Create Codex Plugin

[clockwork-tien]

Description of Changes

Add SpacetimeDB Codex plugin at codex-plugin/ with agent skills (incl. MCP skill) and MCP server config. Also introduce additions to the MCP server to support the config:

• spacetime mcp CLI subcommand which is a stdio to HTTP bridge for the MCP route, since local agents launch MCP servers over stdio
• POST /v1/mcp MCP route with inherited auth which takes database as a tool argument, so the command needs no per user config (database name or identity) passed in, which simplifies users' MCP server config setup

The plugin's MCP server config:

{
  "mcpServers": {
    "spacetimedb": {
      "command": "spacetime",
      "args": ["mcp"]
    }
  }
}

Plugin usage:

codex plugin marketplace add clockworklabs/SpacetimeDB --sparse .agents --sparse codex-plugin
codex plugin add spacetimedb@spacetimedb-plugins

API and ABI breaking changes

None.

Expected complexity level and risk

2

Testing

• I tested the implementation with Codex CLI and Desktop app. Tests, lint and format checks passed