Serialize node block in the requested form, stripping witness.

[echennells]

A peer requesting a block without witness (getdata MSG_BLOCK) crashes the node.

messages::block held the store's wire bytes plus an advisory witnessed_ flag, and serialize/size guarded on witness == witnessed_. The generic serializer calls serialize with the default witness = true, so the guard fails, serialize returns false, and the null payload is sent without a null check — any peer can trigger it (in debug the size() assert trips first).

The guard is the root error, but the witness argument must also function: a witness node servicing a non-witness peer must strip the witness on serialize, and the serializer cannot rely on the held object's form, because one object may be sent to peers with differing requirements.

The message now holds a system::chain::block_view instead of the wire bytes and delegates serialize/size to block.to_data(witness) / block.serialized_size(witness) — the view strips the witness when serialized without it. protocol_block_out_106 selects the form at read time. The incorrect guard and assert are removed.

messages::transaction carries the same guard, but nothing serializes it yet (transaction-out re-serializes from the parsed transaction), so it is left unchanged.

Depends on libbitcoin/libbitcoin-system#1905 — will not build without it.

Full node test suite green.

[evoskuil]

Looks like this needs rebase.

[echennells]

Rebased onto master (ada11dc7). The change itself is unchanged — range-diff against the prior head is identical and the patch-id matches; only the base moved.

The previous CI red was the stale base rather than this change: the old head predated the database::store template signature change, so node no longer compiled against current database master (define.hpp:60: type/value mismatch at argument 1 in template parameter list for 'template<template<size_t...> class Storage> class database::store'). The system dependency this PR needs (#1905, block_view::to_data) merged on 2026-07-09.

Re-verified on a from-source build against current deps (system 35b3e4c5, database a69f1c96, network 41caed22), two binaries differing only in the node tree:

• Serving a legacy getdata MSG_BLOCK on master node SIGSEGVs — messages::block::serialize returns false for the non-witness form, and the resulting null payload is dereferenced in channel_peer::send. With this change the block is served.
• Real testnet3 block 5,103,550 (Core: 2438 B witness, 1309 B stripped): block_view::to_data(false) = 1309 B and is byte-equal to chain::block::to_data(false); to_data(true) is byte-identical to the stored wire block. Same result end-to-end over the P2P wire — MSG_BLOCK 1309 B, MSG_WITNESS_BLOCK 2438 B.

This build is currently running as a live testnet3 node at tip.

CI has not picked up the new head yet — it may need an approve-and-run.

[echennells]

CI is green on the rebased head (14/14). Three jobs failed on the first attempt — two cmake release configs and the macOS gnu job — but that run was cancelled mid-flight; they pass on re-run with no change to the head.