chore(config) personality as a feature (#10116)

## Summary
Sets up an explicit Feature flag for `/personality`, so users can now
opt in to it via `/experimental`. #10114 also updates the config

## Testing
- [x] Tested locally

codex-rs/core/src/features.rs

@@ -119,6 +119,8 @@ pub enum Feature {
     Steer,
     /// Enable collaboration modes (Plan, Code, Pair Programming, Execute).
     CollaborationModes,
+    /// Enable personality selection in the TUI.
+    Personality,
     /// Use the Responses API WebSocket transport for OpenAI by default.
     ResponsesWebsockets,
 }
@@ -543,6 +545,16 @@ pub const FEATURES: &[FeatureSpec] = &[
         stage: Stage::UnderDevelopment,
         default_enabled: false,
     },
+    FeatureSpec {
+        id: Feature::Personality,
+        key: "personality",
+        stage: Stage::Experimental {
+            name: "Personality",
+            menu_description: "Choose a communication style for Codex.",
+            announcement: "NEW! Update codex's communication style with /personality. Enable in /experimental!",
+        },
+        default_enabled: false,
+    },
     FeatureSpec {
         id: Feature::ResponsesWebsockets,
         key: "responses_websockets",

codex-rs/core/src/models_manager/model_info.rs

@@ -213,6 +213,16 @@ pub(crate) fn find_model_info_for_slug(slug: &str) -> ModelInfo {
             truncation_policy: TruncationPolicyConfig::tokens(10_000),
             context_window: Some(CONTEXT_WINDOW_272K),
             supported_reasoning_levels: supported_reasoning_level_low_medium_high_xhigh(),
+            model_instructions_template: Some(ModelInstructionsTemplate {
+                template: GPT_5_2_CODEX_INSTRUCTIONS_TEMPLATE.to_string(),
+                personality_messages: Some(PersonalityMessages(BTreeMap::from([(
+                    Personality::Friendly,
+                    PERSONALITY_FRIENDLY.to_string(),
+                ), (
+                    Personality::Pragmatic,
+                    PERSONALITY_PRAGMATIC.to_string(),
+                )]))),
+            }),
         )
     } else if slug.starts_with("gpt-5.1-codex-max") {
         model_info!(