fix(events): address Codex confirmation review — strengthen /goal guard, fix doc drift

Second-round Codex review of the PR-A taxonomy change found four issues, all
verified against the code:

- The /goal regression guard asserted only that the steered content reached
  requests[1], which passes even with the hasSteering override (loop.ts) disabled:
  leftover steering is re-enqueued as a next-turn queued message and also lands in
  requests[1], one turn later. The guard now asserts the same-turn shape — ONE
  turn, TWO steps, a steering/message recorded before step 2 — which is the
  mechanism the override drives. Proven to fail red with the override disabled.
- The event-domain-semantics RFC's consequence list still described the pre-fix
  behavior (step marked open AFTER step/start, so no step/end owed). It now states
  the shipped behavior: the loop marks the step open BEFORE the append, so a
  throwing step/start listener gets a balancing step/end via closeStep().
- architecture.md's loop pseudocode said only continuation listeners force
  continuation; step/end session-event listeners (the /goal pattern) do too.
- The agent/turn-end JSDoc listed a `rejected` TurnEndReason that does not exist on
  this branch (it belongs to the later interception work). Removed it and
  regenerated the cordis catalog; `interrupted` (a real variant) stays.

packages/core/agent/src/types.ts

@@ -197,8 +197,9 @@ declare module 'cordis' {
     'agent/turn-start'(agent: Agent, turn: number): void
     /**
      * A turn ended. `reason` distinguishes a clean stop from a truncated,
-     * aborted, or hook-rejected one (`completed` | `aborted` | `error` |
-     * `disposed` | `max-tokens` | `rejected` | `interrupted`).
+     * aborted, failed, disposed, or crash-interrupted one (`completed` |
+     * `aborted` | `error` | `disposed` | `max-tokens` | `interrupted`); the
+     * reason union is merge-extensible, so a plugin can add further variants.
      * @mode emit
      */
     'agent/turn-end'(agent: Agent, turn: number, reason: TurnEndReason): void