# MCP Thread Persistence Demo

A minimal MCP (Model Context Protocol) server that persists chat-thread
notes to SQLite, with a real client that exercises it over the actual
stdio transport (not just calling the underlying functions directly).

Built as a learning exercise mirroring a real freelance job pattern:
"fix/implement MCP tool calls that persist chat thread state to a
database, with upsert semantics (create if new, update if existing,
no duplicate rows per thread)."

## What's here

- `server.py` — MCP server exposing three tools:
  - `save_note(user_id, thread_id, content)` — upsert into SQLite,
    keyed on `(user_id, thread_id)`. Second call on the same thread
    updates the existing row instead of creating a duplicate.
  - `get_note(user_id, thread_id)` — read back the saved note.
  - `list_threads(user_id)` — list all threads for a user.
- `test_client.py` — a real MCP client that connects to `server.py`
  over stdio, calls `list_tools`, then exercises all three tools in
  sequence (including calling `save_note` twice on the same thread to
  verify the upsert doesn't create a duplicate row).

## Running it

```bash
python3.12 -m venv .venv
source .venv/bin/activate
pip install -r requirements.txt

python test_client.py
```

## Notes

Pinned to `mcp<2` deliberately: the `mcp` SDK's 2.x release renamed
`FastMCP` to `MCPServer` and changed other APIs. Most existing
tutorials/codebases in the wild still target the 1.x `FastMCP` API,
so that's what this targets too.