Send not_found for unservable get_data.

[echennells]

The node stops the channel when a peer requests a block or transaction that it cannot serve. bitcoind replies notfound and stays connected. Implements libbitcoin#986.

The node now replies and resumes the send loop at four sites: a hash that resolves to no header, a pruned block, a block that cannot be read from the archive, and an absent transaction. Each reply is sent from the send completion handler, as a block is, so nothing is produced until the prior write completes.

The hash that resolves to no header is tested first, because the checkpoint height query faults the store on a terminal link. Such a hash is ordinary peer input, so the query is no longer reached with one.

protocol_block_out_106 is attached without a version condition, so its peer may be below bip37, where not_found is undefined. It captures the negotiated level at construction and retains the existing stop below that level. protocol_transaction_out_106 is attached only above bip37, so the level is asserted there.

A request is already bounded by max_inventory at deserialization, so no additional limit is imposed.

Four cases cover the block sites, including a peer below bip37. The transaction site awaits a fixture that negotiates relay.

[echennells]

Closing — this branch is now the upstream PR.

ech99-send-not-found is the head branch of libbitcoin#1106. It was force-pushed on 2026-09-08 to carry the reworked implementation (0f6b385e3), so this fork PR and #9 now point at the same commit, and the title here describes the superseded design. Track it at libbitcoin#1106.