fix: boulder continuation now respects /stop-continuation guard

Add isContinuationStopped check to atlas hook's session.idle handler
so boulder continuation stops when user runs /stop-continuation.

Previously, todo continuation and session recovery checked the guard,
but boulder continuation did not — causing work to resume after stop.

Fixes #1575

src/hooks/atlas/index.test.ts

@@ -755,40 +755,71 @@ describe("atlas hook", () => {
       expect(mockInput._promptMock).not.toHaveBeenCalled()
     })
 
-    test("should skip when background tasks are running", async () => {
-      // given - boulder state with incomplete plan
-      const planPath = join(TEST_DIR, "test-plan.md")
-      writeFileSync(planPath, "# Plan\n- [ ] Task 1")
+     test("should skip when background tasks are running", async () => {
+       // given - boulder state with incomplete plan
+       const planPath = join(TEST_DIR, "test-plan.md")
+       writeFileSync(planPath, "# Plan\n- [ ] Task 1")
 
-      const state: BoulderState = {
-        active_plan: planPath,
-        started_at: "2026-01-02T10:00:00Z",
-        session_ids: [MAIN_SESSION_ID],
-        plan_name: "test-plan",
-      }
-      writeBoulderState(TEST_DIR, state)
+       const state: BoulderState = {
+         active_plan: planPath,
+         started_at: "2026-01-02T10:00:00Z",
+         session_ids: [MAIN_SESSION_ID],
+         plan_name: "test-plan",
+       }
+       writeBoulderState(TEST_DIR, state)
 
-      const mockBackgroundManager = {
-        getTasksByParentSession: () => [{ status: "running" }],
-      }
+       const mockBackgroundManager = {
+         getTasksByParentSession: () => [{ status: "running" }],
+       }
 
-      const mockInput = createMockPluginInput()
-      const hook = createAtlasHook(mockInput, {
-        directory: TEST_DIR,
-        backgroundManager: mockBackgroundManager as any,
-      })
+       const mockInput = createMockPluginInput()
+       const hook = createAtlasHook(mockInput, {
+         directory: TEST_DIR,
+         backgroundManager: mockBackgroundManager as any,
+       })
 
-      // when
-      await hook.handler({
-        event: {
-          type: "session.idle",
-          properties: { sessionID: MAIN_SESSION_ID },
-        },
-      })
+       // when
+       await hook.handler({
+         event: {
+           type: "session.idle",
+           properties: { sessionID: MAIN_SESSION_ID },
+         },
+       })
 
-      // then - should not call prompt
-      expect(mockInput._promptMock).not.toHaveBeenCalled()
-    })
+       // then - should not call prompt
+       expect(mockInput._promptMock).not.toHaveBeenCalled()
+     })
+
+     test("should skip when continuation is stopped via isContinuationStopped", async () => {
+       // given - boulder state with incomplete plan
+       const planPath = join(TEST_DIR, "test-plan.md")
+       writeFileSync(planPath, "# Plan\n- [ ] Task 1\n- [ ] Task 2")
+
+       const state: BoulderState = {
+         active_plan: planPath,
+         started_at: "2026-01-02T10:00:00Z",
+         session_ids: [MAIN_SESSION_ID],
+         plan_name: "test-plan",
+       }
+       writeBoulderState(TEST_DIR, state)
+
+       const mockInput = createMockPluginInput()
+       const hook = createAtlasHook(mockInput, {
+         directory: TEST_DIR,
+         isContinuationStopped: (sessionID: string) => sessionID === MAIN_SESSION_ID,
+       })
+
+       // when
+       await hook.handler({
+         event: {
+           type: "session.idle",
+           properties: { sessionID: MAIN_SESSION_ID },
+         },
+       })
+
+       // then - should not call prompt because continuation is stopped
+       expect(mockInput._promptMock).not.toHaveBeenCalled()
+     })
 
     test("should clear abort state on message.updated", async () => {
       // given - boulder with incomplete plan

src/hooks/atlas/index.ts

@@ -399,6 +399,7 @@ const CONTINUATION_COOLDOWN_MS = 5000
 export interface AtlasHookOptions {
   directory: string
   backgroundManager?: BackgroundManager
+  isContinuationStopped?: (sessionID: string) => boolean
 }
 
 function isAbortError(error: unknown): boolean {
@@ -573,6 +574,11 @@ export function createAtlasHook(
           return
         }
 
+        if (options?.isContinuationStopped?.(sessionID)) {
+          log(`[${HOOK_NAME}] Skipped: continuation stopped for session`, { sessionID })
+          return
+        }
+
         const requiredAgent = (boulderState.agent ?? "atlas").toLowerCase()
         const lastAgent = getLastAgentFromSession(sessionID)
         if (!lastAgent || lastAgent !== requiredAgent) {