Plugin cache not refreshed on update/reinstall when version string unchanged

Bug Description

When a marketplace plugin's content changes but its version string stays the same (e.g., 1.0.0), /plugin update and /plugin uninstall + /plugin install fail to refresh the cached plugin files.

Steps to Reproduce

1. Add a marketplace and install a plugin: /plugin install my-plugin@my-marketplace
2. Push new content to the marketplace repo without changing the version in plugin.json or marketplace.json
3. The marketplace clone at ~/.claude/plugins/marketplaces/<marketplace>/ updates correctly (via autoUpdate: true)
4. Run /plugin update my-plugin@my-marketplace
5. Observe that ~/.claude/plugins/cache/<marketplace>/<plugin>/<version>/ still has stale files
6. installed_plugins.json still shows the old lastUpdated timestamp and gitCommitSha

Attempting /plugin uninstall followed by /plugin install also fails — the cache directory remains empty and the metadata is unchanged.

Expected Behavior

• /plugin update should detect content changes (e.g., by comparing git SHAs) and refresh the cache, even if the version string hasn't changed.
• /plugin uninstall should fully remove the plugin entry from installed_plugins.json.
• /plugin install after uninstall should create a fresh cache from the current marketplace state.

Actual Behavior

• /plugin update is a no-op when the version string is unchanged, ignoring content changes.
• /plugin uninstall leaves the plugin entry in installed_plugins.json.
• /plugin install after uninstall doesn't re-cache the plugin files.

Workaround

Manually copy files from the marketplace clone to the cache:

rm -rf ~/.claude/plugins/cache/<marketplace>/<plugin>/<version>
cp -r ~/.claude/plugins/marketplaces/<marketplace>/<plugin> ~/.claude/plugins/cache/<marketplace>/<plugin>/<version>

Environment

• Claude Code CLI (latest as of 2026-03-10)
• macOS Darwin 24.6.0