::default());
        let actors = path.meta.unwrap().actors.unwrap();
        assert!(actors.contains_key("human:user"));
        assert!(actors.contains_key("agent:claude-opus-4-7"));
        let agent = &actors["agent:claude-opus-4-7"];
        assert_eq!(agent.provider.as_deref(), Some("pi"));
        assert_eq!(agent.model.as_deref(), Some("claude-opus-4-7"));
        let human = &actors["human:user"];
        assert_eq!(human.name.as_deref(), Some("user"));
    }

    #[test]
    fn test_head_is_last_step_id() {
        let turns = vec![
            base_turn("t1", Role::User),
            base_turn("t2", Role::User),
            base_turn("t3", Role::User),
        ];
        let view = view_with(turns);
        let path = derive_path(&view, &DeriveConfig::default());
        assert_eq!(path.path.head, "t3");
    }

    #[test]
    fn test_token_usage_in_extras() {
        let mut turn = base_turn("t1", Role::Assistant);
        turn.token_usage = Some(TokenUsage {
            input_tokens: Some(100),
            output_tokens: Some(50),
            cache_read_tokens: None,
            cache_write_tokens: None,
            ..Default::default()
        });
        let view = view_with(vec![turn]);
        let path = derive_path(&view, &DeriveConfig::default());
        let sc = conv_change(&path.steps[0]);
        assert!(sc.extra.contains_key("token_usage"));
        assert_eq!(
            sc.extra["token_usage"]["input_tokens"],
            serde_json::json!(100)
        );
    }

    fn usage(output: u32) -> TokenUsage {
        TokenUsage {
            input_tokens: Some(6),
            output_tokens: Some(output),
            cache_read_tokens: Some(14_842),
            cache_write_tokens: Some(429_831),
            ..Default::default()
        }
    }

    #[test]
    fn test_message_group_carries_usage_once_on_last_step() {
        // Three turns split from one provider message (Claude Code repeats
        // message.usage on every content-block line), then one singleton
        // message. Usage must land exactly once per group_id group — on
        // the group's last step — and group_id on every grouped step.
        let mut turns: Vec<Turn> = (1..=3)
            .map(|i| {
                let mut t = base_turn(&format!("t{i}"), Role::Assistant);
                t.group_id = Some("msg_01".into());
                t.token_usage = Some(usage(997));
                t
            })
            .collect();
        let mut t4 = base_turn("t4", Role::Assistant);
        t4.group_id = Some("msg_02".into());
        t4.token_usage = Some(usage(11));
        turns.push(t4);

        let view = view_with(turns);
        let path = derive_path(&view, &DeriveConfig::default());
        let changes: Vec<&StructuralChange> = path.steps.iter().map(conv_change).collect();

        assert!(!changes[0].extra.contains_key("token_usage"));
        assert!(!changes[1].extra.contains_key("token_usage"));
        assert_eq!(
            changes[2].extra["token_usage"]["output_tokens"],
            serde_json::json!(997)
        );
        assert_eq!(
            changes[3].extra["token_usage"]["output_tokens"],
            serde_json::json!(11)
        );
        for c in &changes[..3] {
            assert_eq!(c.extra["group_id"], serde_json::json!("msg_01"));
        }
        assert_eq!(changes[3].extra["group_id"], serde_json::json!("msg_02"));
    }

    #[test]
    fn test_turn_without_group_id_is_its_own_accounting_unit() {
        // Providers that never split a message (gemini, pi, opencode)
        // leave group_id unset; every turn keeps its own usage.
        let mut turns = Vec::new();
        for i in 1..=2 {
            let mut t = base_turn(&format!("t{i}"), Role::Assistant);
            t.token_usage = Some(usage(50 + i));
            turns.push(t);
        }
        let view = view_with(turns);
        let path = derive_path(&view, &DeriveConfig::default());
        for (i, step) in path.steps.iter().enumerate() {
            let sc = conv_change(step);
            assert_eq!(
                sc.extra["token_usage"]["output_tokens"],
                serde_json::json!(51 + i as u64)
            );
            assert!(!sc.extra.contains_key("group_id"));
        }
    }

    #[test]
    fn test_message_grouping_is_consecutive_only() {
        // A group_id reappearing after an intervening message starts a
        // new group (defensive: source formats never interleave, but the
        // rule is defined over consecutive runs in document order).
        let mk = |id: &str, msg: &str, out: u32| {
            let mut t = base_turn(id, Role::Assistant);
            t.group_id = Some(msg.into());
            t.token_usage = Some(usage(out));
            t
        };
        let view = view_with(vec![
            mk("t1", "msg_01", 100),
            mk("t2", "msg_02", 200),
            mk("t3", "msg_01", 300),
        ]);
        let path = derive_path(&view, &DeriveConfig::default());
        let changes: Vec<&StructuralChange> = path.steps.iter().map(conv_change).collect();
        assert_eq!(
            changes[0].extra["token_usage"]["output_tokens"],
            serde_json::json!(100)
        );
        assert_eq!(
            changes[1].extra["token_usage"]["output_tokens"],
            serde_json::json!(200)
        );
        assert_eq!(
            changes[2].extra["token_usage"]["output_tokens"],
            serde_json::json!(300)
        );
    }

    #[test]
    fn test_delegations_in_extras() {
        let mut turn = base_turn("t1", Role::Assistant);
        turn.delegations = vec![DelegatedWork {
            agent_id: "sub-1".into(),
            prompt: "do a thing".into(),
            turns: vec![],
            result: None,
        }];
        let view = view_with(vec![turn]);
        let path = derive_path(&view, &DeriveConfig::default());
        let sc = conv_change(&path.steps[0]);
        assert!(sc.extra.contains_key("delegations"));
        assert_eq!(
            sc.extra["delegations"][0]["agent_id"],
            serde_json::json!("sub-1")
        );
    }

    #[test]
    fn test_title_from_config() {
        let view = view_with(vec![]);
        let cfg = DeriveConfig {
            title: Some("My Session".into()),
            ..Default::default()
        };
        let path = derive_path(&view, &cfg);
        assert_eq!(path.meta.unwrap().title.as_deref(), Some("My Session"));
    }

    #[test]
    fn test_title_default_when_unset() {
        let view = view_with(vec![]);
        let path = derive_path(&view, &DeriveConfig::default());
        assert_eq!(
            path.meta.unwrap().title.as_deref(),
            Some("pi session: abcdef01")
        );
    }

    #[test]
    fn test_serde_roundtrip() {
        let mut t1 = base_turn("t1", Role::User);
        t1.text = "hello".into();
        t1.environment = Some(EnvironmentSnapshot {
            working_dir: Some("/proj".into()),
            ..Default::default()
        });
        let mut t2 = base_turn("t2", Role::Assistant);
        t2.parent_id = Some("t1".into());
        t2.model = Some("m".into());
        t2.tool_uses = vec![fw_tool(
            "Write",
            "tu1",
            serde_json::json!({"file_path": "x.rs"}),
        )];

        let mut view = view_with(vec![t1, t2]);
        view.files_changed = vec!["x.rs".into()];

        let path = derive_path(&view, &DeriveConfig::default());
        let json = serde_json::to_string(&path).unwrap();
        let back: Path = serde_json::from_str(&json).unwrap();
        assert_eq!(back.path.id, path.path.id);
        assert_eq!(back.path.head, path.path.head);
        assert_eq!(back.steps.len(), 2);
        assert_eq!(back.steps[1].step.parents, vec!["t1".to_string()]);
        assert!(back.steps[1].change.contains_key("x.rs"));
    }
}