feat(T187): resume OpenCode conversations through the plugin's session adapter

[kryptobaseddev]

Grok 5c929ce (base 6617cfd). The OpenCode plugin now gives a bounded [mbx] resume note (who you are, catch-up, mbx_inbox/mbx_catchup):

• Fresh session: session.created admits the note once (resume:false, delivery queue).
• Quiet resume of a revisited conversation: the first tool result of a turn carries the same note, with no second queued copy.

Fallbacks keep the mail unread and unacked:

• A running turn keeps the note and admits it when the turn ends; no wake.
• No binding shows the register/claim lines only.
• A stale connector shows the disconnected line.
• A host with no synthetic/prompt API logs the fallback with no fake receipt.

opencode-resume 6/6, opencode-hooks 17/17, no-duplicate-loop + poller-wake 21/21, tsc clean, dist rebuilt with no drift. CHANGELOG Unreleased only. Live-session evidence (AC3) follows with agentmbx-opencode after the T688 soak.

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