fix review findings: sync stale v1/removed-event doc references

Codex's re-confirmation pass verified both blocker fixes correct but found
doc/comment drift the fix commit missed:

- session/index.ts + session/README.md: "minimal v1 header" → "minimal header
  (stamped with the current SESSION_FORMAT_VERSION)" — the version is 0, not 1.
- session/index.ts deriveMessages comment listed "usage, and errors" as trace
  data — those standalone events no longer exist; only boundaries + chunks are.
- session-persistence RFC: "no v1 migration" → the pinned-v0 pre-release stance.
- collapse-trace-only RFC format-version note: reframed off the "bump the
  version and reject" wording (which now reads as the OTHER AGENTS.md stance)
  onto the pinned-0 unstable stance the session log actually uses.
- agent-loop/loop.ts finishError JSDoc: "with a logged `error` event" → the
  failure is recorded on turn/end.reason (no standalone error event).
- acp/acp-feature-support.md (two spots): usage is recorded on assistant/message
  now, not as standalone internal usage events.
- Regenerate the cordis catalog (finishError JSDoc line shift).

packages/core/session/src/index.ts

@@ -79,9 +79,10 @@ 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 v1 header is synthesized so
-   * `session.header` is always present. Kept out of the event log — it is a
-   * storage concern, not replayable conversation state.
+   * 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
 
@@ -180,8 +181,7 @@ export class Session {
     const messages: Message[] = []
     for (const event of this.log) {
       // Intentionally non-exhaustive: only message-producing events derive
-      // history; turn/step boundaries, chunks, usage, and errors are
-      // trace/replay data.
+      // history; turn/step boundaries and chunks are trace/replay data.
       // eslint-disable-next-line @typescript-eslint/switch-exhaustiveness-check
       switch (event.type) {
         case 'user/message': {