fix(agent): close attention recovery gaps

[oscarlehuu]

Summary

Follow-up hardening for merged #108 after exact-tree concurrency, durability, security, projection, and realtime recovery review.

• preserves exact signed ACP request, receipt, and resolution authority across transient/malformed ACKs, restart, shutdown, dead-letter, and spool backpressure paths
• verifies inbound Nostr events, canonical tags, requested ancestry, agent/owner/channel/root relationships, and exact agent-trigger receipt pairs before projection
• keeps concurrent conversations/producers isolated while making review projection immediate only after the owner’s publish succeeds
• makes hydration live-first and generation-safe, recovers every durable lifecycle filter from a zero floor, bounds overflow fail-closed, and rejects stale wire generations/EOSE authority
• removes unsigned home-feed DTO authority and prevents unrelated signed events from exhausting durable projection buffers

Verification

Exact PR head 59ab743ef064ed140b1f303747d857172d22f76e:

• just ci — pass
• pnpm check — pass
• desktop unit suite — pass
• cargo test -p buzz-acp — pass
• cargo clippy -p buzz-acp --all-targets -- -D warnings — pass
• just desktop-tauri-test — pass
• just desktop-tauri-clippy — pass
• Mission Inbox Playwright smoke — 4/4 pass
• git diff --check — pass

Context

• Follow-up to feat(desktop): add agent attention and recovery #108
• Continues Agent attention & recovery: distinguish liveness from progress and surface actionable exceptions #105