client side modelinfo overrides (#12101)

TL;DR
Add top-level `model_catalog_json` config support so users can supply a
local model catalog override from a JSON file path (including adding new
models) without backend changes.

### Problem
Codex previously had no clean client-side way to replace/overlay model
catalog data for local testing of model metadata and new model entries.

### Fix
- Add top-level `model_catalog_json` config field (JSON file path).
- Apply catalog entries when resolving `ModelInfo`:
  1. Base resolved model metadata (remote/fallback)
  2. Catalog overlay from `model_catalog_json`
3. Existing global top-level overrides (`model_context_window`,
`model_supports_reasoning_summaries`, etc.)

### Note
Will revisit per-field overrides in a follow-up

### Tests
Added tests

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

@@ -66,6 +66,7 @@ use codex_protocol::config_types::TrustLevel;
 use codex_protocol::config_types::Verbosity;
 use codex_protocol::config_types::WebSearchMode;
 use codex_protocol::config_types::WindowsSandboxLevel;
+use codex_protocol::openai_models::ModelsResponse;
 use codex_protocol::openai_models::ReasoningEffort;
 use codex_rmcp_client::OAuthCredentialsStoreMode;
 use codex_utils_absolute_path::AbsolutePathBuf;
@@ -359,6 +360,10 @@ pub struct Config {
     /// Optional override to force-enable reasoning summaries for the configured model.
     pub model_supports_reasoning_summaries: Option<bool>,
 
+    /// Optional full model catalog loaded from `model_catalog_json`.
+    /// When set, this replaces the bundled catalog for the current process.
+    pub model_catalog: Option<ModelsResponse>,
+
     /// Optional verbosity control for GPT-5 models (Responses API `text.verbosity`).
     pub model_verbosity: Option<Verbosity>,
 
@@ -618,6 +623,27 @@ pub(crate) fn deserialize_config_toml_with_base(
         .map_err(|e| std::io::Error::new(std::io::ErrorKind::InvalidData, e))
 }
 
+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| {
+        std::io::Error::new(
+            ErrorKind::InvalidData,
+            format!(
+                "failed to parse model_catalog_json path `{}` as JSON: {err}",
+                path.display()
+            ),
+        )
+    })
+}
+
+fn load_model_catalog(
+    model_catalog_json: Option<AbsolutePathBuf>,
+) -> std::io::Result<Option<ModelsResponse>> {
+    model_catalog_json
+        .map(|path| load_catalog_json(&path))
+        .transpose()
+}
+
 fn filter_mcp_servers_by_requirements(
     mcp_servers: &mut HashMap<String, McpServerConfig>,
     mcp_requirements: Option<&Sourced<BTreeMap<String, McpServerRequirement>>>,
@@ -1039,6 +1065,10 @@ pub struct ConfigToml {
     /// Override to force-enable reasoning summaries for the configured model.
     pub model_supports_reasoning_summaries: Option<bool>,
 
+    /// Optional path to a JSON file containing a complete model catalog.
+    /// When set, this replaces the bundled catalog for this process.
+    pub model_catalog_json: Option<AbsolutePathBuf>,
+
     /// Optionally specify a personality for the model
     pub personality: Option<Personality>,
 
@@ -1793,6 +1823,7 @@ impl Config {
         let review_model = override_review_model.or(cfg.review_model);
 
         let check_for_update_on_startup = cfg.check_for_update_on_startup.unwrap_or(true);
+        let model_catalog = load_model_catalog(cfg.model_catalog_json.clone())?;
 
         let log_dir = cfg
             .log_dir
@@ -1929,6 +1960,7 @@ impl Config {
                 .or(cfg.model_reasoning_summary)
                 .unwrap_or_default(),
             model_supports_reasoning_summaries: cfg.model_supports_reasoning_summaries,
+            model_catalog,
             model_verbosity: config_profile.model_verbosity.or(cfg.model_verbosity),
             chatgpt_base_url: config_profile
                 .chatgpt_base_url
@@ -4177,6 +4209,33 @@ config_file = "./agents/researcher.toml"
         Ok(())
     }
 
+    #[test]
+    fn model_catalog_json_loads_from_path() -> std::io::Result<()> {
+        let codex_home = TempDir::new()?;
+        let catalog_path = codex_home.path().join("catalog.json");
+        let mut catalog: ModelsResponse =
+            serde_json::from_str(include_str!("../../models.json")).expect("valid models.json");
+        catalog.models = catalog.models.into_iter().take(1).collect();
+        std::fs::write(
+            &catalog_path,
+            serde_json::to_string(&catalog).expect("serialize catalog"),
+        )?;
+
+        let cfg = ConfigToml {
+            model_catalog_json: Some(AbsolutePathBuf::from_absolute_path(catalog_path)?),
+            ..Default::default()
+        };
+
+        let config = Config::load_from_base_config_with_overrides(
+            cfg,
+            ConfigOverrides::default(),
+            codex_home.path().to_path_buf(),
+        )?;
+
+        assert_eq!(config.model_catalog, Some(catalog));
+        Ok(())
+    }
+
     fn create_test_fixture() -> std::io::Result<PrecedenceTestFixture> {
         let toml = r#"
 model = "o3"
@@ -4349,6 +4408,7 @@ model_verbosity = "high"
                 model_reasoning_effort: Some(ReasoningEffort::High),
                 model_reasoning_summary: ReasoningSummary::Detailed,
                 model_supports_reasoning_summaries: None,
+                model_catalog: None,
                 model_verbosity: None,
                 personality: Some(Personality::Pragmatic),
                 chatgpt_base_url: "https://chatgpt.com/backend-api/".to_string(),
@@ -4464,6 +4524,7 @@ model_verbosity = "high"
             model_reasoning_effort: None,
             model_reasoning_summary: ReasoningSummary::default(),
             model_supports_reasoning_summaries: None,
+            model_catalog: None,
             model_verbosity: None,
             personality: Some(Personality::Pragmatic),
             chatgpt_base_url: "https://chatgpt.com/backend-api/".to_string(),
@@ -4577,6 +4638,7 @@ model_verbosity = "high"
             model_reasoning_effort: None,
             model_reasoning_summary: ReasoningSummary::default(),
             model_supports_reasoning_summaries: None,
+            model_catalog: None,
             model_verbosity: None,
             personality: Some(Personality::Pragmatic),
             chatgpt_base_url: "https://chatgpt.com/backend-api/".to_string(),
@@ -4676,6 +4738,7 @@ model_verbosity = "high"
             model_reasoning_effort: Some(ReasoningEffort::High),
             model_reasoning_summary: ReasoningSummary::Detailed,
             model_supports_reasoning_summaries: None,
+            model_catalog: None,
             model_verbosity: Some(Verbosity::High),
             personality: Some(Personality::Pragmatic),
             chatgpt_base_url: "https://chatgpt.com/backend-api/".to_string(),