fix: convert executeSyncTask to async prompt + polling pattern

Oracle agent (and all sync subagent tasks) fails with JSON Parse
error in ACP environments because session.prompt() (blocking HTTP)
returns empty/incomplete responses.

Replace promptSyncWithModelSuggestionRetry with promptWithModelSuggestionRetry
(async, fire-and-forget) and add polling loop to wait for response
stability, matching the proven pattern from executeUnstableAgentTask.

Fixes #1681

signatures/cla.json

@@ -1239,6 +1239,30 @@
       "created_at": "2026-02-08T02:34:46Z",
       "repoId": 1108837393,
       "pullRequestNo": 1641
+    },
+    {
+      "name": "JunyeongChoi0",
+      "id": 99778164,
+      "comment_id": 3867461224,
+      "created_at": "2026-02-08T16:02:31Z",
+      "repoId": 1108837393,
+      "pullRequestNo": 1674
+    },
+    {
+      "name": "aliozdenisik",
+      "id": 106994209,
+      "comment_id": 3867619266,
+      "created_at": "2026-02-08T17:12:34Z",
+      "repoId": 1108837393,
+      "pullRequestNo": 1676
+    },
+    {
+      "name": "mrm007",
+      "id": 3297808,
+      "comment_id": 3868350953,
+      "created_at": "2026-02-08T21:41:35Z",
+      "repoId": 1108837393,
+      "pullRequestNo": 1680
     }
   ]
 }

src/tools/delegate-task/executor.sync-task.test.ts

@@ -0,0 +1,306 @@
+import { describe, it, expect, mock, beforeEach } from "bun:test"
+import { executeSyncTask } from "./executor"
+import { __setTimingConfig, __resetTimingConfig } from "./timing"
+import type { DelegateTaskArgs, ToolContextWithMetadata } from "./types"
+import type { ExecutorContext, ParentContext } from "./executor"
+
+function createMockClient(overrides: {
+  sessionCreateResult?: { data: { id: string }; error?: string }
+  promptAsyncFn?: () => Promise<void>
+  statusFn?: () => Promise<{ data: Record<string, { type: string }> }>
+  messagesFn?: () => Promise<{ data: Array<{ info?: { role?: string; time?: { created?: number } }; parts?: Array<{ type?: string; text?: string }> }> }>
+  configGetFn?: () => Promise<{ data?: { model?: string } }>
+  sessionGetFn?: () => Promise<{ data?: { directory?: string } }>
+} = {}) {
+  return {
+    session: {
+      create: mock(() =>
+        Promise.resolve(
+          overrides.sessionCreateResult ?? {
+            data: { id: "ses_test123" },
+          }
+        )
+      ),
+      prompt: mock(() => Promise.resolve()),
+      promptAsync: mock(overrides.promptAsyncFn ?? (() => Promise.resolve())),
+      status: mock(
+        overrides.statusFn ??
+          (() =>
+            Promise.resolve({
+              data: { ses_test123: { type: "idle" } },
+            }))
+      ),
+      messages: mock(
+        overrides.messagesFn ??
+          (() =>
+            Promise.resolve({
+              data: [
+                {
+                  info: { role: "assistant", time: { created: 1000 } },
+                  parts: [{ type: "text", text: "Oracle response content" }],
+                },
+              ],
+            }))
+      ),
+      get: mock(
+        overrides.sessionGetFn ??
+          (() => Promise.resolve({ data: { directory: "/test" } }))
+      ),
+    },
+    config: {
+      get: mock(
+        overrides.configGetFn ??
+          (() => Promise.resolve({ data: { model: "anthropic/claude-sonnet-4" } }))
+      ),
+    },
+    app: {
+      agents: mock(() => Promise.resolve({ data: [] })),
+    },
+  }
+}
+
+function createMockCtx(overrides: Partial<ToolContextWithMetadata> = {}): ToolContextWithMetadata {
+  return {
+    sessionID: "ses_parent",
+    messageID: "msg_parent",
+    agent: "sisyphus",
+    abort: new AbortController().signal,
+    metadata: mock(() => Promise.resolve()),
+    ...overrides,
+  }
+}
+
+function createMockExecutorCtx(client: ReturnType<typeof createMockClient>): ExecutorContext {
+  return {
+    manager: {
+      launch: mock(() => Promise.resolve({ id: "task_1", sessionID: "ses_test123", description: "test", agent: "oracle", status: "running" })),
+      getTask: mock(() => ({ id: "task_1", sessionID: "ses_test123" })),
+      resume: mock(() => Promise.resolve()),
+    } as unknown as ExecutorContext["manager"],
+    client: client as unknown as ExecutorContext["client"],
+    directory: "/test",
+  }
+}
+
+function createDefaultArgs(overrides: Partial<DelegateTaskArgs> = {}): DelegateTaskArgs {
+  return {
+    description: "Consult Oracle",
+    prompt: "Review this architecture",
+    run_in_background: false,
+    load_skills: [],
+    subagent_type: "oracle",
+    ...overrides,
+  }
+}
+
+function createDefaultParentContext(): ParentContext {
+  return {
+    sessionID: "ses_parent",
+    messageID: "msg_parent",
+    agent: "sisyphus",
+  }
+}
+
+describe("executeSyncTask", () => {
+  beforeEach(() => {
+    __resetTimingConfig()
+    __setTimingConfig({
+      POLL_INTERVAL_MS: 10,
+      MIN_STABILITY_TIME_MS: 0,
+      STABILITY_POLLS_REQUIRED: 1,
+      MAX_POLL_TIME_MS: 5000,
+    })
+  })
+
+  describe("async prompt + polling pattern", () => {
+    it("should use promptAsync instead of blocking prompt", async () => {
+      //#given a mock client with both prompt and promptAsync
+      const client = createMockClient()
+      const executorCtx = createMockExecutorCtx(client)
+      const args = createDefaultArgs()
+      const ctx = createMockCtx()
+      const parentContext = createDefaultParentContext()
+
+      //#when executeSyncTask is called
+      await executeSyncTask(args, ctx, executorCtx, parentContext, "oracle", undefined, undefined)
+
+      //#then it should use promptAsync (fire-and-forget), NOT blocking prompt
+      expect(client.session.promptAsync).toHaveBeenCalledTimes(1)
+      expect(client.session.prompt).toHaveBeenCalledTimes(0)
+    })
+
+    it("should poll session status until idle and messages stabilize", async () => {
+      //#given a client that transitions from busy to idle
+      let callCount = 0
+      const client = createMockClient({
+        statusFn: () => {
+          callCount++
+          if (callCount <= 2) {
+            return Promise.resolve({ data: { ses_test123: { type: "busy" } } })
+          }
+          return Promise.resolve({ data: { ses_test123: { type: "idle" } } })
+        },
+      })
+      const executorCtx = createMockExecutorCtx(client)
+      const args = createDefaultArgs()
+      const ctx = createMockCtx()
+      const parentContext = createDefaultParentContext()
+
+      //#when executeSyncTask is called
+      const result = await executeSyncTask(args, ctx, executorCtx, parentContext, "oracle", undefined, undefined)
+
+      //#then it should have polled status multiple times
+      expect(client.session.status.mock.calls.length).toBeGreaterThanOrEqual(3)
+
+      //#then the result should contain the assistant response
+      expect(result).toContain("Oracle response content")
+    })
+
+    it("should return result after message count stabilizes", async () => {
+      //#given a client where messages stabilize immediately
+      const client = createMockClient()
+      const executorCtx = createMockExecutorCtx(client)
+      const args = createDefaultArgs()
+      const ctx = createMockCtx()
+      const parentContext = createDefaultParentContext()
+
+      //#when executeSyncTask is called
+      const result = await executeSyncTask(args, ctx, executorCtx, parentContext, "oracle", undefined, undefined)
+
+      //#then the result should contain the assistant response text
+      expect(result).toContain("Oracle response content")
+      expect(result).toContain("Task completed")
+      expect(result).toContain("ses_test123")
+    })
+  })
+
+  describe("session creation", () => {
+    it("should create a session before sending prompt", async () => {
+      //#given a mock client
+      const client = createMockClient()
+      const executorCtx = createMockExecutorCtx(client)
+      const args = createDefaultArgs()
+      const ctx = createMockCtx()
+      const parentContext = createDefaultParentContext()
+
+      //#when executeSyncTask is called
+      await executeSyncTask(args, ctx, executorCtx, parentContext, "oracle", undefined, undefined)
+
+      //#then session.create should have been called
+      expect(client.session.create).toHaveBeenCalledTimes(1)
+    })
+
+    it("should return error when session creation fails", async () => {
+      //#given a client that fails to create session
+      const client = createMockClient({
+        sessionCreateResult: { data: { id: "" }, error: "Failed to create" },
+      })
+      const executorCtx = createMockExecutorCtx(client)
+      const args = createDefaultArgs()
+      const ctx = createMockCtx()
+      const parentContext = createDefaultParentContext()
+
+      //#when executeSyncTask is called
+      const result = await executeSyncTask(args, ctx, executorCtx, parentContext, "oracle", undefined, undefined)
+
+      //#then it should return an error message
+      expect(result).toContain("Failed to create")
+    })
+  })
+
+  describe("abort handling", () => {
+    it("should abort polling when abort signal fires", async () => {
+      //#given a client that stays busy and an abort controller
+      const abortController = new AbortController()
+      const client = createMockClient({
+        statusFn: () => {
+          // Abort after first poll
+          abortController.abort()
+          return Promise.resolve({ data: { ses_test123: { type: "busy" } } })
+        },
+      })
+      const executorCtx = createMockExecutorCtx(client)
+      const args = createDefaultArgs()
+      const ctx = createMockCtx({ abort: abortController.signal })
+      const parentContext = createDefaultParentContext()
+
+      //#when executeSyncTask is called with an aborting signal
+      const result = await executeSyncTask(args, ctx, executorCtx, parentContext, "oracle", undefined, undefined)
+
+      //#then it should indicate the task was aborted
+      expect(result).toContain("aborted")
+    })
+  })
+
+  describe("model passthrough", () => {
+    it("should pass categoryModel to promptAsync body", async () => {
+      //#given a category model
+      const categoryModel = { providerID: "openai", modelID: "gpt-5.2" }
+      const client = createMockClient()
+      const executorCtx = createMockExecutorCtx(client)
+      const args = createDefaultArgs()
+      const ctx = createMockCtx()
+      const parentContext = createDefaultParentContext()
+
+      //#when executeSyncTask is called with a category model
+      await executeSyncTask(args, ctx, executorCtx, parentContext, "oracle", categoryModel, undefined)
+
+      //#then promptAsync should include the model in the body
+      const promptCall = client.session.promptAsync.mock.calls[0][0] as { body: { model?: { providerID: string; modelID: string } } }
+      expect(promptCall.body.model).toEqual({ providerID: "openai", modelID: "gpt-5.2" })
+    })
+
+    it("should pass variant when categoryModel has variant", async () => {
+      //#given a category model with variant
+      const categoryModel = { providerID: "openai", modelID: "gpt-5.2", variant: "high" }
+      const client = createMockClient()
+      const executorCtx = createMockExecutorCtx(client)
+      const args = createDefaultArgs()
+      const ctx = createMockCtx()
+      const parentContext = createDefaultParentContext()
+
+      //#when executeSyncTask is called with a model+variant
+      await executeSyncTask(args, ctx, executorCtx, parentContext, "oracle", categoryModel, undefined)
+
+      //#then promptAsync should include the variant
+      const promptCall = client.session.promptAsync.mock.calls[0][0] as { body: { variant?: string } }
+      expect(promptCall.body.variant).toBe("high")
+    })
+  })
+
+  describe("error handling", () => {
+    it("should handle promptAsync failure gracefully", async () => {
+      //#given a client where promptAsync throws
+      const client = createMockClient({
+        promptAsyncFn: () => Promise.reject(new Error("Network error")),
+      })
+      const executorCtx = createMockExecutorCtx(client)
+      const args = createDefaultArgs()
+      const ctx = createMockCtx()
+      const parentContext = createDefaultParentContext()
+
+      //#when executeSyncTask is called
+      const result = await executeSyncTask(args, ctx, executorCtx, parentContext, "oracle", undefined, undefined)
+
+      //#then it should return an error message
+      expect(result).toContain("Network error")
+    })
+
+    it("should return no-response message when no assistant messages exist", async () => {
+      //#given a client that returns empty messages
+      const client = createMockClient({
+        messagesFn: () => Promise.resolve({ data: [] }),
+      })
+      const executorCtx = createMockExecutorCtx(client)
+      const args = createDefaultArgs()
+      const ctx = createMockCtx()
+      const parentContext = createDefaultParentContext()
+
+      //#when executeSyncTask is called
+      const result = await executeSyncTask(args, ctx, executorCtx, parentContext, "oracle", undefined, undefined)
+
+      //#then it should indicate no response
+      expect(result).toContain("No assistant response")
+    })
+  })
+})

src/tools/delegate-task/executor.ts

@@ -615,7 +615,7 @@ export async function executeSyncTask(
 
     try {
       const allowTask = isPlanFamily(agentToUse)
-      await promptSyncWithModelSuggestionRetry(client, {
+      await promptWithModelSuggestionRetry(client, {
         path: { id: sessionID },
         body: {
           agent: agentToUse,
@@ -653,6 +653,47 @@ export async function executeSyncTask(
       })
     }
 
+    const timingCfg = getTimingConfig()
+    const pollStart = Date.now()
+    let lastMsgCount = 0
+    let stablePolls = 0
+
+    while (Date.now() - pollStart < timingCfg.MAX_POLL_TIME_MS) {
+      if (ctx.abort?.aborted) {
+        if (toastManager && taskId !== undefined) {
+          toastManager.removeTask(taskId)
+        }
+        subagentSessions.delete(sessionID)
+        return `Task aborted.\n\nSession ID: ${sessionID}`
+      }
+
+      await new Promise(resolve => setTimeout(resolve, timingCfg.POLL_INTERVAL_MS))
+
+      const statusResult = await client.session.status()
+      const allStatuses = (statusResult.data ?? {}) as Record<string, { type: string }>
+      const sessionStatus = allStatuses[sessionID]
+
+      if (sessionStatus && sessionStatus.type !== "idle") {
+        stablePolls = 0
+        lastMsgCount = 0
+        continue
+      }
+
+      if (Date.now() - pollStart < timingCfg.MIN_STABILITY_TIME_MS) continue
+
+      const messagesCheck = await client.session.messages({ path: { id: sessionID } })
+      const msgs = ((messagesCheck as { data?: unknown }).data ?? messagesCheck) as Array<unknown>
+      const currentMsgCount = msgs.length
+
+      if (currentMsgCount === lastMsgCount) {
+        stablePolls++
+        if (stablePolls >= timingCfg.STABILITY_POLLS_REQUIRED) break
+      } else {
+        stablePolls = 0
+        lastMsgCount = currentMsgCount
+      }
+    }
+
     const messagesResult = await client.session.messages({
       path: { id: sessionID },
     })