MemPalace MCP sidecar integration — wire palace tools into Legion sessions

[Esity]

Summary

MemPalace (96.6% R@5 recall, MIT, no API key required) can run as an MCP sidecar alongside Legion, giving Legion agents access to verbatim drawer storage, temporal knowledge graph, agent diaries, and BM25 hybrid search — all without changes to Legion core. This issue tracks the integration wiring.

What MemPalace Provides via MCP (29 tools)

Read:

• mempalace_status — palace overview, drawer counts, AAAK dialect spec
• mempalace_search — hybrid semantic+BM25 search, optional wing/room filter
• mempalace_list_wings / mempalace_list_rooms / mempalace_get_taxonomy
• mempalace_kg_query — temporal KG query (entity facts with as_of support)
• mempalace_kg_traverse — walk entity relationships
• tool_diary_read — read agent diary chronologically

Write:

• mempalace_add_drawer — file verbatim content into a wing/room
• mempalace_delete_drawer — remove by ID
• tool_diary_write — append to agent diary

Maintenance:

• mempalace_reconnect — force cache invalidation after external writes

Current Blockers

1. ChromaDB is local-only — works for single-node/dev workstations, not clustered Legion deployments. MemPalace v4 PostgreSQL backend (#665 in their repo) resolves this.
2. No RBAC/PHI classification — raw content goes to ~/.mempalace, no Vault integration. Not suitable for Optum/UHC PHI data as-is.
3. Python dependency — MemPalace is a Python package; Legion is Ruby. MCP stdio transport bridges this cleanly but adds a process dependency.

Integration Steps (Dev/Local Only Until v4 Postgres Backend)

# 1. Install
pip install mempalace

# 2. Initialize a palace for Legion
mempalace init ~/.mempalace/legion-palace

# 3. Mine existing project context (optional)
mempalace mine /path/to/legion/codebase

# 4. Add to Legion's MCP config

{
  "name": "mempalace",
  "command": "mempalace-mcp",
  "args": ["--palace", "~/.mempalace/legion-palace"],
  "transport": "stdio"
}

What to Validate

• Confirm MCP stdio transport works with Legion's MCP client
• Confirm mempalace_status wake-up call latency (<100ms target)
• Test mempalace_search alongside Apollo.query for the same query — compare result quality
• Test mempalace_add_drawer from within a Legion session
• Evaluate whether dual-write (Apollo + MemPalace) is practical or creates divergence

Long-term Path

Once MemPalace's PostgreSQL backend lands (v4), evaluate:

• Pointing MemPalace at Legion's existing Postgres instance
• Using MemPalace as the verbatim layer and Apollo as the governed index layer
• Replacing the MCP sidecar with a native Legion absorber that writes to both stores

References

• MemPalace repo: https://github.com/MemPalace/mempalace
• MemPalace MCP server: mempalace/mcp_server.py
• MemPalace roadmap v4.0.0-alpha — PostgreSQL backend (#665)
• Related: agent diary pattern (Agent diary pattern — per-agent chronological memory wings #26)
• Related: pre-compaction hook (Pre-compaction hook — emergency memory save before context window compression #27)

[github-actions]

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