Function sig_fold

src/watcher/watcher.c:490–497

#define SIG_FNV_PRIME 1099511628211ULL

static uint64_t sig_fold(uint64_t h, const void *data, size_t len) {
    const unsigned char *p = data;
    for (size_t i = 0; i < len; i++) {
        h ^= p[i];
        h *= SIG_FNV_PRIME;
    }
    return h;
}

/* Platform-portable mtime_ns (mirrors pipeline_incremental.c). */
static int64_t sig_stat_mtime_ns(const struct stat *st) {