Adds buildOutgoingControl: builds the two 0-value memo outputs for a control
signal (a "Ctrl" header carrying `op` + a plaintext label payload) addressed to
the sender's OWN z-address, so only this wallet's seed harvests it and it never
reaches the peer. buildHeaderMemo gains an optional `op` (emitted only for
Control; existing Memo/Cont headers stay byte-identical). Round-trip + guard
tested through the receive parser.
Phase A, step 2 (compose) of on-chain chat delete/restore.
Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>
DanSandClaude Opus 4.8
7320a98505