fix(table): SQL cancellation guard allows worker to claim a null-execId cell

The dispatcher's pre-batch `pending` stamp leaves executionId unset so any
cell-task that wins the cascade lock can claim the cell. The cancellation-
guard SQL clause was rejecting these claims because it tested
`executions->gid IS NULL` (whole exec missing) but the pre-stamp leaves
the exec present with executionId=null.

Add a third carve-out: `executions->gid->>'executionId' IS NULL`. Now the
guard reads "write allowed if no exec exists, OR no executionId is set
yet, OR the executionId matches ours."

Symptom: every cell-task's first markWorkflowGroupPickedUp call would log
"SQL guard saw cancelled" and skip, leaving cells stuck at the dispatcher's
pending stamp.

Author: TheodoreSpeaks

apps/sim/lib/table/service.ts

@@ -1722,10 +1722,12 @@ export async function updateRow(
         // (NULL) cleanly evaluates as "different" rather than NULL-poisoning.
         sql`(executions->${guard.groupId}->>'status' IS DISTINCT FROM 'cancelled' OR executions->${guard.groupId}->>'executionId' IS DISTINCT FROM ${guard.executionId})`,
         // Reject writes from a stale worker — the cell's active run has moved
-        // on. `OR exec IS NULL` lets the worker land its first `running`
-        // stamp on a row that has no prior exec record (initial stamp from
-        // the scheduler may not have committed yet).
-        sql`(executions->${guard.groupId} IS NULL OR executions->${guard.groupId}->>'executionId' = ${guard.executionId})`
+        // on. Two carve-outs let a fresh worker land its first stamp:
+        //  - `exec IS NULL`: no prior exec at all.
+        //  - `executionId IS NULL`: dispatcher's pre-batch `pending` stamp
+        //    leaves the executionId unset so any cell-task that wins the
+        //    cascade lock can claim the cell.
+        sql`(executions->${guard.groupId} IS NULL OR executions->${guard.groupId}->>'executionId' IS NULL OR executions->${guard.groupId}->>'executionId' = ${guard.executionId})`
       )
     : eq(userTableRows.id, data.rowId)