Last extraction of Phase 3. Moves inter-agent messaging + create_agent +
destination projection into src/modules/agent-to-agent/. Core retains:
- `channel_type === 'agent'` dispatch in delivery.ts, guarded by
hasTable('agent_destinations') + dynamic import into module.
- Channel-permission ACL in delivery.ts, guarded by hasTable, with
inlined SQL (no module import from core).
- writeDestinations call in container-runner.ts, guarded by hasTable +
dynamic import into module.
- createMessagingGroupAgent's destination side effect in db/messaging-groups.ts,
guarded by hasTable. This is a documented transitional tier violation
(core imports from optional module), analogous to src/access.ts.
Migration `004-agent-destinations.ts` renamed to `module-agent-to-agent-
destinations.ts` preserving `name: 'agent-destinations'` so existing DBs
don't re-run it.
delivery.ts: 600 → 449 lines. handleSystemAction's last switch case gone
(just registry + default log-and-drop). notifyAgent helper removed (only
create_agent used it).
Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>
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