fix(subagent): reap shell children so interrupt and close settle

src/agent/background-shell-tool.test.ts

@@ -129,6 +129,81 @@ describe("background shell through the agent toolset", () => {
     }
   });
 
+  test("shell_collect with an aborted signal releases as running without killing the child", async () => {
+    const toolset = await createAgentToolset({
+      cwd: process.cwd(),
+      permissionGate: gate(process.cwd()),
+    });
+    try {
+      const started = await toolset.dynamicRunner.run(
+        {
+          id: "a-start",
+          name: "run_shell",
+          arguments: {
+            command: "sleep 60",
+            background: true,
+          },
+        },
+        new AbortController().signal,
+      );
+      const { shell_id } = JSON.parse(String(started.content)) as {
+        shell_id: string;
+      };
+      const aborted = new AbortController();
+      aborted.abort(new Error("interrupted by interrupt_agent"));
+      const out = await toolset.dynamicRunner.run(
+        {
+          id: "a-collect",
+          name: "shell_collect",
+          arguments: { shell_id, action: "collect", wait_ms: 60_000 },
+        },
+        aborted.signal,
+      );
+      expect(JSON.parse(String(out.content))).toMatchObject({
+        status: "running",
+      });
+      // A live-signal collect still sees the child running: the abort above
+      // released the waiter instead of killing the process. Had the abort
+      // killed it, this would already report completed.
+      const stillThere = await toolset.dynamicRunner.run(
+        {
+          id: "a-collect2",
+          name: "shell_collect",
+          arguments: { shell_id, action: "collect" },
+        },
+        new AbortController().signal,
+      );
+      expect(JSON.parse(String(stillThere.content))).toMatchObject({
+        status: "running",
+      });
+      // And the child is still killable: cancel settles it as completed.
+      const cancelled = await toolset.dynamicRunner.run(
+        {
+          id: "a-cancel",
+          name: "shell_collect",
+          arguments: { shell_id, action: "cancel" },
+        },
+        new AbortController().signal,
+      );
+      expect(JSON.parse(String(cancelled.content))).toMatchObject({
+        status: "cancelling",
+      });
+      const final = await toolset.dynamicRunner.run(
+        {
+          id: "a-collect3",
+          name: "shell_collect",
+          arguments: { shell_id, action: "collect", wait_ms: 5_000 },
+        },
+        new AbortController().signal,
+      );
+      expect(JSON.parse(String(final.content))).toMatchObject({
+        status: "completed",
+      });
+    } finally {
+      await toolset.dispose();
+    }
+  });
+
   test("toolset dispose kills every live background process group", async () => {
     const token = `ic_toolset_dispose_${randomUUID()}`;
     const toolset = await createAgentToolset({

src/agent/background-shell-tool.ts

@@ -79,7 +79,10 @@ export function createShellCollectTool(
 ) {
   return {
     definition: shellCollectDefinition,
-    handler: async (rawArgs: Record<string, unknown>): Promise<string> => {
+    handler: async (
+      rawArgs: Record<string, unknown>,
+      signal?: AbortSignal,
+    ): Promise<string> => {
       const parsed = ShellCollectArgs(rawArgs);
       if (parsed instanceof type.errors) {
         return "Error: shell_collect requires shell_id (string) and action ('collect' | 'cancel').";
@@ -91,7 +94,11 @@ export function createShellCollectTool(
         }
         return JSON.stringify({ shell_id, status: "cancelling" });
       }
-      const snapshot = await registry.collect(shell_id, parsed.wait_ms ?? 0);
+      const snapshot = await registry.collect(
+        shell_id,
+        parsed.wait_ms ?? 0,
+        signal,
+      );
       if (snapshot.state === "running") {
         return JSON.stringify({ shell_id, status: "running" });
       }

src/shell/background-shell.test.ts

@@ -122,4 +122,53 @@ describe("background shell registry", () => {
     const after = await registry.collect(started.id, 0);
     expect(after.state).toBe("not-found");
   });
+
+  test("collect with an aborted signal releases as running without killing the child", async () => {
+    const token = `ic_bg_abort_${randomUUID()}`;
+    const registry = createBackgroundShellRegistry();
+    const started = registry.start({
+      command: `bash -c 'exec -a ${token} sleep 600'`,
+      cwd: tmpCwd,
+    });
+    if ("error" in started) throw new Error(started.error);
+    try {
+      const aborted = new AbortController();
+      aborted.abort(new Error("interrupted by interrupt_agent"));
+      const snapshot = await registry.collect(
+        started.id,
+        60_000,
+        aborted.signal,
+      );
+      expect(snapshot.state).toBe("running");
+      const stillThere = await registry.collect(started.id, 0);
+      expect(stillThere.state).toBe("running");
+      const probe = spawnSync("pgrep", ["-f", token], { encoding: "utf8" });
+      expect(probe.status).toBe(0);
+    } finally {
+      registry.disposeAll("test done");
+    }
+  });
+
+  test("releaseWaiters wakes a parked collect without killing the child", async () => {
+    const token = `ic_bg_release_${randomUUID()}`;
+    const registry = createBackgroundShellRegistry();
+    const started = registry.start({
+      command: `bash -c 'exec -a ${token} sleep 600'`,
+      cwd: tmpCwd,
+    });
+    if ("error" in started) throw new Error(started.error);
+    try {
+      const pending = registry.collect(started.id, 60_000);
+      await new Promise((r) => setTimeout(r, 100));
+      registry.releaseWaiters();
+      const snapshot = await pending;
+      expect(snapshot.state).toBe("running");
+      const stillThere = await registry.collect(started.id, 0);
+      expect(stillThere.state).toBe("running");
+      const probe = spawnSync("pgrep", ["-f", token], { encoding: "utf8" });
+      expect(probe.status).toBe(0);
+    } finally {
+      registry.disposeAll("test done");
+    }
+  });
 });

src/shell/background-shell.ts

@@ -64,9 +64,14 @@ export type BackgroundShellSnapshot =
 
 export interface BackgroundShellRegistry {
   start: (args: StartBackgroundShellArgs) => { id: string } | { error: string };
-  collect: (id: string, waitMs?: number) => Promise<BackgroundShellSnapshot>;
+  collect: (
+    id: string,
+    waitMs?: number,
+    signal?: AbortSignal,
+  ) => Promise<BackgroundShellSnapshot>;
   cancel: (id: string) => boolean;
   disposeAll: (reason: string) => void;
+  releaseWaiters: () => void;
   runningCount: () => number;
 }
 
@@ -151,14 +156,33 @@ export function createBackgroundShellRegistry(
   const collect = async (
     id: string,
     waitMs = 0,
+    signal?: AbortSignal,
   ): Promise<BackgroundShellSnapshot> => {
     const done = completed.get(id);
     if (done !== undefined) return { state: "completed", exit: done };
     if (!running.has(id)) return { state: "not-found" };
     if (waitMs > 0) {
+      // An already-aborted collect releases immediately as still-running:
+      // interrupt must not park the session on a live descendant, and must
+      // not kill it either — the child belongs to the still-alive session.
+      if (signal?.aborted === true) return { state: "running" };
       await new Promise<void>((resolve) => {
-        exitWaiters.set(id, resolve);
-        setTimeout(resolve, waitMs);
+        const timer = setTimeout(() => {
+          exitWaiters.delete(id);
+          signal?.removeEventListener("abort", onAbort);
+          resolve();
+        }, waitMs);
+        const onAbort = (): void => {
+          clearTimeout(timer);
+          exitWaiters.delete(id);
+          resolve();
+        };
+        signal?.addEventListener("abort", onAbort, { once: true });
+        exitWaiters.set(id, () => {
+          clearTimeout(timer);
+          signal?.removeEventListener("abort", onAbort);
+          resolve();
+        });
       }).finally(() => exitWaiters.delete(id));
       const finished = completed.get(id);
       if (finished !== undefined) return { state: "completed", exit: finished };
@@ -173,12 +197,22 @@ export function createBackgroundShellRegistry(
     return true;
   };
 
+  /**
+   * Wake every parked `collect` waiter as still-running without touching the
+   * children. Interrupt paths call this so a live descendant releases the
+   * session instead of wedging teardown; close paths use `disposeAll`, which
+   * wakes waiters and then kills the trees.
+   */
+  const releaseWaiters = (): void => {
+    for (const wake of exitWaiters.values()) wake();
+    exitWaiters.clear();
+  };
+
   const disposeAll = (reason: string): void => {
     for (const child of running.values()) killProcessTree(child);
     running.clear();
     completed.clear();
-    for (const wake of exitWaiters.values()) wake();
-    exitWaiters.clear();
+    releaseWaiters();
     // onExit is intentionally not fired for disposed shells: the session is
     // gone, so there is no later turn to deliver to (`reason` is for callers
     // that log it).
@@ -190,6 +224,7 @@ export function createBackgroundShellRegistry(
     collect,
     cancel,
     disposeAll,
+    releaseWaiters,
     runningCount: () => running.size,
   };
 }