Define how non-snapshot files commit — whole-root staging, path-shaped events

The composer was a pure snapshot diff while the repo tracked files outside
the model (agent guide, strays, .gitignore), leaving stray-only windows
uncommittable and the guide's own subject underivable. Settled: the
committer stages the whole root with the tree as its commit condition; the
composer also receives the changed-path list, composing "Update agent
guide (vN)" (version from the marker line) and "Update '<path>'" events
that ride as body bullets under model-event subjects; attribution falls
out of the path-keyed EchoLedger.

Claude-Session: https://claude.ai/code/session_01HJ7PhFNmQ19bvy9RMD6GSb

DESIGN/08-agent-integration.md

@@ -28,7 +28,7 @@ Mechanics: version marker in the first line (`lanework-agent-guide vN`); rewritt
 
 **`CLAUDE.user.md`** is the user's extension point: an optional, user-authored file at board root carrying board-specific agent instructions. The generated guide tells agents to read it when present, so it lands in agent context without the app ever touching it — the app never writes, upgrades, or validates it.
 
-On git boards, a guide write rides the normal watcher → auto-commit path with an honest message ("Update agent guide (v3)"), not "External edit" (06-history-undo.md).
+On git boards, a guide write rides the normal watcher → auto-commit path with an honest message ("Update agent guide (v3)"), not "External edit" (06-history-undo.md ▸ Commit messages — the non-snapshot-files rule: the committer stages the whole root, and the composer reads the subject's version from the guide's marker line, a pure function of file content).
 
 ## Agent conventions worth specifying (new in the rewrite)