File upload backpressure bug

A production symptom appears first: flaky tests, stale state, slow UI, late cleanup, or growing memory. This causes upload memory spikes, slow proxies, stalled file imports, and high RSS in Node services.

Ignoring the false return value from writable.write or avoiding pipeline.

Fix the root scheduling, cleanup, or concurrency pattern instead of adding arbitrary waits.

try {
  await operation();
} finally {
  cleanup();
}

The visual proof is the active runtime event: watch what is retained, blocked, queued, or released at each step.

Reproduce the symptom with a small test, apply the safer pattern, then verify the flaky, slow, or leaking behavior disappears.