Use model catalog approval messages (#31312)

## Why

Approval guidance is currently assembled entirely by the client. Model
Messages V2 needs model catalogs to provide model-specific `on_request`
guidance for both user-reviewed and auto-reviewed approval flows while
retaining the existing generated prompt as a compatibility fallback.

## What changed

- add nullable `on_request` and `on_request_auto_review` catalog
messages
- select the message matching the active approvals reviewer for
`on_request` policies
- replace the complete legacy approval section when the selected catalog
value exists, including support for an empty string that suppresses the
section
- retain legacy rendering when the object or selected key is absent, and
for non-`on_request` policies
- preserve approval messages when base-instruction or personality
overrides clear instruction templates
- refresh permissions instructions when the active model changes
- pass catalog messages through initial and incremental permissions
construction

## Relationship to reviewer persistence

PR #31309 independently persists the approvals reviewer in turn context
and refreshes permissions when that reviewer changes. This PR is based
directly on `main` and does not duplicate that rollout migration; once
both land, reviewer switches will also select and append the new catalog
variant.

## Testing

- `just test -p codex-protocol`
- `just test -p codex-prompts`
- `just test -p codex-models-manager`
- `just test -p codex-core permissions_messages`

codex-rs/protocol/src/openai_models.rs

@@ -485,6 +485,13 @@ impl ModelInfo {
 pub struct ModelMessages {
     pub instructions_template: Option<String>,
     pub instructions_variables: Option<ModelInstructionsVariables>,
+    pub approvals: Option<ApprovalMessages>,
+}
+
+#[derive(Debug, Serialize, Deserialize, Clone, PartialEq, Eq, TS, JsonSchema)]
+pub struct ApprovalMessages {
+    pub on_request: Option<String>,
+    pub on_request_auto_review: Option<String>,
 }
 
 impl ModelMessages {
@@ -704,6 +711,37 @@ mod tests {
         }
     }
 
+    #[test]
+    fn model_messages_deserialize_without_approvals() {
+        let messages: ModelMessages =
+            from_str(r#"{"instructions_template":null,"instructions_variables":null}"#)
+                .expect("model messages should deserialize");
+
+        assert_eq!(messages.approvals, None);
+    }
+
+    #[test]
+    fn approval_messages_preserve_missing_and_empty_values() {
+        let messages: ModelMessages = from_str(
+            r#"{
+                "instructions_template": null,
+                "instructions_variables": null,
+                "approvals": {
+                    "on_request": ""
+                }
+            }"#,
+        )
+        .expect("approval messages should deserialize");
+
+        assert_eq!(
+            messages.approvals,
+            Some(ApprovalMessages {
+                on_request: Some(String::new()),
+                on_request_auto_review: None,
+            })
+        );
+    }
+
     #[test]
     fn reasoning_effort_accepts_known_and_custom_values() {
         let custom = ReasoningEffort::Custom("future".to_string());
@@ -775,6 +813,7 @@ mod tests {
         let model = test_model(Some(ModelMessages {
             instructions_template: Some("Hello {{ personality }}".to_string()),
             instructions_variables: Some(personality_variables()),
+            approvals: None,
         }));
 
         let instructions = model.get_model_instructions(Some(Personality::Friendly));
@@ -791,6 +830,7 @@ mod tests {
                 personality_friendly: Some("friendly".to_string()),
                 personality_pragmatic: None,
             }),
+            approvals: None,
         }));
         assert_eq!(
             model.get_model_instructions(Some(Personality::Friendly)),
@@ -816,6 +856,7 @@ mod tests {
                 personality_friendly: None,
                 personality_pragmatic: None,
             }),
+            approvals: None,
         }));
         assert_eq!(
             model_no_personality.get_model_instructions(Some(Personality::Friendly)),
@@ -844,6 +885,7 @@ mod tests {
                 personality_friendly: None,
                 personality_pragmatic: None,
             }),
+            approvals: None,
         }));
 
         let instructions = model.get_model_instructions(Some(Personality::Friendly));