Add active-turn steering (#3394)

* feat(agents): add active-turn steering

Let users choose whether an immediate prompt interrupts or joins the active turn. The daemon owns exact-turn admission, provider delivery, safe fallback, and canonical timeline identity while queueing remains client-side.

* fix(agents): stabilize steering history and replay QA

* fix(agents): preserve steering timeline order

* fix(agents): reconcile resumed provider history

* fix(agents): serialize steering with cancellation

* test(agents): prove Claude multi-tool steering

* test(agents): force explicit history hydration

* fix(agents): flush output before steer admission

docs/providers.md

@@ -81,6 +81,8 @@ OpenCode owns user message IDs. Do not pass Paseo-generated IDs to OpenCode prom
 
 `AgentManager` owns the one canonical timeline row for a foreground prompt carrying a Paseo `clientMessageId`. It records that row when `startTurn` accepts, with the wire `messageId` set to the same value. Provider adapters still emit their native user-message echo with the same `clientMessageId` when available; the manager records its provider identity on the internal row without changing or redispatching the wire item. If an adapter emits the echo before `startTurn` resolves, the manager records the provider identity with the row at acceptance. Provider adapters continue to own externally initiated user rows that have no Paseo client identity. Do not perform global transcript text dedupe.
 
+Active-turn steering is an optional `AgentSession.steerActiveTurn` operation. The manager owns admission against its exact foreground turn, canonical user-message creation, echo reconciliation, and falls back to the normal interrupt-and-replace path only when the adapter reports `unavailable`. An adapter error is ambiguous delivery and must surface without an interrupt or retry. Codex calls `turn/steer` with the native expected turn and Paseo client user-message ID. Claude pushes an admitted steer into the exact active SDK query input; isolated control commands remain unavailable. The released OpenCode v1 adapter does not implement this operation.
+
 Rewind accepts the canonical wire `messageId` and resolves it to the provider identity before calling the adapter. A submitted prompt cannot be rewound until its provider echo supplies that identity.
 
 Submitted user-message wire items carry the same Paseo ID in `messageId` and `clientMessageId`. Provider adapters attach `clientMessageId` only to the echo for that foreground submission; provider history and externally initiated user rows do not have a Paseo client ID.
@@ -424,6 +426,7 @@ interface AgentSession {
   readonly features?: AgentFeature[];
   run(prompt: AgentPromptInput, options?: AgentRunOptions): Promise<AgentRunResult>;
   startTurn(prompt: AgentPromptInput, options?: AgentRunOptions): Promise<{ turnId: string }>;
+  steerActiveTurn?(prompt: AgentPromptInput, options: SteerActiveTurnOptions): Promise<SteerResult>;
   subscribe(callback: (event: AgentStreamEvent) => void): () => void;
   streamHistory(): AsyncGenerator<AgentStreamEvent>;
   getRuntimeInfo(): Promise<AgentRuntimeInfo>;