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…ent` receives `undefined` (cast as `Trace`) and immediately accesses `trace.spans`, causing "Cannot read properties of undefined".
This commit fixes the issue reported at packages/web-shared/src/components/trace-viewer-new.tsx:28
**Bug Analysis:**
In `trace-viewer-new.tsx`, the `buildTrace` function returns `undefined` when `!run?.runId`. The result is stored in `trace` which has type `TraceWithMeta | undefined`. However, on line 28, `trace` is passed directly to `NewTraceViewerComponent` with a type assertion `trace as Trace`, which silences the TypeScript error but does not prevent the runtime crash.
Inside `NewTraceViewerComponent` (in `new-trace-viewer/trace-viewer.tsx` line 98), the component immediately accesses `trace.spans`:
```tsx
<ActiveSpanProvider spans={trace.spans}>
```
When `trace` is `undefined`, this produces: `TypeError: Cannot read properties of undefined (reading 'spans')`.
This happens whenever the component renders before `run.runId` is available — a normal scenario during initial loading.
The old `WorkflowTraceViewer` component (in `workflow-trace-view.tsx` line 953) correctly handles this with a `if (!trace)` guard that renders a loading skeleton. The new component lacks this guard.
**Fix:**
Added a null guard in `trace-viewer-new.tsx` that checks `if (!trace)` before rendering `NewTraceViewerComponent`. When trace is undefined, a simple loading placeholder is rendered instead. This prevents the crash and follows the same pattern as the existing `WorkflowTraceViewer`. The `as Trace` cast on line 28 is now safe because `trace` is guaranteed to be defined after the guard.
Co-authored-by: Vercel <vercel[bot]@users.noreply.github.com>
Co-authored-by: mitul-s <mitulxshah@gmail.com>
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CleanShot.2026-04-30.at.15.41.26.mp4