fix: preserve completed Pascal agent streams

services/pascal-editor/apps/editor/app/api/agent/chat/route.ts

@@ -119,7 +119,13 @@ export async function POST(request: Request) {
     finalized = true
     try {
       if (save && !abortSignal.aborted) {
-        await session.saveDraft(abortSignal)
+        try {
+          await session.saveDraft(abortSignal)
+        } catch (error) {
+          // Semantic tools live-sync each successful change. A redundant final
+          // save must not tear down an otherwise completed streaming response.
+          console.error('Pascal agent final draft save failed.', error)
+        }
       }
     } finally {
       await session.close()

services/pascal-editor/apps/editor/lib/pascal-agent-mcp.ts

@@ -97,7 +97,22 @@ function readSceneName(result: unknown, fallback: string): string {
 
 function assertToolSucceeded(result: unknown, operation: string): void {
   if ((result as { isError?: unknown })?.isError === true) {
-    throw new Error(`Pascal MCP ${operation} failed.`)
+    const content = (result as { content?: unknown })?.content
+    const detail = Array.isArray(content)
+      ? content
+          .filter((item): item is { text: string; type: 'text' } =>
+            Boolean(
+              item &&
+                typeof item === 'object' &&
+                (item as { type?: unknown }).type === 'text' &&
+                typeof (item as { text?: unknown }).text === 'string',
+            ),
+          )
+          .map((item) => item.text)
+          .join(' ')
+          .slice(0, 1000)
+      : ''
+    throw new Error(`Pascal MCP ${operation} failed${detail ? `: ${detail}` : '.'}`)
   }
 }