diff --git a/apps/backend/internal/orchestrator/peer_message_resume_test.go b/apps/backend/internal/orchestrator/peer_message_resume_test.go
new file mode 100644
index 0000000000..3012ea7ec5
--- /dev/null
+++ b/apps/backend/internal/orchestrator/peer_message_resume_test.go
@@ -0,0 +1,120 @@
+package orchestrator
+
+import (
+	"context"
+	"sync"
+	"testing"
+	"time"
+
+	"github.com/kandev/kandev/internal/orchestrator/executor"
+	"github.com/kandev/kandev/internal/task/models"
+)
+
+// TestQueueAndInterruptForPeerMessage_StoppedSessionResumesAgent pins the
+// "a message received from another task auto-starts the agent" contract
+// behind the composer hint: a recovered-idle session (WAITING_FOR_INPUT with
+// a resume token and no running agent — the post-restart shape the
+// prevent-auto-start-on-open preference leaves it in) must be RESUMED by the
+// queue dispatch when a peer (sub-task) message arrives, and the message must
+// reach the agent. The preference only gates open-time starts in the
+// frontend; message-driven starts go through ensureSessionRunning here.
+func TestQueueAndInterruptForPeerMessage_StoppedSessionResumesAgent(t *testing.T) {
+	ctx := context.Background()
+	repo := setupTestRepo(t)
+	agentMgr := &mockAgentManager{isAgentRunning: false, promptDone: make(chan struct{})}
+	taskRepo := newMockTaskRepo()
+	svc := createTestServiceWithAgent(repo, newMockStepGetter(), taskRepo, agentMgr)
+	svc.executor = executor.NewExecutor(agentMgr, repo, testLogger(), executor.ExecutorConfig{})
+	msgCreator := &mockMessageCreator{}
+	svc.messageCreator = msgCreator
+	// Mirrors real agentctl bootstrap timing: LaunchAgent fires
+	// handleAgentBootReady ~50ms later so the resume path completes in unit
+	// tests without a real subprocess. Wrap the simulator to capture the
+	// LaunchAgent request so we can assert the RESUME semantics (the seeded
+	// ACP token must be passed through), not merely that some launch fired.
+	wireBootReadySimulator(svc, agentMgr, "exec-resumed")
+	var launchMu sync.Mutex
+	var launchReqs []*executor.LaunchAgentRequest
+	baseLaunch := agentMgr.launchAgentFunc
+	agentMgr.launchAgentFunc = func(
+		launchCtx context.Context,
+		req *executor.LaunchAgentRequest,
+	) (*executor.LaunchAgentResponse, error) {
+		launchMu.Lock()
+		launchReqs = append(launchReqs, req)
+		launchMu.Unlock()
+		return baseLaunch(launchCtx, req)
+	}
+
+	// The post-restart recovered-idle shape: session stopped with history,
+	// resumable via its executors_running resume token, no agent process.
+	seedTaskAndSession(t, repo, "task1", "session1", models.TaskSessionStateWaitingForInput)
+	session, err := repo.GetTaskSession(ctx, "session1")
+	if err != nil {
+		t.Fatalf("GetTaskSession: %v", err)
+	}
+	session.AgentProfileID = "profile-1"
+	if err := repo.UpdateTaskSession(ctx, session); err != nil {
+		t.Fatalf("UpdateTaskSession: %v", err)
+	}
+	now := time.Now().UTC()
+	if err := repo.UpsertExecutorRunning(ctx, &models.ExecutorRunning{
+		ID: "er1", SessionID: "session1", TaskID: "task1",
+		ResumeToken: "acp-session-xyz",
+		Resumable:   true,
+		CreatedAt:   now, UpdatedAt: now,
+	}); err != nil {
+		t.Fatalf("UpsertExecutorRunning: %v", err)
+	}
+
+	queued, dispatched, err := svc.QueueAndInterruptForPeerMessage(
+		ctx, "task1", "session1", "subtask status update",
+		map[string]interface{}{"sender_task_id": "subtask-1"},
+	)
+	if err != nil {
+		t.Fatalf("queue and interrupt for peer message: %v", err)
+	}
+	if queued == nil {
+		t.Fatal("expected a queued entry")
+	}
+	if !dispatched {
+		t.Fatal("expected QueueAndInterruptForPeerMessage to report the message as dispatched")
+	}
+
+	// The dispatch is async: join the executeQueuedMessage goroutine via the
+	// mock's PromptAgent signal — PromptAgent only runs AFTER
+	// ensureSessionRunning resumed the agent, so this proves both halves.
+	select {
+	case <-agentMgr.promptDone:
+	case <-time.After(5 * time.Second):
+		t.Fatal("timed out waiting for the peer message to be dispatched after resuming the agent")
+	}
+	agentMgr.mu.Lock()
+	prompts := append([]string(nil), agentMgr.capturedPrompts...)
+	agentMgr.mu.Unlock()
+	if len(prompts) != 1 || prompts[0] != "subtask status update" {
+		t.Fatalf("expected the peer message to be dispatched to the agent, got prompts=%v", prompts)
+	}
+
+	// The agent must have been RESUMED by the dispatch: the launch the
+	// boot-ready simulator wires into LaunchAgent must have registered the
+	// new execution on the session's executors_running row, and it must have
+	// carried the seeded ACP resume token (a fresh-start regression would
+	// lose the prior ACP conversation but still satisfy the execution-ID
+	// check).
+	er, err := repo.GetExecutorRunningBySessionID(ctx, "session1")
+	if err != nil || er == nil {
+		t.Fatalf("ExecutorRunning lookup after dispatch failed: err=%v nil=%v", err, er == nil)
+	}
+	if er.AgentExecutionID != "exec-resumed" {
+		t.Fatalf("expected the peer-message dispatch to resume the agent (execution exec-resumed), got %q", er.AgentExecutionID)
+	}
+	launchMu.Lock()
+	defer launchMu.Unlock()
+	if len(launchReqs) != 1 {
+		t.Fatalf("expected exactly 1 resume launch, got %d", len(launchReqs))
+	}
+	if got := launchReqs[0].ACPSessionID; got != "acp-session-xyz" {
+		t.Fatalf("expected the resume launch to carry the seeded ACP token, got %q", got)
+	}
+}
diff --git a/apps/web/components/task/chat/chat-input-area.tsx b/apps/web/components/task/chat/chat-input-area.tsx
index 19d2b664e6..d796385893 100644
--- a/apps/web/components/task/chat/chat-input-area.tsx
+++ b/apps/web/components/task/chat/chat-input-area.tsx
@@ -13,6 +13,7 @@ import {
   type ChatInputContainerHandle,
 } from "@/components/task/chat/chat-input-container";
 import { QueueAffordance } from "@/components/task/chat/queued-ghost-list";
+import { ComposerAgentStartHint } from "./composer-agent-start-hint";
 import {
   formatReviewCommentsAsMarkdown,
   formatPRFeedbackAsMarkdown,
@@ -339,6 +340,10 @@ type ChatInputAreaProps = {
    * dependency chip is about.
    */
   statusTaskId?: string | null;
+  /** Recovered-idle (resume-skipped) sessions render the "a message will
+   * auto-start the agent" hint above the composer while the agent is
+   * stopped. */
+  showAgentStartHint?: boolean;
 };
 
 /** Resolves whether this session's executor environment is unavailable, and why. */
@@ -426,6 +431,7 @@ export function ChatInputArea({
   showScrollToStart,
   onScrollToStart,
   statusTaskId = null,
+  showAgentStartHint = false,
 }: ChatInputAreaProps) {
   const { resolvedSessionId, taskId, isAgentBusy } = panelState;
   const statusRowTaskId = resolveStatusRowTaskId(taskId, statusTaskId);
@@ -461,6 +467,12 @@ export function ChatInputArea({
       data-testid="chat-input-area"
       className={cn("bg-card flex-shrink-0 px-2 pb-2 pt-1", surfaceClassName)}
     >
+      <ComposerAgentStartHint
+        show={showAgentStartHint}
+        needsRecovery={panelState.needsRecovery}
+        executorUnavailable={executor.unavailable}
+        hasPendingClarification={Boolean(panelState.pendingClarification)}
+      />
       <QueueAffordance
         sessionId={resolvedSessionId}
         canDrain={canDrainQueue}
diff --git a/apps/web/components/task/chat/composer-agent-start-hint.test.tsx b/apps/web/components/task/chat/composer-agent-start-hint.test.tsx
new file mode 100644
index 0000000000..788b607839
--- /dev/null
+++ b/apps/web/components/task/chat/composer-agent-start-hint.test.tsx
@@ -0,0 +1,34 @@
+import { cleanup, render, screen } from "@testing-library/react";
+import { afterEach, describe, expect, it } from "vitest";
+import { ComposerAgentStartHint } from "./composer-agent-start-hint";
+
+const HINT_TEST_ID = "composer-agent-start-hint";
+
+afterEach(cleanup);
+
+describe("ComposerAgentStartHint", () => {
+  it("renders the hint line when shown and the composer accepts sends", () => {
+    render(<ComposerAgentStartHint show />);
+    expect(screen.getByTestId(HINT_TEST_ID)).toBeTruthy();
+  });
+
+  it("renders nothing when hidden", () => {
+    render(<ComposerAgentStartHint show={false} />);
+    expect(screen.queryByTestId(HINT_TEST_ID)).toBeNull();
+  });
+
+  it("renders nothing while a recovery is required (the composer is disabled)", () => {
+    render(<ComposerAgentStartHint show needsRecovery />);
+    expect(screen.queryByTestId(HINT_TEST_ID)).toBeNull();
+  });
+
+  it("renders nothing while the executor environment is unavailable", () => {
+    render(<ComposerAgentStartHint show executorUnavailable />);
+    expect(screen.queryByTestId(HINT_TEST_ID)).toBeNull();
+  });
+
+  it("renders nothing while a clarification is pending (sends only enqueue)", () => {
+    render(<ComposerAgentStartHint show hasPendingClarification />);
+    expect(screen.queryByTestId(HINT_TEST_ID)).toBeNull();
+  });
+});
diff --git a/apps/web/components/task/chat/composer-agent-start-hint.tsx b/apps/web/components/task/chat/composer-agent-start-hint.tsx
new file mode 100644
index 0000000000..7c06dff424
--- /dev/null
+++ b/apps/web/components/task/chat/composer-agent-start-hint.tsx
@@ -0,0 +1,38 @@
+"use client";
+
+import { useTranslation } from "react-i18next";
+
+/**
+ * The composer's "a message will auto-start the agent" hint for
+ * recovered-idle (resume-skipped) sessions, shown while the agent is
+ * stopped AND the composer can actually accept a send. Informational only:
+ * no click action.
+ *
+ * The extra gates mirror the composer's own send-availability signals: a
+ * session in recovery (needsRecovery — WAITING_FOR_INPUT with an error
+ * message) disables the editor, an unavailable executor environment
+ * replaces it with the FailedSessionBanner, and a pending clarification
+ * routes every submission to the message queue (which only persists —
+ * it does not resume the stopped agent). In all three cases no message can
+ * be delivered to the agent, so promising that sending will start it would
+ * be a dead end.
+ */
+export function ComposerAgentStartHint({
+  show,
+  needsRecovery = false,
+  executorUnavailable = false,
+  hasPendingClarification = false,
+}: {
+  show: boolean;
+  needsRecovery?: boolean;
+  executorUnavailable?: boolean;
+  hasPendingClarification?: boolean;
+}) {
+  const { t } = useTranslation();
+  if (!show || needsRecovery || executorUnavailable || hasPendingClarification) return null;
+  return (
+    <p data-testid="composer-agent-start-hint" className="px-1 pb-1 text-xs text-muted-foreground">
+      {t("task:composerStartAgentHint")}
+    </p>
+  );
+}
diff --git a/apps/web/components/task/chat/message-list-footer.test.tsx b/apps/web/components/task/chat/message-list-footer.test.tsx
index a48389711b..ea6d1c1781 100644
--- a/apps/web/components/task/chat/message-list-footer.test.tsx
+++ b/apps/web/components/task/chat/message-list-footer.test.tsx
@@ -12,23 +12,10 @@ vi.mock("@/components/task/chat/message-renderer", () => ({
   ),
 }));
 
-let mockResumeSkippedSessionIds: Record<string, true> = {};
-
-vi.mock("@/components/state-provider", () => ({
-  useAppStore: (
-    selector: (state: { tasks: { resumeSkippedSessionIds: Record<string, true> } }) => unknown,
-  ) => selector({ tasks: { resumeSkippedSessionIds: mockResumeSkippedSessionIds } }),
-}));
-
-vi.mock("@/components/task/chat/session-resume-start-button", () => ({
-  SessionResumeStartButton: () => <div data-testid={RESUME_BUTTON_TEST_ID}>Start agent</div>,
-}));
-
 import { MessageListFooter } from "./message-list-footer";
 
 const AGENT_STATUS_TEST_ID = "agent-status";
 const SESSION_ID = "session-1";
-const RESUME_BUTTON_TEST_ID = "resume-start-button";
 
 afterEach(cleanup);
 
@@ -125,85 +112,3 @@ describe("MessageListFooter", () => {
     expect(screen.queryByTestId("action-message")).toBeNull();
   });
 });
-
-const recoveryMessage = {
-  id: "recovery-1",
-  session_id: toSessionId("session-1"),
-  task_id: toTaskId("task-1"),
-  author_type: "agent",
-  type: "status",
-  created_at: "2026-07-22T00:00:00Z",
-  content: "Agent process exited with code 1",
-  metadata: {
-    variant: "danger",
-    recovery_actions: true,
-    actions: [
-      { type: "resume_session", label: "Resume session" },
-      { type: "start_fresh", label: "Start fresh session" },
-    ],
-  },
-} satisfies Message;
-
-describe("MessageListFooter resume-skipped start button", () => {
-  const withMessages = [actionableFailure];
-
-  it("renders the Start agent button for a resume-skipped session with messages", () => {
-    mockResumeSkippedSessionIds = { [SESSION_ID]: true };
-    render(
-      <MessageListFooter
-        sessionState="WAITING_FOR_INPUT"
-        sessionId={SESSION_ID}
-        messages={withMessages}
-      />,
-    );
-    expect(screen.getByTestId(RESUME_BUTTON_TEST_ID)).toBeTruthy();
-  });
-
-  it("hides the Start agent button for a resume-skipped FAILED session (recovery owns the affordance)", () => {
-    mockResumeSkippedSessionIds = { [SESSION_ID]: true };
-    render(
-      <MessageListFooter sessionState="FAILED" sessionId={SESSION_ID} messages={withMessages} />,
-    );
-    expect(screen.queryByTestId(RESUME_BUTTON_TEST_ID)).toBeNull();
-  });
-
-  it("renders the Start agent button for an empty resume-skipped session (empty description fallback)", () => {
-    mockResumeSkippedSessionIds = { [SESSION_ID]: true };
-    render(
-      <MessageListFooter sessionState="WAITING_FOR_INPUT" sessionId={SESSION_ID} messages={[]} />,
-    );
-    expect(screen.getByTestId(RESUME_BUTTON_TEST_ID)).toBeTruthy();
-  });
-
-  it("hides the Start agent button when recovery actions are already visible", () => {
-    mockResumeSkippedSessionIds = { [SESSION_ID]: true };
-    render(
-      <MessageListFooter
-        sessionState="WAITING_FOR_INPUT"
-        sessionId={SESSION_ID}
-        messages={[recoveryMessage]}
-      />,
-    );
-    expect(screen.queryByTestId(RESUME_BUTTON_TEST_ID)).toBeNull();
-  });
-
-  it("renders the Start agent button when no recovery actions are visible", () => {
-    mockResumeSkippedSessionIds = { [SESSION_ID]: true };
-    render(
-      <MessageListFooter
-        sessionState="WAITING_FOR_INPUT"
-        sessionId={SESSION_ID}
-        messages={withMessages}
-      />,
-    );
-    expect(screen.getByTestId(RESUME_BUTTON_TEST_ID)).toBeTruthy();
-  });
-
-  it("hides the Start agent button for a resume-skipped RUNNING session", () => {
-    mockResumeSkippedSessionIds = { [SESSION_ID]: true };
-    render(
-      <MessageListFooter sessionState="RUNNING" sessionId={SESSION_ID} messages={withMessages} />,
-    );
-    expect(screen.queryByTestId(RESUME_BUTTON_TEST_ID)).toBeNull();
-  });
-});
diff --git a/apps/web/components/task/chat/message-list-footer.tsx b/apps/web/components/task/chat/message-list-footer.tsx
index 243e25a74b..6cd8dcffce 100644
--- a/apps/web/components/task/chat/message-list-footer.tsx
+++ b/apps/web/components/task/chat/message-list-footer.tsx
@@ -1,11 +1,8 @@
 "use client";
 
-import { useMemo } from "react";
 import type { Message, TaskSessionState } from "@/lib/types/http";
 import { AgentStatus } from "@/components/task/chat/messages/agent-status";
 import { MessageRenderer } from "@/components/task/chat/message-renderer";
-import { SessionResumeStartButton } from "@/components/task/chat/session-resume-start-button";
-import { useAppStore } from "@/components/state-provider";
 
 type MessageListFooterProps = {
   sessionState?: TaskSessionState;
@@ -37,6 +34,11 @@ function findCurrentActionableFailure(
   return footerActionMessages.at(-1);
 }
 
+/**
+ * Footer rendered below the transcript rows: the agent status summary plus
+ * any footer action messages (actionable failures / recovery), with
+ * missing-branch recovery owning the failure presentation when present.
+ */
 export function MessageListFooter({
   sessionState,
   sessionId,
@@ -52,39 +54,6 @@ export function MessageListFooter({
   const visibleFooterActionMessages = footerActionMessages.filter(
     (message) => !isMissingBranchFailure(message) || message.id === currentActionableFailure?.id,
   );
-  // The task-description start button only renders for EMPTY sessions. A
-  // resume-skipped session (prevent-auto-start-on-open preference, agent
-  // stopped with history) gets its Start agent button here instead — but only
-  // when no recovery actions are already visible: if the conversation shows
-  // "Resume session" / "Start fresh session" (an agent-kill recovery action
-  // message), that is the manual affordance and a second Start agent button
-  // would be duplicate noise.
-  const resumeSkipped = useAppStore((state) =>
-    sessionId ? state.tasks.resumeSkippedSessionIds[sessionId] === true : false,
-  );
-  const hasRecoveryActions = useMemo(
-    () =>
-      messages.some(
-        (message) =>
-          (message.metadata as Record<string, unknown> | undefined)?.recovery_actions === true,
-      ) ||
-      footerActionMessages.some(
-        (message) =>
-          (message.metadata as Record<string, unknown> | undefined)?.recovery_actions === true,
-      ),
-    [messages, footerActionMessages],
-  );
-  // The footer is the single Start-agent surface for resume-skipped sessions
-  // (prevent-auto-start-on-open): it must render even when the session has
-  // no messages or the task has no description, so every gated recovered-idle
-  // session keeps the manual affordance.
-  const showResumeStartButton =
-    resumeSkipped &&
-    !hasRecoveryActions &&
-    sessionState !== "FAILED" &&
-    sessionState !== "RUNNING" &&
-    sessionState !== "STARTING" &&
-    sessionId !== null;
   return (
     <>
       {!recoveryOwnsFailure && (
@@ -95,9 +64,6 @@ export function MessageListFooter({
           isWorking={isWorking}
         />
       )}
-      {showResumeStartButton && sessionId !== null && (
-        <SessionResumeStartButton sessionId={sessionId} />
-      )}
       {visibleFooterActionMessages.map((message) => (
         <MessageRenderer key={message.id} comment={message} isTaskDescription={false} />
       ))}
diff --git a/apps/web/components/task/chat/message-renderer.test.ts b/apps/web/components/task/chat/message-renderer.test.ts
index 5085d5747a..301ece09d1 100644
--- a/apps/web/components/task/chat/message-renderer.test.ts
+++ b/apps/web/components/task/chat/message-renderer.test.ts
@@ -17,7 +17,7 @@ describe("shouldShowDescriptionStartButton", () => {
     ).toBe(true);
   });
 
-  it("does NOT show for a resume-skipped session (the footer owns that surface)", () => {
+  it("does NOT show for a resume-skipped session (the composer hint owns that surface)", () => {
     expect(
       shouldShowDescriptionStartButton({
         sessionState: "WAITING_FOR_INPUT",
diff --git a/apps/web/components/task/chat/message-renderer.tsx b/apps/web/components/task/chat/message-renderer.tsx
index 262f174bbb..b048b169f8 100644
--- a/apps/web/components/task/chat/message-renderer.tsx
+++ b/apps/web/components/task/chat/message-renderer.tsx
@@ -8,10 +8,7 @@ import type { Message, TaskSessionState } from "@/lib/types/http";
 import type { ToolCallMetadata } from "@/components/task/chat/types";
 import { launchSession } from "@/lib/services/session-launch-service";
 import { isLaunchStateRegression } from "@/lib/session-state";
-import {
-  buildResumeRequest,
-  buildStartCreatedRequest,
-} from "@/lib/services/session-launch-helpers";
+import { buildStartCreatedRequest } from "@/lib/services/session-launch-helpers";
 import { useAppStore } from "@/components/state-provider";
 import { useTask } from "@/hooks/use-task";
 import { ChatMessage } from "@/components/task/chat/messages/chat-message";
@@ -53,10 +50,10 @@ type AdapterContext = {
 /**
  * Decides whether the task-description message renders the Start agent
  * button. Shown only for never-started (CREATED) sessions; resume-skipped
- * (prevent-auto-start-on-open) sessions get their Start agent button from
- * the message-list footer instead (which also covers empty sessions and
- * empty descriptions). Hidden while the task is SCHEDULING (the launch is
- * in flight) and when no task/session context is bound.
+ * (prevent-auto-start-on-open) sessions get the composer hint affordance
+ * instead (which also covers empty sessions and empty descriptions). Hidden
+ * while the task is SCHEDULING (the launch is in flight) and when no
+ * task/session context is bound.
  */
 export function shouldShowDescriptionStartButton({
   sessionState,
@@ -72,31 +69,32 @@ export function shouldShowDescriptionStartButton({
   return sessionState === "CREATED" && taskState !== "SCHEDULING" && !!taskId && !!sessionId;
 }
 
+/**
+ * "Start agent" button inside the task-description message, shown only for
+ * never-started (CREATED) sessions. Dispatches the start_created launch and
+ * hides while the workspace environment is being prepared.
+ */
 function TaskDescriptionStartButton({ taskId, sessionId }: { taskId: string; sessionId: string }) {
   const { t } = useTranslation();
   const [isStarting, setIsStarting] = useState(false);
   const prepareStatus = useAppStore(
     (state) => state.prepareProgress.bySessionId[sessionId]?.status ?? null,
   );
-  const resumeSkipped = useAppStore(
-    (state) => state.tasks.resumeSkippedSessionIds[sessionId] === true,
-  );
-  const setResumeSkipped = useAppStore((state) => state.setResumeSkipped);
   const session = useAppStore((state) => state.taskSessions.items[sessionId] ?? null);
   const setTaskSession = useAppStore((state) => state.setTaskSession);
 
   const handleStart = useCallback(async () => {
     setIsStarting(true);
     try {
-      // Never-started (CREATED) sessions use the start_created intent; a
-      // resume-skipped (recovered-idle) session resumes its existing agent.
-      const { request } = resumeSkipped
-        ? buildResumeRequest(taskId, sessionId)
-        : buildStartCreatedRequest(taskId, sessionId);
+      // This button only renders for never-started (CREATED) sessions
+      // (shouldShowDescriptionStartButton); resume-skipped (recovered-idle)
+      // sessions get their affordance from the composer hint instead, so the
+      // launch intent is always start_created.
+      const { request } = buildStartCreatedRequest(taskId, sessionId);
       const response = await launchSession(request);
       if (response.success && response.state) {
         // Hydrate the launch state (commonly STARTING) so the button hides
-        // immediately and repeated start_created/resume requests cannot fire
+        // immediately and repeated start_created requests cannot fire
         // against an already-starting session before the WS transition lands.
         // Never apply it over a newer live state: a WS RUNNING/FAILED
         // transition can land before the launch response resolves, and the
@@ -112,19 +110,12 @@ function TaskDescriptionStartButton({ taskId, sessionId }: { taskId: string; ses
           });
         }
       }
-      // Only confirmed RUNNING clears the resume-skipped marker: a resume
-      // response commonly reports STARTING (launch accepted, agent starting),
-      // and the WS RUNNING transition clears it later. Failed launches keep
-      // the button as a retry affordance.
-      if (response.state === "RUNNING") {
-        setResumeSkipped(sessionId, false);
-      }
     } catch (error) {
       console.error("Failed to start agent:", error);
     } finally {
       setIsStarting(false);
     }
-  }, [taskId, sessionId, resumeSkipped, setResumeSkipped, session, setTaskSession]);
+  }, [taskId, sessionId, session, setTaskSession]);
 
   // Hide while environment is being prepared
   if (prepareStatus === "preparing") return null;
diff --git a/apps/web/components/task/chat/session-resume-start-button.tsx b/apps/web/components/task/chat/session-resume-start-button.tsx
deleted file mode 100644
index 9764074947..0000000000
--- a/apps/web/components/task/chat/session-resume-start-button.tsx
+++ /dev/null
@@ -1,82 +0,0 @@
-"use client";
-
-import { useCallback, useState } from "react";
-import { IconPlayerPlay } from "@tabler/icons-react";
-import { Button } from "@kandev/ui/button";
-import { useTranslation } from "react-i18next";
-import type { TaskSessionState } from "@/lib/types/http";
-import { useAppStore } from "@/components/state-provider";
-import { launchSession } from "@/lib/services/session-launch-service";
-import { buildResumeRequest } from "@/lib/services/session-launch-helpers";
-import { isLaunchStateRegression } from "@/lib/session-state";
-
-/**
- * "Start agent" affordance for a resume-skipped session (prevent-auto-start-on-
- * open preference): the session exists with history (its agent process is not
- * running) and the open-time auto-resume was skipped, so the session stayed
- * stopped. Clicking resumes the agent.
- *
- * Rendered in the message-list footer for resume-skipped sessions (the
- * task-description start button only handles never-started CREATED sessions). The resume
- * is NOT gated by the preference — it is the explicit manual action.
- */
-export function SessionResumeStartButton({ sessionId }: { sessionId: string }) {
-  const { t } = useTranslation();
-  const [isStarting, setIsStarting] = useState(false);
-  const session = useAppStore((state) => state.taskSessions.items[sessionId] ?? null);
-  const setTaskSession = useAppStore((state) => state.setTaskSession);
-  const setResumeSkipped = useAppStore((state) => state.setResumeSkipped);
-
-  const handleStart = useCallback(async () => {
-    if (!session) return;
-    setIsStarting(true);
-    try {
-      const { request } = buildResumeRequest(session.task_id, sessionId);
-      const response = await launchSession(request);
-      if (response.success && response.state) {
-        // Hydrate the launch state (commonly STARTING) so the button hides
-        // immediately and the UI reflects the in-flight resume instead of
-        // staying stopped and clickable for repeated resumes. Never apply it
-        // over a newer live state: a WS RUNNING/FAILED transition can land
-        // before the launch response resolves, and the delayed STARTING must
-        // not hide a running agent or a failure's recovery affordances.
-        if (!isLaunchStateRegression(session.state, response.state)) {
-          setTaskSession({
-            id: session.id,
-            task_id: session.task_id,
-            state: response.state as TaskSessionState,
-            started_at: session.started_at ?? "",
-            updated_at: session.updated_at ?? "",
-          });
-        }
-      }
-      // Only confirmed RUNNING clears the resume-skipped marker: a resume
-      // response commonly reports STARTING (launch accepted, agent starting),
-      // and the WS RUNNING transition clears it later. Failed launches keep
-      // the button as a retry affordance.
-      if (response.state === "RUNNING") {
-        setResumeSkipped(sessionId, false);
-      }
-    } catch (error) {
-      console.error("Failed to resume agent:", error);
-    } finally {
-      setIsStarting(false);
-    }
-  }, [session, sessionId, setTaskSession, setResumeSkipped]);
-
-  return (
-    <div className="flex justify-end mt-1.5">
-      <Button
-        size="sm"
-        variant="default"
-        className="cursor-pointer gap-1.5"
-        onClick={handleStart}
-        disabled={isStarting}
-        data-testid="session-resume-start-button"
-      >
-        <IconPlayerPlay className="h-3.5 w-3.5" />
-        {isStarting ? t("task:startingEllipsis") : t("task:startAgent")}
-      </Button>
-    </div>
-  );
-}
diff --git a/apps/web/components/task/chat/use-composer-agent-start-hint.test.ts b/apps/web/components/task/chat/use-composer-agent-start-hint.test.ts
new file mode 100644
index 0000000000..af21b8932d
--- /dev/null
+++ b/apps/web/components/task/chat/use-composer-agent-start-hint.test.ts
@@ -0,0 +1,92 @@
+import { cleanup, renderHook } from "@testing-library/react";
+import { afterEach, beforeEach, describe, expect, it, vi } from "vitest";
+import { sessionId as toSessionId, taskId as toTaskId, type Message } from "@/lib/types/http";
+
+let mockResumeSkippedSessionIds: Record<string, true> = {};
+
+type MockState = {
+  tasks: { resumeSkippedSessionIds: Record<string, true> };
+};
+
+vi.mock("@/components/state-provider", () => ({
+  useAppStore: (selector: (state: MockState) => unknown) =>
+    selector({ tasks: { resumeSkippedSessionIds: mockResumeSkippedSessionIds } }),
+}));
+
+import { useComposerAgentStartHint } from "./use-composer-agent-start-hint";
+
+const SESSION_ID = "session-1";
+
+function message(overrides: Partial<Message> = {}): Message {
+  return {
+    id: "m1",
+    session_id: toSessionId(SESSION_ID),
+    task_id: toTaskId("task-1"),
+    author_type: "user",
+    type: "text",
+    created_at: "2026-07-22T00:00:00Z",
+    content: "hello",
+    ...overrides,
+  } as Message;
+}
+
+afterEach(cleanup);
+
+beforeEach(() => {
+  mockResumeSkippedSessionIds = {};
+});
+
+describe("useComposerAgentStartHint", () => {
+  it("shows for a resume-skipped WAITING_FOR_INPUT session without recovery actions", () => {
+    mockResumeSkippedSessionIds = { [SESSION_ID]: true };
+    const { result } = renderHook(() =>
+      useComposerAgentStartHint(SESSION_ID, "WAITING_FOR_INPUT", [], []),
+    );
+    expect(result.current).toBe(true);
+  });
+
+  it("hides when the session is not marked resume-skipped", () => {
+    const { result } = renderHook(() =>
+      useComposerAgentStartHint(SESSION_ID, "WAITING_FOR_INPUT", [], []),
+    );
+    expect(result.current).toBe(false);
+  });
+
+  it("hides when no session is bound", () => {
+    mockResumeSkippedSessionIds = { [SESSION_ID]: true };
+    const { result } = renderHook(() =>
+      useComposerAgentStartHint(null, "WAITING_FOR_INPUT", [], []),
+    );
+    expect(result.current).toBe(false);
+  });
+
+  it("hides when a transcript message carries recovery actions", () => {
+    mockResumeSkippedSessionIds = { [SESSION_ID]: true };
+    const recovery = message({
+      metadata: { recovery_actions: true, actions: [{ type: "resume_session", label: "Resume" }] },
+    });
+    const { result } = renderHook(() =>
+      useComposerAgentStartHint(SESSION_ID, "WAITING_FOR_INPUT", [recovery], []),
+    );
+    expect(result.current).toBe(false);
+  });
+
+  it("hides when a footer action message carries recovery actions", () => {
+    mockResumeSkippedSessionIds = { [SESSION_ID]: true };
+    const recovery = message({
+      metadata: { recovery_actions: true, actions: [{ type: "resume_session", label: "Resume" }] },
+    });
+    const { result } = renderHook(() =>
+      useComposerAgentStartHint(SESSION_ID, "WAITING_FOR_INPUT", [], [recovery]),
+    );
+    expect(result.current).toBe(false);
+  });
+
+  it("hides for FAILED, STARTING, RUNNING and terminal sessions", () => {
+    mockResumeSkippedSessionIds = { [SESSION_ID]: true };
+    for (const state of ["FAILED", "STARTING", "RUNNING", "CANCELLED", "COMPLETED"] as const) {
+      const { result } = renderHook(() => useComposerAgentStartHint(SESSION_ID, state, [], []));
+      expect(result.current).toBe(false);
+    }
+  });
+});
diff --git a/apps/web/components/task/chat/use-composer-agent-start-hint.ts b/apps/web/components/task/chat/use-composer-agent-start-hint.ts
new file mode 100644
index 0000000000..b953946112
--- /dev/null
+++ b/apps/web/components/task/chat/use-composer-agent-start-hint.ts
@@ -0,0 +1,43 @@
+"use client";
+
+import { useMemo } from "react";
+import type { Message, TaskSessionState } from "@/lib/types/http";
+import { useAppStore } from "@/components/state-provider";
+import { shouldShowComposerAgentStartHint } from "@/lib/session-state";
+
+/** True when any message in the list carries recovery-action metadata. */
+function hasRecoveryActions(messages: Message[]): boolean {
+  return messages.some(
+    (message) =>
+      (message.metadata as Record<string, unknown> | undefined)?.recovery_actions === true,
+  );
+}
+
+/**
+ * Whether the composer shows the "a message will auto-start the agent" hint
+ * for a recovered-idle (resume-skipped) session — the affordance that
+ * replaced the footer Start agent button (prevent-auto-start-on-open
+ * preference). Reads the resume-skipped flag from the store and derives the
+ * recovery-actions check from the transcript, then delegates to the shared
+ * {@link shouldShowComposerAgentStartHint} predicate.
+ */
+export function useComposerAgentStartHint(
+  sessionId: string | null,
+  sessionState: TaskSessionState | undefined,
+  messages: Message[],
+  footerActionMessages: Message[],
+): boolean {
+  const resumeSkipped = useAppStore((state) =>
+    sessionId ? state.tasks.resumeSkippedSessionIds[sessionId] === true : false,
+  );
+  const recoveryActionsVisible = useMemo(
+    () => hasRecoveryActions(messages) || hasRecoveryActions(footerActionMessages),
+    [messages, footerActionMessages],
+  );
+  return shouldShowComposerAgentStartHint({
+    resumeSkipped,
+    sessionState,
+    hasRecoveryActions: recoveryActionsVisible,
+    sessionId,
+  });
+}
diff --git a/apps/web/components/task/task-chat-panel.tsx b/apps/web/components/task/task-chat-panel.tsx
index c1d1d0d0c4..60e9877808 100644
--- a/apps/web/components/task/task-chat-panel.tsx
+++ b/apps/web/components/task/task-chat-panel.tsx
@@ -23,6 +23,7 @@ import { useIsTaskArchived } from "./task-archived-context";
 import { useChatPanelState } from "./chat/use-chat-panel-state";
 import { ChatInputArea, useSubmitHandler, useChatPanelHandlers } from "./chat/chat-input-area";
 import { ClarificationInputOverlay } from "./chat/clarification-input-overlay";
+import { useComposerAgentStartHint } from "./chat/use-composer-agent-start-hint";
 import { ResizeHandle } from "./chat/resize-handle";
 import { useResizableClarificationOverlay } from "@/hooks/use-resizable-clarification-overlay";
 import { PanelSearchBar } from "@/components/search/panel-search-bar";
@@ -241,6 +242,12 @@ export const TaskChatPanel = memo(function TaskChatPanel({
     groupedItems,
     isInitialMessagesLoading,
   );
+  const showAgentStartHint = useComposerAgentStartHint(
+    resolvedSessionId,
+    session?.state,
+    allMessages,
+    footerActionMessages,
+  );
   const { handleCancelTurn } = useChatPanelHandlers(resolvedSessionId, chatInputRef);
   const { clarificationKey, handleClarificationResolved } = useClarificationKey(agentMessageCount);
   const {
@@ -423,6 +430,7 @@ export const TaskChatPanel = memo(function TaskChatPanel({
         showScrollToStart={showScrollToStartButton}
         onScrollToStart={scrollToStart}
         statusTaskId={statusTaskId ?? taskIdHint}
+        showAgentStartHint={showAgentStartHint}
       />
     </PanelRoot>
   );
@@ -489,8 +497,15 @@ type ChatFooterProps = {
   showScrollToStart: boolean;
   onScrollToStart: () => void;
   statusTaskId: string | null;
+  /** Recovered-idle sessions render the composer hint (see ChatInputArea). */
+  showAgentStartHint: boolean;
 };
 
+/**
+ * Composer footer: renders the chat input area (or the read-only archived
+ * banner) and forwards the recovered-idle agent-start-hint visibility from
+ * the panel down to the input.
+ */
 function ChatFooter({
   isArchived,
   chatInputRef,
@@ -509,6 +524,7 @@ function ChatFooter({
   showScrollToStart,
   onScrollToStart,
   statusTaskId,
+  showAgentStartHint,
 }: ChatFooterProps) {
   const { t } = useTranslation();
   if (isArchived) {
@@ -536,6 +552,7 @@ function ChatFooter({
       showScrollToStart={showScrollToStart}
       onScrollToStart={onScrollToStart}
       statusTaskId={statusTaskId}
+      showAgentStartHint={showAgentStartHint}
     />
   );
 }
diff --git a/apps/web/e2e/tests/settings/mobile-agent-start-hint.spec.ts b/apps/web/e2e/tests/settings/mobile-agent-start-hint.spec.ts
new file mode 100644
index 0000000000..cadd76f148
--- /dev/null
+++ b/apps/web/e2e/tests/settings/mobile-agent-start-hint.spec.ts
@@ -0,0 +1,68 @@
+import { test, expect } from "../../fixtures/test-base";
+import { openTaskSession } from "../../helpers/git-helper";
+
+// Mobile variant of the composer agent-start hint: the resume-skipped gate
+// and the hint render through the shared responsive TaskPageContent
+// (session-mobile-layout renders TaskChatPanel), so a recovered-idle session
+// must show the hint on a phone viewport and a sent message must start the
+// agent. Mirrors the desktop restart-resume flow in
+// settings/prevent-auto-start-on-open.spec.ts.
+
+test.describe("Mobile agent-start hint", () => {
+  test("recovered-idle session shows the composer hint and a message starts the agent", async ({
+    testPage,
+    apiClient,
+    seedData,
+    backend,
+  }) => {
+    test.setTimeout(180_000);
+    await apiClient.saveUserSettings({ prevent_auto_start_agent_on_open: true });
+    try {
+      await apiClient.createTaskWithAgent(
+        seedData.workspaceId,
+        "Mobile Agent Start Hint Task",
+        seedData.agentProfileId,
+        {
+          description: "/e2e:simple-message",
+          workflow_id: seedData.workflowId,
+          workflow_step_id: seedData.startStepId,
+          repository_ids: [seedData.repositoryId],
+        },
+      );
+
+      // Let the agent finish its first turn so the session ends idle with a
+      // resume token (the post-restart needs_resume shape).
+      const session = await openTaskSession(testPage, "Mobile Agent Start Hint Task");
+      await expect(session.chat.getByText("simple mock response", { exact: false })).toBeVisible({
+        timeout: 30_000,
+      });
+      await session.waitForChatIdle({ timeout: 15_000 });
+
+      // Restart the backend and reload — the resume-skipped gate must keep
+      // the agent stopped and the composer hint must replace the footer
+      // Start agent button.
+      await backend.restart();
+      await testPage.reload();
+      await session.waitForLoad();
+
+      await expect(testPage.getByTestId("composer-agent-start-hint")).toBeVisible({
+        timeout: 60_000,
+      });
+      await expect(testPage.getByTestId("session-resume-start-button")).toHaveCount(0);
+      await expect(testPage.getByText("Resumed agent", { exact: false })).toHaveCount(0);
+
+      // Sending a message is the explicit start: the agent resumes and
+      // keeps working. Touch layouts don't submit on Ctrl/Cmd+Enter, so use
+      // the Send-button path like the other mobile specs. Index 1: the first
+      // "simple mock response" from the pre-restart turn is still in the
+      // transcript, so the post-send reply must be the SECOND match.
+      await session.sendMessageViaButton("/e2e:simple-message");
+      await expect(testPage.getByText("Resumed agent", { exact: false })).toBeVisible({
+        timeout: 30_000,
+      });
+      await session.expectChatResponseVisible("simple mock response", 1, { timeout: 30_000 });
+    } finally {
+      await apiClient.saveUserSettings({ prevent_auto_start_agent_on_open: false });
+    }
+  });
+});
diff --git a/apps/web/e2e/tests/settings/prevent-auto-start-on-open.spec.ts b/apps/web/e2e/tests/settings/prevent-auto-start-on-open.spec.ts
index e31b2f73d6..d5db8c04f9 100644
--- a/apps/web/e2e/tests/settings/prevent-auto-start-on-open.spec.ts
+++ b/apps/web/e2e/tests/settings/prevent-auto-start-on-open.spec.ts
@@ -152,22 +152,30 @@ test.describe("Prevent auto-start on open", () => {
       await session.waitForChatIdle({ timeout: 15_000 });
 
       // Restart the backend and reload — the resume-skipped gate must keep
-      // the agent stopped and render the Start agent button instead.
+      // the agent stopped. The composer hint replaces the footer Start agent
+      // button: it says a message will auto-start the agent, and it is
+      // always visible (the composer sits outside the transcript scroll
+      // container, so the clipped-button failure cannot occur).
       await backend.restart();
       await testPage.reload();
       await session.waitForLoad();
 
-      const startButton = testPage.getByTestId("session-resume-start-button");
-      await expect(startButton).toBeVisible({ timeout: 60_000 });
+      await expect(testPage.getByTestId("composer-agent-start-hint")).toBeVisible({
+        timeout: 60_000,
+      });
+      await expect(testPage.getByTestId("session-resume-start-button")).toHaveCount(0);
       await expect(testPage.getByText("Resumed agent", { exact: false })).toHaveCount(0);
 
-      // Manual start resumes the agent and it keeps working.
-      await startButton.click();
+      // Sending a message is the explicit start: the agent resumes and
+      // keeps working. Index 1: the first "simple mock response" from the
+      // pre-restart turn is still in the transcript, so the post-send reply
+      // must be the SECOND match — asserting index 0 would pass even if the
+      // resumed launch dropped the prompt.
+      await session.sendMessage("/e2e:simple-message");
       await expect(testPage.getByText("Resumed agent", { exact: false })).toBeVisible({
         timeout: 30_000,
       });
-      await session.sendMessage("/e2e:simple-message");
-      await session.expectChatResponseVisible("simple mock response", 0, { timeout: 30_000 });
+      await session.expectChatResponseVisible("simple mock response", 1, { timeout: 30_000 });
     } finally {
       await apiClient.saveUserSettings({ prevent_auto_start_agent_on_open: false });
     }
diff --git a/apps/web/lib/session-state.test.ts b/apps/web/lib/session-state.test.ts
index c2e3c74290..3e5325db38 100644
--- a/apps/web/lib/session-state.test.ts
+++ b/apps/web/lib/session-state.test.ts
@@ -1,5 +1,5 @@
 import { describe, expect, it } from "vitest";
-import { isLaunchStateRegression } from "./session-state";
+import { isLaunchStateRegression, shouldShowComposerAgentStartHint } from "./session-state";
 
 describe("isLaunchStateRegression", () => {
   it("applies the launch response over a never-started (CREATED) session", () => {
@@ -44,3 +44,58 @@ describe("isLaunchStateRegression", () => {
     expect(isLaunchStateRegression("CREATED", "SOMETHING_NEW")).toBe(false);
   });
 });
+
+describe("shouldShowComposerAgentStartHint", () => {
+  const base = {
+    resumeSkipped: true,
+    hasRecoveryActions: false,
+    sessionId: "s1",
+  } as const;
+
+  it("shows for a resume-skipped WAITING_FOR_INPUT session without recovery actions", () => {
+    expect(shouldShowComposerAgentStartHint({ ...base, sessionState: "WAITING_FOR_INPUT" })).toBe(
+      true,
+    );
+  });
+
+  it("shows for a resume-skipped IDLE session (office idle shape)", () => {
+    expect(shouldShowComposerAgentStartHint({ ...base, sessionState: "IDLE" })).toBe(true);
+  });
+
+  it("hides when the session state is unknown/absent (a send might be rejected)", () => {
+    expect(shouldShowComposerAgentStartHint({ ...base, sessionState: undefined })).toBe(false);
+  });
+
+  it("hides when the session is not resume-skipped", () => {
+    expect(shouldShowComposerAgentStartHint({ ...base, resumeSkipped: false })).toBe(false);
+  });
+
+  it("hides for a FAILED session (recovery owns the surface)", () => {
+    expect(shouldShowComposerAgentStartHint({ ...base, sessionState: "FAILED" })).toBe(false);
+  });
+
+  it("hides for terminal CANCELLED/COMPLETED sessions (the composer rejects sends)", () => {
+    expect(shouldShowComposerAgentStartHint({ ...base, sessionState: "CANCELLED" })).toBe(false);
+    expect(shouldShowComposerAgentStartHint({ ...base, sessionState: "COMPLETED" })).toBe(false);
+  });
+
+  it("hides while the session is STARTING", () => {
+    expect(shouldShowComposerAgentStartHint({ ...base, sessionState: "STARTING" })).toBe(false);
+  });
+
+  it("hides while the session is RUNNING", () => {
+    expect(shouldShowComposerAgentStartHint({ ...base, sessionState: "RUNNING" })).toBe(false);
+  });
+
+  it("hides for a never-started CREATED session (the description button owns that surface)", () => {
+    expect(shouldShowComposerAgentStartHint({ ...base, sessionState: "CREATED" })).toBe(false);
+  });
+
+  it("hides when recovery actions are already visible", () => {
+    expect(shouldShowComposerAgentStartHint({ ...base, hasRecoveryActions: true })).toBe(false);
+  });
+
+  it("hides when no session is bound", () => {
+    expect(shouldShowComposerAgentStartHint({ ...base, sessionId: null })).toBe(false);
+  });
+});
diff --git a/apps/web/lib/session-state.ts b/apps/web/lib/session-state.ts
index 53d974df5a..5a110af400 100644
--- a/apps/web/lib/session-state.ts
+++ b/apps/web/lib/session-state.ts
@@ -36,3 +36,33 @@ export function isLaunchStateRegression(
   if (live === undefined || incoming === undefined) return false;
   return incoming < live;
 }
+
+/**
+ * Visibility rule for the composer's "a message will auto-start the agent"
+ * hint (the recovered-idle / resume-skipped affordance that replaced the
+ * footer Start agent button). The hint promises that sending a message will
+ * start the agent, so it may only render for states the composer can
+ * actually send into: WAITING_FOR_INPUT or IDLE (deriveSessionInputMode's
+ * "direct" set for non-CREATED sessions). Terminal states (FAILED,
+ * CANCELLED, COMPLETED) are excluded: the composer rejects sends there
+ * ("Session has ended"), so the hint would be a dead-end promise; recovery
+ * actions or the session menu own those surfaces.
+ */
+export function shouldShowComposerAgentStartHint({
+  resumeSkipped,
+  sessionState,
+  hasRecoveryActions,
+  sessionId,
+}: {
+  resumeSkipped: boolean;
+  sessionState?: TaskSessionState;
+  hasRecoveryActions: boolean;
+  sessionId: string | null;
+}): boolean {
+  return (
+    resumeSkipped &&
+    !hasRecoveryActions &&
+    (sessionState === "WAITING_FOR_INPUT" || sessionState === "IDLE") &&
+    sessionId !== null
+  );
+}
diff --git a/apps/web/src/locales/en/task.json b/apps/web/src/locales/en/task.json
index 2cad240210..87623eddd0 100644
--- a/apps/web/src/locales/en/task.json
+++ b/apps/web/src/locales/en/task.json
@@ -1270,6 +1270,7 @@
   "start2": "Start",
   "startAgent": "Start agent",
   "startAgent2": "Start Agent",
+  "composerStartAgentHint": "Sending a message will auto-start the agent.",
   "startDevServerPreview": "Start dev server preview",
   "startFreshSession": "Start fresh session",
   "startPlanMode": "Start Plan Mode",
diff --git a/apps/web/src/locales/pseudo/task.json b/apps/web/src/locales/pseudo/task.json
index 9a8641d0e9..a206d2451c 100644
--- a/apps/web/src/locales/pseudo/task.json
+++ b/apps/web/src/locales/pseudo/task.json
@@ -1270,6 +1270,7 @@
   "start2": "Śţàŕţ",
   "startAgent": "Śţàŕţ àĝēńţ",
   "startAgent2": "Śţàŕţ Àĝēńţ",
+  "composerStartAgentHint": "Śēńďĩńĝ à ḿēśśàĝē ŵĩļļ àũţō-śţàŕţ ţħē àĝēńţ.",
   "startDevServerPreview": "Śţàŕţ ďēv śēŕvēŕ ƥŕēvĩēŵ",
   "startFreshSession": "Śţàŕţ ƒŕēśĥ śēśśĩōń",
   "startPlanMode": "Śţàŕţ Ƥĺàń Ḿōďē",
diff --git a/apps/web/src/locales/pt-pt/task.json b/apps/web/src/locales/pt-pt/task.json
index 3381728a9f..de038b133f 100644
--- a/apps/web/src/locales/pt-pt/task.json
+++ b/apps/web/src/locales/pt-pt/task.json
@@ -1249,6 +1249,7 @@
   "start2": "Iniciar",
   "startAgent": "Iniciar o agente",
   "startAgent2": "Iniciar o agente",
+  "composerStartAgentHint": "Enviar uma mensagem iniciará automaticamente o agente.",
   "startDevServerPreview": "Iniciar a pré-visualização do servidor de desenvolvimento",
   "startFreshSession": "Iniciar uma sessão nova",
   "startPlanMode": "Iniciar o modo de planeamento",
diff --git a/apps/web/src/locales/zh-cn/task.json b/apps/web/src/locales/zh-cn/task.json
index 2c1b0034ba..c9e2e17492 100644
--- a/apps/web/src/locales/zh-cn/task.json
+++ b/apps/web/src/locales/zh-cn/task.json
@@ -1249,6 +1249,7 @@
   "start2": "开始",
   "startAgent": "启动智能体",
   "startAgent2": "启动智能体",
+  "composerStartAgentHint": "发送消息将自动启动智能体。",
   "startDevServerPreview": "启动开发服务器预览",
   "startFreshSession": "开始全新会话",
   "startPlanMode": "启动计划模式",
diff --git a/docs/plans/start-agent-composer-hint/plan.md b/docs/plans/start-agent-composer-hint/plan.md
new file mode 100644
index 0000000000..29994b984c
--- /dev/null
+++ b/docs/plans/start-agent-composer-hint/plan.md
@@ -0,0 +1,188 @@
+---
+spec: ../../specs/prevent-agent-autostart-on-open/spec.md
+created: 2026-08-13
+status: done
+---
+
+# Implementation Plan: Start-Agent Composer Hint
+
+## Overview
+
+PR #2556 added the Start agent button for recovered-idle (resume-skipped)
+sessions in the message-list footer. The button sits at the bottom of the
+transcript and can be clipped (only a few pixels of its top visible) when the
+transcript is not fully scrolled down, e.g. right after navigating into a
+task whose auto-scroll did not reach the bottom.
+
+Product decision (2026-08-13): for recovered-idle sessions the footer Start
+agent button is REMOVED and replaced by a single informational hint line in
+the chat composer: "Sending a message will auto-start the agent." Sending a
+message already is the explicit user action that starts the agent, so the
+hint describes real behavior and removes the clipped-button failure entirely
+(the composer sits outside the transcript scroll container and is always
+visible). The never-started (`CREATED`) task-description Start agent button is
+UNCHANGED: an explicitly-never-started task keeps its explicit Start agent
+affordance under the task description.
+
+The hint's promise must also hold for messages RECEIVED by the session, not
+only the user's composer sends: a message from another task (a sub-task via
+`message_task_kandev`) lands on the same message queue
+(`QueueAndInterruptForPeerMessage` → `QueueMessageWithMetadata` with
+`QueuedByAgent`), and the queue dispatch
+(`takeIfPromptableLocked` → `executeQueuedMessage` → `PromptTask` →
+`ensureSessionRunning`) resumes a stopped-but-resumable agent. This path
+already exists on the backend and is never gated by the preference; it has no
+direct test pinning "peer message at a stopped session → agent resumed", so a
+backend regression test is added (task-04).
+
+## Behavior
+
+| Surface | Before | After |
+|---|---|---|
+| Recovered-idle session (resume-skipped, non-FAILED, no recovery actions, not STARTING/RUNNING) | footer `SessionResumeStartButton` ("Start agent") | composer hint line, no button |
+| FAILED-but-resumable session | recovery actions own the surface (no button) | unchanged; hint also hidden |
+| Never-started (`CREATED`) session | `TaskDescriptionStartButton` under the task description | unchanged; no hint |
+
+The composer hint condition is the exact condition set the footer button used
+today: `resumeSkipped && !hasRecoveryActions && sessionState not in
+{FAILED, RUNNING, STARTING} && sessionId != null`.
+
+## Frontend Changes
+
+### 1. Shared predicate (`apps/web/lib/session-state.ts`)
+
+Add a pure, exported `shouldShowComposerAgentStartHint({ resumeSkipped,
+sessionState, hasRecoveryActions, sessionId })` next to the existing
+`isLaunchStateRegression`, unit-tested in `apps/web/lib/session-state.test.ts`.
+This keeps the visibility decision testable without rendering the composer.
+
+### 2. Remove the footer resume button
+
+- Delete `apps/web/components/task/chat/session-resume-start-button.tsx` (its
+  launch/resume logic dies with it; no other file imports it).
+- `apps/web/components/task/chat/message-list-footer.tsx`: remove the
+  `resumeSkipped` selector, the `hasRecoveryActions` memo, the
+  `showResumeStartButton` computation, and the `SessionResumeStartButton`
+  render.
+- `apps/web/components/task/chat/message-list-footer.test.tsx`: remove the
+  `SessionResumeStartButton` mock and the "resume-skipped start button"
+  describe blocks.
+- `apps/web/components/task/chat/message-renderer.tsx`: remove the now
+  unreachable `resumeSkipped` branch in `TaskDescriptionStartButton`'s
+  `handleStart` (the description button only renders for CREATED sessions,
+  which are never resume-skipped; the resume intent can no longer reach this
+  button). Keep `shouldShowDescriptionStartButton` CREATED-only. Update the
+  stale test comment in `message-renderer.test.ts` ("the footer owns that
+  surface" → "the composer hint owns that surface").
+- i18n: no copy change here; `task:startAgent` stays (used by the CREATED
+  description button).
+
+### 3. Composer hint UI
+
+- New hook `useComposerAgentStartHint(sessionId, sessionState, messages,
+  footerActionMessages)` in `apps/web/components/task/chat/` (+ test): reads
+  `state.tasks.resumeSkippedSessionIds[sessionId] === true` from the store,
+  derives `hasRecoveryActions` from `messages`/`footerActionMessages`
+  (`metadata.recovery_actions === true`, same rule the footer used), and
+  calls the shared predicate.
+- `apps/web/components/task/task-chat-panel.tsx`: compute
+  `showAgentStartHint` from the hook (session id, `session?.state`,
+  `allMessages`, `footerActionMessages`) and thread it through `ChatFooter`
+  into `ChatInputArea` (`apps/web/components/task/chat/chat-input-area.tsx`)
+  as a new `showAgentStartHint?: boolean` prop.
+- `chat-input-area.tsx`: render a muted one-line hint above
+  `QueueAffordance`, e.g.
+  `<p data-testid="composer-agent-start-hint" className="...">` with
+  `t("task:composerStartAgentHint")`. No click action.
+- i18n: add `composerStartAgentHint` to
+  `apps/web/src/locales/{en,pseudo,pt-pt,zh-cn}/task.json`. Copy: "Sending a
+  message will auto-start the agent." (plain punctuation, no em dash).
+- Component test: extend `chat-input-area.test.tsx` (or a focused test) to
+  assert the hint renders when `showAgentStartHint` is true and is absent
+  when false.
+
+## E2E Changes
+
+- `apps/web/e2e/tests/settings/prevent-auto-start-on-open.spec.ts`,
+  "post-restart session does not auto-resume when the preference is on":
+  - assert `composer-agent-start-hint` visible and
+    `session-resume-start-button` count 0 (no "Resumed agent" on its own);
+  - send `/e2e:simple-message` via the composer (`session.sendMessage`) and
+    assert the mock response appears and "Resumed agent" becomes visible
+    (sending a message is now the explicit start).
+  - The two final-step (CREATED) tests keep asserting
+    `task-description-start-button`; unchanged.
+- Mobile (`mobile-chrome` project): new
+  `apps/web/e2e/tests/settings/mobile-agent-start-hint.spec.ts` using the
+  same restart pattern (task + first turn → `backend.restart()` →
+  `testPage.reload()`) on a phone viewport: hint visible, no resume button,
+  send message → mock response. The existing
+  `mobile-prevent-auto-start-on-open.spec.ts` (CREATED button) stays green.
+
+## Risks
+
+- The desktop restart test's send-message path must prove auto-start-on-send
+  (same mock flow as today's post-click send; the mock agent answers
+  `/e2e:simple-message` after a resumed launch).
+- Mobile restart flow is slower (desktop restart test already needs
+  `test.setTimeout(180_000)`); reuse the same timeouts.
+- i18n ratchet: the hint copy must go through `t()` in the component, and the
+  new key must exist in all four locale files (`i18n:check` fails otherwise).
+
+## Verification
+
+```bash
+(cd apps/web && pnpm run typecheck)
+```
+
+```bash
+(cd apps/web && pnpm vitest run lib/session-state.test.ts components/task/chat/message-list-footer.test.tsx components/task/chat/message-renderer.test.ts components/task/chat/chat-input-area.test.tsx)
+```
+
+```bash
+(cd apps/web && pnpm run i18n:check && pnpm run i18n:ratchet)
+```
+
+```bash
+(cd apps/backend && go test ./internal/orchestrator/ -run TestQueueAndInterruptForPeerMessage_StoppedSessionResumesAgent -race)
+```
+
+```bash
+(cd apps/web && KANDEV_E2E_MOCK=true pnpm e2e:raw --project=chromium settings/prevent-auto-start-on-open.spec.ts)
+(cd apps/web && KANDEV_E2E_MOCK=true pnpm e2e:raw --project=mobile-chrome settings/mobile-agent-start-hint.spec.ts settings/mobile-prevent-auto-start-on-open.spec.ts)
+```
+
+## Implementation Waves And Parallel Candidates
+
+```
+Wave 1 (sequential):
+- [x] [task-01-shared-predicate-and-removal](task-01-shared-predicate-and-removal.md)
+- [x] [task-02-composer-hint-ui](task-02-composer-hint-ui.md)
+- [x] [task-03-e2e](task-03-e2e.md)
+- [x] [task-04-peer-message-resumes-stopped-session](task-04-peer-message-resumes-stopped-session.md)
+```
+
+Tasks 01→03 are sequential (02 depends on 01's predicate, 03 depends on 02's
+rendered hint). Task 04 is backend-only and independent of the frontend
+tasks; it can run at any point in the wave.
+
+## Verification Results
+
+- Frontend: `make typecheck` and `make fmt` clean; `make lint` clean (0
+  warnings). Targeted vitest (session-state, message-list-footer,
+  message-renderer, use-composer-agent-start-hint, composer-agent-start-hint)
+  38/38 passing. `pnpm run i18n:check` + `pnpm run i18n:ratchet` clean.
+- Backend: `go test ./internal/orchestrator/ -count=1` clean (75s, includes
+  the new `TestQueueAndInterruptForPeerMessage_StoppedSessionResumesAgent`
+  with `-race`).
+- E2E (mock agent): `settings/prevent-auto-start-on-open.spec.ts` on
+  chromium 3/3; `settings/mobile-agent-start-hint.spec.ts` +
+  `settings/mobile-prevent-auto-start-on-open.spec.ts` on mobile-chrome 2/2.
+- Full `make test` was NOT clean on this VM, but every failure is unrelated
+  to this change: `internal/agentctl/server/{api,config,process}`,
+  `internal/launcher`, `internal/system/updates` reproduce on a clean tree
+  (host init-system/process-output environment tests), and the web suite's
+  18 failures are load-flaky 5-10s timeouts (git-server, azure-devops,
+  sentry, file-browser, settings, git-base) that all pass in isolation on
+  both the clean tree and this branch. `lib/http-git-server.test.ts` fails
+  on the clean tree too.
diff --git a/docs/plans/start-agent-composer-hint/task-01-shared-predicate-and-removal.md b/docs/plans/start-agent-composer-hint/task-01-shared-predicate-and-removal.md
new file mode 100644
index 0000000000..0a74b0c682
--- /dev/null
+++ b/docs/plans/start-agent-composer-hint/task-01-shared-predicate-and-removal.md
@@ -0,0 +1,76 @@
+---
+id: "01-shared-predicate-and-removal"
+title: "Shared hint predicate and footer resume-button removal"
+status: done
+wave: 1
+parallelism: sequential
+depends_on: []
+plan: "plan.md"
+spec: "../../specs/prevent-agent-autostart-on-open/spec.md"
+---
+
+# Task 01: Shared hint predicate and footer resume-button removal
+
+## Acceptance
+
+- `shouldShowComposerAgentStartHint({ resumeSkipped, sessionState,
+  hasRecoveryActions, sessionId })` is exported from
+  `apps/web/lib/session-state.ts` and returns true only when ALL of:
+  `resumeSkipped === true`, `hasRecoveryActions === false`, `sessionState` is
+  not `FAILED` / `RUNNING` / `STARTING`, and `sessionId` is non-null. This is
+  the exact condition set the footer button used.
+- Unit tests in `apps/web/lib/session-state.test.ts` cover: visible for a
+  resume-skipped `WAITING_FOR_INPUT` session; hidden when not resume-skipped;
+  hidden for `FAILED`; hidden for `RUNNING` and `STARTING`; hidden when
+  recovery actions are present; hidden when `sessionId` is null.
+- `apps/web/components/task/chat/session-resume-start-button.tsx` is deleted
+  and no file imports `session-resume-start-button` anymore.
+- `apps/web/components/task/chat/message-list-footer.tsx` no longer renders
+  `SessionResumeStartButton` and no longer reads
+  `resumeSkippedSessionIds` / computes `hasRecoveryActions` /
+  `showResumeStartButton` (those existed only for the button).
+- `apps/web/components/task/chat/message-list-footer.test.tsx` has no
+  `SessionResumeStartButton` mock and no resume-button describe blocks; the
+  remaining footer tests (AgentStatus, failure presentation) still pass.
+- `apps/web/components/task/chat/message-renderer.tsx`:
+  `TaskDescriptionStartButton`'s `handleStart` drops the now-unreachable
+  `resumeSkipped ? buildResumeRequest : buildStartCreatedRequest` branch and
+  always dispatches `buildStartCreatedRequest`; `shouldShowDescriptionStartButton`
+  stays CREATED-only. The test comment "the footer owns that surface" in
+  `message-renderer.test.ts` is updated to name the composer hint.
+
+## Verification
+
+```bash
+(cd apps/web && pnpm run typecheck)
+```
+
+```bash
+(cd apps/web && pnpm vitest run lib/session-state.test.ts components/task/chat/message-list-footer.test.tsx components/task/chat/message-renderer.test.ts)
+```
+
+## Files Likely Touched
+
+- `apps/web/lib/session-state.ts` (+ `session-state.test.ts`)
+- `apps/web/components/task/chat/session-resume-start-button.tsx` (deleted)
+- `apps/web/components/task/chat/message-list-footer.tsx` (+ test)
+- `apps/web/components/task/chat/message-renderer.tsx` (+ test)
+
+## Dependencies
+
+None. The predicate is new and the removal is independent of the hint UI.
+
+## Inputs
+
+- Spec: "What" bullets 1 and 3, scenarios 1 and 5.
+- Current footer predicate at `message-list-footer.tsx:62-88`
+  (`resumeSkipped`, `hasRecoveryActions`, `showResumeStartButton`).
+- Current `TaskDescriptionStartButton` branch at `message-renderer.tsx:90-95`
+  and `shouldShowDescriptionStartButton` at `message-renderer.tsx:67-72`.
+
+## Output Contract
+
+No UI change yet (the hint renders in task 02): the resume-skipped session
+simply has no Start agent button anywhere, and the shared predicate pins the
+exact condition set the hint will reuse. The CREATED description button is
+behaviorally unchanged.
diff --git a/docs/plans/start-agent-composer-hint/task-02-composer-hint-ui.md b/docs/plans/start-agent-composer-hint/task-02-composer-hint-ui.md
new file mode 100644
index 0000000000..87f688212e
--- /dev/null
+++ b/docs/plans/start-agent-composer-hint/task-02-composer-hint-ui.md
@@ -0,0 +1,85 @@
+---
+id: "02-composer-hint-ui"
+title: "Composer hint UI and i18n"
+status: done
+wave: 1
+parallelism: sequential
+depends_on: ["01-shared-predicate-and-removal"]
+plan: "plan.md"
+spec: "../../specs/prevent-agent-autostart-on-open/spec.md"
+---
+
+# Task 02: Composer hint UI and i18n
+
+## Acceptance
+
+- `useComposerAgentStartHint(sessionId, sessionState, messages,
+  footerActionMessages)` (new hook in `apps/web/components/task/chat/`)
+  returns `shouldShowComposerAgentStartHint(...)` with `resumeSkipped` read
+  from `state.tasks.resumeSkippedSessionIds[sessionId] === true` and
+  `hasRecoveryActions` derived from `messages`/`footerActionMessages` using
+  the same rule the footer used (`metadata.recovery_actions === true` on any
+  message). `sessionId === null` short-circuits to false. Hook unit tests
+  cover: resume-skipped + `WAITING_FOR_INPUT` + no recovery → true; FAILED /
+  STARTING / RUNNING → false; recovery action present in `messages` or
+  `footerActionMessages` → false; no resume-skipped flag → false.
+- `apps/web/components/task/task-chat-panel.tsx` computes
+  `showAgentStartHint` from the hook (`session?.state`, `allMessages`,
+  `footerActionMessages`) and passes it through `ChatFooter` to
+  `ChatInputArea` (`apps/web/components/task/chat/chat-input-area.tsx`) as a
+  new optional `showAgentStartHint` prop.
+- `chat-input-area.tsx` renders, above `QueueAffordance`, a single muted
+  one-line hint when `showAgentStartHint` is true:
+  `<p data-testid="composer-agent-start-hint" …>{t("task:composerStartAgentHint")}</p>`.
+  It is absent when the prop is false/undefined. No click handler.
+- Component test (extend `chat-input-area.test.tsx` or a focused test)
+  asserts the hint element renders for `showAgentStartHint` true and is
+  absent for false.
+- i18n: `composerStartAgentHint` added to
+  `apps/web/src/locales/{en,pseudo,pt-pt,zh-cn}/task.json` with copy "Sending
+  a message will auto-start the agent." (plain punctuation; pseudo and
+  translations follow the existing per-locale style). `pnpm run i18n:check`
+  and `pnpm run i18n:ratchet` pass.
+
+## Verification
+
+```bash
+(cd apps/web && pnpm run typecheck)
+```
+
+```bash
+(cd apps/web && pnpm vitest run components/task/chat/chat-input-area.test.tsx components/task/chat/use-composer-agent-start-hint.test.ts)
+```
+
+```bash
+(cd apps/web && pnpm run i18n:check && pnpm run i18n:ratchet)
+```
+
+## Files Likely Touched
+
+- `apps/web/components/task/chat/use-composer-agent-start-hint.ts` (new, + test)
+- `apps/web/components/task/task-chat-panel.tsx` (`ChatFooter` props)
+- `apps/web/components/task/chat/chat-input-area.tsx` (+ test)
+- `apps/web/src/locales/en/task.json`, `pseudo/task.json`,
+  `pt-pt/task.json`, `zh-cn/task.json`
+
+## Dependencies
+
+Task 01 (the `shouldShowComposerAgentStartHint` predicate and the removal of
+the footer button, so no second affordance competes with the hint).
+
+## Inputs
+
+- Spec: "What" bullet 3 (hint visibility rules), scenarios 6 and 7.
+- `ChatInputArea` render at `chat-input-area.tsx:629-659` (the
+  `data-testid="chat-input-area"` wrapper above `QueueAffordance`).
+- `ChatFooter` prop threading at `task-chat-panel.tsx:400-418` and
+  `484-528`.
+
+## Output Contract
+
+A recovered-idle session shows exactly one affordance: the composer hint
+("Sending a message will auto-start the agent."), always visible because the
+composer is outside the transcript scroll container. The hint disappears when
+the session starts/runs, fails, or recovery actions are visible. The CREATED
+description button remains the never-started affordance.
diff --git a/docs/plans/start-agent-composer-hint/task-03-e2e.md b/docs/plans/start-agent-composer-hint/task-03-e2e.md
new file mode 100644
index 0000000000..9cc152e74b
--- /dev/null
+++ b/docs/plans/start-agent-composer-hint/task-03-e2e.md
@@ -0,0 +1,71 @@
+---
+id: "03-e2e"
+title: "E2E: hint replaces resume button, desktop and mobile"
+status: done
+wave: 1
+parallelism: sequential
+depends_on: ["02-composer-hint-ui"]
+plan: "plan.md"
+spec: "../../specs/prevent-agent-autostart-on-open/spec.md"
+---
+
+# Task 03: E2E — hint replaces resume button, desktop and mobile
+
+## Acceptance
+
+- `apps/web/e2e/tests/settings/prevent-auto-start-on-open.spec.ts`,
+  "post-restart session does not auto-resume when the preference is on":
+  - after `backend.restart()` + `testPage.reload()`, asserts
+    `composer-agent-start-hint` is visible and
+    `session-resume-start-button` has count 0 (and "Resumed agent" never
+    appears on its own);
+  - sends `/e2e:simple-message` via the composer (`session.sendMessage`) and
+    asserts the mock response ("simple mock response") becomes visible and
+    "Resumed agent" appears — sending a message is the explicit start.
+  - `test.setTimeout(180_000)` retained; settings/task teardown unchanged.
+- The two final-step tests in the same file still assert
+  `task-description-start-button` visibility/absence exactly as today
+  (CREATED button unchanged, setting-off control unchanged).
+- `apps/web/e2e/tests/settings/mobile-prevent-auto-start-on-open.spec.ts`
+  (CREATED button on mobile) stays green unchanged.
+- New `apps/web/e2e/tests/settings/mobile-agent-start-hint.spec.ts`
+  (`mobile-chrome` project, phone viewport from the project device, no
+  per-test `setViewportSize`): same restart pattern — task with
+  `/e2e:simple-message` description, first turn completes, `backend.restart()`
+  + `testPage.reload()`, then asserts `composer-agent-start-hint` visible,
+  `session-resume-start-button` count 0, sends a message, and asserts the
+  mock response appears. Timeouts mirror the desktop restart test
+  (`test.setTimeout(180_000)`).
+
+## Verification
+
+```bash
+(cd apps/web && KANDEV_E2E_MOCK=true pnpm e2e:raw --project=chromium settings/prevent-auto-start-on-open.spec.ts)
+(cd apps/web && KANDEV_E2E_MOCK=true pnpm e2e:raw --project=mobile-chrome settings/mobile-agent-start-hint.spec.ts settings/mobile-prevent-auto-start-on-open.spec.ts)
+```
+
+## Files Likely Touched
+
+- `apps/web/e2e/tests/settings/prevent-auto-start-on-open.spec.ts`
+- `apps/web/e2e/tests/settings/mobile-agent-start-hint.spec.ts` (new)
+
+## Dependencies
+
+Task 02 (the hint must be rendered before the specs can assert it).
+
+## Inputs
+
+- Current restart test body at
+  `prevent-auto-start-on-open.spec.ts:117-166` (uses `backend.restart()` +
+  `testPage.reload()`, `SessionPage.waitForLoad`,
+  `session.sendMessage("/e2e:simple-message")`,
+  `session.expectChatResponseVisible("simple mock response", 0, …)`).
+- Mobile restart flow mirrors the desktop one; the mobile-chrome project
+  auto-selects `mobile-*.spec.ts` files and supplies the device.
+
+## Output Contract
+
+Desktop and mobile E2E prove: a recovered-idle session shows the composer
+hint and no Start agent button; sending a message starts the agent and the
+mock response appears; the CREATED final-step button flows (desktop and
+mobile) are regression-green.
diff --git a/docs/plans/start-agent-composer-hint/task-04-peer-message-resumes-stopped-session.md b/docs/plans/start-agent-composer-hint/task-04-peer-message-resumes-stopped-session.md
new file mode 100644
index 0000000000..cf39c19dc6
--- /dev/null
+++ b/docs/plans/start-agent-composer-hint/task-04-peer-message-resumes-stopped-session.md
@@ -0,0 +1,81 @@
+---
+id: "04-peer-message-resumes-stopped-session"
+title: "Backend pin test: peer message resumes a stopped session"
+status: done
+wave: 1
+parallelism: sequential
+depends_on: []
+plan: "plan.md"
+spec: "../../specs/prevent-agent-autostart-on-open/spec.md"
+---
+
+# Task 04: Backend pin test — peer message resumes a stopped session
+
+## Acceptance
+
+- A new Go test in `apps/backend/internal/orchestrator/`
+  (`task_operations_test.go`, next to the other
+  `TestQueueAndInterruptForPeerMessage_*` tests) pins the requirement that a
+  message received from another task (sub-task via `message_task_kandev`,
+  delivered as `QueueAndInterruptForPeerMessage` with `QueuedByAgent`)
+  auto-starts the agent when the receiving session is stopped-but-resumable
+  (the post-restart / recovered-idle shape the prevent-auto-start preference
+  leaves the session in).
+- Test shape: seed a task + session in `WAITING_FOR_INPUT` with a resume
+  token (an `executors_running` row carrying the token, like
+  `TestResumeTaskSession_*` / `TestEnsureSessionRunning_*` fixtures), an
+  agent manager reporting `isAgentRunning: false` (so `ensureSessionRunning`
+  takes the resume path) with a recording `LaunchAgent`, and the executor
+  wired like the existing resume-path tests. Call
+  `QueueAndInterruptForPeerMessage(ctx, taskID, sessionID, prompt, metadata)`
+  and assert the agent was launched (resume) and the queued message was
+  dispatched to the agent (PromptAgent reached), mirroring the assertions of
+  `TestQueueAndInterruptForPeerMessage_DeliversQueuedMessageWithoutUserCancelSideEffects`
+  but with the stopped-agent resume path instead of
+  `isAgentRunning: true`.
+- The test must PASS against the current backend (the behavior already
+  exists: `takeIfPromptableLocked` → `executeQueuedMessage` → `PromptTask` →
+  `ensureSessionRunning` resumes). It is a regression pin, not a fix; if it
+  fails, stop and report — that would mean the requirement is actually
+  broken and needs a fix design.
+
+## Verification
+
+```bash
+(cd apps/backend && go test ./internal/orchestrator/ -run TestQueueAndInterruptForPeerMessage_StoppedSessionResumesAgent -race)
+```
+
+## Files Likely Touched
+
+- `apps/backend/internal/orchestrator/task_operations_test.go` (new test)
+- Possibly `apps/backend/internal/orchestrator/task_operations.go` ONLY if the
+  test proves the behavior is broken (then stop and report; do not fix
+  silently)
+
+## Dependencies
+
+None. Backend-only; independent of the frontend hint tasks.
+
+## Inputs
+
+- Spec: "What" bullet "A message auto-starts the agent covers every message…"
+  and the scenario "GIVEN a recovered-idle session whose composer hint is
+  visible, WHEN a message is received from another task…".
+- `QueueAndInterruptForPeerMessage` at
+  `task_operations.go:5363-5423` (queues with `QueuedByAgent`, dispatches via
+  `takeIfPromptableLocked` when promptable).
+- Resume-path fixture examples: `TestResumeTaskSession_*` at
+  `task_operations_test.go:5161-5204` (sets `AgentProfileID`, wires the
+  executor with the mock agent manager, asserts the resumed state and prompt
+  dispatch); `TestQueueAndInterruptForPeerMessage_*` at
+  `task_operations_test.go:1905-2920` (queue + dispatch assertions).
+- `ensureSessionRunning` at `task_operations.go:1891` (resumes
+  WAITING_FOR_INPUT sessions with a resume token).
+
+## Output Contract
+
+The backend test suite proves: a peer (sub-task) message delivered to a
+stopped-but-resumable session starts the agent and the message reaches the
+agent. Combined with the frontend E2E (task-03), the hint's promise —
+"a message auto-starts the agent" — is verified for both the user's composer
+sends and received sub-task messages.
diff --git a/docs/specs/prevent-agent-autostart-on-open/spec.md b/docs/specs/prevent-agent-autostart-on-open/spec.md
index 88d8ca5808..bae1ab306a 100644
--- a/docs/specs/prevent-agent-autostart-on-open/spec.md
+++ b/docs/specs/prevent-agent-autostart-on-open/spec.md
@@ -1,9 +1,17 @@
 ---
 status: draft
 created: 2026-08-11
+updated: 2026-08-13
 owner: platform
 ---
 
+> Follow-up (2026-08-13): for recovered-idle sessions the in-chat Start agent
+> button was replaced by a hint in the chat composer ("sending a message will
+> auto-start the agent"), because the button rendered at the bottom of the
+> transcript and could be clipped when the transcript was not scrolled all the
+> way down. The never-started (CREATED) task-description Start agent button is
+> unchanged. The sections below describe the current behavior.
+
 # Prevent Agent Auto-Start On Open
 
 ## Why
@@ -22,16 +30,36 @@ open and start it explicitly instead.
   surfaced in Settings → Task Actions as a switch.
 - When the setting is ON, opening a task whose session exists but whose agent
   is not running (the post-restart / recovered-idle shape) MUST NOT
-  automatically resume the agent. The task opens with the agent stopped and a
-  Start agent button is shown in the chat; clicking it resumes the agent.
-  (The existing session-menu resume and chat composer remain available too.)
-  For FAILED-but-resumable sessions the existing recovery actions (Resume
-  session / Start fresh session buttons) remain the manual affordance; the
-  new Start agent button is not rendered for FAILED sessions.
+  automatically resume the agent. The task opens with the agent stopped and
+  the chat composer shows a hint that sending a message will auto-start the
+  agent; sending a message starts it (the explicit-user-action rule below).
+  The Start agent button is NOT shown for recovered-idle sessions: the
+  composer hint replaces it (a footer button could be clipped when the
+  transcript is not scrolled to the bottom). For FAILED-but-resumable
+  sessions the existing recovery actions (Resume session / Start fresh
+  session buttons) remain the manual affordance; the hint is not rendered for
+  FAILED sessions.
 - When the setting is ON, opening a task whose current workflow step is the
   final step of its workflow MUST NOT auto-start the agent when the task has
   no session. The session is created in the never-started (prepared) state
-  and the Start agent button is shown.
+  and the Start agent button is shown under the task description. This button
+  is unchanged: a task that was explicitly never started keeps its explicit
+  Start agent affordance (no hint replaces it, because the CREATED transcript
+  is short and the button cannot be clipped).
+- The composer hint is a single informational line above the chat input,
+  shown exactly when the recovered-idle session is stopped and no other
+  affordance owns the surface: it is hidden while the session is FAILED
+  (recovery actions own the surface), while it is STARTING or RUNNING, and
+  when recovery actions are already visible in the transcript. The hint has
+  no click action; it only communicates that a message auto-starts the
+  agent.
+- "A message auto-starts the agent" covers every message that reaches the
+  session's message queue, not only the user's composer sends: messages
+  received from other tasks (`message_task_kandev`, e.g. a sub-task
+  reporting back) are queued the same way and the queue dispatch resumes a
+  stopped-but-resumable agent through the same
+  `ensureSessionRunning` path. The preference never gates message-driven
+  starts — it only gates starts triggered by *opening* the task.
 - When the setting is OFF (default), opening a task behaves exactly as today.
 - The setting gates only automatic starts triggered by *opening* a task. It
   MUST NOT affect: workflow step transitions whose on-enter actions include
@@ -84,10 +112,11 @@ auto-start or auto-resume is *triggered by opening the task page*:
 | Trigger | Setting OFF (default) | Setting ON |
 |---|---|---|
 | Open task, no session, step allows auto-start | agent starts (`created_start`) | non-final step: unchanged; final step: `created_prepare`, Start agent button shown |
-| Open task, session exists, agent not running, session resumable | auto-resume (`session.launch` intent=resume) | no auto-resume; session stays stopped and a Start agent button (resume action) is shown in the chat |
+| Open task, session exists, agent not running, session resumable | auto-resume (`session.launch` intent=resume) | no auto-resume; session stays stopped; the chat composer shows a hint that sending a message will auto-start the agent |
 | Open task, agent already running | no-op | no-op (unchanged) |
 | Workflow step transition with `auto_start_agent` on-enter | agent starts | agent starts (unchanged) |
 | User clicks Start agent / Resume / sends a message | agent starts | agent starts (unchanged) |
+| Message received from another task (sub-task via `message_task`), agent stopped | agent resumes (queue dispatch runs `ensureSessionRunning`) | agent resumes (unchanged; message-driven starts are never gated by the preference) |
 
 ## Failure modes
 
@@ -113,13 +142,14 @@ per-task variant in this feature.
 - **GIVEN** the setting is ON and a task's session is in an active state with a
   resume token but no running agent (post-restart shape), **WHEN** the user
   opens the task page, **THEN** no `session.launch` resume request is sent on
-  open, the session stays stopped, and the task page shows a Start agent
-  button that resumes the agent when clicked.
+  open, the session stays stopped, and the chat composer shows a hint that
+  sending a message will auto-start the agent; sending a message starts the
+  agent.
 - **GIVEN** the setting is ON and a task's session is FAILED but resumable,
   **WHEN** the user opens the task page, **THEN** no auto-resume is sent on
   open and the session keeps the existing recovery actions (Resume session and
-  Start fresh session buttons). The new Start agent button is not rendered for
-  FAILED sessions.
+  Start fresh session buttons). The composer hint is not rendered for FAILED
+  sessions.
 - **GIVEN** the setting is ON and the task's current workflow step is the final
   step, **WHEN** the user opens the task and it has no session, **THEN**
   `session.ensure` is called with `auto_start: false`, the session is created
@@ -133,7 +163,18 @@ per-task variant in this feature.
   **THEN** today's auto-start and auto-resume behavior is unchanged.
 - **GIVEN** the setting is ON and a task in the final step already has a
   never-started (`CREATED`) session, **WHEN** the task is opened, **THEN** the
-  Start agent button is shown and no agent starts.
+  Start agent button is shown under the task description and no agent starts.
+- **GIVEN** a recovered-idle session whose composer hint is visible, **WHEN**
+  a message is received from another task (e.g. a sub-task via
+  `message_task_kandev`), **THEN** the agent resumes automatically (the
+  message is queued and the queue dispatch runs `ensureSessionRunning`) and
+  the hint disappears once the session reports STARTING/RUNNING.
+- **GIVEN** a recovered-idle session whose composer hint is visible, **WHEN**
+  the session state becomes STARTING or RUNNING (e.g. the user sent a
+  message), **THEN** the hint disappears.
+- **GIVEN** a recovered-idle session, **WHEN** recovery actions are already
+  visible in the transcript, **THEN** the composer hint is hidden (recovery
+  owns the surface).
 - **GIVEN** the setting is ON, **WHEN** the user explicitly starts or resumes
   the agent (Start agent button, session menu Resume, or sending a message),
   **THEN** the agent starts normally.