Checkpoint: Safe Accumulator + Honest Probe

Implement three functions: 1. int safe_accum(int init, const int *deltas, size_t n, int *out) — repeatedly add each delta using your overflow-guard pattern; on any overflow return 0 leaving *out untouched; on success store the total and return 1. 2. unsigned int hash_span(const unsigned char *bytes, size_t n) — FNV-1a over the bytes (offset basis 2166136261u, prime 16777619u) — defined wraparound by design. 3. int probe_kept(int (*work)(void), int expected) — volatile file-scope static int probe = 0; is in your editor; reset it, run work(), return 1 iff probe == expected. work() itself increments probe.