src/orchestrator/remote-prefetch.ts — background remote GETs

Purpose

With a LayeredCache, remote GET latency would sit on each task’s critical path. This derives every STABLE task’s pure-input key up front (reusing the run’s hashCache memo — no double hashing) and fires the remote GETs concurrently before scheduling, so network overlaps execution. LayeredCache ingests hits into local and de-dups against the lazy read-through: at most ONE remote GET per key.

Public surface

• startRemotePrefetch(args) → Promise<void> handle. Fire-and-forget for scheduling; run() awaits it before cache.close() only.

Invariants

• Remote-only: gated on cache instanceof LayeredCache; local runs never derive keys or probe anything here.
• Stability gate via deriveStableKeys — unstable (codegen-consumer) tasks stay on the lazy path.
• Never-fail: every path degrades to a miss.