plugin marketplace update fetches new version but doesn't update installed_plugins.json

Bug

claude plugin marketplace update <plugin> downloads the new plugin version into the cache directory but does not update the installPath and version fields in ~/.claude/plugins/installed_plugins.json. New sessions continue using the old version.

Reproduction

1. Publish a new version of a plugin (bump version in plugin.json, push to git)
2. Run claude plugin marketplace update <plugin-name>
3. Start a new Claude session

Expected: New skills/features from the updated plugin are available.
Actual: Session loads the old version. New skills missing.

Root cause

After update, the cache has both versions:

~/.claude/plugins/cache/bat-skills/bat-skills/1.20.0/skills/  # old — 7 skills
~/.claude/plugins/cache/bat-skills/bat-skills/1.21.0/skills/  # new — 10 skills (3 added)

But installed_plugins.json still points to the old version:

"bat-skills@bat-skills": [
  {
    "installPath": "…/cache/bat-skills/bat-skills/1.20.0",
    "version": "1.20.0",
    …
  }
]

Workaround

Manually edit ~/.claude/plugins/installed_plugins.json — update installPath and version to the new version directory.

Environment

• Claude Code CLI (latest as of 2026-07-12)
• Linux (Fedora 44)
• Plugin: custom marketplace plugin with plugin.json versioning