[OskarEichler]

Problem

FuseWorker accepts any numeric numWorkers. Zero silently falls back to the default, negative values initialize no shards, fractional values create an inconsistent shard count, and Infinity enters an unbounded worker-spawn loop when initialization starts.

Fix

• Require an explicitly supplied numWorkers to be a finite positive integer.
• Use nullish fallback after validation so only an omitted value selects the hardware-based default.
• Add regressions for zero, negative, fractional, NaN, and infinite counts.
• Rebuild the committed worker proxy distributions.

Verification

• Focused worker suite: 23 tests passed.
• Full suite: 22 files and 454 tests passed.
• ESLint and TypeScript checks passed.
• Worker distributions rebuilt successfully.
• Changed files pass Prettier and git diff --check.