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/error.rs

@@ -39,6 +39,11 @@ pub enum ApiError {
     RateLimit(String),
     #[error("invalid request: {message}")]
     InvalidRequest { message: String },
+    #[error("{message}")]
+    ModelNotFound {
+        message: String,
+        status: Option<StatusCode>,
+    },
     #[error("invalid prompt: {message}")]
     InvalidPrompt { message: String },
     #[error("cyber policy: {message}")]
@@ -62,9 +67,30 @@ impl From<RateLimitError> for ApiError {
     }
 }
 
-pub(crate) fn parse_flex_unavailable(error: &Value) -> Option<ApiError> {
-    (error.get("code").and_then(Value::as_str) == Some("flex_unavailable"))
-        .then_some(ApiError::FlexUnavailable)
+pub(crate) fn parse_terminal_provider_error(
+    error: Option<&Value>,
+    status: Option<StatusCode>,
+) -> Option<ApiError> {
+    let error = error?;
+    let code = error.get("code")?.as_str()?;
+    match (code, status) {
+        ("flex_unavailable", None | Some(StatusCode::TOO_MANY_REQUESTS)) => {
+            Some(ApiError::FlexUnavailable)
+        }
+        (
+            "model_not_found",
+            None | Some(StatusCode::BAD_REQUEST | StatusCode::FORBIDDEN | StatusCode::NOT_FOUND),
+        ) => Some(ApiError::ModelNotFound {
+            message: error
+                .get("message")
+                .and_then(Value::as_str)
+                .filter(|message| !message.trim().is_empty())
+                .unwrap_or(code)
+                .to_owned(),
+            status,
+        }),
+        _ => None,
+    }
 }
 
 impl From<crate::AuthError> for ApiError {