Adds a notification seam to the universal molecule-mcp wheel so push-
notification-capable MCP hosts (Claude Code today; any compliant
client tomorrow) get inbound A2A messages as conversation interrupts
instead of having to poll wait_for_message / inbox_peek.
Wire-up:
- inbox.py: module-level _NOTIFICATION_CALLBACK + set_notification_callback()
Fires from InboxState.record() AFTER lock release, with same dict
shape inbox_peek returns. Best-effort — a raising callback never
prevents the message from landing in the queue.
- a2a_mcp_server.py: _build_channel_notification() pure helper +
bridge wiring in main() that schedules notifications via
asyncio.run_coroutine_threadsafe (poller is a daemon thread, MCP
loop is asyncio).
- Method name 'notifications/claude/channel' matches the contract
documented in molecule-mcp-claude-channel/server.ts:509.
- wheel_smoke.py: pin set_notification_callback as a published name,
same regression class as the 0.1.16 main_sync incident.
Pollers (wait_for_message / inbox_peek) keep working unchanged for
runtimes without notification support.
Tests: 6 new in test_inbox.py (callback fires once on record, dedupe
short-circuits before fire, raising cb doesn't break inbox, set/clear
semantics), 5 new in test_a2a_mcp_server.py (method name pin, content
mapping, meta routing, no-id JSON-RPC notification spec, missing-
field tolerance). All 59 combined tests pass.
Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>
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