## Why
Repeated plugin discovery and loading reparse unchanged manifests and repeat warnings for invalid fields.
## What changed
- Share a manifest cache through `PluginStore` across marketplace listing, plugin loading, capability inspection, and tool suggestion metadata.
- Reuse successful parses by plugin root, manifest path, and content digests, including the Codex overlay. Reread files on each load so manifest edits and overlay changes or removal remain visible.
- Bound the cache to 128 entries and bypass caching for inputs larger than 64 KiB. Retry failed parses and share entries across store clones while keeping independent stores isolated.
- Reuse loaded manifest data when loading apps and MCP metadata.
## Testing
Add unit coverage for parse reuse, warning deduplication, revision invalidation, repair after parse failures, equivalent Windows paths, store isolation, and oversized inputs. Add an app-server regression test that verifies repeated `plugin/list` requests observe manifest and overlay revisions in one running server.
GitOrigin-RevId: ed082cd7d198015cd8ed35db7f2af74e13f49915
