Plugin install fails without SSH keys - marketplace.json should use relative source

[drewbitt]

The nx plugin fails to install on machines without SSH keys configured for GitHub:

✘ Failed to install plugin "nx": Failed to clone repository:
git@github.com: Permission denied (publickey).

The marketplace itself clones fine because Claude Code falls back to HTTPS. But the plugin install step uses a separate clone path that doesn't have that fallback, and your marketplace.json triggers it by using an absolute GitHub source:

{
  "name": "nx",
  "source": {
    "source": "github",
    "repo": "nrwl/nx-ai-agents-config"
  }
}

Since the plugin lives in the same repo as the marketplace, changing this to "source": "./" would avoid the second clone entirely. This is what vercel-labs/agent-browser does and it works without SSH:

{
  "name": "agent-browser",
  "source": "./",
  "skills": ["./skills/agent-browser"]
}

The same issue affects the polygraph plugin which uses "source": "git-subdir" with the SSH-only path.

Repro:

1. Machine with no SSH keys for GitHub (HTTPS-only, common in corporate environments)
2. claude plugin marketplace add nrwl/nx-ai-agents-config — succeeds (HTTPS fallback)
3. claude plugin install nx — fails (SSH clone, no fallback)

[tschaffter]

Hitting this in a GitHub devcontainer (Docker on Linux). The failure is slightly different from a missing key -- it's a host key verification failure because GitHub's host key isn't in known_hosts:

Host key verification failed.
fatal: Could not read from remote repository.

Please make sure you have the correct access rights
and the repository exists.

This happens before authentication, so even a container with SSH keys configured would fail unless github.com has been added to known_hosts. The result in Claude Code is that the skill silently fails to load -- no error surfaced in the UI, just a red circle on execution.

Repro environment:

• GitHub Codespaces / devcontainer (Docker, Linux)
• Claude Code VS Code extension
• .claude/settings.json with "source": { "source": "github", "repo": "nrwl/nx-ai-agents-config" }

The workaround from this issue (switching to "source": "./" with local copies of the skill files) should fix it.