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.

packages/core/session/src/index.ts

@@ -155,7 +155,6 @@ export function snapshotSessionEvent<T extends SessionEvent>(event: T): T {
       break
     case 'assistant/message':
     case 'tool/result':
-    case 'steering/message':
       deepFreeze(snapshot.data.message)
       break
     default:
@@ -207,7 +206,7 @@ function assertCurrentLlmShape(event: Record<string, unknown>, index: number): v
   }
   const type = event['type']
   if (type !== 'user/message' && type !== 'assistant/message'
-    && type !== 'tool/result' && type !== 'steering/message') return
+    && type !== 'tool/result') return
   assertMessageEventShape(event, `seed ${type} at index ${index}`)
 }
 
@@ -235,7 +234,7 @@ function assertAdapterDefaults(
 function assertMessageEventShape(event: Record<string, unknown>, subject: string): void {
   const type = event['type']
   if (type !== 'user/message' && type !== 'assistant/message'
-    && type !== 'tool/result' && type !== 'steering/message') return
+    && type !== 'tool/result') return
   const data = event['data']
   const record = typeof data === 'object' && data !== null
     ? data as Record<string, unknown>
@@ -665,10 +664,9 @@ export class Session {
     // trace/replay data.
 
     switch (event.type) {
-      // Ordinary prompts, injected context, and mid-turn steering project
-      // identically in user role: the event's model-facing content stays
-      // verbatim. Steering's `turn` is log-only. Do NOT
-      // re-add per-type framing (e.g. `<context>`/`<steering>`) here: framing is
+      // Ordinary prompts and injected context project in user role: the
+      // event's model-facing content stays verbatim. Do NOT
+      // re-add per-type framing (e.g. `<context>`) here: framing is
       // caller-owned — a producer bakes it into `content`, as workspace-context
       // does with `<system-reminder>` — or, if reintroduced, must be driven by
       // the event `meta` map and a dedicated renderer, keeping this projection a
@@ -677,9 +675,6 @@ export class Session {
       case 'user/message': {
         return event.data
       }
-      case 'steering/message': {
-        return event.data.message
-      }
       case 'assistant/message': {
         // Skip an empty-content assistant/message: it exists only to host a
         // max-tokens step's usage and must not inject a content-less assistant
@@ -747,7 +742,7 @@ export class SessionStore extends Service {
    * {@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).
@@ -779,7 +774,7 @@ export class SessionStore extends Service {
    * `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.