[Fix] Let a script go three seconds after npm exits when a descendant still holds its output

[juanmaguitar]

Why

A script's run settles on the runner's close event, which waits for the stdio pipes. A descendant that outlives npm keeps them open: on Windows, wp-build after the console window it ran in was closed (#497). npm exits, the checklist stays IN PROGRESS, the button stays busy and the terminal keeps receiving the orphan's lines for as long as it runs (#498). Ctrl+C was the only way out. The close-vs-exit logic is shared, so a POSIX orphan holding the pipe hangs the same way.

What changes

runNpmWithEngineRetry in src/main.js, which installs and scripts share, mirrors the Stop escalation of #479 on the natural-exit path. On the runner's exit it arms a three-second grace; close stands it down. If the grace runs out it logs why, forces the group by pid (killTreeByPid, the same call Stop escalates with) and destroys the runner's stdio pipes. Destroying the pipes is what makes Node emit close with the exit code npm gave, so the existing close handler settles the run and the engines-retry decision stays in one place. Whatever the orphan writes afterwards goes with the destroyed stream.

On POSIX the detached process group outlives its leader, so the forced signal ends the orphan. On Windows nothing is forced, for the reason npm:kill already gives: the pid is certainly dead, a taskkill /T on it reaches nothing of the orphan and could land on a reissued pid. There the step ends and the orphan runs on until it finishes on its own. A line in the terminal says which of the two happened.

The Playground and web servers keep their close-only lifecycle: their runners load the CLI in-process and have no descendant to orphan.

How to test this

Platform: either; the mechanism is covered on macOS by an integration test and the Windows case is the one the issue reports. Build: the Buildkite artifact for the current head, or npm start from the repository root.

Windows, Gutenberg site past install: click Run full build and, while it runs, end the cmd.exe that runs wp-build from Task Manager or Process Explorer (with #497 in, there is no window to close, so break the tree by hand). Expected within about three seconds of npm's exit 1 in the terminal: the build step turns FAILED, the button frees, the terminal stops receiving wp-build's lines. wp-build itself may run on in Task Manager until it finishes; that is the stated limitation.

Done on Windows 11 (UTM VM, arm64 host), by hand, on the Buildkite artifact for f49c77f, with the build watch instead of the build (same helper): Start build watch, then from Task Manager's Details tab ended the cmd.exe /d /s /c node ./dev.mjs under npm. npm printed its command failed stack and exit 1, dev.mjs kept transpiling packages into the tab for a moment, then the let-go line ("npm exited with code 1, but something it started is still running and holding its output. Letting go; that process runs on until it finishes on its own.") and npm run dev exited with code 1 closed the run with the tab at (exited 1); dev.mjs stayed alive in Task Manager, as stated.

macOS, by script, on the current head: a scratch Gutenberg copy with its build script replaced by sh -c 'sleep 90 & echo npm-side-done; exit 1'; Run full build. Expected: the terminal shows npm-side-done and npm's exit, the button frees about three seconds later, the terminal says npm exited but something it started was still holding its output, and pgrep -f 'sleep 90' finds nothing.

Done on macOS, current head, by a Playwright script driving the app against a scratch copy of a built Gutenberg trunk, the command sent through the app's terminal: npm's side done at 0.5 s with the orphan alive, the terminal freed 2.8 s after npm's exit, the orphan gone 1.5 s later.

What must not have happened: a run that closed on its own being forced (the grace is cleared by close); a done event sent twice; an install being retried by the let-go (the retry decision is untouched and reads npm's real code).

Tests: tests/unit/ipc-wiring.test.cjs, three #498 cases (script let go after the grace with npm's code; a close inside the grace is left alone; an install the same way), fail on trunk and pass here. tests/unit/orphan-pipe.integration.test.cjs (POSIX) pins the Node and POSIX facts against a real orphan: exit without close while it holds the pipes, close with the runner's code once they are destroyed, the orphan ending on the group signal by pid. Lint clean, 1619 unit tests pass.

Risks and limitations

• Three seconds is the same grace Stop gives; a runner whose pipes take longer than that to drain after exit would be cut short. Nothing prints for three seconds after its own exit.
• On Windows the orphan survives (above). Ending it would need a job object, which Node does not expose.
• The quit sweep and the pre-delete stop are unchanged ([Fix] Force the whole process tree when Stop's SIGTERM is ignored, not only the runner #479's own follow-ups).

Related

Fixes #498. Stacked on #497's PR. Builds on #479. Part of #251, v1.2.0-beta.2.

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Review outcome (required — see AGENTS.md)

3 [fix here] · 2 [follow-up] on c6f152c, the three fixed and one follow-up taken in f49c77f.

• Fixed: killTreeByPid ran on Windows against a pid that is certainly dead, which npm:kill's own rule forbids; POSIX only now, and the tests assert both branches the way the [Fix] Force the whole process tree when Stop's SIGTERM is ignored, not only the runner #479 test does.
• Fixed: the let-go reached only the log file; the terminal now says npm exited with something still holding its output, and whether it was ended or runs on.
• Fixed: the integration test's cleanup went through the pid fallback; it signals the group and the orphan directly, like its sibling.
• Taken: TESTING.md layer 2 now names real processes beside real Git repositories.
• CodeRabbit on 55f41a4: 2 actionable, both fixed in b81a422: the let-go now signals the group only (killTreeByPid gained groupOnly), never the bare pid of a leader that is certainly dead; the integration test reads the orphan's pid by line.
• Follow-up, not taken: fakeChild does not set exitCode when a test emits exit; harmless while the let-go kills by pid, worth doing if it ever goes through killChildTree.
• The review also raised whether a test that spends a second proving a negative belongs in the default suite; one second here, left as is.

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📝 Walkthrough

Walkthrough

The npm child handling now observes exit as well as close. If close does not follow within three seconds, POSIX runs kill the process group and all stdio streams are destroyed. The existing close handler then completes the run with npm's exit code. Unit tests cover run-script and install handlers. A POSIX integration test verifies orphaned pipe behavior. TESTING.md documents real-process integration coverage.

Assessment against linked issues

Objective	Addressed	Explanation
Finish runs after npm exits while a descendant holds stdio pipes, including run-script, install, and Playground server paths [#498]	❌	The diff covers run-script and install handlers, but does not show a corresponding Playground server change.

Fixed issue severity

Priority: ➖ Normal

Severity of issue fixed: Medium

Merge Risk: 🟡 Moderate · up to f49c7

The new recovery path needs safer PID handling before merge: its integration test can target the wrong process, and rare post-exit cleanup can signal an unrelated reused PID.

🚥 Pre-merge checks | ✅ 1

✅ Passed checks (1 passed)

Check name	Status	Explanation
Description check	✅ Passed	The description is complete and follows the required structure. It explains the problem, implementation, testing steps and results, expected non-regressions, risks, related issues, and review outcome.

✨ Finishing Touches 💡 1

🛠️ Fix failing CI checks 💡

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[juanmaguitar]

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Inline comments:
In `@src/main.js`:
- Line 3453: Update the POSIX cleanup call around killTreeByPid so it cannot
fall back to signaling the reused positive child.pid; use a process-group-only
termination operation or remove the positive-PID fallback while preserving the
existing Windows behavior.

In `@tests/unit/orphan-pipe.integration.test.cjs`:
- Line 52: Update the runner.stdout data handler to buffer chunks until the
first newline before parsing the PID. In the orphanPid capture logic, parse only
the complete first line and assign it only when it is a positive integer,
preserving the existing liveness, final assertion, and cleanup targets.

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