Aborts startup when another live dsh instance holds the same DSH_HOME data directory, preventing the concurrent session-log writes that corrupt transcripts.
Install
# from GitHub (first run asks for allowBuilds approval — follow the hint, retry)
dsh plugin --profile web add github:Tang-mm95/dsh-single-instance-guard
Any plugin you install runs third-party code with your own permissions — it can read your files, use your credentials, and reach the network, and tool approvals don’t sandbox it. GitHub-sourced plugins also run build scripts at install time — pnpm blocks those until you allow them, so an install can stop with ERR_PNPM_GIT_DEP_PREPARE_NOT_ALLOWED or ERR_PNPM_IGNORED_BUILDS; dsh prints the exact key to add under allowBuilds in your profile’s pnpm-workspace.yaml, and the install works on the next run. Allowing a build is a trust decision: only install sources you trust, and pin a commit (github:owner/repo#sha).
README
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.
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
- Creates
<DSH_HOME>/.dsh-server.lockatomically (O_EXCL), holding{ pid, startedAt, hostname }. - 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.
- 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_EXCLwrite 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
Links
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