Resolve MCP server registrations through a catalog

[jif-oai]

Why

MCP servers currently come from user config, local plugins, compatibility Apps synthesis, and host extensions. Those sources were composed by mutating a shared map, leaving registration identity, precedence, removal, and provenance implicit in assembly order.

Before adding executor-owned MCPs, Codex needs one durable resolution boundary above McpConnectionManager. This PR introduces that boundary while preserving current server configuration, policy, and runtime behavior. Executor-scoped registrations and explicit policy layers remain follow-ups.

What changed

• Add typed McpServerRegistration inputs and an immutable ResolvedMcpCatalog in codex-mcp.
• Retain each registration's complete McpServerConfig, including its environment binding, while recording its source and provenance.
• Preserve the existing structural precedence between plugin, config, compatibility, and ordered extension sources.
• Resolve equal-precedence actions by contribution order; provenance IDs are used only for diagnostics and cannot affect the winner.
• Preserve extension removals and the existing name-scoped enabled = false veto.
• Report same-tier conflicts with every contender and the final catalog outcome, including whether the winning action registers or removes the server.
• Require MCP contributors to provide a stable diagnostic identity.
• Derive materialized server maps and plugin ownership from the resolved catalog.

McpConnectionManager, transport startup, tool calls, and resource routing continue to consume the same effective McpServerConfig values.

Scope

This PR does not add new MCP capabilities or change user-visible behavior. It does not add executor plugin discovery, thread-scoped registrations, dynamic refresh generations, or new user/managed policy semantics.

Verification

• Added focused catalog coverage for source precedence, complete configuration preservation, disabled vetoes, plugin ownership, contribution-order tie breaking, removal outcomes, and conflict diagnostics.
• Extended hosted Apps coverage for ordered extension removal and Apps-disabled hosts with and without the hosted extension installed.
• cargo check -p codex-mcp --tests -p codex-extension-api -p codex-core