Install fails: .claude-plugin/marketplace.json is missing, so the README's `marketplace add` command errors out

[kesjam]

The README's documented install command fails because the repo ships .claude-plugin/plugin.json but no .claude-plugin/marketplace.json.

Repro

$ claude plugin marketplace add loopgain-ai/loopgain-plugin
Adding marketplace…
✘ Failed to add marketplace: Marketplace file not found at
  /Users/<me>/.claude/plugins/marketplaces/loopgain-ai-loopgain-plugin/.claude-plugin/marketplace.json

The clone succeeds; the resolver then looks for marketplace.json and bails. Since /plugin install loopgain depends on the marketplace being registered first, step 2 of the README is unreachable.

Repo contents

.claude-plugin/plugin.json      <- present
.claude-plugin/marketplace.json <- missing

Suggested fix

Add a .claude-plugin/marketplace.json alongside the existing plugin.json, e.g.

{
  "name": "loopgain",
  "owner": { "name": "Dave Fitzsimmons", "email": "hello@loopgain.ai" },
  "plugins": [{ "source": "./", "name": "loopgain" }]
}

Workaround

Copying the repo to ~/.claude/skills/loopgain/ installs it as loopgain@skills-dir with no marketplace involved. claude plugin details loopgain then resolves correctly (1 skill, 0 agents/hooks/MCP servers).

Environment

• Claude Code 2.1.214
• macOS 15 (Darwin 24.6.0)