NextUint64ID now retries up to 3 times when Int64() is negative, then
returns an error instead of 0 or Fatalf. All call sites propagate the
error to avoid GORM omitting zero-value primary keys.
- Only show the manual retry button for failed tasks (status === "failed") on the frontend.
- Remove the maximum retry limit validation for manual retries in the task executor.
- Remove obsolete test cases verifying maximum retry limit for manual retries.
ryan