Flaky test: lifetime-pipe watcher may not observe Close on Linux

Bug description

The root-b race shard intermittently fails in TestSDKServerEnablers_Scenario8_LifetimePipeIsQuietOnCleanShutdown after waiting 10 seconds for the lifetime-pipe watcher to observe p.Close().

Observed failures:

• https://github.com/stacklok/mecatl/actions/runs/35215461411/job/105182991940
• https://github.com/stacklok/mecatl/actions/runs/35225076659/job/105214547427

Both fail with:

--- FAIL: TestSDKServerEnablers_Scenario8_LifetimePipeIsQuietOnCleanShutdown (10.00s)
    daemonhosting_test.go:959: the watcher did not observe its own Close within 10s

No race-detector report is present.

Steps to reproduce

Run the root-b race shard repeatedly on Linux:

task test:race-root-b

The scheduling-sensitive sequence is:

1. openLifetimePipe wraps a blocking inherited pipe descriptor with os.NewFile and starts watch.
2. watch may enter a blocking Read while the writer remains open.
3. The test calls p.Close() and waits for p.Closed().

On Linux, closing the descriptor from another goroutine does not guarantee that an already-blocked read wakes. If Close wins before Read, the test passes; if Read wins, it can remain blocked until the writer closes.

Expected behavior

The test should verify that clean shutdown does not emit lifetime pipe read failed without requiring an unsupported join guarantee from lifetimePipe.Close.

Actual behavior

The test asserts that Close wakes and joins the watcher within 10 seconds. This contradicts both the implementation comment and ADR 0027 List 1 row 66, which explicitly state that Close does not join the watcher and that it exits when the parent endpoint reaches EOF.

Environment

• OS/version: GitHub-hosted Ubuntu 24.04 runners
• Go: 1.27.x with -race
• Deployment shape: cmd/mecated unit test in the root-b race shard

Suggested fix

Align the fixture with the documented lifecycle: call p.Close(), close the writer to release any in-flight Linux read, then wait for p.Closed() before checking the captured logs. Increasing the timeout alone will retain the race.

Tracked alongside #815 because both surfaced in the race shards, but the causes and fixes are independent.

Start with daemonhosting_test.go and TestSDKServerEnablers_Scenario8_LifetimePipeIsQuietOnCleanShutdown. Run task test:race-root-b repeatedly on Linux, then inspect the lifetime-pipe fixture and its Close/Closed sequence. Align the test with the documented lifecycle by releasing the writer before waiting for Closed, and verify clean shutdown does not log lifetime pipe read failed.