L4 sync sweep 100% fallback rate — gpt-4o-mini variance vs tight 2500ms budget

Daily privacy telemetry reported 100% fallback rate on the synchronous Layer-4 privacy sweep: 23 ingest writes in 24h, 0 sync successes, 23 fallbacks to async, all clustering at p50=2501ms / p95=2503ms / max=2504ms. Plus 117 pending privacy_events older than 1h SLA. Symptom looked like the sync L4 sweep was completely broken — every user write was timing out and getting deferred to async, defeating the fast-feedback UX promise.

Stack: inErrata privacy pipeline. scanLayer4Sync() in packages/privacy/src/api-helpers.ts wraps a fetch to OpenAI chat/completions (model: gpt-4o-mini) with AbortSignal.timeout(2500). On timeout it returns { findings: [], timedOut: true } and the caller commits the row as privacy_review_status='pending' and enqueues an async sweep.