test(runtime): write the probe's report aside and rename it into place

[mrgoonie]

Refs #543 (item 1). Found while working on #497.

What changed

The probe service in apps/runtime/test/service-artifact-input.spec.ts wrote its report with writeFileSync(args.report, ...) at the path the test polls. The test reads the file as soon as existsSync is true and parses it, so it could read the file after it was created and before its bytes were in it:

FAIL  ... > answers no read once the call has ended, even one sent while it was in flight
SyntaxError: Unexpected end of JSON input
 > apps/runtime/test/service-artifact-input.spec.ts:651:23

The probe now writes <report>.partial and renames it to <report>, so the report exists only once it is complete. The fix is in the writer; the test's assertions are unchanged.

What stays the same

Product code, every assertion, and the other probe steps (signal files are only checked for existence, never read).

Verification

• corepack pnpm vitest run apps/runtime/test/service-artifact-input.spec.ts, 5 runs in a row: 15/15 passed each time. (The race was intermittent and was not reproduced on demand before the fix either.)
• corepack pnpm verify on this head:
  • first run: exit 1. All 13 invariant checks passed, typecheck and lint passed. Two unrelated suites failed in Windows temp-dir cleanup with EPERM (packs/browser-playwright/test/driver.spec.ts, injection.spec.ts). Both pass alone (2 files, 18 tests). Recorded on Windows: runtime suites time out under parallel verify, then fail cleanup with EPERM #535.
  • second run: exit 0. All 13 invariant checks passed; 519 test files passed, 1 skipped; 6910 tests passed, 37 skipped, 1 todo.

Known limitations / remaining

The e2e failures in #543 item 2 (seen only in the full Playwright run) are not addressed here; their causes are not yet found.

Docs impact

None (test only).

[mrgoonie]

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[mrgoonie]

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[mrgoonie]

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[mrgoonie]

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[mrgoonie]

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[mrgoonie]

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