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

packages/protocol/src/messages.ts

@@ -748,6 +748,7 @@ export const AgentStreamEventPayloadSchema = z.discriminatedUnion("type", [
     type: z.literal("timeline"),
     provider: AgentProviderSchema,
     item: AgentTimelineItemPayloadSchema,
+    turnId: z.string().optional(),
   }),
   z.object({
     type: z.literal("permission_requested"),
@@ -1138,11 +1139,15 @@ const ImageAttachmentSchema = z.object({
   mimeType: z.string(), // e.g., "image/jpeg", "image/png"
 });
 
+export const ActiveTurnBehaviorSchema = z.enum(["interrupt", "steer"]);
+export type ActiveTurnBehavior = z.infer<typeof ActiveTurnBehaviorSchema>;
+
 export const SendAgentMessageSchema = z.object({
   type: z.literal("send_agent_message"),
   agentId: z.string(),
   text: z.string(),
   messageId: z.string().optional(), // Client-provided ID for deduplication
+  activeTurnBehavior: ActiveTurnBehaviorSchema.optional(),
   images: z.array(ImageAttachmentSchema).optional(),
   attachments: AgentAttachmentsSchema,
 });
@@ -1295,6 +1300,7 @@ export const SendAgentMessageRequestSchema = z.object({
   agentId: z.string(),
   text: z.string(),
   messageId: z.string().optional(), // Client-provided ID for deduplication
+  activeTurnBehavior: ActiveTurnBehaviorSchema.optional(),
   images: z.array(ImageAttachmentSchema).optional(),
   attachments: AgentAttachmentsSchema,
 });
@@ -4035,6 +4041,7 @@ const AgentTimelineSeqRangeSchema = z.object({
 export const AgentTimelineEntryPayloadSchema = z.object({
   provider: AgentProviderSchema,
   item: AgentTimelineItemPayloadSchema,
+  turnId: z.string().optional(),
   timestamp: z.string(),
   seqStart: z.number().int().nonnegative(),
   seqEnd: z.number().int().nonnegative(),