Prefetch TTL validation can crash Swift and does not consistently disable zero-TTL hits

The JS builders accept NaN and Infinity, and Swift request/prefetch paths convert prefetchCacheTtlMs directly to Int64, which traps for non-finite or out-of-range values. Both caches also allow a zero TTL to hit when elapsed milliseconds is zero despite the documented <=0 disables cache hits contract. I plan to validate finite JS TTL inputs, avoid trapping native conversions, use monotonic elapsed time, and enforce <=0 cache misses. Ordinary finite TTLs and shared pending requests remain supported.

Inspect the JS builders and the Swift request and prefetch paths that handle prefetchCacheTtlMs. Check how non-finite and out-of-range values are converted, how elapsed time is measured, and how zero-TTL entries are considered hits. Done means invalid inputs cannot trap, zero-TTL hits are disabled, and ordinary finite TTLs and shared pending requests still work.