feat(shared-memory): Extend mempalace coordination with 6 missing features (issue #382)

[quangdang46]

Summary

Extend mempalace_rust's existing coordination/ module with 6 missing features for cross-agent shared memory, then wire into jcode via jcode-mempalace-adapter.

Closes #382
Supersedes #396 (was creating separate crate, now extends mempalace)

Why This Approach?

mempalace_rust already has a coordination module with SignalStore, LeaseStore, Team, Mesh, ActionStore, CheckpointStore, RoutineStore, Frontier, and 20+ MCP tools. No need to build a separate crate. Just add the 6 missing features.

6 Features to Add to mempalace

1. Live Delivery (oh-my-openagent) — Inject messages into idle agent sessions at turn boundaries
2. Event Sourcing (oh-my-codex) — Append-only log for deterministic replay and crash recovery
3. File Reservations (pi-agent-rust) — Exclusive/shared file-level locks for workspace coordination
4. Saturation Signals (pi-agent-rust) — Detect duplicate work, stale threads, repeated blockers
5. Artifact Handoff (oh-my-claudecode) — Large payload (>2KB) separation with retention levels
6. Two-Phase Claim (oh-my-openagent) — Claim → re-check → write to prevent race conditions

jcode Integration

• 8 new tools: shared_memory_write/read/list/delete/cleanup, file_reserve, file_conflicts, saturation_check
• Agent turn loop: poll live delivery + check saturation at turn start
• ~540 lines in jcode, ~1,586 lines in mempalace

Estimate

~2,126 lines total (1,586 in mempalace + 540 in jcode)

Full Plan

docs/mempalace-shared-memory-master-plan.md (704 lines)

[quangdang46]

Closed — wrong approach. The 6 features should be implemented in mempalace_rust first, then jcode adapter updated. Creating issues in mempalace_rust repo instead.