subosito/flutter-action's cache is the whole SDK, 1.6 GB: ~38 s to restore
on every Flutter job even on a hit, which alone kept them over a minute.
This composite action caches a depth-1 clone of the release tag with only
the host and web artifacts (393 MB zstd'd); verified locally that test,
analyze --fatal-infos and build web run on it without lazy downloads.
Release APK builds keep subosito, which they need for the Android engines.
Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01FBbkN4ZB4aUPJPzR2prRan
