Extract MCP into codex-mcp crate (#15919)

- Split MCP runtime/server code out of `codex-core` into the new
`codex-mcp` crate. New/moved public structs/types include `McpConfig`,
`McpConnectionManager`, `ToolInfo`, `ToolPluginProvenance`,
`CodexAppsToolsCacheKey`, and the `McpManager` API
(`codex_mcp::mcp::McpManager` plus the `codex_core::mcp::McpManager`
wrapper/shim). New/moved functions include `with_codex_apps_mcp`,
`configured_mcp_servers`, `effective_mcp_servers`,
`collect_mcp_snapshot`, `collect_mcp_snapshot_from_manager`,
`qualified_mcp_tool_name_prefix`, and the MCP auth/skill-dependency
helpers. Why: this creates a focused MCP crate boundary and shrinks
`codex-core` without forcing every consumer to migrate in the same PR.

- Move MCP server config schema and persistence into `codex-config`.
New/moved structs/enums include `AppToolApproval`,
`McpServerToolConfig`, `McpServerConfig`, `RawMcpServerConfig`,
`McpServerTransportConfig`, `McpServerDisabledReason`, and
`codex_config::ConfigEditsBuilder`. New/moved functions include
`load_global_mcp_servers` and
`ConfigEditsBuilder::replace_mcp_servers`/`apply`. Why: MCP TOML
parsing/editing is config ownership, and this keeps config
validation/round-tripping (including per-tool approval overrides and
inline bearer-token rejection) in the config crate instead of
`codex-core`.

- Rewire `codex-core`, app-server, and plugin call sites onto the new
crates. Updated `Config::to_mcp_config(&self, plugins_manager)`,
`codex-rs/core/src/mcp.rs`, `codex-rs/core/src/connectors.rs`,
`codex-rs/core/src/codex.rs`,
`CodexMessageProcessor::list_mcp_server_status_task`, and
`utils/plugins/src/mcp_connector.rs` to build/pass the new MCP
config/runtime types. Why: plugin-provided MCP servers still merge with
user-configured servers, and runtime auth (`CodexAuth`) is threaded into
`with_codex_apps_mcp` / `collect_mcp_snapshot` explicitly so `McpConfig`
stays config-only.

codex-rs/core/src/config/mod.rs

@@ -66,6 +66,7 @@ use codex_features::FeatureOverrides;
 use codex_features::Features;
 use codex_features::FeaturesToml;
 use codex_git_utils::resolve_root_git_project_for_trust;
+use codex_mcp::mcp::McpConfig;
 use codex_protocol::config_types::AltScreenMode;
 use codex_protocol::config_types::ForcedLoginMethod;
 use codex_protocol::config_types::Personality;
@@ -683,6 +684,31 @@ impl ConfigBuilder {
 }
 
 impl Config {
+    pub fn to_mcp_config(&self, plugins_manager: &crate::plugins::PluginsManager) -> McpConfig {
+        let loaded_plugins = plugins_manager.plugins_for_config(self);
+        let mut configured_mcp_servers = self.mcp_servers.get().clone();
+        for (name, plugin_server) in loaded_plugins.effective_mcp_servers() {
+            configured_mcp_servers.entry(name).or_insert(plugin_server);
+        }
+
+        McpConfig {
+            chatgpt_base_url: self.chatgpt_base_url.clone(),
+            codex_home: self.codex_home.clone(),
+            mcp_oauth_credentials_store_mode: self.mcp_oauth_credentials_store_mode,
+            mcp_oauth_callback_port: self.mcp_oauth_callback_port,
+            mcp_oauth_callback_url: self.mcp_oauth_callback_url.clone(),
+            skill_mcp_dependency_install_enabled: self
+                .features
+                .enabled(Feature::SkillMcpDependencyInstall),
+            approval_policy: self.permissions.approval_policy.clone(),
+            codex_linux_sandbox_exe: self.codex_linux_sandbox_exe.clone(),
+            use_legacy_landlock: self.features.use_legacy_landlock(),
+            apps_enabled: self.features.enabled(Feature::Apps),
+            configured_mcp_servers,
+            plugin_capability_summaries: loaded_plugins.capability_summaries().to_vec(),
+        }
+    }
+
     /// This is the preferred way to create an instance of [Config].
     pub async fn load_with_cli_overrides(
         cli_overrides: Vec<(String, TomlValue)>,