[FEATURE]: GitHub-based Agent Marketplace for Sharing and Discovering Agents

[mporracindie]

Feature hasn't been suggested before.

• [x] I have verified this feature I'm about to request hasn't been suggested before.

Describe the enhancement you want to request

Problem Statement

Currently, sharing agents between users and teams requires manual file copying or maintaining separate configuration repositories. There's no integrated way to:

• Discover useful agents created by the community
• Install agents from remote sources directly into OpenCode
• Maintain a curated collection of agents across an organization
• Browse agents compatible with Claude Code's marketplace format

Proposed Solution

Implement a decentralized agent marketplace using GitHub repositories as registries, similar to Claude Code Marketplaces.

Key Features

1. GitHub as Registry: Use any GitHub repository (public or private) as an agent source
2. TUI Integration: Browse, search, and install agents directly from the terminal interface
3. Multiple Installation Scopes: Install agents globally (~/.config/opencode/agent/) or per-project (.opencode/agent/)
4. Claude Code Compatibility: Support repos that use Claude Code's directory conventions (.claude/agents/, .claude/skills/) without requiring a registry.json
5. Private Repository Support: Authenticate via GITHUB_TOKEN, gh CLI, or OpenCode's auth store

Configuration Example

  {
    "marketplace": {
      "sources": [
        {
          "repo": "myorg/agent-collection",
          "ref": "main"
        },
        {
          "repo": "anthropics/claude-code-agents",
          "private": false
        }
      ],
      "cacheDuration": 3600000
    }
  }

Use Cases

• Teams: Share standardized agents across an organization via a private GitHub repo
• Community: Discover and install community-contributed agents
• Cross-tool: Use the same agent repositories with both OpenCode and Claude Code

Additional Context

This would enable the ecosystem growth seen in other plugin/extension marketplaces while maintaining OpenCode's decentralized philosophy by using GitHub as the storage backend rather than a centralized server.