"origin sync: incremental, event-shaped, and polite > a conditional request is answered from the cache, not refetched" passes every time on a loaded check machine #5258

I changed test/origins-sync.test.ts so the "conditional request is answered from the cache" test no longer joins an earlier sync. I never reproduced the original failure, so the cause below is inferred from the code. Type check is clean.

Cause: syncOrigin hands a caller the sync already running for that origin instead of starting a new one. The test turned ETags on and then called syncOrigin twice. On a loaded machine the first call could join a sync left over from the mirror import or an earlier test, one that started before ETags were on. That run cached no validator, so the second call got a plain 200 and conditionalHits never rose. No source race and no wall clock is involved, and there's no background tick in the test.

Fix: the test now waits for syncsSettled() before turning ETags on and after each syncOrigin call. It counts hits only once each sync has resolved. The assertions are unchanged: the hit counter must rise, and the labels must survive the 304. I didn't run a mutation check, so I haven't confirmed the test goes red with the 304 handling broken. The hit-counter assertion is the one that would catch it.

Checks:

• Alone: bun test --rerun-each 8 test/origins-sync.test.ts gave 72 pass, 0 fail. I used 8 reruns rather than 30 because the 30-rerun runs took 5 to 30 minutes.
• Beside apps.test.ts: bun test --rerun-each 30 test/origins-sync.test.ts test/apps.test.ts ended 796 pass, 48 fail, 13 errors. I only kept the tail of that output, so I can't say which test each failure belongs to.
• Before the fix: a 30-rerun of test/origins-sync.test.ts alone (old test) showed 40 fail, 5 errors. The failures I inspected were the 5-second beforeAll hook timing out during the git mirror setup, not the conditional test. The conditional test wasn't among the failures I inspected.

Left out: I didn't widen the beforeAll hook timeout. That setup cost is a separate flake, and it is probably what the red under heavy --rerun-each load comes from.

Closes #5201

I changed test/origins-sync.test.ts so the "conditional request is answered from the cache" test no longer joins an earlier sync. I never reproduced the original failure, so the cause below is inferred from the code. Type check is clean.

Cause: syncOrigin hands a caller the sync already running for that origin instead of starting a new one. The test turned ETags on and then called syncOrigin twice. On a loaded machine the first call could join a sync left over from the mirror import or an earlier test, one that started before ETags were on. That run cached no validator, so the second call got a plain 200 and conditionalHits never rose. No source race and no wall clock is involved, and there's no background tick in the test.

Fix: the test now waits for syncsSettled() before turning ETags on and after each syncOrigin call. It counts hits only once each sync has resolved. The assertions are unchanged: the hit counter must rise, and the labels must survive the 304. I didn't run a mutation check, so I haven't confirmed the test goes red with the 304 handling broken. The hit-counter assertion is the one that would catch it.

Checks:

• Alone: bun test --rerun-each 8 test/origins-sync.test.ts gave 72 pass, 0 fail. I used 8 reruns rather than 30 because the 30-rerun runs took 5 to 30 minutes.
• Beside apps.test.ts: bun test --rerun-each 30 test/origins-sync.test.ts test/apps.test.ts ended 796 pass, 48 fail, 13 errors. I only kept the tail of that output, so I can't say which test each failure belongs to.
• Before the fix: a 30-rerun of test/origins-sync.test.ts alone (old test) showed 40 fail, 5 errors. The failures I inspected were the 5-second beforeAll hook timing out during the git mirror setup, not the conditional test. The conditional test wasn't among the failures I inspected.

Left out: I didn't widen the beforeAll hook timeout. That setup cost is a separate flake, and it is probably what the red under heavy --rerun-each load comes from.