fix(cli): 1.31.1 — reaper no longer blocks the daemon event loop

1.31.0 introduced a session reaper that called execFileSync(ps) once
per registered session every 5s. With many sessions registered, the
daemon's event loop stalled for hundreds of ms — long enough that
incoming /v1/version probes from the CLI timed out against a healthy
daemon and the new service-managed warning fired.

Fix:

- getProcessStartTime is now async (execFile + promisify); never
  blocks the event loop
- New getProcessStartTimes(pids) issues one batched ps for all
  survivors instead of N separate forks. Sweep cost is fixed
  regardless of session count.
- registerSession stays sync; start-time capture is fire-and-forget
- reapDead is now async; the setInterval wrapper voids it so a
  rejected sweep cannot crash the daemon

Behavior is otherwise unchanged from 1.31.0: same 5s cadence, same
PID-reuse guard semantics, same broker-WS teardown via the registry
hook. 83/83 tests still green.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

apps/cli/tests/unit/session-reaper.test.ts

@@ -30,7 +30,7 @@ afterEach(() => {
 });
 
 describe("session reaper", () => {
-  test("drops entry when pid is dead", () => {
+  test("drops entry when pid is dead", async () => {
     const onDeregister = vi.fn();
     setRegistryHooks({ onDeregister });
 
@@ -47,7 +47,7 @@ describe("session reaper", () => {
     });
     expect(listSessions()).toHaveLength(1);
 
-    _runReaperOnce();
+    await _runReaperOnce();
 
     expect(listSessions()).toHaveLength(0);
     expect(onDeregister).toHaveBeenCalledTimes(1);
@@ -55,15 +55,14 @@ describe("session reaper", () => {
     expect(arg.sessionId).toBe("sess-dead");
   });
 
-  test("keeps entry when pid is alive and start-time matches", () => {
+  test("keeps entry when pid is alive and start-time matches", async () => {
     const onDeregister = vi.fn();
     setRegistryHooks({ onDeregister });
 
     // Use the test runner's own pid (process.pid is always alive here)
     // and capture its real start-time so the start-time guard sees a
-    // match. Without pre-seeding startTime, registerSession would
-    // probe ps and we'd race with that — explicit value keeps the
-    // test deterministic.
+    // match. Pre-seed startTime so registerSession's async ps probe
+    // doesn't race the test.
     const { execFileSync } = require("node:child_process");
     const realStart = execFileSync("ps", ["-o", "lstart=", "-p", String(process.pid)], {
       encoding: "utf8",
@@ -78,13 +77,13 @@ describe("session reaper", () => {
       startTime: realStart,
     });
 
-    _runReaperOnce();
+    await _runReaperOnce();
 
     expect(listSessions()).toHaveLength(1);
     expect(onDeregister).not.toHaveBeenCalled();
   });
 
-  test("drops entry when pid is alive but start-time mismatched (PID reuse)", () => {
+  test("drops entry when pid is alive but start-time mismatched (PID reuse)", async () => {
     const onDeregister = vi.fn();
     setRegistryHooks({ onDeregister });
 
@@ -99,27 +98,30 @@ describe("session reaper", () => {
       startTime: "Sat Jan  1 00:00:00 1980",
     });
 
-    _runReaperOnce();
+    await _runReaperOnce();
 
     expect(listSessions()).toHaveLength(0);
     expect(onDeregister).toHaveBeenCalledTimes(1);
   });
 
-  test("keeps entry when start-time wasn't captured (best-effort fallback)", () => {
+  test("keeps entry when start-time wasn't captured (best-effort fallback)", async () => {
     const onDeregister = vi.fn();
     setRegistryHooks({ onDeregister });
 
     // Register without startTime → reaper falls back to bare liveness.
-    // process.pid is alive, so the entry must survive.
+    // process.pid is alive, so the entry must survive. (The fire-and-
+    // forget capture inside registerSession will eventually populate
+    // startTime, but it does so after a real fork — for this test we
+    // rely on the synchronous reaper pass not seeing it yet.)
     registerSession({
       token: "d".repeat(64),
-      sessionId: "sess-no-start",
+      sessionId: "sess-no-start-" + Math.random().toString(36).slice(2),
       mesh: "m",
       displayName: "x",
       pid: process.pid,
     });
 
-    _runReaperOnce();
+    await _runReaperOnce();
 
     expect(listSessions()).toHaveLength(1);
     expect(onDeregister).not.toHaveBeenCalled();