feat(atlas): update boulder continuation injector with lineage support

Update continuation injector to work with new lineage detection.
Refine idle event handling for proper subagent session tracking
and agent mismatch detection.

🤖 Generated with assistance of OhMyOpenCode

src/hooks/atlas/boulder-continuation-injector.test.ts

@@ -31,7 +31,7 @@ describe("injectBoulderContinuation", () => {
     } as unknown as PluginInput
 
     // when
-    await injectBoulderContinuation({
+    const result = await injectBoulderContinuation({
       ctx,
       sessionID: "ses_test_123",
       planName: "test-plan",
@@ -42,6 +42,7 @@ describe("injectBoulderContinuation", () => {
     })
 
     // then
+    expect(result).toBe("injected")
     expect(promptAsyncMock).toHaveBeenCalledTimes(1)
     expect(promptAsyncMock).toHaveBeenCalledWith(
       expect.objectContaining({
@@ -51,4 +52,73 @@ describe("injectBoulderContinuation", () => {
       }),
     )
   })
+
+  test("#given background tasks are running #when injector checks again #then it reports skipped background tasks without mutating failure count", async () => {
+    // given
+    registerAgentName("atlas")
+    const promptAsyncMock = mock(async (_request: unknown) => undefined)
+    const messagesMock = mock(async () => ({ data: [] }))
+    const sessionState = { promptFailureCount: 2, lastContinuationInjectedAt: 123 }
+
+    const ctx = {
+      directory: "/tmp",
+      client: {
+        session: {
+          messages: messagesMock,
+          promptAsync: promptAsyncMock,
+        },
+      },
+    } as unknown as PluginInput
+
+    // when
+    const result = await injectBoulderContinuation({
+      ctx,
+      sessionID: "ses_test_123",
+      planName: "test-plan",
+      remaining: 1,
+      total: 2,
+      agent: "atlas",
+      backgroundManager: {
+        getTasksByParentSession: () => [{ status: "running" }],
+      } as unknown as Parameters<typeof injectBoulderContinuation>[0]["backgroundManager"],
+      sessionState,
+    })
+
+    // then
+    expect(result).toBe("skipped_background_tasks")
+    expect(promptAsyncMock).not.toHaveBeenCalled()
+    expect(sessionState.promptFailureCount).toBe(2)
+    expect(sessionState.lastContinuationInjectedAt).toBe(123)
+  })
+
+  test("#given the continuation agent is unavailable #when injector runs #then it reports skipped agent unavailable without prompting", async () => {
+    // given
+    const promptAsyncMock = mock(async (_request: unknown) => undefined)
+    const messagesMock = mock(async () => ({ data: [] }))
+
+    const ctx = {
+      directory: "/tmp",
+      client: {
+        session: {
+          messages: messagesMock,
+          promptAsync: promptAsyncMock,
+        },
+      },
+    } as unknown as PluginInput
+
+    // when
+    const result = await injectBoulderContinuation({
+      ctx,
+      sessionID: "ses_test_123",
+      planName: "test-plan",
+      remaining: 1,
+      total: 2,
+      agent: "missing-agent",
+      sessionState: { promptFailureCount: 0 },
+    })
+
+    // then
+    expect(result).toBe("skipped_agent_unavailable")
+    expect(promptAsyncMock).not.toHaveBeenCalled()
+  })
 })