Proposal: codex plugin install from git (MVP)

Context

Read #8512; this is a concrete MVP proposal. Happy to move/merge there if preferred.

Proposal

Add a small “git bundle” install path for sharing skills/prompts/MCP without a marketplace.

MVP behavior

• codex plugin install <git-url|path>
• Clone into ~/.codex/plugins/<name> and record source/version
• Materialize:
• skills/ → ~/.codex/skills/<plugin>/<skill>
• prompts/ → ~/.codex/prompts/<plugin>__<prompt>
• mcp.json → translate into Codex MCP config
• MCP auth: prompt at install time; store env var names by default (values opt‑in)
• MVP scoped to CLI only for now; if IDE/web parity is required, I can expand the scope.

Out of scope

• Marketplace/registry
• Hooks / agents / LSP
• Slash namespace changes (e.g. /plugin:cmd)

Why

Fast team sharing via git; low‑risk, composable first step.

Open questions

1. Prompt name collisions: force prefix vs warn+keep?
2. MCP creds: env names only vs allow value storage?
3. CLI‑only MVP ok, or should TUI /plugin ship with it?

Contribution

Happy to implement once scope is approved.