Fix automation timeline cause detail omission and detailKind/detailLength mismatch

- Add toTimelineMessage() to PreviewAutomationEvaluationError and
  PreviewAutomationInvalidSelectorError to extract cause details for
  timeline entries, matching the existing PreviewOperationError pattern.
- Update finalizeControlAction to use these methods instead of falling
  through to the generic error.message for these error types.
- Fix evaluateWithDebugger to use truthiness checks for description/text
  instead of !== undefined, preventing null and empty string from being
  misclassified as exception-description while detailLength resolves to
  a different field's length.

Author: cursoragent

apps/desktop/src/preview/Manager.ts

@@ -876,9 +876,13 @@ const makeNativeOperations = Effect.fn("PreviewManager.makeOperations")(function
         const interrupted = isPreviewAutomationControlInterruptedError(error);
         const errorMessage = isPreviewOperationError(error)
           ? PreviewOperationError.toTimelineMessage(error)
-          : error instanceof Error
-            ? error.message
-            : String(error);
+          : isPreviewAutomationEvaluationError(error)
+            ? PreviewAutomationEvaluationError.toTimelineMessage(error)
+            : isPreviewAutomationInvalidSelectorError(error)
+              ? PreviewAutomationInvalidSelectorError.toTimelineMessage(error)
+              : error instanceof Error
+                ? error.message
+                : String(error);
         yield* replaceAction(tabId, {
           ...actionEvent,
           status: interrupted ? "interrupted" : "failed",
@@ -915,13 +919,8 @@ const makeNativeOperations = Effect.fn("PreviewManager.makeOperations")(function
         return Effect.fail(
           new PreviewAutomationEvaluationError({
             tabId,
-            detailKind:
-              description !== undefined
-                ? "exception-description"
-                : text !== undefined
-                  ? "exception-text"
-                  : "unknown",
-            detailLength: description?.length ?? text?.length ?? 0,
+            detailKind: description ? "exception-description" : text ? "exception-text" : "unknown",
+            detailLength: description?.length || text?.length || 0,
             cause: response.exceptionDetails,
           }),
         );
@@ -2467,6 +2466,13 @@ export class PreviewAutomationEvaluationError extends Schema.TaggedErrorClass<Pr
     cause: Schema.Defect(),
   },
 ) {
+  static toTimelineMessage(error: PreviewAutomationEvaluationError): string {
+    const cause = error.cause as
+      | { text?: string; exception?: { description?: string } }
+      | undefined;
+    return cause?.exception?.description || cause?.text || error.message;
+  }
+
   override get message(): string {
     return `Preview JavaScript evaluation failed in tab ${this.tabId}`;
   }
@@ -2513,6 +2519,11 @@ export class PreviewAutomationInvalidSelectorError extends Schema.TaggedErrorCla
     cause: Schema.Defect(),
   },
 ) {
+  static toTimelineMessage(error: PreviewAutomationInvalidSelectorError): string {
+    const cause = error.cause as { message?: string } | undefined;
+    return cause?.message || error.message;
+  }
+
   get detail(): {
     readonly selectorKind: PreviewAutomationSelectorKind;
     readonly selectorLength?: number;
@@ -2595,6 +2606,10 @@ export const isPreviewManagerError = Schema.is(PreviewManagerError);
 export const isPreviewAutomationControlInterruptedError = Schema.is(
   PreviewAutomationControlInterruptedError,
 );
+export const isPreviewAutomationEvaluationError = Schema.is(PreviewAutomationEvaluationError);
+export const isPreviewAutomationInvalidSelectorError = Schema.is(
+  PreviewAutomationInvalidSelectorError,
+);
 
 export class PreviewManager extends Context.Service<
   PreviewManager,