Multi-plugin custom marketplace: only first plugin registered in installed_plugins.json, skills don't load

Summary

When using a custom marketplace (via extraKnownMarketplaces) that contains multiple plugins, the /plugin install command reports "Installed 5 plugins" but only the first plugin gets written to installed_plugins.json. The remaining plugins are cached to disk but never registered, so their skills are never discoverable.

Agents from all plugins appear to load (the reload count shows them), but skills from none of the plugins appear in /skills or the system reminder.

Environment

• Claude Code Version: 2.1.109 (Homebrew)
• Platform: macOS Darwin 25.3.0
• Date: 2026-05-28

Reproduction

1. Create a custom marketplace with multiple plugins, each containing skills/ and agents/ directories:

marketplace-repo/
  .claude-plugin/
    marketplace.json    # lists 5 plugins
  plugins/
    plugin-a/
      .claude-plugin/plugin.json
      skills/skill-1/SKILL.md
      agents/agent-1.md
    plugin-b/
      .claude-plugin/plugin.json
      skills/skill-2/SKILL.md
      agents/agent-2.md
    ...

1. Register the marketplace in settings.json:

{
  "extraKnownMarketplaces": {
    "my-marketplace": {
      "source": { "source": "git", "url": "https://github.com/org/repo.git" }
    }
  }
}

1. Run /plugin to install all plugins — reports "Installed 5 plugins"
2. Run /reload-plugins — reports "0 skills" and skills don't appear in /skills
3. Check ~/.claude/plugins/installed_plugins.json — only the first plugin from marketplace.json is registered

Expected Behavior

All 5 plugins should be registered in installed_plugins.json and their skills should be discoverable via /skills.

Actual Behavior

• installed_plugins.json contains only 1 of 5 plugins (the first one listed in marketplace.json)
• All 5 plugins are correctly cached to ~/.claude/plugins/cache/
• All 5 plugins are enabled in settings.json under enabledPlugins
• /reload-plugins shows "5 agents" but "0 skills"
• No skills from any plugin appear in /skills or the system reminder

Diagnostic Details

Cache is correct — all 5 plugin directories exist under ~/.claude/plugins/cache/my-marketplace/ with proper skills/*/SKILL.md files.

Skills format is valid — copying a SKILL.md from the custom marketplace into the superpowers plugin's skills/ directory causes it to load correctly, confirming the SKILL.md format is not the issue.

Single-plugin marketplaces work — the superpowers plugin (a single-plugin marketplace) loads all its skills correctly from the same type of SKILL.md files.

Workaround

None found yet. The specific marketplace is constellize-plugins-official with 5 plugins (constellize:memory, constellize:design, constellize:craft, constellize:deliver, constellize:grow).

Possibly Related

• #10568 — Marketplace Skills Not Exposed Through Skill Tool (closed)
• #55493 — Plugin caching drops entry.skills + wipes sibling plugins (closed)
• #29074 — Plugin cache not cleared on uninstall/reinstall