The cursor-channel sweep grew AddReply by the cursor_excluded u32 tail (24
bytes, legacy prefix 20) and bumped PROTOCOL_VERSION to 6, but left two lib
tests behind: the AddReply byte-layout roundtrip still built the legacy
initializer (a compile error that turned the rust CI leg red on main), and
the version-coherence assertion still pinned v5 (hidden behind that compile
error). Cover the new tail bytes + the legacy-size constant, and widen the
compat-window note to v4–v6 (floor stays 3).
Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>
enricobuehlerandClaude Fable 5
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