"anonymous spawn > a signed-in spawn still works (regression)" passes every time on a loaded check machine #5233

I changed only test/spawn-anon.test.ts: each test now waits for a child's background boot to finish before it uses that child or the test run ends. It passes 30 reruns and alongside apps.test.ts, but I never saw the signed-in test itself fail, so the cause below is inferred.

Cause: a shared resource, not the clock or a port. Every successful spawn starts its child booting in the background (void bootHostedChild in src/spawn/door.ts), and the test never waited for it. That left two races, both visible in the logs as hosted child did not open:

• Contention: the signed-in test ran while the boots of kid, kid2 and kid3 were still working. On a loaded machine those boots slow the signed-in spawn until it hits Bun's 5 s default timeout.
• Shared git readers: test 4 opened the child's directory while the same child's background boot was using it. The two share the repo's git readers, so the boot died with cat-file --batch exited mid-response. It also failed with posix_spawn 'git' ENOENT when afterAll removed the directory under a boot still running.

Fix: a small settle(...names) helper awaits bootHostedChild, which is deduplicated per child. I call it before the signed-in spawn, before each test opens a child's directory, and in afterAll before the directory is removed.

What I left alone:

• Product code: the background boot is deliberate, so I didn't change it.
• Timeouts and assertions: the 5 s timeout and every assertion are unchanged, and no budget was widened. The test still fails if the signed-in spawn or the child's fork breaks.

Checked:

• Before the fix: bun test --rerun-each 30 test/spawn-anon.test.ts passed on this machine, but the log showed the boot errors above.
• After the fix: the same command passes (210 of 210) with no hosted child did not open errors.
• With other files running: bun test test/spawn-anon.test.ts test/apps.test.ts passes (28 of 28).
• Type check: tsc --noEmit is clean.
• Heavier load: I also ran six copies of the rerun at once (80 cores) before the fix, and none failed. So I couldn't reproduce the timeout directly.

Closes #5209

I changed only test/spawn-anon.test.ts: each test now waits for a child's background boot to finish before it uses that child or the test run ends. It passes 30 reruns and alongside apps.test.ts, but I never saw the signed-in test itself fail, so the cause below is inferred.

Cause: a shared resource, not the clock or a port. Every successful spawn starts its child booting in the background (void bootHostedChild in src/spawn/door.ts), and the test never waited for it. That left two races, both visible in the logs as hosted child did not open:

• Contention: the signed-in test ran while the boots of kid, kid2 and kid3 were still working. On a loaded machine those boots slow the signed-in spawn until it hits Bun's 5 s default timeout.
• Shared git readers: test 4 opened the child's directory while the same child's background boot was using it. The two share the repo's git readers, so the boot died with cat-file --batch exited mid-response. It also failed with posix_spawn 'git' ENOENT when afterAll removed the directory under a boot still running.

Fix: a small settle(...names) helper awaits bootHostedChild, which is deduplicated per child. I call it before the signed-in spawn, before each test opens a child's directory, and in afterAll before the directory is removed.

What I left alone:

• Product code: the background boot is deliberate, so I didn't change it.
• Timeouts and assertions: the 5 s timeout and every assertion are unchanged, and no budget was widened. The test still fails if the signed-in spawn or the child's fork breaks.

Checked:

• Before the fix: bun test --rerun-each 30 test/spawn-anon.test.ts passed on this machine, but the log showed the boot errors above.
• After the fix: the same command passes (210 of 210) with no hosted child did not open errors.
• With other files running: bun test test/spawn-anon.test.ts test/apps.test.ts passes (28 of 28).
• Type check: tsc --noEmit is clean.
• Heavier load: I also ran six copies of the rerun at once (80 cores) before the fix, and none failed. So I couldn't reproduce the timeout directly.

This pull makes the spawn-anon test wait for each child's background boot. It changes only test/spawn-anon.test.ts. I never saw the signed-in test fail, so the cause is inferred.

Cause (inferred): a spawn starts its child booting in the background (void bootHostedChild in src/spawn/door.ts), and the test never waited for it. The logs from before the fix show two kinds of failure from that:

• Shared git readers: the test opened a child's directory while that child's own boot was using it, and the boot died with cat-file --batch exited mid-response.
• Directory removed under a boot: afterAll removed the directory under a boot still running, giving posix_spawn 'git' ENOENT.

The signed-in test timing out under load is the part I did not reproduce. The theory is that the still-running boots of kid, kid2 and kid3 slow its spawn past the 5 s default timeout. I ran six copies of the rerun at once (80 cores) before the fix and none failed.

Fix: a settle(...names) helper awaits bootHostedChild. I call it before the signed-in spawn, before a test opens a child's directory, and at the top of afterAll.

Changed after review:

• Order in afterAll: settle now runs before servers.stop() and app.close(). Stopping the servers empties the child cache, so a boot started afterwards would open a child nothing closes.
• Once per child: settle skips a child it has already waited for. A second bootHostedChild after the first finishes would start the child's apps again, so the old comment about deduplication was wrong. I reworded it.

Not done:

• Product code: the background boot is deliberate, so I left it alone.
• Timeouts and assertions: the 5 s timeout and every assertion are unchanged.
• A test that fails without settle: I didn't add one, because the race needs timing I couldn't force. What I have is the absence of boot errors in the log across 30 reruns, and the log did show those errors before the fix.

Checked:

• bun test --rerun-each 30 test/spawn-anon.test.ts passes (210 of 210), and the log has no hosted child did not open lines.
• bun test test/spawn-anon.test.ts test/apps.test.ts passes (28 of 28).
• tsc --noEmit is clean.

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