chore: ignore half-written snapshots

Every snapshot is written to a sibling `.tmp-*` and renamed into place, so a
run killed mid-write leaves one behind. `refresh.yml` commits the whole
snapshots/ directory, which would pin that truncated page in git forever — and
the point of the atomic write was that a crash leaves nothing a reader can
mistake for a page.

Co-Authored-By: Claude Opus 5 (1M context) <[email protected]>

.gitignore

@@ -126,3 +126,9 @@ public/
 # but this file changes on every cycle, and committing it would mean a commit
 # per run saying nothing changed.
 snapshots/*.state.json
+
+# Half-written snapshots. Every snapshot is written to a sibling temp file and
+# renamed into place, so a run killed mid-write leaves one of these behind — and
+# the refresh workflow commits the whole snapshots/ directory, which would
+# otherwise pin a truncated page in git forever.
+snapshots/*.tmp-*

snapshots/README.md

@@ -17,7 +17,8 @@ localStorage keys).
 
 Every file is written to a sibling `.tmp-*` and renamed into place, body before metadata, so an
 interrupted run leaves a stray temp file rather than a truncated snapshot or metadata describing
-bytes that were never stored.
+bytes that were never stored. Those temp files are gitignored: `refresh.yml` commits the whole
+directory, so otherwise a run killed mid-write would pin a half-page in git forever.
 
 Three reasons this is committed rather than cached: