Two fixes from the independent review of f043cd7.
RationalNs::checked_add cross-multiplied into u128 and then added without a check. Each
product fits, but their sum does not: two reduced fractions near the U64 maximum add to about
2^129, which panics in debug and wraps in release, after which the reduction returns a
confidently wrong rational. Every multiplication and the addition now go through a checked
path, as ipc-v1 section 2 requires, with a fixture row and a test that reaches the overflow
rather than the "does not fit U64" reduction limit.
The schema-set test checked fourteen hardcoded type names, so a new payload type could have
shipped outside contractDigest. It now iterates the readers own list, all fifty of them.
Also amends ipc-v1 section 5, dated: Worker.Acknowledge carries req-<U64> request ids, not
arbitrary Ids, because the serial watermark rule in that same section cannot reject reuse
after acknowledgment unless the acknowledged id carries its serial.
Two specifications CONTRACT-01 owes the slices that cannot be built without them.
seed-derivation-v1: the versioned derivation of independent per-agent seeds from a recorded
master seed and stable agent ids, the exact hashed material, the lane rule that keeps a seed
away from zero (the pinned kernel RNG is an xorshift, whose state must not be zero), the
properties a composition may rely on, and the test vectors both languages reproduce.
checkpoint-envelope-v1: the exact byte layout of the new envelope per state-media-v1 section
4, with the header, canonical-JSON manifest, 112-byte payload table entries, eight-byte
aligned payloads and the digest footer; the manifest field set; what a reader enforces and in
what order; and the durable commit sequence of section 6, whose commit point is the store
manifest rename. FLYSIM01 is unchanged, refused at the magic, and stays separately readable.
Both are specifications with fixtures, not the store: generations, rotation, the capture
queue and the restore flow remain STATE-01.
