Honor personality = "none" in model instructions (#32277)

## Why

Model catalog instructions can include a baked-in `# Personality` section. An
explicit `none` setting should omit that section instead of sending it as part
of the model's base instructions.

## What changed

- Pass the configured personality into the models manager.
- When personality support is enabled and the setting is explicitly `none`,
  remove the `# Personality` section through the next level-one heading from
  catalog base instructions and instruction templates.
- Preserve explicit `base_instructions` overrides and avoid warning when no
  personality was requested.

## Testing

Added unit and integration coverage for section removal, heading boundaries,
CRLF input, preserved configurations, and explicit base instructions.

GitOrigin-RevId: 452c88d3ac6001c2ac7d4fef269cd75dc239fa61

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

@@ -1473,6 +1473,7 @@ impl Config {
             tool_output_token_limit: self.tool_output_token_limit,
             base_instructions: self.base_instructions.clone(),
             personality_enabled: self.features.enabled(Feature::Personality),
+            personality: self.personality,
             model_catalog: self.model_catalog.clone(),
         }
     }

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

@@ -259,6 +259,82 @@ async fn config_personality_none_sends_no_personality() -> anyhow::Result<()> {
     Ok(())
 }
 
+#[tokio::test(flavor = "multi_thread", worker_threads = 2)]
+async fn config_personality_none_strips_baked_personality_section() -> anyhow::Result<()> {
+    skip_if_no_network!(Ok(()));
+
+    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_info_override("gpt-5.4", |model_info| {
+            model_info.base_instructions = "Base instructions\n# Personality\nBaked personality\n## Writing Style\nNested writing style\n# General\nGeneral instructions".to_string();
+            model_info.model_messages = None;
+        })
+        .with_config(|config| {
+            config
+                .features
+                .enable(Feature::Personality)
+                .expect("test config should allow feature update");
+            config.personality = Some(Personality::None);
+        });
+    let test = builder.build(&server).await?;
+
+    test.codex
+        .submit(read_only_text_turn(
+            &test,
+            "hello",
+            test.session_configured.model.clone(),
+            test.config.permissions.approval_policy.value(),
+        ))
+        .await?;
+
+    wait_for_event(&test.codex, |ev| matches!(ev, EventMsg::TurnComplete(_))).await;
+
+    assert_eq!(
+        resp_mock.single_request().instructions_text(),
+        "Base instructions\n# General\nGeneral instructions"
+    );
+
+    Ok(())
+}
+
+#[tokio::test(flavor = "multi_thread", worker_threads = 2)]
+async fn config_personality_none_preserves_explicit_base_instructions() -> anyhow::Result<()> {
+    skip_if_no_network!(Ok(()));
+
+    const CUSTOM_INSTRUCTIONS: &str = "Custom instructions\n# Personality\nThis must remain\n## Writing Style\nThis must also remain\n# General\nGeneral instructions";
+
+    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-5.4").with_config(|config| {
+        config
+            .features
+            .enable(Feature::Personality)
+            .expect("test config should allow feature update");
+        config.personality = Some(Personality::None);
+        config.base_instructions = Some(CUSTOM_INSTRUCTIONS.to_string());
+    });
+    let test = builder.build(&server).await?;
+
+    test.codex
+        .submit(read_only_text_turn(
+            &test,
+            "hello",
+            test.session_configured.model.clone(),
+            test.config.permissions.approval_policy.value(),
+        ))
+        .await?;
+
+    wait_for_event(&test.codex, |ev| matches!(ev, EventMsg::TurnComplete(_))).await;
+
+    assert_eq!(
+        resp_mock.single_request().instructions_text(),
+        CUSTOM_INSTRUCTIONS
+    );
+
+    Ok(())
+}
+
 #[tokio::test(flavor = "multi_thread", worker_threads = 2)]
 async fn default_personality_is_pragmatic_without_config_toml() -> anyhow::Result<()> {
     skip_if_no_network!(Ok(()));

codex-rs/models-manager/src/config.rs

@@ -1,3 +1,4 @@
+use codex_protocol::config_types::Personality;
 use codex_protocol::openai_models::ModelsResponse;
 
 #[derive(Debug, Clone, Default)]
@@ -7,5 +8,6 @@ pub struct ModelsManagerConfig {
     pub tool_output_token_limit: Option<usize>,
     pub base_instructions: Option<String>,
     pub personality_enabled: bool,
+    pub personality: Option<Personality>,
     pub model_catalog: Option<ModelsResponse>,
 }

codex-rs/models-manager/src/model_info.rs

@@ -1,3 +1,4 @@
+use codex_protocol::config_types::Personality;
 use codex_protocol::config_types::ReasoningSummary;
 use codex_protocol::openai_models::ConfigShellToolType;
 use codex_protocol::openai_models::ModelInfo;
@@ -19,6 +20,7 @@ const LOCAL_FRIENDLY_TEMPLATE: &str =
     "You optimize for team morale and being a supportive teammate as much as code quality.";
 const LOCAL_PRAGMATIC_TEMPLATE: &str = "You are a deeply pragmatic, effective software engineer.";
 const PERSONALITY_PLACEHOLDER: &str = "{{ personality }}";
+const PERSONALITY_SECTION_HEADER: &str = "# Personality";
 
 pub fn with_config_overrides(mut model: ModelInfo, config: &ModelsManagerConfig) -> ModelInfo {
     if let Some(context_window) = config.model_context_window {
@@ -50,13 +52,62 @@ pub fn with_config_overrides(mut model: ModelInfo, config: &ModelsManagerConfig)
     if let Some(base_instructions) = &config.base_instructions {
         model.base_instructions = base_instructions.clone();
         clear_instruction_messages(&mut model);
-    } else if !config.personality_enabled {
-        clear_instruction_messages(&mut model);
+    } else {
+        if config.personality_enabled && config.personality == Some(Personality::None) {
+            model.base_instructions = strip_personality_section(model.base_instructions);
+            if let Some(instructions_template) = model
+                .model_messages
+                .as_mut()
+                .and_then(|messages| messages.instructions_template.as_mut())
+            {
+                *instructions_template =
+                    strip_personality_section(std::mem::take(instructions_template));
+            }
+        }
+        if !config.personality_enabled {
+            clear_instruction_messages(&mut model);
+        }
     }
 
     model
 }
 
+fn strip_personality_section(mut instructions: String) -> String {
+    let mut section_start = None;
+    let mut section_end = None;
+    let mut offset = 0;
+
+    for line_with_ending in instructions.split_inclusive('\n') {
+        let line = match line_with_ending.strip_suffix('\n') {
+            Some(line) => line.strip_suffix('\r').unwrap_or(line),
+            None => line_with_ending,
+        };
+        if section_start.is_some() {
+            if is_h1_heading(line) {
+                section_end = Some(offset);
+                break;
+            }
+        } else if line == PERSONALITY_SECTION_HEADER {
+            section_start = Some(offset);
+        }
+        offset += line_with_ending.len();
+    }
+
+    if let Some(section_start) = section_start {
+        let section_end = section_end.unwrap_or(instructions.len());
+        instructions.replace_range(section_start..section_end, "");
+    }
+
+    instructions
+}
+
+fn is_h1_heading(line: &str) -> bool {
+    let Some(rest) = line.strip_prefix('#') else {
+        return false;
+    };
+    rest.is_empty() || rest.starts_with(' ') || rest.starts_with('\t')
+}
+
 fn clear_instruction_messages(model: &mut ModelInfo) {
     if let Some(model_messages) = &mut model.model_messages {
         model_messages.instructions_template = None;

codex-rs/models-manager/src/model_info_tests.rs

@@ -1,8 +1,17 @@
 use super::*;
 use crate::ModelsManagerConfig;
+use codex_protocol::config_types::Personality;
 use codex_protocol::openai_models::ApprovalMessages;
 use pretty_assertions::assert_eq;
 
+fn config_with_personality(personality: Option<Personality>) -> ModelsManagerConfig {
+    ModelsManagerConfig {
+        personality_enabled: true,
+        personality,
+        ..Default::default()
+    }
+}
+
 #[test]
 fn base_instruction_override_preserves_catalog_approval_messages() {
     let mut model = model_info_from_slug("unknown-model");
@@ -65,6 +74,75 @@ fn disabled_personality_preserves_catalog_approval_messages() {
     );
 }
 
+#[test]
+fn personality_none_strips_catalog_instruction_sources_through_the_next_h1() {
+    let cases = [
+        (
+            "Intro\n\n# Personality\n\nRemove me\n\n## Writing Style\n\nRemove me too\n\n# Safety\n\nKeep me",
+            "Intro\n\n# Safety\n\nKeep me",
+        ),
+        ("Intro\n\n# Personality\n\nRemove me", "Intro\n\n"),
+        (
+            "Intro\n\n## Personality\n\nKeep me",
+            "Intro\n\n## Personality\n\nKeep me",
+        ),
+        (
+            "Intro\n\n# Personality \n\nKeep me",
+            "Intro\n\n# Personality \n\nKeep me",
+        ),
+        (
+            "Intro\r\n\r\n# Personality\r\n\r\nRemove me\r\n\r\n## Writing Style\r\n\r\nRemove me too\r\n\r\n# General\r\n\r\nKeep me",
+            "Intro\r\n\r\n# General\r\n\r\nKeep me",
+        ),
+    ];
+    let config = config_with_personality(Some(Personality::None));
+
+    for (instructions, expected) in cases {
+        let mut model = model_info_from_slug("unknown-model");
+        model.base_instructions = instructions.to_string();
+        model.model_messages = Some(ModelMessages {
+            instructions_template: Some(instructions.to_string()),
+            instructions_variables: None,
+            approvals: None,
+        });
+
+        let updated = with_config_overrides(model, &config);
+        let instructions_template = updated
+            .model_messages
+            .as_ref()
+            .and_then(|messages| messages.instructions_template.as_deref());
+
+        assert_eq!(
+            (updated.base_instructions.as_str(), instructions_template),
+            (expected, Some(expected))
+        );
+    }
+}
+
+#[test]
+fn baked_personality_section_is_preserved_without_enabled_explicit_none() {
+    let instructions = "Intro\n# Personality\nKeep me\n# General\nKeep me too";
+    let configs = [
+        config_with_personality(/*personality*/ None),
+        config_with_personality(Some(Personality::Friendly)),
+        config_with_personality(Some(Personality::Pragmatic)),
+        ModelsManagerConfig {
+            personality: Some(Personality::None),
+            ..Default::default()
+        },
+    ];
+
+    for config in configs {
+        let mut model = model_info_from_slug("unknown-model");
+        model.base_instructions = instructions.to_string();
+
+        assert_eq!(
+            with_config_overrides(model, &config).base_instructions,
+            instructions
+        );
+    }
+}
+
 #[test]
 fn model_context_window_override_clamps_to_max_context_window() {
     let mut model = model_info_from_slug("unknown-model");

codex-rs/protocol/src/openai_models.rs

@@ -465,14 +465,17 @@ impl ModelInfo {
                 .get_personality_message(personality)
                 .unwrap_or_default();
             template.replace(PERSONALITY_PLACEHOLDER, personality_message.as_str())
-        } else if let Some(personality) = personality {
-            warn!(
-                model = %self.slug,
-                %personality,
-                "Model personality requested but model_messages is missing, falling back to base instructions."
-            );
-            self.base_instructions.clone()
         } else {
+            match personality {
+                Some(personality @ (Personality::Friendly | Personality::Pragmatic)) => {
+                    warn!(
+                        model = %self.slug,
+                        %personality,
+                        "Model personality requested but model_messages is missing, falling back to base instructions."
+                    );
+                }
+                Some(Personality::None) | None => {}
+            }
             self.base_instructions.clone()
         }
     }