diff --git a/src/agent/modify.ts b/src/agent/modify.ts
index 98794cc..f6b302b 100644
--- a/src/agent/modify.ts
+++ b/src/agent/modify.ts
@@ -247,6 +247,45 @@ export async function updateConversationLLMConfig(
   return client.conversations.update(conversationId, payload);
 }
 
+export interface RecompileAgentSystemPromptOptions {
+  dryRun?: boolean;
+  updateTimestamp?: boolean;
+}
+
+interface AgentSystemPromptRecompileClient {
+  agents: {
+    recompile: (
+      agentId: string,
+      params: {
+        dry_run?: boolean;
+        update_timestamp?: boolean;
+      },
+    ) => Promise<string>;
+  };
+}
+
+/**
+ * Recompile an agent's system prompt after memory writes so server-side prompt
+ * state picks up the latest memory content.
+ *
+ * @param agentId - The agent ID to recompile
+ * @param options - Optional dry-run/timestamp controls
+ * @param clientOverride - Optional injected client for tests
+ * @returns The compiled system prompt returned by the API
+ */
+export async function recompileAgentSystemPrompt(
+  agentId: string,
+  options: RecompileAgentSystemPromptOptions = {},
+  clientOverride?: AgentSystemPromptRecompileClient,
+): Promise<string> {
+  const client = clientOverride ?? (await getClient());
+
+  return client.agents.recompile(agentId, {
+    dry_run: options.dryRun,
+    update_timestamp: options.updateTimestamp,
+  });
+}
+
 export interface SystemPromptUpdateResult {
   success: boolean;
   message: string;
diff --git a/src/cli/App.tsx b/src/cli/App.tsx
index 5efb444..4cdd308 100644
--- a/src/cli/App.tsx
+++ b/src/cli/App.tsx
@@ -232,6 +232,7 @@ import {
   type ReflectionSettings,
   reflectionSettingsToLegacyMode,
 } from "./helpers/memoryReminder";
+import { handleMemorySubagentCompletion } from "./helpers/memorySubagentCompletion";
 import {
   type QueuedMessage,
   setMessageQueueAdder,
@@ -1746,6 +1747,10 @@ export default function App({
   const initProgressByAgentRef = useRef(
     new Map<string, { shallowCompleted: boolean; deepFired: boolean }>(),
   );
+  const systemPromptRecompileByAgentRef = useRef(
+    new Map<string, Promise<void>>(),
+  );
+  const queuedSystemPromptRecompileByAgentRef = useRef(new Set<string>());
   const updateInitProgress = (
     forAgentId: string,
     update: Partial<{ shallowCompleted: boolean; deepFired: boolean }>,
@@ -9305,13 +9310,24 @@ export default function App({
                 prompt: initPrompt,
                 description: "Initializing memory",
                 silentCompletion: true,
-                onComplete: ({ success, error }) => {
-                  if (success) {
-                    updateInitProgress(agentId, { deepFired: true });
-                  }
-                  const msg = success
-                    ? "Built a memory palace of you. Visit it with /palace."
-                    : `Memory initialization failed: ${error || "Unknown error"}`;
+                onComplete: async ({ success, error }) => {
+                  const msg = await handleMemorySubagentCompletion(
+                    {
+                      agentId,
+                      subagentType: "init",
+                      initDepth: "deep",
+                      success,
+                      error,
+                    },
+                    {
+                      recompileByAgent: systemPromptRecompileByAgentRef.current,
+                      recompileQueuedByAgent:
+                        queuedSystemPromptRecompileByAgentRef.current,
+                      updateInitProgress,
+                      logRecompileFailure: (message) =>
+                        debugWarn("memory", message),
+                    },
+                  );
                   appendTaskNotificationEvents([msg]);
                 },
               });
@@ -9479,15 +9495,29 @@ export default function App({
       // attempt (e.g. another /init subagent in flight) preserves the entry for retry.
       if (autoInitPendingAgentIdsRef.current.has(agentId) && !isSystemOnly) {
         try {
-          const fired = await fireAutoInit(agentId, ({ success, error }) => {
-            if (success) {
-              updateInitProgress(agentId, { shallowCompleted: true });
-            }
-            const msg = success
-              ? "Built a memory palace of you. Visit it with /palace."
-              : `Memory initialization failed: ${error || "Unknown error"}`;
-            appendTaskNotificationEvents([msg]);
-          });
+          const fired = await fireAutoInit(
+            agentId,
+            async ({ success, error }) => {
+              const msg = await handleMemorySubagentCompletion(
+                {
+                  agentId,
+                  subagentType: "init",
+                  initDepth: "shallow",
+                  success,
+                  error,
+                },
+                {
+                  recompileByAgent: systemPromptRecompileByAgentRef.current,
+                  recompileQueuedByAgent:
+                    queuedSystemPromptRecompileByAgentRef.current,
+                  updateInitProgress,
+                  logRecompileFailure: (message) =>
+                    debugWarn("memory", message),
+                },
+              );
+              appendTaskNotificationEvents([msg]);
+            },
+          );
           if (fired) {
             autoInitPendingAgentIdsRef.current.delete(agentId);
             sharedReminderStateRef.current.pendingAutoInitReminder = true;
@@ -9596,10 +9626,23 @@ ${SYSTEM_REMINDER_CLOSE}
             prompt: AUTO_REFLECTION_PROMPT,
             description: AUTO_REFLECTION_DESCRIPTION,
             silentCompletion: true,
-            onComplete: ({ success, error }) => {
-              const msg = success
-                ? "Reflected on /palace, the halls remember more now."
-                : `Tried to reflect, but got lost in the palace: ${error}`;
+            onComplete: async ({ success, error }) => {
+              const msg = await handleMemorySubagentCompletion(
+                {
+                  agentId,
+                  subagentType: "reflection",
+                  success,
+                  error,
+                },
+                {
+                  recompileByAgent: systemPromptRecompileByAgentRef.current,
+                  recompileQueuedByAgent:
+                    queuedSystemPromptRecompileByAgentRef.current,
+                  updateInitProgress,
+                  logRecompileFailure: (message) =>
+                    debugWarn("memory", message),
+                },
+              );
               appendTaskNotificationEvents([msg]);
             },
           });
@@ -9638,13 +9681,24 @@ ${SYSTEM_REMINDER_CLOSE}
             prompt: initPrompt,
             description: "Deep memory initialization",
             silentCompletion: true,
-            onComplete: ({ success, error }) => {
-              if (success) {
-                updateInitProgress(agentId, { deepFired: true });
-              }
-              const msg = success
-                ? "Built a memory palace of you. Visit it with /palace."
-                : `Deep memory initialization failed: ${error || "Unknown error"}`;
+            onComplete: async ({ success, error }) => {
+              const msg = await handleMemorySubagentCompletion(
+                {
+                  agentId,
+                  subagentType: "init",
+                  initDepth: "deep",
+                  success,
+                  error,
+                },
+                {
+                  recompileByAgent: systemPromptRecompileByAgentRef.current,
+                  recompileQueuedByAgent:
+                    queuedSystemPromptRecompileByAgentRef.current,
+                  updateInitProgress,
+                  logRecompileFailure: (message) =>
+                    debugWarn("memory", message),
+                },
+              );
               appendTaskNotificationEvents([msg]);
             },
           });
diff --git a/src/cli/helpers/initCommand.ts b/src/cli/helpers/initCommand.ts
index 64064e4..b840d35 100644
--- a/src/cli/helpers/initCommand.ts
+++ b/src/cli/helpers/initCommand.ts
@@ -139,7 +139,10 @@ Instructions:
  */
 export async function fireAutoInit(
   agentId: string,
-  onComplete: (result: { success: boolean; error?: string }) => void,
+  onComplete: (result: {
+    success: boolean;
+    error?: string;
+  }) => void | Promise<void>,
 ): Promise<boolean> {
   if (hasActiveInitSubagent()) return false;
   if (!settingsManager.isMemfsEnabled(agentId)) return false;
diff --git a/src/cli/helpers/memorySubagentCompletion.ts b/src/cli/helpers/memorySubagentCompletion.ts
new file mode 100644
index 0000000..0ef282d
--- /dev/null
+++ b/src/cli/helpers/memorySubagentCompletion.ts
@@ -0,0 +1,123 @@
+import {
+  type RecompileAgentSystemPromptOptions,
+  recompileAgentSystemPrompt,
+} from "../../agent/modify";
+
+export type MemorySubagentType = "init" | "reflection";
+export type MemoryInitDepth = "shallow" | "deep";
+
+export interface MemoryInitProgressUpdate {
+  shallowCompleted: boolean;
+  deepFired: boolean;
+}
+
+type RecompileAgentSystemPromptFn = (
+  agentId: string,
+  options?: RecompileAgentSystemPromptOptions,
+) => Promise<string>;
+
+export type MemorySubagentCompletionArgs =
+  | {
+      agentId: string;
+      subagentType: "init";
+      initDepth: MemoryInitDepth;
+      success: boolean;
+      error?: string;
+    }
+  | {
+      agentId: string;
+      subagentType: "reflection";
+      initDepth?: never;
+      success: boolean;
+      error?: string;
+    };
+
+export interface MemorySubagentCompletionDeps {
+  recompileByAgent: Map<string, Promise<void>>;
+  recompileQueuedByAgent: Set<string>;
+  updateInitProgress: (
+    agentId: string,
+    update: Partial<MemoryInitProgressUpdate>,
+  ) => void;
+  logRecompileFailure?: (message: string) => void;
+  recompileAgentSystemPromptImpl?: RecompileAgentSystemPromptFn;
+}
+
+/**
+ * Finalize a memory-writing subagent by updating init progress, recompiling the
+ * parent agent's system prompt, and returning the user-facing completion text.
+ */
+export async function handleMemorySubagentCompletion(
+  args: MemorySubagentCompletionArgs,
+  deps: MemorySubagentCompletionDeps,
+): Promise<string> {
+  const { agentId, subagentType, initDepth, success, error } = args;
+  const recompileAgentSystemPromptFn =
+    deps.recompileAgentSystemPromptImpl ?? recompileAgentSystemPrompt;
+  let recompileError: string | null = null;
+
+  if (success) {
+    if (subagentType === "init") {
+      deps.updateInitProgress(
+        agentId,
+        initDepth === "shallow"
+          ? { shallowCompleted: true }
+          : { deepFired: true },
+      );
+    }
+
+    try {
+      let inFlight = deps.recompileByAgent.get(agentId);
+
+      if (!inFlight) {
+        inFlight = (async () => {
+          do {
+            deps.recompileQueuedByAgent.delete(agentId);
+            await recompileAgentSystemPromptFn(agentId, {
+              updateTimestamp: true,
+            });
+          } while (deps.recompileQueuedByAgent.has(agentId));
+        })().finally(() => {
+          // Cleanup runs only after the shared promise settles, so every
+          // concurrent caller awaits the same full recompile lifecycle.
+          deps.recompileQueuedByAgent.delete(agentId);
+          deps.recompileByAgent.delete(agentId);
+        });
+        deps.recompileByAgent.set(agentId, inFlight);
+      } else {
+        deps.recompileQueuedByAgent.add(agentId);
+      }
+
+      await inFlight;
+    } catch (recompileFailure) {
+      recompileError =
+        recompileFailure instanceof Error
+          ? recompileFailure.message
+          : String(recompileFailure);
+      deps.logRecompileFailure?.(
+        `Failed to recompile system prompt after ${subagentType} subagent for ${agentId}: ${recompileError}`,
+      );
+    }
+  }
+
+  if (!success) {
+    const normalizedError = error || "Unknown error";
+    if (subagentType === "reflection") {
+      return `Tried to reflect, but got lost in the palace: ${normalizedError}`;
+    }
+    return initDepth === "deep"
+      ? `Deep memory initialization failed: ${normalizedError}`
+      : `Memory initialization failed: ${normalizedError}`;
+  }
+
+  const baseMessage =
+    subagentType === "reflection"
+      ? "Reflected on /palace, the halls remember more now."
+      : "Built a memory palace of you. Visit it with /palace.";
+
+  if (!recompileError) {
+    return baseMessage;
+  }
+
+  return `${baseMessage} System prompt recompilation failed: ${recompileError}`;
+}
diff --git a/src/tests/agent/recompile-system-prompt.test.ts b/src/tests/agent/recompile-system-prompt.test.ts
new file mode 100644
index 0000000..c7945eb
--- /dev/null
+++ b/src/tests/agent/recompile-system-prompt.test.ts
@@ -0,0 +1,31 @@
+import { describe, expect, mock, test } from "bun:test";
+import { recompileAgentSystemPrompt } from "../../agent/modify";
+
+describe("recompileAgentSystemPrompt", () => {
+  test("calls the Letta agent recompile endpoint with mapped params", async () => {
+    const agentsRecompileMock = mock(
+      (_agentId: string, _params?: Record<string, unknown>) =>
+        Promise.resolve("compiled-system-prompt"),
+    );
+    const client = {
+      agents: {
+        recompile: agentsRecompileMock,
+      },
+    };
+
+    const compiledPrompt = await recompileAgentSystemPrompt(
+      "agent-123",
+      {
+        updateTimestamp: true,
+        dryRun: true,
+      },
+      client,
+    );
+
+    expect(compiledPrompt).toBe("compiled-system-prompt");
+    expect(agentsRecompileMock).toHaveBeenCalledWith("agent-123", {
+      dry_run: true,
+      update_timestamp: true,
+    });
+  });
+});
diff --git a/src/tests/cli/memory-subagent-recompile-wiring.test.ts b/src/tests/cli/memory-subagent-recompile-wiring.test.ts
new file mode 100644
index 0000000..07dbbf7
--- /dev/null
+++ b/src/tests/cli/memory-subagent-recompile-wiring.test.ts
@@ -0,0 +1,140 @@
+import { beforeEach, describe, expect, mock, test } from "bun:test";
+import type { RecompileAgentSystemPromptOptions } from "../../agent/modify";
+import { handleMemorySubagentCompletion } from "../../cli/helpers/memorySubagentCompletion";
+
+const recompileAgentSystemPromptMock = mock(
+  (_agentId: string, _opts?: RecompileAgentSystemPromptOptions) =>
+    Promise.resolve("compiled-system-prompt"),
+);
+
+function createDeferred<T>() {
+  let resolve!: (value: T | PromiseLike<T>) => void;
+  const promise = new Promise<T>((res) => {
+    resolve = res;
+  });
+  return { promise, resolve };
+}
+
+describe("memory subagent recompile handling", () => {
+  beforeEach(() => {
+    recompileAgentSystemPromptMock.mockReset();
+    recompileAgentSystemPromptMock.mockImplementation(
+      (_agentId: string, _opts?: RecompileAgentSystemPromptOptions) =>
+        Promise.resolve("compiled-system-prompt"),
+    );
+  });
+
+  test("updates init progress and recompiles after successful shallow init", async () => {
+    const progressUpdates: Array<{
+      agentId: string;
+      update: Record<string, boolean>;
+    }> = [];
+
+    const message = await handleMemorySubagentCompletion(
+      {
+        agentId: "agent-init-1",
+        subagentType: "init",
+        initDepth: "shallow",
+        success: true,
+      },
+      {
+        recompileByAgent: new Map(),
+        recompileQueuedByAgent: new Set(),
+        recompileAgentSystemPromptImpl: recompileAgentSystemPromptMock,
+        updateInitProgress: (agentId, update) => {
+          progressUpdates.push({
+            agentId,
+            update: update as Record<string, boolean>,
+          });
+        },
+      },
+    );
+
+    expect(message).toBe(
+      "Built a memory palace of you. Visit it with /palace.",
+    );
+    expect(progressUpdates).toEqual([
+      {
+        agentId: "agent-init-1",
+        update: { shallowCompleted: true },
+      },
+    ]);
+    expect(recompileAgentSystemPromptMock).toHaveBeenCalledWith(
+      "agent-init-1",
+      {
+        updateTimestamp: true,
+      },
+    );
+  });
+
+  test("queues a trailing recompile when later completions land mid-flight", async () => {
+    const firstDeferred = createDeferred<string>();
+    const secondDeferred = createDeferred<string>();
+    recompileAgentSystemPromptMock
+      .mockImplementationOnce(() => firstDeferred.promise)
+      .mockImplementationOnce(() => secondDeferred.promise);
+
+    const recompileByAgent = new Map<string, Promise<void>>();
+    const recompileQueuedByAgent = new Set<string>();
+    const deps = {
+      recompileByAgent,
+      recompileQueuedByAgent,
+      recompileAgentSystemPromptImpl: recompileAgentSystemPromptMock,
+      updateInitProgress: () => {},
+    };
+
+    const first = handleMemorySubagentCompletion(
+      {
+        agentId: "agent-shared",
+        subagentType: "reflection",
+        success: true,
+      },
+      deps,
+    );
+    const second = handleMemorySubagentCompletion(
+      {
+        agentId: "agent-shared",
+        subagentType: "reflection",
+        success: true,
+      },
+      deps,
+    );
+    const third = handleMemorySubagentCompletion(
+      {
+        agentId: "agent-shared",
+        subagentType: "reflection",
+        success: true,
+      },
+      deps,
+    );
+
+    expect(recompileAgentSystemPromptMock).toHaveBeenCalledTimes(1);
+    expect(recompileByAgent.has("agent-shared")).toBe(true);
+    expect(recompileQueuedByAgent.has("agent-shared")).toBe(true);
+
+    firstDeferred.resolve("compiled-system-prompt");
+    await Promise.resolve();
+
+    expect(recompileAgentSystemPromptMock).toHaveBeenCalledTimes(2);
+    expect(recompileByAgent.has("agent-shared")).toBe(true);
+
+    secondDeferred.resolve("compiled-system-prompt");
+
+    const [firstMessage, secondMessage, thirdMessage] = await Promise.all([
+      first,
+      second,
+      third,
+    ]);
+    expect(firstMessage).toBe(
+      "Reflected on /palace, the halls remember more now.",
+    );
+    expect(secondMessage).toBe(
+      "Reflected on /palace, the halls remember more now.",
+    );
+    expect(thirdMessage).toBe(
+      "Reflected on /palace, the halls remember more now.",
+    );
+    expect(recompileByAgent.size).toBe(0);
+    expect(recompileQueuedByAgent.size).toBe(0);
+  });
+});
diff --git a/src/tests/cli/task-notification-flush.test.ts b/src/tests/cli/task-notification-flush.test.ts
index 3b6a403..4208756 100644
--- a/src/tests/cli/task-notification-flush.test.ts
+++ b/src/tests/cli/task-notification-flush.test.ts
@@ -143,17 +143,9 @@ describe("background onComplete → flush wiring in App.tsx", () => {
     const onCompleteIdx = source.indexOf("onComplete:", initBlock);
     expect(onCompleteIdx).toBeGreaterThan(-1);
 
-    // The appendTaskNotificationEvents call must be within the onComplete body
-    // (before the closing of spawnBackgroundSubagentTask).
-    // Use "});" with leading whitespace to match the spawn call's closing,
-    // not inner statements like updateInitProgress(...});
-    const callIdx = source.indexOf(
-      "appendTaskNotificationEvents(",
-      onCompleteIdx,
-    );
-    const blockEnd = source.indexOf("              });", onCompleteIdx);
-    expect(callIdx).toBeGreaterThan(onCompleteIdx);
-    expect(callIdx).toBeLessThan(blockEnd);
+    const onCompleteWindow = source.slice(onCompleteIdx, onCompleteIdx + 900);
+    expect(onCompleteWindow).toContain("await handleMemorySubagentCompletion(");
+    expect(onCompleteWindow).toContain("appendTaskNotificationEvents(");
   });
 
   test("reflection onComplete calls appendTaskNotificationEvents", () => {
@@ -165,12 +157,8 @@ describe("background onComplete → flush wiring in App.tsx", () => {
     const onCompleteIdx = source.indexOf("onComplete:", reflectionBlock);
     expect(onCompleteIdx).toBeGreaterThan(-1);
 
-    const callIdx = source.indexOf(
-      "appendTaskNotificationEvents(",
-      onCompleteIdx,
-    );
-    const blockEnd = source.indexOf("});", onCompleteIdx);
-    expect(callIdx).toBeGreaterThan(onCompleteIdx);
-    expect(callIdx).toBeLessThan(blockEnd);
+    const onCompleteWindow = source.slice(onCompleteIdx, onCompleteIdx + 700);
+    expect(onCompleteWindow).toContain("await handleMemorySubagentCompletion(");
+    expect(onCompleteWindow).toContain("appendTaskNotificationEvents(");
   });
 });
diff --git a/src/tests/tools/task-background-helper.test.ts b/src/tests/tools/task-background-helper.test.ts
index 325cbb4..c15e73c 100644
--- a/src/tests/tools/task-background-helper.test.ts
+++ b/src/tests/tools/task-background-helper.test.ts
@@ -181,6 +181,99 @@ describe("spawnBackgroundSubagentTask", () => {
     expect(runSubagentStopHooksImpl).toHaveBeenCalledTimes(1);
   });
 
+  test("awaits async onComplete before queue notification and hooks", async () => {
+    const callOrder: string[] = [];
+    const spawnSubagentImpl = mock(async () => ({
+      agentId: "agent-ordered",
+      conversationId: "default",
+      report: "reflection done",
+      success: true,
+      totalTokens: 22,
+    }));
+    const addToMessageQueueOrdered = mock(
+      (_msg: { kind: "user" | "task_notification"; text: string }) => {
+        callOrder.push("queue");
+      },
+    );
+    const runSubagentStopHooksOrdered = mock(async () => {
+      callOrder.push("hooks");
+      return {
+        blocked: false,
+        errored: false,
+        feedback: [],
+        results: [],
+      };
+    });
+    const onComplete = mock(async () => {
+      callOrder.push("onComplete:start");
+      await new Promise((resolve) => setTimeout(resolve, 20));
+      callOrder.push("onComplete:end");
+    });
+
+    spawnBackgroundSubagentTask({
+      subagentType: "reflection",
+      prompt: "Reflect",
+      description: "Reflect on memory",
+      onComplete,
+      deps: {
+        spawnSubagentImpl,
+        addToMessageQueueImpl: addToMessageQueueOrdered,
+        formatTaskNotificationImpl,
+        runSubagentStopHooksImpl: runSubagentStopHooksOrdered,
+        generateSubagentIdImpl,
+        registerSubagentImpl,
+        completeSubagentImpl,
+        getSubagentSnapshotImpl,
+      },
+    });
+
+    await new Promise((resolve) => setTimeout(resolve, 60));
+
+    expect(callOrder).toEqual([
+      "onComplete:start",
+      "onComplete:end",
+      "queue",
+      "hooks",
+    ]);
+  });
+
+  test("continues queue notification and hooks when onComplete throws", async () => {
+    const spawnSubagentImpl = mock(async () => ({
+      agentId: "agent-oncomplete-error",
+      conversationId: "default",
+      report: "reflection done",
+      success: true,
+      totalTokens: 19,
+    }));
+    const onComplete = mock(async () => {
+      throw new Error("callback exploded");
+    });
+
+    const launched = spawnBackgroundSubagentTask({
+      subagentType: "reflection",
+      prompt: "Reflect",
+      description: "Reflect on memory",
+      onComplete,
+      deps: {
+        spawnSubagentImpl,
+        addToMessageQueueImpl,
+        formatTaskNotificationImpl,
+        runSubagentStopHooksImpl,
+        generateSubagentIdImpl,
+        registerSubagentImpl,
+        completeSubagentImpl,
+        getSubagentSnapshotImpl,
+      },
+    });
+
+    await new Promise((resolve) => setTimeout(resolve, 20));
+
+    expect(queueMessages).toHaveLength(1);
+    expect(runSubagentStopHooksImpl).toHaveBeenCalledTimes(1);
+    const outputContent = readFileSync(launched.outputFile, "utf-8");
+    expect(outputContent).toContain("[onComplete error] callback exploded");
+  });
+
   test("marks background task failed and emits notification on error", async () => {
     const spawnSubagentImpl = mock(async () => {
       throw new Error("subagent exploded");
diff --git a/src/tools/impl/Task.ts b/src/tools/impl/Task.ts
index 8b239be..772a69b 100644
--- a/src/tools/impl/Task.ts
+++ b/src/tools/impl/Task.ts
@@ -75,9 +75,13 @@ export interface SpawnBackgroundSubagentTaskArgs {
   silentCompletion?: boolean;
   /**
    * Called after the subagent finishes (success or failure).
-   * Runs regardless of `silentCompletion`.
+   * Runs regardless of `silentCompletion` and is awaited before
+   * completion notifications/hooks continue.
    */
-  onComplete?: (result: { success: boolean; error?: string }) => void;
+  onComplete?: (result: {
+    success: boolean;
+    error?: string;
+  }) => void | Promise<void>;
   /**
    * Optional dependency overrides for tests.
    * Production callers should not provide this.
@@ -248,6 +252,9 @@ export function spawnBackgroundSubagentTask(
   backgroundTasks.set(taskId, bgTask);
   writeTaskTranscriptStart(outputFile, description, subagentType);
 
+  // Intentionally fire-and-forget: background tasks own their lifecycle and
+  // capture failures in task state/transcripts instead of surfacing a promise
+  // back to the caller.
   spawnSubagentFn(
     subagentType,
     prompt,
@@ -258,7 +265,7 @@ export function spawnBackgroundSubagentTask(
     existingConversationId,
     maxTurns,
   )
-    .then((result) => {
+    .then(async (result) => {
       bgTask.status = result.success ? "completed" : "failed";
       if (result.error) {
         bgTask.error = result.error;
@@ -276,7 +283,13 @@ export function spawnBackgroundSubagentTask(
         totalTokens: result.totalTokens,
       });
 
-      onComplete?.({ success: result.success, error: result.error });
+      try {
+        await onComplete?.({ success: result.success, error: result.error });
+      } catch (error) {
+        const errorMessage =
+          error instanceof Error ? error.message : String(error);
+        appendToOutputFile(outputFile, `[onComplete error] ${errorMessage}\n`);
+      }
 
       if (!silentCompletion) {
         const subagentSnapshot = getSubagentSnapshotFn();
@@ -325,7 +338,7 @@ export function spawnBackgroundSubagentTask(
         // Silently ignore hook errors
       });
     })
-    .catch((error) => {
+    .catch(async (error) => {
       const errorMessage =
         error instanceof Error ? error.message : String(error);
       bgTask.status = "failed";
@@ -333,7 +346,18 @@ export function spawnBackgroundSubagentTask(
       appendToOutputFile(outputFile, `[error] ${errorMessage}\n`);
       completeSubagentFn(subagentId, { success: false, error: errorMessage });
 
-      onComplete?.({ success: false, error: errorMessage });
+      try {
+        await onComplete?.({ success: false, error: errorMessage });
+      } catch (onCompleteError) {
+        const callbackMessage =
+          onCompleteError instanceof Error
+            ? onCompleteError.message
+            : String(onCompleteError);
+        appendToOutputFile(
+          outputFile,
+          `[onComplete error] ${callbackMessage}\n`,
+        );
+      }
 
       if (!silentCompletion) {
         const subagentSnapshot = getSubagentSnapshotFn();