fix(providers): return error on Codex response.failed instead of silent success (#888)

response.failed was lumped with response.completed/incomplete, causing
silent empty responses with no retry. Split into its own case that
returns a descriptive error from processSSEEvent, propagated up to
ChatStream caller for proper error surface and retry logic.

Added codexErrorDetail to codexAPIResponse to parse the error payload.

internal/providers/codex.go

@@ -3,6 +3,7 @@ package providers
 import (
 	"context"
 	"encoding/json"
+	"errors"
 	"fmt"
 	"io"
 	"net/http"
@@ -148,7 +149,9 @@ func (p *CodexProvider) ChatStream(ctx context.Context, req ChatRequest, onChunk
 			continue
 		}
 
-		p.processSSEEvent(&event, result, toolCalls, streamState, onChunk, stripThinking)
+		if err := p.processSSEEvent(&event, result, toolCalls, streamState, onChunk, stripThinking); err != nil {
+			return nil, err
+		}
 	}
 
 	if err := sse.Err(); err != nil {
@@ -189,7 +192,7 @@ func (p *CodexProvider) ChatStream(ctx context.Context, req ChatRequest, onChunk
 // processSSEEvent handles a single SSE event during streaming.
 // stripThinking drops reasoning summaries from user-visible output while
 // leaving billing counters (Usage.ThinkingTokens) untouched.
-func (p *CodexProvider) processSSEEvent(event *codexSSEEvent, result *ChatResponse, toolCalls map[string]*codexToolCallAcc, streamState *codexMessageStreamState, onChunk func(StreamChunk), stripThinking bool) {
+func (p *CodexProvider) processSSEEvent(event *codexSSEEvent, result *ChatResponse, toolCalls map[string]*codexToolCallAcc, streamState *codexMessageStreamState, onChunk func(StreamChunk), stripThinking bool) error {
 	switch event.Type {
 	case "response.output_item.added":
 		if event.Item != nil {
@@ -249,7 +252,7 @@ func (p *CodexProvider) processSSEEvent(event *codexSSEEvent, result *ChatRespon
 			}
 		}
 
-	case "response.completed", "response.incomplete", "response.failed":
+	case "response.completed", "response.incomplete":
 		if event.Response != nil {
 			if result.Content == "" {
 				streamState.ingestCompletedResponse(event.Response)
@@ -271,5 +274,17 @@ func (p *CodexProvider) processSSEEvent(event *codexSSEEvent, result *ChatRespon
 				result.FinishReason = "length"
 			}
 		}
+
+	case "response.failed":
+		errMsg := "codex: response failed during generation"
+		if event.Response != nil && event.Response.Error != nil {
+			if event.Response.Error.Message != "" {
+				errMsg = fmt.Sprintf("codex: response failed: %s", event.Response.Error.Message)
+			} else if event.Response.Error.Code != "" {
+				errMsg = fmt.Sprintf("codex: response failed: %s", event.Response.Error.Code)
+			}
+		}
+		return errors.New(errMsg)
 	}
+	return nil
 }

internal/providers/codex_types.go

@@ -3,12 +3,18 @@ package providers
 // Wire types for the OpenAI Responses API (Codex flow).
 
 type codexAPIResponse struct {
-	ID     string      `json:"id"`
-	Object string      `json:"object"`
-	Model  string      `json:"model"`
-	Output []codexItem `json:"output"`
-	Usage  *codexUsage `json:"usage,omitempty"`
-	Status string      `json:"status"`
+	ID     string            `json:"id"`
+	Object string            `json:"object"`
+	Model  string            `json:"model"`
+	Output []codexItem       `json:"output"`
+	Usage  *codexUsage       `json:"usage,omitempty"`
+	Status string            `json:"status"`
+	Error  *codexErrorDetail `json:"error,omitempty"` // set when status="failed"
+}
+
+type codexErrorDetail struct {
+	Code    string `json:"code"`
+	Message string `json:"message"`
 }
 
 type codexItem struct {