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.

docs/architecture.md

@@ -151,7 +151,8 @@ forever:
       drain steering → session('steering/message'); emit agent/steering
       session('step/end')                             ⟵ durable step boundary (no agent/* mirror)
       cont = waterfall agent/turn-continuation(default = hadToolCalls || steered)
-      steering pending from continuation listeners forces cont = true
+      steering pending forces cont = true (from continuation listeners OR from
+        step/end session-event listeners — the /goal pattern; hasSteering override)
       if !cont: break
   session('turn/end'); emit agent/turn-end
   await ctx.parallel('session/flush', session)        ⟵ durability checkpoint (failure