chore(core) move model_instructions_template config (#9871)

## Summary
Move `model_instructions_template` config to the experimental slug while
we iterate on this feature

## Testing
- [x] Tested locally, unit tests still pass

codex-rs/app-server/tests/suite/v2/turn_start.rs

@@ -433,7 +433,7 @@ async fn turn_start_accepts_personality_override_v2() -> Result<()> {
 
     let thread_req = mcp
         .send_thread_start_request(ThreadStartParams {
-            model: Some("gpt-5.2-codex".to_string()),
+            model: Some("exp-codex-personality".to_string()),
             ..Default::default()
         })
         .await?;

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

@@ -169,6 +169,16 @@ pub(crate) fn find_model_info_for_slug(slug: &str) -> ModelInfo {
         model_info!(
             slug,
             base_instructions: GPT_5_2_CODEX_INSTRUCTIONS.to_string(),
+            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(),
+                )]))),
+            }),
             apply_patch_tool_type: Some(ApplyPatchToolType::Freeform),
             shell_type: ConfigShellToolType::ShellCommand,
             supports_parallel_tool_calls: true,
@@ -203,16 +213,6 @@ 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!(

codex-rs/core/tests/suite/personality.rs

@@ -122,7 +122,7 @@ async fn config_personality_some_sets_instructions_template() -> anyhow::Result<
     let server = start_mock_server().await;
     let resp_mock = mount_sse_once(&server, sse_completed("resp-1")).await;
     let mut builder = test_codex()
-        .with_model("gpt-5.2-codex")
+        .with_model("exp-codex-personality")
         .with_config(|config| {
             config.model_personality = Some(Personality::Friendly);
             config.features.disable(Feature::RemoteModels);
@@ -179,7 +179,7 @@ async fn user_turn_personality_some_adds_update_message() -> anyhow::Result<()>
     )
     .await;
     let mut builder = test_codex()
-        .with_model("gpt-5.2-codex")
+        .with_model("exp-codex-personality")
         .with_config(|config| {
             config.features.disable(Feature::RemoteModels);
         });