Merge remote-tracking branch 'origin/worktree-hooks-b-bash-seam' into worktree-hooks-c-interception

# Conflicts:
#	docs/architecture.md
#	packages/core/agent-loop/README.md

packages/core/session/README.md

@@ -8,7 +8,7 @@ Creates and holds event-sourced `Session` instances. Persistence is intentionall
 
 ### Public API
 
-- `ctx.sessions.create(id?: SessionId, options?: { seed?: SessionEvent[]; meta?: { cwd?: string; parentSession?: SessionId; createdAt?: number } }): Session` — Create a session. `options.seed` replays/forks an existing event log; `options.meta` attaches creation metadata (validated absolute `cwd`, `parentSession` lineage) as the immutable `SessionHeader`. The store fills `version`/`id` and defaults `createdAt` to now; a caller reconstructing a persisted session passes the original `createdAt` to preserve it. Disposed with the calling fiber.
+- `ctx.sessions.create(id?: SessionId, options?: { seed?: SessionEvent[]; meta?: { cwd?: string; parentSession?: SessionId; createdAt?: number; seedLength?: number } }): Session` — Create a session. `options.seed` replays/forks an existing event log; `options.meta` attaches creation metadata (validated absolute `cwd`, `parentSession` lineage, seed boundary) as the immutable `SessionHeader`. The store fills `version`/`id` and defaults `createdAt` to now; a caller reconstructing a persisted session passes the original `createdAt` and persisted `seedLength` to preserve them. Disposed with the calling fiber.
 - `ctx.sessions.get(id: SessionId): Session | undefined`
 - `ctx.sessions.list(): Session[]`
 
@@ -38,7 +38,7 @@ Plain class (not a Cordis Service). Create via `ctx.sessions.create()`.
 - `session.deriveMessages(): Message[]` — derive the LLM message history by walking the surface linked list (skipping non-surface events like chunks and boundaries; a `replace` shadows the nodes it covers). The surface is the single source of derived history — there is no raw-log fallback.
 - `session.surface: SurfaceManager` — the derived surface, lazily rebuilt from `surfaceOp` markers in the log. Processes only new events (delta) on each access — the log is append-only, so prior events never change.
 - `session.events`, `session.seq`, `session.id`
-- `session.header: SessionHeader` — immutable creation metadata (`version`, `id`, `createdAt`, optional `cwd`/`parentSession`). Kept out of the event log (a storage concern, not replayable state); a minimal header (stamped with the current `SESSION_FORMAT_VERSION`) is synthesized for bare `Session` construction.
+- `session.header: SessionHeader` — immutable creation metadata (`version`, `id`, `createdAt`, optional `cwd`/`parentSession`/`seedLength`). Kept out of the event log (a storage concern, not replayable state); a minimal header (stamped with the current `SESSION_FORMAT_VERSION`) is synthesized for bare `Session` construction.
 
 ### Surface types
 
@@ -49,9 +49,9 @@ Plain class (not a Cordis Service). Create via `ctx.sessions.create()`.
 
 ### Session event vocabulary (`types.ts`)
 
-The append-only log: `turn/start`, `turn/end`, `step/start`, `step/end`, `user/message`, `assistant/message`, `assistant/chunk`, `tool/call`, `tool/result`, `steering/message`, `context/message`. Token usage rides on `assistant/message.usage`; an operational error's step is on `turn/end.reason` for `kind: 'error'`.
+The append-only log: `turn/start`, `turn/end`, `step/start`, `step/end`, `user/message`, `assistant/message`, `assistant/chunk`, `tool/call`, `tool/result`, `steering/message`, `context/message`, `todo/write`. Token usage rides on `assistant/message.usage`; an operational error's step is on `turn/end.reason` for `kind: 'error'`.
 
-Merge-extensible via `SessionEventMap` — a compaction plugin adds `compaction/marker`, etc.
+Merge-extensible via `SessionEventMap` — the compaction seam adds `compact/start`, `compact/summary`, and `compact/end`.
 
 Also defines `TurnTriggerMap` and `TurnEndReasonMap` (merge-extensible sum types for typed turn boundaries — `kind`-tagged instead of strings).
 
@@ -62,7 +62,7 @@ Every `SessionEvent` carries two optional top-level fields (structural metadata)
 
 ### Metadata types (`types.ts`)
 
-- `SessionHeader` — immutable session metadata, written once: `{ version, id, createdAt, cwd?, parentSession? }`. Owned here (beside `SessionId`) because `Session.header` is typed by it; persistence backends re-export it rather than own it (which would force a package cycle).
+- `SessionHeader` — immutable session metadata, written once: `{ version, id, createdAt, cwd?, parentSession?, seedLength? }`. Owned here (beside `SessionId`) because `Session.header` is typed by it; persistence backends re-export it rather than own it (which would force a package cycle).
 
 ### Extension points
 

packages/core/session/src/index.ts

@@ -95,12 +95,12 @@ export class Session {
   }
 
   /**
-   * Immutable creation metadata (format version, cwd, lineage). Supplied by
-   * the store via `ctx.sessions.create()`. When a `Session` is constructed
-   * bare (tests, ad-hoc replay), a minimal header is synthesized (stamped with
-   * the current {@link SESSION_FORMAT_VERSION}) so `session.header` is always
-   * present. Kept out of the event log — it is a storage concern, not
-   * replayable conversation state.
+   * Immutable creation metadata (format version, cwd, lineage, seed boundary).
+   * Supplied by the store via `ctx.sessions.create()`. When a `Session` is
+   * constructed bare (tests, ad-hoc replay), a minimal header is synthesized
+   * (stamped with the current {@link SESSION_FORMAT_VERSION}) so
+   * `session.header` is always present. Kept out of the event log — it is a
+   * storage concern, not replayable conversation state.
    */
   readonly header: SessionHeader