fix(mcp): async tool handlers + pre-computed embeddings — parallel-store hang

[Huntehhh]

Summary

Resolves the 10-15 second Claude Code harness hang when 3+ parallel truememory_store (or truememory_search) MCP calls are issued in a single tool batch. Server-side writes complete in ~60ms — the hang is at the MCP transport + engine-lock layers.

Two-layer fix:

1. MCP layer: 7 hot-path @mcp.tool() handlers changed def → async def. Engine calls wrapped in asyncio.to_thread() so FastMCP's single event-loop thread stays free for concurrent JSON-RPC requests. Also fixes @tracked to return an async wrapper for coroutine functions (otherwise the async-ification is silently defeated by the existing sync wrapper).

2. Engine layer: TrueMemoryEngine.add() pre-computes both embeddings OUTSIDE _write_lock. Previously the lock was held during ~10-50ms of model.encode() per store, serializing all concurrent writes. PyTorch releases the GIL inside .encode(), so concurrent stores now overlap on inference; they only contend at the actual INSERTs (μs).

Changes

File	Change
truememory/mcp_server.py	7 tool handlers def → async def; engine calls via await asyncio.to_thread(...)
truememory/engine.py	add() pre-computes content + separation embeddings outside _write_lock
truememory/telemetry.py	@tracked detects coroutine functions and returns an async wrapper for them
tests/test_health_stats.py	Update test_truememory_stats_includes_health to await the now-async handler
tests/test_concurrent_store_hang.py	NEW — 3 regression tests (threaded engine.add(), handler-shape check, asyncio.gather() end-to-end)

truememory_configure intentionally stays sync — heavy state mutation, called once at setup, not on the hot path.

Test Plan

• New regression tests pass: pytest tests/test_concurrent_store_hang.py (3/3)
• Health stats tests pass: pytest tests/test_health_stats.py (11/11)
• Threading tests pass: pytest tests/test_ensure_connection_threading.py (2/2)
• Wider suite on Windows: 572 pass / 17 pre-existing failures unrelated to this change (test_platform_compat.py POSIX-path tests, test_spawn_gate.py system-memory dependent, test_cli_help.py locale issues, etc.)
• Manual verification needed on POSIX — pytest on Linux/macOS to confirm no regression in the Windows-failing tests

Breaking Changes

The 7 MCP tool handlers are now async def. Transparent for MCP clients (JSON-RPC wire protocol unchanged). Direct Python callers must update:

- result = truememory_store(content="...", user_id="...")
+ result = await truememory_store(content="...", user_id="...")
+ # or, from sync code:  result = asyncio.run(truememory_store(content="...", user_id="..."))

Co-Authored-By: claude-opus-4-7 wontreply@getfucked.ai