Expose managed policy for browser settings imports (#39720)

## What changed

- Add `in_app_browser.allow_external_browser_settings_import` to managed requirements, preserving explicit Boolean values through layered composition while leaving an omitted value unset.
- Return the policy as `inAppBrowser.allowExternalBrowserSettingsImport` from `configRequirements/read` and include it in the generated protocol schemas.
- Keep the import policy independent from the in-app browser feature flag and agent Browser Use requirements.

## Testing

- Cover parsing, managed-layer precedence, invalid values, user and session override resistance, and app-server response serialization.

GitOrigin-RevId: efa2621d2b1cf503f1bee2505d9914cb4fb7221d

codex-rs/app-server-protocol/src/protocol/v2/config.rs

@@ -399,6 +399,7 @@ pub struct ConfigRequirements {
     pub allow_remote_control: Option<bool>,
     pub computer_use: Option<ComputerUseRequirements>,
     pub browser_use: Option<BrowserUseRequirements>,
+    pub in_app_browser: Option<InAppBrowserRequirements>,
     pub feature_requirements: Option<BTreeMap<String, bool>>,
     #[experimental("configRequirements/read.hooks")]
     pub hooks: Option<ManagedHooksRequirements>,
@@ -474,6 +475,13 @@ pub struct BrowserUseRequirements {
     pub disable_auto_review: Option<bool>,
 }
 
+#[derive(Serialize, Deserialize, Debug, Clone, PartialEq, Eq, JsonSchema, TS)]
+#[serde(rename_all = "camelCase")]
+#[ts(export_to = "v2/")]
+pub struct InAppBrowserRequirements {
+    pub allow_external_browser_settings_import: Option<bool>,
+}
+
 #[derive(Serialize, Deserialize, Debug, Clone, PartialEq, Eq, JsonSchema, TS)]
 #[serde(rename_all = "camelCase")]
 #[ts(export_to = "v2/")]

codex-rs/app-server-protocol/src/protocol/v2/tests.rs

@@ -2060,6 +2060,7 @@ fn config_requirements_granular_allowed_approval_policy_is_marked_experimental()
             allow_remote_control: None,
             computer_use: None,
             browser_use: None,
+            in_app_browser: None,
             feature_requirements: None,
             hooks: None,
             enforce_residency: None,