Spike: connector_urls resolution for MCP tool servers

[leseb]

Parent

Part of #93

Context

The Responses API supports a connector_id field on MCP tool entries as an alternative to server_url. Connectors are pre-configured MCP server definitions that let clients reference servers by ID instead of embedding URLs directly.

tool_parse (#42) already preserves MCP tool entries as opaque JSON, and mcp_tool_list (#43) will resolve server_url directly for MVP. This spike investigates how to surface connector configuration in Praxis so that connector_id references can be resolved.

Questions to answer

• How does the OpenAI Responses API define connectors? What fields does a connector carry (URL, headers, auth, allowed_tools)?
• Should connectors be defined in Praxis YAML config (static) or managed via an admin API (dynamic)?
• Where does connector resolution happen — in tool_parse, in a separate filter, or as a shared service?
• How do connectors interact with Praxis clusters (is a connector just a named reference to a cluster + path)?
• What is the relationship between connectors and the MCP broker's static server registry (McpBrokerConfig.servers)?

Deliverable

A short design doc or proposal section answering the above, with a recommended approach for implementation.