fix: relay ACP sessions_spawn parent streaming (#34310) (thanks @vincentkoc) (#34310)

Co-authored-by: Onur Solmaz <2453968+osolmaz@users.noreply.github.com>

src/agents/acp-spawn.ts

@@ -32,12 +32,19 @@ import {
 } from "../infra/outbound/session-binding-service.js";
 import { normalizeAgentId } from "../routing/session-key.js";
 import { normalizeDeliveryContext } from "../utils/delivery-context.js";
+import {
+  type AcpSpawnParentRelayHandle,
+  resolveAcpSpawnStreamLogPath,
+  startAcpSpawnParentStreamRelay,
+} from "./acp-spawn-parent-stream.js";
 import { resolveSandboxRuntimeStatus } from "./sandbox/runtime-status.js";
 
 export const ACP_SPAWN_MODES = ["run", "session"] as const;
 export type SpawnAcpMode = (typeof ACP_SPAWN_MODES)[number];
 export const ACP_SPAWN_SANDBOX_MODES = ["inherit", "require"] as const;
 export type SpawnAcpSandboxMode = (typeof ACP_SPAWN_SANDBOX_MODES)[number];
+export const ACP_SPAWN_STREAM_TARGETS = ["parent"] as const;
+export type SpawnAcpStreamTarget = (typeof ACP_SPAWN_STREAM_TARGETS)[number];
 
 export type SpawnAcpParams = {
   task: string;
@@ -47,6 +54,7 @@ export type SpawnAcpParams = {
   mode?: SpawnAcpMode;
   thread?: boolean;
   sandbox?: SpawnAcpSandboxMode;
+  streamTo?: SpawnAcpStreamTarget;
 };
 
 export type SpawnAcpContext = {
@@ -63,6 +71,7 @@ export type SpawnAcpResult = {
   childSessionKey?: string;
   runId?: string;
   mode?: SpawnAcpMode;
+  streamLogPath?: string;
   note?: string;
   error?: string;
 };
@@ -234,6 +243,14 @@ export async function spawnAcpDirect(
     };
   }
   const sandboxMode = params.sandbox === "require" ? "require" : "inherit";
+  const streamToParentRequested = params.streamTo === "parent";
+  const parentSessionKey = ctx.agentSessionKey?.trim();
+  if (streamToParentRequested && !parentSessionKey) {
+    return {
+      status: "error",
+      error: 'sessions_spawn streamTo="parent" requires an active requester session context.',
+    };
+  }
   const requesterRuntime = resolveSandboxRuntimeStatus({
     cfg,
     sessionKey: ctx.agentSessionKey,
@@ -410,8 +427,27 @@ export async function spawnAcpDirect(
     ? `channel:${boundThreadId}`
     : requesterOrigin?.to?.trim() || (deliveryThreadId ? `channel:${deliveryThreadId}` : undefined);
   const hasDeliveryTarget = Boolean(requesterOrigin?.channel && inferredDeliveryTo);
+  const deliverToBoundTarget = hasDeliveryTarget && !streamToParentRequested;
   const childIdem = crypto.randomUUID();
   let childRunId: string = childIdem;
+  const streamLogPath =
+    streamToParentRequested && parentSessionKey
+      ? resolveAcpSpawnStreamLogPath({
+          childSessionKey: sessionKey,
+        })
+      : undefined;
+  let parentRelay: AcpSpawnParentRelayHandle | undefined;
+  if (streamToParentRequested && parentSessionKey) {
+    // Register relay before dispatch so fast lifecycle failures are not missed.
+    parentRelay = startAcpSpawnParentStreamRelay({
+      runId: childIdem,
+      parentSessionKey,
+      childSessionKey: sessionKey,
+      agentId: targetAgentId,
+      logPath: streamLogPath,
+      emitStartNotice: false,
+    });
+  }
   try {
     const response = await callGateway<{ runId?: string }>({
       method: "agent",
@@ -423,7 +459,7 @@ export async function spawnAcpDirect(
         accountId: hasDeliveryTarget ? (requesterOrigin?.accountId ?? undefined) : undefined,
         threadId: hasDeliveryTarget ? deliveryThreadId : undefined,
         idempotencyKey: childIdem,
-        deliver: hasDeliveryTarget,
+        deliver: deliverToBoundTarget,
         label: params.label || undefined,
       },
       timeoutMs: 10_000,
@@ -432,6 +468,7 @@ export async function spawnAcpDirect(
       childRunId = response.runId.trim();
     }
   } catch (err) {
+    parentRelay?.dispose();
     await cleanupFailedAcpSpawn({
       cfg,
       sessionKey,
@@ -445,6 +482,30 @@ export async function spawnAcpDirect(
     };
   }
 
+  if (streamToParentRequested && parentSessionKey) {
+    if (parentRelay && childRunId !== childIdem) {
+      parentRelay.dispose();
+      // Defensive fallback if gateway returns a runId that differs from idempotency key.
+      parentRelay = startAcpSpawnParentStreamRelay({
+        runId: childRunId,
+        parentSessionKey,
+        childSessionKey: sessionKey,
+        agentId: targetAgentId,
+        logPath: streamLogPath,
+        emitStartNotice: false,
+      });
+    }
+    parentRelay?.notifyStarted();
+    return {
+      status: "accepted",
+      childSessionKey: sessionKey,
+      runId: childRunId,
+      mode: spawnMode,
+      ...(streamLogPath ? { streamLogPath } : {}),
+      note: spawnMode === "session" ? ACP_SPAWN_SESSION_ACCEPTED_NOTE : ACP_SPAWN_ACCEPTED_NOTE,
+    };
+  }
+
   return {
     status: "accepted",
     childSessionKey: sessionKey,