tests: TestHostedWelcomeCarriesUnreadProfileKeysToSurface leaves a writer under its home — TempDir cleanup fails under load #1647

What happened

TestHostedWelcomeCarriesUnreadProfileKeysToSurface (cmd/codeaf/chatv3_host_test.go) fails intermittently in CI's touched packages, on unrelated heads:

--- FAIL: TestHostedWelcomeCarriesUnreadProfileKeysToSurface (0.00s)
    testing.go:1464: TempDir RemoveAll cleanup: unlinkat /tmp/codeaf-ci/TestHostedWelcomeCarriesUnreadProfileKeysToSurface631757294/002/ffb9da6858774e23: directory not empty

• Consolidate verified CodeAF task, chat and runtime fixes #1627 at 0f8386abd, run 36350780225 (the folder was …/002/f45dd4f237356013).
• Consolidate reviewed CodeAF fixes — batch 2 #1632 at 9a2c7cdd5, run on 2026-09-28 05:20Z.

The test passes locally when run alone. The failing folder is the test's second temp dir (the home made by v3TrackedAgent), inside a 16-hex place folder, so something the agent or the loopback engine started is still writing there after the test returns. Only loop.Close() is registered for cleanup.

Replication

Deterministic (no model). Under load:

GOMAXPROCS=2 go test -run '^TestHostedWelcomeCarriesUnreadProfileKeysToSurface$' -count=200 ./cmd/codeaf

Run it with another package's tests beside it. Today a few runs fail on the TempDir cleanup.

Where

• TestHostedWelcomeCarriesUnreadProfileKeysToSurface and v3TrackedAgent in cmd/codeaf.
• remote.Loopback in internal/remote.
• The writer is to be found: something started by the agent or the engine boot that writes under the home's place folder and is not joined by loop.Close() or the agent's cleanup.

The fix

Every goroutine the agent or the loopback engine starts that writes under a home is joined by the close the test already calls, or by the agent's own cleanup, before the TempDir is removed. The test is not changed to tolerate it. A test in this package that fails only under load is a bug report (CLAUDE.md).

Acceptance

• Unit: the command above passes 200/200 at GOMAXPROCS=2 with another package's tests running beside it.
• Unit: the writer's own close is proven to join it: a test that closes and then asserts nothing is written under the home afterwards.