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fix(mcp): fail fast on a second direct-mode writer per project (#1740) (#1744)

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Concurrent CODEGRAPH_NO_DAEMON / in-process fallback serve --mcp instances
each started a FileWatcher and contended on codegraph.lock until auto-sync
degraded. Add an exclusive .codegraph/writer.pid lock held by the daemon or
the single direct writer; a second writer exits with actionable guidance.
Daemon mode still multiplexes N proxies onto one writer.

Co-authored-by: Colby McHenry <colbymchenry@users.noreply.github.com>
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Colby Mchenry
2026-09-07 23:56:52 -05:00
committed by GitHub
co-authored by Colby McHenry
parent df435d50d1
commit 7440d2c475
8 changed files with 467 additions and 0 deletions
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README.md
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@@ -944,6 +944,8 @@ Framework routing is validated the same way, on a canonical app per framework: E
**MCP server not connecting** — Your agent starts the server itself, so you don't launch it by hand. Make sure the project is initialized and indexed (`codegraph status`) and that the path in your MCP config is correct. If it still won't connect, re-run `codegraph install` to rewrite the config.
**Two `codegraph serve --mcp` on one project fight over the index / auto-sync stops** — CodeGraph allows one live MCP *writer* per project (the shared background daemon, or a single direct-mode process). Extra clients should proxy to that daemon. If you set `CODEGRAPH_NO_DAEMON=1`, run only one `serve --mcp` for that project; a second instance exits with a clear writer-lock error (see `writer.pid` under `.codegraph/`). Prefer leaving the daemon enabled so multiple MCP hosts share one watcher.
**MCP tool calls fail with `Transport closed` while `codegraph status`/`sync` are healthy** — almost always WSL2 with the project on a Windows drive (a `/mnt/c` or `/mnt/d` path), where the local socket CodeGraph uses to share one background server across sessions is unreliable. CodeGraph now falls back to serving the session in-process instead of dropping the connection, but if you still hit it, set `CODEGRAPH_NO_DAEMON=1` in your MCP server's environment to skip the shared server entirely (each session runs in its own process). Moving the project onto the Linux-native filesystem (e.g. under `~/` instead of `/mnt/`) restores the shared server.
**Missing symbols** — The MCP server auto-syncs on save (wait a couple seconds). Run `codegraph sync` manually if needed. Check that the file's language is supported and isn't inside a `.gitignore`d or default-excluded directory (e.g. `node_modules`, `dist`).