Add Oh My Pi (omp) integration: client entry + extension for deterministic read/write paths - #4

Summary

Adds first-class support for Oh My Pi (omp), a local-first coding agent with a full MCP client and an extension system. omp was missing from clients.py (so integrate omp / integrate --all did not cover it) and had no documented wiring or deterministic write/read path.

Changes

1. src/compartment/clients.py — new omp client entry (writes ~/.omp/agent/mcp.json, stdio, standard mcpServers root; aliases oh-my-pi). ~/.omp/mcp.json noted as fallback path.
2. integrations/omp/extension.ts — omp extension giving the deterministic paths the MCP entry alone cannot provide:
   • before_agent_start: recalls project memory into a DATA block (automatic read)
   • context: buffers user turns; flushed to the vault at session_shutdown and pre-compaction (automatic write, dedup + caps)
   • session.compacting: injects recalled memory into the compaction context so summaries do not drop prior decisions
   • memory_search / memory_store registered as tools, MCP-independent
   • All vault access via the compartment CLI — offline, no new dependencies, silent on failure (never blocks the agent loop)
3. docs/INTEGRATIONS.md — omp section.
4. tests/test_clients.py — omp entry test (resolve, path, snippet shape).

Why an extension (not just MCP)

omp has a first-class hook/extension subsystem (pi.on("tool_result" | "context" | "session.compacting" | ...)). The extension mirrors the Claude Code integration experience: automatic recall at session start and a write path that does not depend on model discretion. The MCP entry works alongside it and shares the same vault.

Validation

• pytest tests/ — 731 passed, 8 skipped (usearch optional dep installed to verify the parity test), 0 failed
• compartment integrate omp entry resolves: compartment --vault <vault> --caller omp serve
• Extension transpiles cleanly with Bun (same runtime omp uses to load extensions)

Notes

• Extension install: cp integrations/omp/extension.ts ~/.omp/agent/extensions/compartment.ts (auto-discovered on next omp start).
• omp also ships its own local memory backend (Mnemopi); Compartment complements it with encryption, deterministic ranking, and cross-agent sharing. The two can coexist.