diff --git a/src/session-runtime.ts b/src/session-runtime.ts
index e918a3a..92882f9 100644
--- a/src/session-runtime.ts
+++ b/src/session-runtime.ts
@@ -838,6 +838,20 @@ export async function runSessionQueueOwner(options: QueueOwnerRuntimeOptions): P
       await owner.close();
     }
     await releaseQueueOwnerLease(lease);
+
+    // Auto-close the session when the queue owner shuts down and the agent
+    // has exited, preventing zombie session accumulation (#47).
+    try {
+      const record = await resolveSessionRecord(options.sessionId);
+      if (!record.closed && record.lastAgentExitAt) {
+        record.closed = true;
+        record.closedAt = isoNow();
+        await writeSessionRecord(record);
+      }
+    } catch {
+      // best effort — session may already be cleaned up
+    }
+
     if (options.verbose) {
       process.stderr.write(`[acpx] queue owner stopped for session ${options.sessionId}\n`);
     }
diff --git a/test/integration.test.ts b/test/integration.test.ts
index 526eef5..e0b194c 100644
--- a/test/integration.test.ts
+++ b/test/integration.test.ts
@@ -660,6 +660,93 @@ test("integration: prompt exits after done while detached owner stays warm", asy
   });
 });
 
+test("integration: session auto-closes when queue owner exits and agent has exited (#47)", async () => {
+  await withTempHome(async (homeDir) => {
+    const cwd = await fs.mkdtemp(path.join(os.tmpdir(), "acpx-integration-cwd-"));
+
+    try {
+      // 1. Create a persistent session
+      const created = await runCli(
+        [...baseAgentArgs(cwd), "--format", "json", "sessions", "new"],
+        homeDir,
+      );
+      assert.equal(created.code, 0, created.stderr);
+      const createdPayload = JSON.parse(created.stdout.trim()) as {
+        acpxRecordId?: string;
+      };
+      const sessionId = createdPayload.acpxRecordId;
+      assert.equal(typeof sessionId, "string");
+
+      // 2. Send a prompt with a very short TTL so the queue owner exits quickly
+      const prompt = await runCli(
+        [...baseAgentArgs(cwd), "--format", "quiet", "--ttl", "1", "prompt", "echo oneshot-done"],
+        homeDir,
+      );
+      assert.equal(prompt.code, 0, prompt.stderr);
+      assert.match(prompt.stdout, /oneshot-done/);
+
+      // 3. Wait for the queue owner to exit (it should exit after 1s TTL)
+      const { lockPath } = queuePaths(homeDir, sessionId as string);
+      let ownerPid: number | undefined;
+      try {
+        const lockPayload = JSON.parse(await fs.readFile(lockPath, "utf8")) as {
+          pid?: number;
+        };
+        ownerPid = lockPayload.pid;
+      } catch {
+        // lock file may already be gone
+      }
+
+      if (typeof ownerPid === "number") {
+        assert.equal(await waitForPidExit(ownerPid, 10_000), true, "queue owner did not exit");
+      }
+
+      // Give a moment for final writes
+      await sleep(500);
+
+      // 4. Read the session record from disk
+      const recordPath = path.join(
+        homeDir,
+        ".acpx",
+        "sessions",
+        `${encodeURIComponent(sessionId as string)}.json`,
+      );
+      const storedRecord = JSON.parse(await fs.readFile(recordPath, "utf8")) as {
+        closed?: boolean;
+        closed_at?: string;
+        last_agent_exit_at?: string;
+        last_agent_exit_code?: number | null;
+      };
+
+      // 5. After the fix for #47, the queue owner auto-closes the session
+      //    when it shuts down and the agent has exited.
+      assert.equal(
+        storedRecord.last_agent_exit_at != null,
+        true,
+        "expected last_agent_exit_at to be set (agent has exited)",
+      );
+
+      assert.equal(
+        storedRecord.closed,
+        true,
+        "session should be auto-closed after agent exit and queue owner shutdown (#47)",
+      );
+
+      assert.equal(
+        typeof storedRecord.closed_at,
+        "string",
+        "closed_at should be set when session is auto-closed",
+      );
+    } finally {
+      // Clean up: close session if it's still around
+      await runCli([...baseAgentArgs(cwd), "--format", "json", "sessions", "close"], homeDir).catch(
+        () => {},
+      );
+      await fs.rm(cwd, { recursive: true, force: true });
+    }
+  });
+});
+
 function baseAgentArgs(cwd: string): string[] {
   return ["--agent", MOCK_AGENT_COMMAND, "--approve-all", "--cwd", cwd];
 }