convention: commit by path, not by index

`git add <path>` then a bare `git commit` commits the whole index, so a
concurrent session's staged work rides along under your message and your session
trailer. Two agents share this tree most nights and it happened tonight —
6e092c32 names one file and holds ten.

`git commit -- <paths>` is the form that does what the two-step version looks
like it does. Note the argument order: -m or -F comes BEFORE the --, or git
reads the message as a pathspec.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>
Officer-Session: 656f5c85-e49a-4f1f-b9f3-042a04b4d043

CLAUDE.md

@@ -361,6 +361,17 @@ withholding the commit until it is good.
 
 Commit messages: simple lowercase, no prefixes.
 
+**Stage and commit in ONE step, naming the paths.** `git add <path>` then a bare `git commit` commits the
+whole **index**, not the path just named — so anything a concurrent session had staged goes into your
+commit, under your message and your session trailer. Use `git commit -- <paths>` instead, which does what
+the two-step form only looks like it does.
+
+This is not hypothetical and it is not rare: two agents share this working tree most nights. On
+2026-08-23 commit `6e092c32` says "marketplace: minesweeper in the catalogue" and contains nine files of
+another session's roles work, swept up mid-`git add`. The other session was right not to amend it —
+rewriting shared history to fix a message is the worse trade — so the record was corrected with a
+follow-up note instead. Cheap to avoid, awkward to undo.
+
 **An agent's commit names the session that made it.** A trailer, below `Co-Authored-By`:
 
 ```