Plugin update check doesn't fetch latest from marketplace git repo

Bug Description

When running /plugin to check for updates to an installed plugin from a GitHub-sourced marketplace, the command returns no results even when a newer version is available on the remote. The marketplace cache (~/.claude/plugins/marketplaces/<name>/) is not git pulled before comparing versions, so it compares stale cached data against the installed version.

Steps to Reproduce

1. Register a GitHub-sourced marketplace (known_marketplaces.json entry with "source": "github")
2. Install a plugin from it (e.g., version 1.0.0)
3. Push a new commit to the marketplace repo that bumps the plugin version (e.g., to 1.1.0)
4. Run /plugin to check for updates
5. Result: Returns (no content) — no update detected
6. Expected: Should detect version 1.1.0 is available and offer to update

Root Cause

The marketplace git clone at ~/.claude/plugins/marketplaces/<name>/ is not fetched/pulled during the update check. The lastUpdated field in known_marketplaces.json appears to control cache freshness, but the TTL seems too aggressive — it doesn't re-fetch even when there are known remote changes.

In my case:

• Marketplace registered: 2026-02-25T01:29:39Z
• Plugin installed: 2026-02-25T01:30:44Z (version 1.0.0, commit 3798f4d)
• New commit pushed to remote: 394681e (bumps version to 1.1.0)
• /plugin update check: returns nothing
• Manual git pull in the marketplace cache dir, then /plugin: works correctly

Workaround

Manually pull the marketplace cache before running /plugin:

cd ~/.claude/plugins/marketplaces/<marketplace-name> && git pull origin main

Environment

• Claude Code CLI
• Linux (WSL2)
• Marketplace source: GitHub repo ("source": "github")