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/host/apiproxy/README.md

@@ -10,7 +10,7 @@ Wire messages form a four-quadrant discriminated union — who initiates × requ
 
 The layering/protocol decisions are recorded in the [GUI layering and RPC protocol RFC](../../../.agents/notes/implemented/architecture/2026-07-19-gui-layering-and-rpc-protocol.md); the browser-side consumption architecture in the [web client architecture RFC](../../../.agents/notes/implemented/architecture/2026-07-19-gui-web-client-architecture.md).
 
-`session.history` pages on append-origin message boundaries: `maxMessages` counts `user/message`, `assistant/message`, and `steering/message` events that entered the surface by appending, so a model-only replacement copy consumes no quota. Each page stays one contiguous raw event range, which keeps a compaction's log-only provenance on the same page as the replacement that cites it.
+`session.history` pages on append-origin message boundaries: `maxMessages` counts `user/message` and `assistant/message` events that entered the surface by appending, so a model-only replacement copy consumes no quota. Each page stays one contiguous raw event range, which keeps a compaction's log-only provenance on the same page as the replacement that cites it.
 
 `session.history`'s tail page (`beforeSeq` absent) additionally carries an optional `projections` block — the watermark snapshot of every unit registered on `ctx.sessionProjections` (`@deepseek-ai/dsh-session-projection`), with `asOfSeq` = the last event seq the values reflect (`-1` on an empty log). The gateway also subscribes to the registry's change feed and mints a `session/projection` mux frame per changed unit (`{sessionId, key, value, seq}` — live push state, never logged; clients hold one generic per-session value store under higher-seq-wins). The carrier holds zero domain knowledge (each value passed its unit's own schema inside the registry; the wire schemas keep `values`/`value` wide); loadOlder pages never carry the block, and a composition without the registry serves histories without either surface.
 

packages/host/apiproxy/README.zh.md

@@ -10,7 +10,7 @@
 
 分层与协议决策记录在 [GUI 分层与 RPC 协议 RFC](../../../.agents/notes/implemented/architecture/2026-07-19-gui-layering-and-rpc-protocol.md)中；浏览器侧消费架构记录在 [Web 客户端架构 RFC](../../../.agents/notes/implemented/architecture/2026-07-19-gui-web-client-architecture.md)中。
 
-`session.history` 按追加来源的消息边界分页：`maxMessages` 统计以追加方式进入 surface 的 `user/message`、`assistant/message` 和 `steering/message` 事件，因此仅供模型使用的替换副本不占用配额。每一页仍是一段连续的原始事件区间，从而让压缩（compaction）的仅日志溯源信息与引用它的替换留在同一页。
+`session.history` 按追加来源的消息边界分页：`maxMessages` 统计以追加方式进入 surface 的 `user/message` 和 `assistant/message` 事件，因此仅供模型使用的替换副本不占用配额。每一页仍是一段连续的原始事件区间，从而让压缩（compaction）的仅日志溯源信息与引用它的替换留在同一页。
 
 `session.history` 的尾页（不带 `beforeSeq`）额外携带一个可选的 `projections` 块——`ctx.sessionProjections`（`@deepseek-ai/dsh-session-projection`）上每个已注册单元的水位线快照，`asOfSeq` = 这些值共同反映到的最后一个事件 seq（空日志为 `-1`）。网关还订阅注册表的变更流，为每个状态发生变化的单元铸造一个 `session/projection` mux 帧（`{sessionId, key, value, seq}`——实时推送状态，绝不入日志；客户端按 seq 高者胜维护一个按会话的通用值仓）。载体不持有任何领域知识（每个值在注册表内部已过其单元自己的 schema；协议 schema 对 `values`/`value` 保持宽松）；loadOlder 页永不携带该块，未装注册表的组合则两个面都不提供。
 

packages/host/apiproxy/src/api-proxy.ts

@@ -83,7 +83,7 @@ const SESSION_SEARCH_PROVIDER_CALL_LIMIT = 100
 const COLD_SUMMARY_BATCH_SIZE = 16
 
 /** Conversation message event types (the pagination counting unit). */
-const MESSAGE_TYPES = new Set(['user/message', 'assistant/message', 'steering/message'])
+const MESSAGE_TYPES = new Set(['user/message', 'assistant/message'])
 
 /** Product settings intentionally exposed beside model-provider namespaces. */
 const PRODUCT_SETTINGS_NAMESPACES = new Set(['ui-onboarding'])
@@ -1453,7 +1453,7 @@ export function createApiProxy(ctx: Context, defaults: ApiProxyDefaults): ApiPro
               page = await sessionQuery.searchSessions({
                 query: request.payload.query,
                 eventFilters: [
-                  { kind: 'type', values: ['user/message', 'assistant/message', 'steering/message'] },
+                  { kind: 'type', values: ['user/message', 'assistant/message'] },
                   { kind: 'surface', values: ['current'] },
                 ],
                 limit: requestedPageLimit,

packages/host/apiproxy/tests/api-proxy-search.spec.ts

@@ -138,7 +138,7 @@ describe('session.search', () => {
       eventFilters: [
         {
           kind: 'type',
-          values: ['user/message', 'assistant/message', 'steering/message'],
+          values: ['user/message', 'assistant/message'],
         },
         { kind: 'surface', values: ['current'] },
       ],
@@ -182,7 +182,7 @@ describe('session.search', () => {
           withBestMatch(0, { sessionId: sid('hidden') }),
           withBestMatch(1, { surface: 'shadowed' }),
           withBestMatch(2, { type: 'tool/result' }),
-          withBestMatch(3, { type: 'steering/message', snippet: 'allowed snippet' }),
+          withBestMatch(3, { type: 'user/message', snippet: 'allowed snippet' }),
         ],
       }),
     } as never)