Chore: remove rmcp feature and exp flag usages (#8087)

### Summary
With codesigning on Mac, Windows and Linux, we should be able to safely
remove `features.rmcp_client` and `use_experimental_use_rmcp_client`
check from the codebase now.

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

@@ -322,10 +322,6 @@ pub struct Config {
     /// If set to `true`, used only the experimental unified exec tool.
     pub use_experimental_unified_exec_tool: bool,
 
-    /// If set to `true`, use the experimental official Rust MCP client.
-    /// https://github.com/modelcontextprotocol/rust-sdk
-    pub use_experimental_use_rmcp_client: bool,
-
     /// Settings for ghost snapshots (used for undo).
     pub ghost_snapshot: GhostSnapshotConfig,
 
@@ -827,7 +823,6 @@ pub struct ConfigToml {
     pub experimental_instructions_file: Option<AbsolutePathBuf>,
     pub experimental_compact_prompt_file: Option<AbsolutePathBuf>,
     pub experimental_use_unified_exec_tool: Option<bool>,
-    pub experimental_use_rmcp_client: Option<bool>,
     pub experimental_use_freeform_apply_patch: Option<bool>,
     /// Preferred OSS provider for local models, e.g. "lmstudio" or "ollama".
     pub oss_provider: Option<String>,
@@ -1243,7 +1238,6 @@ impl Config {
         let include_apply_patch_tool_flag = features.enabled(Feature::ApplyPatchFreeform);
         let tools_web_search_request = features.enabled(Feature::WebSearchRequest);
         let use_experimental_unified_exec_tool = features.enabled(Feature::UnifiedExec);
-        let use_experimental_use_rmcp_client = features.enabled(Feature::RmcpClient);
 
         let forced_chatgpt_workspace_id =
             cfg.forced_chatgpt_workspace_id.as_ref().and_then(|value| {
@@ -1383,7 +1377,6 @@ impl Config {
             include_apply_patch_tool: include_apply_patch_tool_flag,
             tools_web_search_request,
             use_experimental_unified_exec_tool,
-            use_experimental_use_rmcp_client,
             ghost_snapshot,
             features,
             active_profile: active_profile_name,
@@ -1997,7 +1990,6 @@ trust_level = "trusted"
         let codex_home = TempDir::new()?;
         let cfg = ConfigToml {
             experimental_use_unified_exec_tool: Some(true),
-            experimental_use_rmcp_client: Some(true),
             experimental_use_freeform_apply_patch: Some(true),
             ..Default::default()
         };
@@ -2010,12 +2002,10 @@ trust_level = "trusted"
 
         assert!(config.features.enabled(Feature::ApplyPatchFreeform));
         assert!(config.features.enabled(Feature::UnifiedExec));
-        assert!(config.features.enabled(Feature::RmcpClient));
 
         assert!(config.include_apply_patch_tool);
 
         assert!(config.use_experimental_unified_exec_tool);
-        assert!(config.use_experimental_use_rmcp_client);
 
         Ok(())
     }
@@ -3196,7 +3186,6 @@ model_verbosity = "high"
                 include_apply_patch_tool: false,
                 tools_web_search_request: false,
                 use_experimental_unified_exec_tool: false,
-                use_experimental_use_rmcp_client: false,
                 ghost_snapshot: GhostSnapshotConfig::default(),
                 features: Features::with_defaults(),
                 active_profile: Some("o3".to_string()),
@@ -3280,7 +3269,6 @@ model_verbosity = "high"
             include_apply_patch_tool: false,
             tools_web_search_request: false,
             use_experimental_unified_exec_tool: false,
-            use_experimental_use_rmcp_client: false,
             ghost_snapshot: GhostSnapshotConfig::default(),
             features: Features::with_defaults(),
             active_profile: Some("gpt3".to_string()),
@@ -3379,7 +3367,6 @@ model_verbosity = "high"
             include_apply_patch_tool: false,
             tools_web_search_request: false,
             use_experimental_unified_exec_tool: false,
-            use_experimental_use_rmcp_client: false,
             ghost_snapshot: GhostSnapshotConfig::default(),
             features: Features::with_defaults(),
             active_profile: Some("zdr".to_string()),
@@ -3464,7 +3451,6 @@ model_verbosity = "high"
             include_apply_patch_tool: false,
             tools_web_search_request: false,
             use_experimental_unified_exec_tool: false,
-            use_experimental_use_rmcp_client: false,
             ghost_snapshot: GhostSnapshotConfig::default(),
             features: Features::with_defaults(),
             active_profile: Some("gpt5".to_string()),

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

@@ -25,7 +25,6 @@ pub struct ConfigProfile {
     pub experimental_compact_prompt_file: Option<AbsolutePathBuf>,
     pub include_apply_patch_tool: Option<bool>,
     pub experimental_use_unified_exec_tool: Option<bool>,
-    pub experimental_use_rmcp_client: Option<bool>,
     pub experimental_use_freeform_apply_patch: Option<bool>,
     pub tools_web_search: Option<bool>,
     pub tools_view_image: Option<bool>,

codex-rs/core/src/features.rs

@@ -69,8 +69,6 @@ pub enum Feature {
     // Experimental
     /// Use the single unified PTY-backed exec tool.
     UnifiedExec,
-    /// Enable experimental RMCP features such as OAuth login.
-    RmcpClient,
     /// Include the freeform apply_patch tool.
     ApplyPatchFreeform,
     /// Allow the model to request web searches.
@@ -226,7 +224,6 @@ impl Features {
         let base_legacy = LegacyFeatureToggles {
             experimental_use_freeform_apply_patch: cfg.experimental_use_freeform_apply_patch,
             experimental_use_unified_exec_tool: cfg.experimental_use_unified_exec_tool,
-            experimental_use_rmcp_client: cfg.experimental_use_rmcp_client,
             tools_web_search: cfg.tools.as_ref().and_then(|t| t.web_search),
             tools_view_image: cfg.tools.as_ref().and_then(|t| t.view_image),
             ..Default::default()
@@ -243,7 +240,6 @@ impl Features {
                 .experimental_use_freeform_apply_patch,
 
             experimental_use_unified_exec_tool: config_profile.experimental_use_unified_exec_tool,
-            experimental_use_rmcp_client: config_profile.experimental_use_rmcp_client,
             tools_web_search: config_profile.tools_web_search,
             tools_view_image: config_profile.tools_view_image,
         };
@@ -348,13 +344,6 @@ pub const FEATURES: &[FeatureSpec] = &[
         },
         default_enabled: false,
     },
-    // Unstable features.
-    FeatureSpec {
-        id: Feature::RmcpClient,
-        key: "rmcp_client",
-        stage: Stage::Experimental,
-        default_enabled: false,
-    },
     FeatureSpec {
         id: Feature::ApplyPatchFreeform,
         key: "apply_patch_freeform",

codex-rs/core/src/features/legacy.rs

@@ -17,10 +17,6 @@ const ALIASES: &[Alias] = &[
         legacy_key: "experimental_use_unified_exec_tool",
         feature: Feature::UnifiedExec,
     },
-    Alias {
-        legacy_key: "experimental_use_rmcp_client",
-        feature: Feature::RmcpClient,
-    },
     Alias {
         legacy_key: "experimental_use_freeform_apply_patch",
         feature: Feature::ApplyPatchFreeform,
@@ -50,7 +46,6 @@ pub struct LegacyFeatureToggles {
     pub include_apply_patch_tool: Option<bool>,
     pub experimental_use_freeform_apply_patch: Option<bool>,
     pub experimental_use_unified_exec_tool: Option<bool>,
-    pub experimental_use_rmcp_client: Option<bool>,
     pub tools_web_search: Option<bool>,
     pub tools_view_image: Option<bool>,
 }
@@ -75,12 +70,6 @@ impl LegacyFeatureToggles {
             self.experimental_use_unified_exec_tool,
             "experimental_use_unified_exec_tool",
         );
-        set_if_some(
-            features,
-            Feature::RmcpClient,
-            self.experimental_use_rmcp_client,
-            "experimental_use_rmcp_client",
-        );
         set_if_some(
             features,
             Feature::WebSearchRequest,