Treat model-not-found provider errors as terminal failures (#56445)

## Why

Provider errors with code `model_not_found` should end the turn immediately and preserve the provider's message instead of triggering retries.

## What changed

- Recognize `model_not_found` in HTTP 400, 403, and 404 responses and in streamed `error` and `response.failed` events.
- Preserve the provider message and any available HTTP status, and expose `modelNotFound` through the app-server protocol and generated schemas and SDK types.

## Testing

Add coverage for HTTP classification, statusless stream errors, and terminal failures without retries across HTTP, SSE, and WebSocket responses. Verify that `thread/read` preserves the error reported by the live notification.

GitOrigin-RevId: 88f824ac03c8c9669915b1e40c67b76c08326fbe

codex-rs/codex-api/src/sse/responses.rs

@@ -4,7 +4,7 @@ use crate::common::ResponseStream;
 use crate::common::SafetyBuffering;
 use crate::common::SafetyBufferingTreatment;
 use crate::error::ApiError;
-use crate::error::parse_flex_unavailable;
+use crate::error::parse_terminal_provider_error;
 use crate::rate_limits::parse_all_rate_limits;
 use crate::safety_buffering::treatment_from_headers;
 use crate::telemetry::SseTelemetry;
@@ -347,7 +347,9 @@ pub fn process_responses_event(
 ) -> std::result::Result<Option<ResponseEvent>, ResponsesEventError> {
     match event.kind.as_str() {
         "error" => {
-            if let Some(error) = event.error.as_ref().and_then(parse_flex_unavailable) {
+            if let Some(error) =
+                parse_terminal_provider_error(event.error.as_ref(), /*status*/ None)
+            {
                 return Err(ResponsesEventError::Api(error));
             }
         }

codex-rs/codex-api/src/sse/responses_error.rs

@@ -2,7 +2,7 @@
 //! Only rate-limit codes derive retry delays from plaintext messages.
 
 use crate::error::ApiError;
-use crate::error::parse_flex_unavailable;
+use crate::error::parse_terminal_provider_error;
 use crate::responses_headers::json_headers_to_http_headers;
 use codex_http_client::RetryAfter;
 use codex_protocol::protocol::MisalignmentErrorDetails;
@@ -29,7 +29,7 @@ pub(super) fn parse_failed_response(response: Option<Value>) -> ApiError {
         .and_then(|error| error.get("headers"))
         .and_then(Value::as_object)
         .and_then(|headers| RetryAfter::from_headers(&json_headers_to_http_headers(headers)));
-    if let Some(error) = error.and_then(parse_flex_unavailable) {
+    if let Some(error) = parse_terminal_provider_error(error, /*status*/ None) {
         return error;
     }
     let Some(error) = error.and_then(|error| serde_json::from_value::<Error>(error.clone()).ok())

codex-rs/codex-api/src/sse/responses_error_tests.rs

@@ -61,6 +61,25 @@ async fn flex_failure_with_retry_header_ends_stream_immediately() {
     }
 }
 
+#[test]
+fn statusless_model_errors_have_no_http_status() {
+    let error = json!({"code": "model_not_found"});
+    for event in [
+        json!({"type": "error", "error": error}),
+        json!({"type": "response.failed", "response": {"error": error}}),
+    ] {
+        let event = serde_json::from_value(event).unwrap();
+        let error = map_api_error(process_responses_event(event).unwrap_err().into_api_error());
+        assert_eq!(
+            (
+                error.to_codex_protocol_error(),
+                error.http_status_code_value()
+            ),
+            (CodexErrorInfo::ModelNotFound, None)
+        );
+    }
+}
+
 /// Error headers beat rate-limit message advice; invalid ones fall back.
 #[tokio::test(start_paused = true)]
 async fn rate_limit_plaintext_loses_to_valid_error_header() {