Tang-mm95/dsh-single-instance-guard

dsh-single-instance-guard

A zero-dependency DeepSeek Harness plugin that takes an exclusive lock on the DSH_HOME data directory at startup and aborts loudly when another live dsh server already uses it.

中文说明

Why

The JSONL session persistence backend documents “One live writer per session” and has no cross-process defense. Two dsh servers sharing one DSH_HOME (a desktop wrapper spawning its own server, or two dsh web processes) append batches with stale sequence cursors, corrupting session logs:

history unavailable for session "…": Error: corrupt session log: seq gap in committed region …

See this report for the full diagnosis, a read-only scanner, and a manual repair procedure.

This plugin turns the silent corruption into a loud startup failure.

Install

After publishing to npm:

dsh plugin --profile <profile> add dsh-single-instance-guard

Manual (any dsh install): add the row to the profile’s cordis.patch.yml before session-related bundles:

- insert:
    - id: single-instance-guard
      name: 'dsh-single-instance-guard'

The guard is a profile bundle: its manifest declares the same patch, so the CLI installs it as a patch layer.

How it works

1. Creates <DSH_HOME>/.dsh-server.lock atomically (O_EXCL), holding { pid, startedAt, hostname }.
2. On conflict, probes the holder’s pid liveness: a live holder aborts startup with a clear bilingual error; a stale lock (dead pid or unparsable file) is removed and acquisition retried once.
3. On process exit the lock is removed — only if still owned by this process.

DSH_HOME is resolved exactly like dsh itself: $DSH_HOME or ~/.dsh. Servers with different data roots never conflict.

Known limits

• The unlink+retry path has a tiny race when two processes discover the same stale lock simultaneously; the atomic O_EXCL write still admits exactly one winner, and the loser fails correctly on the retry.
• The lock protects against concurrent servers sharing one DSH_HOME. It does not protect against two dsh instances deliberately pointed at the same session file via different roots (unsupported anyway).

Development

npm test   # node --test

License

MIT