Plugin update command uses stale local marketplace cache instead of fetching remote

Bug Description

The /plugin (or claude plugin update) command does not fetch the latest marketplace.json from the remote repository. Instead, it only checks the local marketplace cache (~/.claude/plugins/marketplaces/<plugin>/), treating whatever version is cached locally as "latest."

This causes the update command to report "already at the latest version" even when a newer version is available on the remote.

Steps to Reproduce

1. Install a plugin from a marketplace (e.g., oh-my-claudecode from the omc marketplace)
2. The plugin author publishes a new version (e.g., 4.8.0 → 4.9.0) to the GitHub repo
3. Run /plugin or claude plugin update
4. Expected: Plugin detects remote 4.9.0 and offers to update
5. Actual: Reports "already at the latest version (4.8.0)" because local cache is stale

Evidence

Remote (GitHub main branch) — .claude-plugin/marketplace.json:

{
  "version": "4.9.0",
  "plugins": [{ "name": "oh-my-claudecode", "version": "4.9.0" }]
}

Local marketplace cache — ~/.claude/plugins/marketplaces/omc/package.json:

{
  "version": "4.8.0"
}

Local installed_plugins.json — locked at 4.8.0:

{
  "oh-my-claudecode@omc": [{
    "version": "4.8.0",
    "lastUpdated": "2026-03-14T00:11:25.646Z"
  }]
}

The npm registry (oh-my-claude-sisyphus) also has 4.9.0 published, confirming the release is valid.

Workaround

Manually delete the stale marketplace cache and reinstall:

rm -rf ~/.claude/plugins/marketplaces/<marketplace-name>
claude plugin marketplace add <marketplace-name>
claude plugin install <plugin-name>

Expected Behavior

When /plugin or claude plugin update runs, it should:

1. Fetch the latest marketplace.json from the remote GitHub repository
2. Compare with the locally installed version
3. Update if a newer version is available

Environment

• Claude Code version: latest (as of 2026-03-22)
• OS: macOS (Darwin 25.2.0, arm64)
• Plugin: oh-my-claudecode v4.8.0 (from omc marketplace)
• Remote available: v4.9.0