&& python3 ~/.local/share/frostyard-mill/mill_state.py publish
+```
+
+The PR title is the spec's title verbatim, so ensure the spec title is a
+valid conventional-commit subject (e.g. `feat: …`), or the squash-merge trips
+commit-lint.
+
+## Concurrency safety (do not break other runs)
+
+The user may run **several mills at once, across different projects**.
+
+- **Never** `conductor stop --all` or `pkill -f conductor` — it is
+ cross-project and kills their other runs. Stop only *your* run, by its
+ dashboard **port** (`conductor gate respond --port --choice abort` to
+ clear a parked gate) or its PID.
+- Clean only the worktree you launched (`.worktrees/mill-`), never a
+ blanket sweep.
+- The driver refuses a second run in the same worktree; honor that rather
+ than forcing `--fresh` over a live run.
+
+## Engine drift hazard
+
+Runs execute `~/.local/share/frostyard-mill/mill_state.py` (and `mill.yaml`),
+re-loaded fresh on every script step — **not** any repo clone. So:
+
+- If a run misbehaves in a way the repo source doesn't explain, diff the
+ installed engine against the repo; they may have drifted.
+- After editing the engine, sync the installed copy (`git pull` in it, or
+ reinstall) before relying on the change.
+- **Do not edit the shared engine while other runs are in flight** — every
+ script step of every live run picks up your change mid-run. Additive
+ changes are usually safe; behavioral ones are not. Wait for the batch to
+ drain, or flag it to the user first.