refactor(agent-loop): drop the steering/message session event

Steer, inject, and followup now land as durable user/message events on the
session surface; the steering/message event type and its ConversationNode
kind are removed from the client projection. Update tests, docs, generated
catalogs, and agent notes to match, and align the steering e2e fixture and
prompt inventory assertions with the durable user/message landing.

docs/cordis-catalog/services.md

@@ -1570,7 +1570,7 @@ Persistence is intentionally not implemented here — persistence plugins subscr
  * {@link SessionHeader} (the store fills `version`/`id`/`createdAt`).
  *
  * For an agent whose session must be torn down IN ORDER with its loop (so the
- * loop's final flush is captured before the store attachment ends), do NOT use this
+ * loop's final events are published before the store attachment ends), do NOT use this
  * — fold the session lifecycle into the agent's own effect via
  * {@link prepare} + {@link enter} + {@link announce} (see
  * `dsh-agent-loop`'s creation transaction).
@@ -1591,7 +1591,7 @@ create(id?: SessionId, options?: CreateSessionOptions): Session
  * `ctx.effect` (the agent factory) folds the session lifecycle into that ONE
  * effect so a fiber unload tears the session + agent down as a single ORDERED
  * chain rather than as racing sibling effects — which would remove the publication hooks
- * before the loop's closing `session/flush`, dropping the closing events.
+ * before the driver's closing events commit, dropping them.
  *
  * @param id - the session id; omitted, the store mints `session-<n>`.
  * @param options - seed events and/or creation metadata for the header.
@@ -1681,7 +1681,7 @@ fork(source: SessionForkSource, boundary?: number, childSessionId?: SessionId):
 
 Types: [CreateSessionOptions](../core-data-structures/persistence.md) · [Session](../core-data-structures/session.md) · [SessionId](../core-data-structures/core.md)
 
-Source: [`packages/core/session/src/index.ts:733`](../../packages/core/session/src/index.ts)
+Source: [`packages/core/session/src/index.ts:728`](../../packages/core/session/src/index.ts)
 
 ## `ctx.sessionTitle` — `SessionTitleService`