debug: add OAI message logging for tool call investigation

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

crates/openfang-runtime/src/drivers/openai.rs

@@ -463,6 +463,25 @@ impl LlmDriver for OpenAIDriver {
         } else {
             (Some(request.max_tokens), None)
         };
+
+        // Debug: log message structure for troubleshooting Copilot proxy issues
+        for (i, msg) in oai_messages.iter().enumerate() {
+            let tc_info = msg.tool_calls.as_ref().map(|tcs| {
+                tcs.iter()
+                    .map(|tc| format!("{}:{}", tc.id, tc.function.name))
+                    .collect::<Vec<_>>()
+                    .join(", ")
+            });
+            debug!(
+                idx = i,
+                role = %msg.role,
+                has_content = msg.content.is_some(),
+                tool_call_id = ?msg.tool_call_id,
+                tool_calls = ?tc_info,
+                "OAI message"
+            );
+        }
+
         let mut oai_request = OaiRequest {
             model: request.model.clone(),
             messages: oai_messages,