fix(run-engine): scope getSnapshotsSince anchor lookup to the polled run

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

Author: d-cs

.server-changes/snapshots-since-scoped-to-run.md

@@ -0,0 +1,7 @@
+---
+area: webapp
+type: fix
+---
+
+Snapshot polling now rejects a since-snapshot id that doesn't belong to the run being polled,
+instead of using its timestamp to return a too-wide window of the run's snapshots.

internal-packages/run-engine/src/engine/systems/executionSnapshotSystem.ts

@@ -274,7 +274,7 @@ export async function getExecutionSnapshotsSince(
 ): Promise<EnhancedExecutionSnapshot[]> {
   // Step 1: Find the createdAt of the sinceSnapshotId
   const sinceSnapshot = await prisma.taskRunExecutionSnapshot.findFirst({
-    where: { id: sinceSnapshotId },
+    where: { id: sinceSnapshotId, runId },
     select: { createdAt: true },
   });