chore: rm hardcoded PRESETS list (#12650)

rm `PRESETS` list harcoded in `model_presets` as we now have bundled
`models.json` with equivalent info.

update logic to rely on bundled models instead, update tests.

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

@@ -665,7 +665,7 @@ pub(crate) fn deserialize_config_toml_with_base(
 
 fn load_catalog_json(path: &AbsolutePathBuf) -> std::io::Result<ModelsResponse> {
     let file_contents = std::fs::read_to_string(path)?;
-    serde_json::from_str::<ModelsResponse>(&file_contents).map_err(|err| {
+    let catalog = serde_json::from_str::<ModelsResponse>(&file_contents).map_err(|err| {
         std::io::Error::new(
             ErrorKind::InvalidData,
             format!(
@@ -673,7 +673,17 @@ fn load_catalog_json(path: &AbsolutePathBuf) -> std::io::Result<ModelsResponse>
                 path.display()
             ),
         )
-    })
+    })?;
+    if catalog.models.is_empty() {
+        return Err(std::io::Error::new(
+            ErrorKind::InvalidData,
+            format!(
+                "model_catalog_json path `{}` must contain at least one model",
+                path.display()
+            ),
+        ));
+    }
+    Ok(catalog)
 }
 
 fn load_model_catalog(
@@ -4466,6 +4476,32 @@ config_file = "./agents/researcher.toml"
         Ok(())
     }
 
+    #[test]
+    fn model_catalog_json_rejects_empty_catalog() -> std::io::Result<()> {
+        let codex_home = TempDir::new()?;
+        let catalog_path = codex_home.path().join("catalog.json");
+        std::fs::write(&catalog_path, r#"{"models":[]}"#)?;
+
+        let cfg = ConfigToml {
+            model_catalog_json: Some(AbsolutePathBuf::from_absolute_path(catalog_path)?),
+            ..Default::default()
+        };
+
+        let err = Config::load_from_base_config_with_overrides(
+            cfg,
+            ConfigOverrides::default(),
+            codex_home.path().to_path_buf(),
+        )
+        .expect_err("empty custom catalog should fail config load");
+
+        assert_eq!(err.kind(), ErrorKind::InvalidData);
+        assert!(
+            err.to_string().contains("must contain at least one model"),
+            "unexpected error: {err}"
+        );
+        Ok(())
+    }
+
     fn create_test_fixture() -> std::io::Result<PrecedenceTestFixture> {
         let toml = r#"
 model = "o3"