fix(openai): use structured input and add probe for Responses API

Updated OpenAI Responses API to use a structured input format (array of objects) for better compatibility. Added a proactive error probe to chat_responses_stream to capture and log API error bodies on failure.

src/providers/openai.rs

@@ -197,27 +197,24 @@ impl super::Provider for OpenAIProvider {
     }
 
     async fn chat_responses(&self, request: UnifiedRequest) -> Result<ProviderResponse, AppError> {
-        // Build a simple `input` string by concatenating message parts.
+        // Build a structured input for the Responses API.
         let messages_json = helpers::messages_to_openai_json(&request.messages).await?;
-        let mut inputs: Vec<String> = Vec::new();
+        let mut input_parts = Vec::new();
         for m in &messages_json {
-            let role = m["role"].as_str().unwrap_or("");
-            let parts = m.get("content").and_then(|c| c.as_array()).cloned().unwrap_or_default();
-            let mut text_parts = Vec::new();
-            for p in parts {
-                if let Some(t) = p.get("text").and_then(|v| v.as_str()) {
-                    text_parts.push(t.to_string());
+            let role = m["role"].as_str().unwrap_or("user");
+            let content = m.get("content").cloned().unwrap_or(serde_json::json!(""));
+            
+            input_parts.push(serde_json::json!({
+                "role": role,
+                "content": content
+            }));
         }
-            }
-            inputs.push(format!("{}: {}", role, text_parts.join("")));
-        }
-        let input_text = inputs.join("\n");
 
         let resp = self
             .client
             .post(format!("{}/responses", self.config.base_url))
             .header("Authorization", format!("Bearer {}", self.api_key))
-            .json(&serde_json::json!({ "model": request.model, "input": input_text }))
+            .json(&serde_json::json!({ "model": request.model, "input": input_parts }))
             .send()
             .await
             .map_err(|e| AppError::ProviderError(e.to_string()))?;
@@ -400,31 +397,30 @@ impl super::Provider for OpenAIProvider {
         &self,
         request: UnifiedRequest,
     ) -> Result<BoxStream<'static, Result<ProviderStreamChunk, AppError>>, AppError> {
-        // Build a simple `input` string by concatenating message parts.
+        // Build a structured input for the Responses API.
         let messages_json = helpers::messages_to_openai_json(&request.messages).await?;
-        let mut inputs: Vec<String> = Vec::new();
+        let mut input_parts = Vec::new();
         for m in &messages_json {
-            let role = m["role"].as_str().unwrap_or("");
-            let parts = m.get("content").and_then(|c| c.as_array()).cloned().unwrap_or_default();
-            let mut text_parts = Vec::new();
-            for p in parts {
-                if let Some(t) = p.get("text").and_then(|v| v.as_str()) {
-                    text_parts.push(t.to_string());
+            let role = m["role"].as_str().unwrap_or("user");
+            let content = m.get("content").cloned().unwrap_or(serde_json::json!(""));
+            
+            input_parts.push(serde_json::json!({
+                "role": role,
+                "content": content
+            }));
         }
-            }
-            inputs.push(format!("{}: {}", role, text_parts.join("")));
-        }
-        let input_text = inputs.join("\n");
 
         let body = serde_json::json!({
             "model": request.model,
-            "input": input_text,
+            "input": input_parts,
             "stream": true
         });
 
         let url = format!("{}/responses", self.config.base_url);
         let api_key = self.api_key.clone();
         let model = request.model.clone();
+        let probe_client = self.client.clone();
+        let probe_body = body.clone();
 
         let es = reqwest_eventsource::EventSource::new(
             self.client
@@ -498,7 +494,29 @@ impl super::Provider for OpenAIProvider {
                     }
                     Ok(_) => continue,
                     Err(e) => {
-                         Err(AppError::ProviderError(format!("Responses stream error: {}", e)))?;
+                         // Attempt to probe for the actual error body
+                        let probe_resp = probe_client
+                            .post(&url)
+                            .header("Authorization", format!("Bearer {}", api_key))
+                            .json(&probe_body)
+                            .send()
+                            .await;
+                        
+                        match probe_resp {
+                            Ok(r) if !r.status().is_success() => {
+                                let status = r.status();
+                                let error_body = r.text().await.unwrap_or_default();
+                                tracing::error!("OpenAI Responses Stream Error Probe ({}): {}", status, error_body);
+                                Err(AppError::ProviderError(format!("OpenAI Responses API error ({}): {}", status, error_body)))?;
+                            }
+                            Ok(_) => {
+                                Err(AppError::ProviderError(format!("Responses stream error (probe returned 200): {}", e)))?;
+                            }
+                            Err(probe_err) => {
+                                tracing::error!("OpenAI Responses Stream Error Probe failed: {}", probe_err);
+                                Err(AppError::ProviderError(format!("Responses stream error (probe failed: {}): {}", probe_err, e)))?;
+                            }
+                        }
                     }
                 }
             }