test: wait for the evidence expiry worker to settle (#18241)

## Thinking Path

> - Paperclip coordinates AI work and retains execution evidence.
> - Evidence retention uses an asynchronous worker and a shared
scheduler.
> - The retention test checked the next deadline as soon as an archive
disappeared.
> - File removal can finish before the worker publishes that deadline.
> - This pull request waits for worker settlement before asserting its
next wake.
> - The test keeps its deletion, busy-session preservation, and
quiet-worker checks.

## Linked Issues or Issue Description

**What happened?**

CI for #18239 failed in `native-harness-backup-expiration.test.ts`. The
healthy-expiry test observed the file removal while `nextWakeAt()` was
still null. Subtracting the current time then produced a large negative
number.

**Expected behavior**

The retention test should check the deadline after the asynchronous
worker has settled.

**Steps to reproduce**

Run the server test shard with a slow filesystem completion. The
deletion predicate can become true before scheduler publication
finishes.

## What Changed

- Keep the existing file-removal wait open until tracked work is idle
and the expected busy-session retry deadline is registered.
- Keep the held archive and quiet-worker assertions.

## Verification

- Original CI failure: [server shard
3/12](https://github.com/paperclipai/paperclip/actions/runs/40976031169/job/123804262266).
- The targeted test passes with its real PostgreSQL fixture: `node
node_modules/vitest/vitest.mjs run --project @paperclipai/server
server/src/__tests__/native-harness-backup-expiration.test.ts -t 'lets
healthy saved expiry preempt' --maxWorkers 1`.
- After rebasing onto master, the focused retention test passes again
with its real PostgreSQL fixture. The PR now changes one test, with
seven insertions and two deletions.
- Master independently fixed the authentication timeout and
GitHub-recovery checkpoint race. Their redundant commits were dropped
during rebase.
- [Full GitHub
CI](https://github.com/paperclipai/paperclip/actions/runs/40984842413)
passes on `bbaa7c3c384f6c220ce2c979f0e9b5d01ddb1f77`: all 48 jobs
succeeded. Standard Greptile is 5/5 on that head, and GitHub reports the
PR clean.
- Broader coverage runs in GitHub CI. No local full build or full test
suite was run for this assertion-only change.

## Risks

Low risk. The retention test waits for the condition it already asserts.
The existing deletion, busy-session preservation, future-deadline, and
quiet-worker checks remain in place. No production code or time budget
changes.

## Model Used

OpenAI GPT-6 through Codex, with repository inspection, terminal tools,
and code execution. The serving variant and context window size are not
exposed in this session.

## Checklist

- [x] I have included a thinking path that traces from project context
to this change
- [x] I have specified the model used (with version and capability
details)
- [x] I have checked ROADMAP.md and confirmed this PR does not duplicate
planned core work
- [x] I have searched GitHub for duplicate or related PRs and linked
them above
- [x] I have either (a) linked existing issues with `Fixes: #` / `Closes
#` / `Refs #` OR (b) described the issue in-PR following the relevant
issue template
- [x] I have not referenced internal/instance-local Paperclip issues or
links (only public GitHub `#NNN` / `github.com/paperclipai/paperclip`
URLs)
- [x] My branch name describes the change (e.g. `docs/...`, `fix/...`)
and contains no internal Paperclip ticket id or instance-derived details
- [x] I have run tests locally and they pass
- [x] I have added or updated tests where applicable
- [x] I have updated relevant documentation to reflect my changes
- [x] I have considered and documented any risks above
- [x] All Paperclip CI gates are green
- [x] Greptile is 5/5 with no open P2s, recommendations, or follow-ups
- [x] I will address all Greptile and reviewer comments before
requesting merge

Co-authored-by: Paperclip <noreply@paperclip.ing>

server/src/__tests__/native-harness-backup-expiration.test.ts

@@ -645,8 +645,13 @@ describeEmbeddedPostgres("native harness backup expiration", () => {
     const available = await seedArchive(healthy.root, { name: `${dueAt - 7 * DAY_MS - 1}-${randomUUID()}` });
     await startEvidence({ isSessionBusy: scope => scope === busy.scope }); await settled(dueAt);
     await vi.advanceTimersByTimeAsync(dueAt - Date.now());
-    await vi.waitFor(async () => { await vi.advanceTimersByTimeAsync(100); expect(await exists(available)).toBe(false); });
-    expect(await exists(held)).toBe(true); expect(coordinator!.nextWakeAt()! - Date.now()).toBeGreaterThan(59 * 60_000);
+    await vi.waitFor(async () => {
+      await vi.advanceTimersByTimeAsync(100);
+      expect(await exists(available)).toBe(false);
+      expect(idleWorkSnapshot().active).toBe(0);
+      expect(coordinator!.nextWakeAt()! - Date.now()).toBeGreaterThan(59 * 60_000);
+    });
+    expect(await exists(held)).toBe(true);
     await quiet(60_000);
   });