Resolve MCP server registrations through a catalog (#27634)

## 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`

codex-rs/ext/extension-api/src/contributors.rs

@@ -48,6 +48,9 @@ pub type ExtensionFuture<'a, T> = Pin<Box<dyn Future<Output = T> + Send + 'a>>;
 /// Plugin-owned servers and their provenance continue to be resolved by the
 /// plugin manager until that ownership moves into an extension explicitly.
 pub trait McpServerContributor<C: Sync>: Send + Sync {
+    /// Stable identity used for registration provenance and conflict diagnostics.
+    fn id(&self) -> &'static str;
+
     fn contribute<'a>(&'a self, config: &'a C) -> ExtensionFuture<'a, Vec<McpServerContribution>>;
 }
 

codex-rs/ext/mcp/src/lib.rs

@@ -9,6 +9,10 @@ use codex_mcp::hosted_plugin_runtime_mcp_server_config;
 struct HostedPluginRuntimeExtension;
 
 impl McpServerContributor<Config> for HostedPluginRuntimeExtension {
+    fn id(&self) -> &'static str {
+        "hosted_plugin_runtime"
+    }
+
     fn contribute<'a>(
         &'a self,
         config: &'a Config,

codex-rs/ext/mcp/tests/hosted_apps_mcp.rs

@@ -104,7 +104,7 @@ async fn legacy_fallback_overwrites_reserved_config_without_an_extension() -> Te
 }
 
 #[tokio::test]
-async fn extension_can_remove_legacy_fallback_while_apps_are_enabled() -> TestResult {
+async fn later_extension_can_remove_same_name_registration() -> TestResult {
     let codex_home = tempfile::tempdir()?;
     let config = ConfigBuilder::default()
         .codex_home(codex_home.path().to_path_buf())
@@ -114,6 +114,7 @@ async fn extension_can_remove_legacy_fallback_while_apps_are_enabled() -> TestRe
         .await?;
     let auth = CodexAuth::create_dummy_chatgpt_auth_for_testing();
     let mut builder = ExtensionRegistryBuilder::new();
+    codex_mcp_extension::install(&mut builder);
     builder.mcp_server_contributor(Arc::new(RemoveCodexApps));
     let manager = McpManager::new_with_extensions(
         Arc::new(PluginsManager::new(config.codex_home.to_path_buf())),
@@ -145,7 +146,7 @@ async fn hosted_apps_mcp_requires_chatgpt_auth() -> TestResult {
 }
 
 #[tokio::test]
-async fn disabled_apps_remove_reserved_server_config() -> TestResult {
+async fn disabled_apps_remove_reserved_server_config_for_all_hosts() -> TestResult {
     let codex_home = tempfile::tempdir()?;
     let config = ConfigBuilder::default()
         .codex_home(codex_home.path().to_path_buf())
@@ -159,11 +160,16 @@ async fn disabled_apps_remove_reserved_server_config() -> TestResult {
         ])
         .build()
         .await?;
-    let manager = installed_manager(&config);
-
-    let servers = manager.runtime_servers(&config).await;
-
-    assert!(!servers.contains_key(CODEX_APPS_MCP_SERVER_NAME));
+    let managers = [
+        installed_manager(&config),
+        McpManager::new(Arc::new(PluginsManager::new(
+            config.codex_home.to_path_buf(),
+        ))),
+    ];
+    for manager in managers {
+        let servers = manager.runtime_servers(&config).await;
+        assert!(!servers.contains_key(CODEX_APPS_MCP_SERVER_NAME));
+    }
     Ok(())
 }
 
@@ -179,6 +185,10 @@ fn installed_manager(config: &Config) -> McpManager {
 struct RemoveCodexApps;
 
 impl McpServerContributor<Config> for RemoveCodexApps {
+    fn id(&self) -> &'static str {
+        "remove_codex_apps"
+    }
+
     fn contribute<'a>(
         &'a self,
         _config: &'a Config,