feat: record upstream response headers in debug traces

packages/backend/drizzle/schema/postgres/debug-logs.ts

@@ -12,6 +12,7 @@ export const debugLogs = pgTable(
     transformedResponse: text('transformed_response'),
     rawResponseSnapshot: text('raw_response_snapshot'),
     transformedResponseSnapshot: text('transformed_response_snapshot'),
+    responseHeaders: text('response_headers'),
     createdAt: bigint('created_at', { mode: 'number' }).notNull(),
   },
   (table) => ({

packages/backend/drizzle/schema/sqlite/debug-logs.ts

@@ -13,6 +13,7 @@ export const debugLogs = sqliteTable(
     transformedResponse: text('transformed_response'),
     rawResponseSnapshot: text('raw_response_snapshot'),
     transformedResponseSnapshot: text('transformed_response_snapshot'),
+    responseHeaders: text('response_headers'),
     createdAt: integer('created_at').notNull(),
   },
   (table) => ({

packages/backend/src/services/debug-manager.ts

@@ -13,6 +13,7 @@ export interface DebugLogRecord {
   transformedResponse?: any;
   rawResponseSnapshot?: any;
   transformedResponseSnapshot?: any;
+  responseHeaders?: Record<string, string> | null;
   provider?: string;
   createdAt?: number;
 }
@@ -171,6 +172,12 @@ export class DebugManager {
     log.transformedResponseSnapshot = payload;
   }
 
+  addResponseHeaders(requestId: string, headers: Record<string, string>): void {
+    if (!this.isCaptureEnabled()) return;
+    const log = this.ensureLog(requestId);
+    log.responseHeaders = headers;
+  }
+
   flush(requestId: string) {
     // Skip flushing ephemeral requests
     if (this.ephemeralRequests.has(requestId)) {

packages/backend/src/services/dispatcher.ts

@@ -780,6 +780,14 @@ export class Dispatcher {
             adapters
           );
 
+          // Record upstream response headers for debug tracing
+          if (currentRequest.requestId) {
+            DebugManager.getInstance().addResponseHeaders(
+              currentRequest.requestId,
+              this.extractResponseHeaders(streamProbe.response)
+            );
+          }
+
           // Wrap the stream to release the concurrency slot when the stream
           // is fully consumed, cancelled, or errors out. Without this, the
           // slot would never be released for streaming responses.
@@ -834,6 +842,14 @@ export class Dispatcher {
           return streamResponse;
         }
 
+        // Record upstream response headers for debug tracing
+        if (currentRequest.requestId) {
+          DebugManager.getInstance().addResponseHeaders(
+            currentRequest.requestId,
+            this.extractResponseHeaders(response)
+          );
+        }
+
         const nonStreamingResponse = await this.handleNonStreamingResponse(
           response,
           currentRequest,

packages/backend/src/services/usage-storage.ts

@@ -292,6 +292,7 @@ export class UsageStorageService extends EventEmitter {
           transformedResponseSnapshot: record.transformedResponseSnapshot
             ? JSON.stringify(record.transformedResponseSnapshot)
             : null,
+          responseHeaders: record.responseHeaders ? JSON.stringify(record.responseHeaders) : null,
           createdAt: record.createdAt || Date.now(),
         });
 
@@ -471,6 +472,7 @@ export class UsageStorageService extends EventEmitter {
         transformedResponse: row.transformedResponse,
         rawResponseSnapshot: row.rawResponseSnapshot,
         transformedResponseSnapshot: row.transformedResponseSnapshot,
+        responseHeaders: row.responseHeaders,
       };
     } catch (error) {
       logger.error(`Failed to get debug log for ${requestId}`, error);

packages/frontend/src/pages/Debug.tsx

@@ -37,6 +37,7 @@ interface DebugLogDetail extends DebugLogMeta {
   transformedResponse: string | object;
   rawResponseSnapshot?: string | object;
   transformedResponseSnapshot?: string | object;
+  responseHeaders?: string | object;
 }
 
 export const Debug: React.FC = () => {
@@ -241,6 +242,7 @@ export const Debug: React.FC = () => {
       rawResponseSnapshot: normalizeExportContent(detail.rawResponseSnapshot),
       transformedResponse: normalizeExportContent(detail.transformedResponse),
       transformedResponseSnapshot: normalizeExportContent(detail.transformedResponseSnapshot),
+      responseHeaders: normalizeExportContent(detail.responseHeaders),
     };
     return JSON.stringify(payload, null, 2);
   }, [detail]);
@@ -501,6 +503,13 @@ export const Debug: React.FC = () => {
                   color="text-green-400"
                 />
               )}
+              {detail.responseHeaders && (
+                <AccordionPanel
+                  title="Response Headers"
+                  content={formatContent(detail.responseHeaders)}
+                  color="text-yellow-400"
+                />
+              )}
             </div>
           ) : (
             <div className="flex flex-col items-center justify-center h-full text-text-muted gap-4">