sync: publish A2A reliability, Host Broker, and meeting intake

[zts212653]

Summary

Full outbound sync from Cat Café source 69d5597eb4bdd9aba9c3de3931f9bbd853384963 onto Clowder AI b8449d13d1ccc5f71bb489d560013df1ed7fca6c.

Fixes

• deliver the exact A2A trigger body under normal visibility gates
• prevent duplicate event/watchdog wakes and drain busy-cat callbacks exactly once
• record A2A receipts only after real prompt exposure, avoiding stale replay
• retain canonical unread/read anchors as visibility cursors advance
• register exact invocation slots on spawn_started
• isolate optional cloud-provider startup failures
• update Gemini 3.6 source handling

Features

• add Host Broker production transport, snapshot, handshake, and call ledger
• add meeting-intake admission, source lease, routing, approval flow, API, and UI
• add source-bound negative-control measurement contracts

Other changes

• synchronize public docs, schemas, governance baselines, and regression coverage
• preserve 60 public-only evidence/test/release paths through the F251 reconciliation ledger

Public behavior / migration

No configuration or data migration is required. A2A dispatch becomes more reliable and once-only; unread position no longer regresses; optional provider startup failures no longer abort healthy local startup. New meeting-intake and Host Broker surfaces are additive.

Verification

• source pnpm test: pass
• source pnpm check: pass
• source pnpm lint: exit 0
• shared/API builds: pass
• sanitized export: 7080 included, 14 excluded, 35 transforms
• secret scan: clean
• full disposable public gate: test:public 0 fail; API 3004 + Web 3003 startup acceptance pass
• F251: 269 pass / 0 block / 0 override; 60 reconciled preserve-public claims
• public behavior reporter: 6 changes, migration notes attached, 0 block
• final diff: 60 added / 114 modified / 0 deleted; git diff --check pass

Provenance

• previous source watermark: ccd61419380bdb85f4c137703a5dba44cc11afb1
• source head: 69d5597eb4bdd9aba9c3de3931f9bbd853384963
• public base: b8449d13d1ccc5f71bb489d560013df1ed7fca6c
• sync commit: 9c768e8e36984c17ace45bc0e408f7ef7b5a6326

[小太阳·砚砚/gpt-5.6-sol🐾]