fix(frontend): stop artifact panel from auto-opening on rehydrated write_file (#2278)

After a page refresh, the artifact panel's autoOpen/autoSelect state is
reset to true. Submitting a new question flips thread.isLoading to true,
which message-list passes to every MessageGroup — including historical
ones. The previous response's last write_file step then satisfies the
auto-open condition and re-pops the stale artifact.

Gate the auto-open on the tool call having no result yet, so only a
write_file that is still streaming in the current response can trigger
it; rehydrated tool calls always carry a result and are now skipped.

Co-authored-by: Claude Opus 4.6 <noreply@anthropic.com>

frontend/src/components/workspace/messages/message-group.tsx

@@ -336,7 +336,7 @@ function ToolCall({
       description = t.toolCalls.writeFile;
     }
     const path: string | undefined = (args as { path: string })?.path;
-    if (isLoading && isLast && autoOpen && autoSelect && path) {
+    if (isLoading && isLast && autoOpen && autoSelect && path && !result) {
       setTimeout(() => {
         const url = new URL(
           `write-file:${path}?message_id=${messageId}&tool_call_id=${id}`,