fix: keep the shared action cache as extracted, re-fetch damaged trees (#1352)

The toolkit patch rewrote bundles in place in the shared action cache. Since https://gitea.com/gitea/runner/pulls/1316 trees are never refreshed, so a bundle left truncated failed every later job using it.

Patched bundles now only overwrite the job container's copy, so the runner no longer writes to an extracted tree.

Extraction records each file's size beside the tree, and a tree that no longer matches is fetched again, offline mode included, as a missing one always was. This also catches damage from outside the runner, such as storage losing a write, for a stat per file, a fraction of the copy each stage already makes. Trees from older runners have no record and download once more, except in offline mode, which keeps using them as before.

Generated with Claude Code.

Reviewed-on: https://gitea.com/gitea/runner/pulls/1352
Reviewed-by: Lunny Xiao <[email protected]>
Reviewed-by: bircni <[email protected]>
Co-authored-by: Zettat123 <[email protected]>

internal/pkg/config/config.example.yaml

@@ -194,7 +194,8 @@ cache:
   #  secret_key_file: "/run/secrets/cache-s3-secret-key"
   # When true, reuse a cached action instead of fetching from the remote on every job.
   # A moved tag (e.g. a re-tagged "v6") or an updated branch stays at the cached commit
-  # until its cache entry expires or is manually removed.
+  # until its cache entry expires or is manually removed. A cached action whose files changed size
+  # since it was downloaded is still fetched again, unless an older runner cached it without sizes.
   #offline_mode: false
   # Serve the actions cache service v2 API. The actions that use it fall back to v1 on any host
   # they do not take for GitHub, so reaching it means editing that check out of their own bundle,