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/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;