DR-009 — MemPalace is single-writer; recall is read-only

The daily HNSW index drift is an upstream chromadb Rust thread-safety bug under concurrent mempalace-mcp writers (multi-session). Ruling: all recall/read paths use lock-free read-only WAL sqlite (mode=ro, never opening a chromadb writer); writes route through a single writer (the opt-in 3.5.0 daemon / one MCP server); worktree subagents recall read-only and never write. Repair recipes + the single-writer posture live in runbooks/mempalace-repair.md.