The service update path stopped and renamed the old container aside before
the new one was confirmed running, but only wired up rollback if
createContainer threw or the 5s health check failed. A throw from
newContainer.start() itself (bad device/GPU config, host port already bound,
image incompatibility) bubbled straight to the outer catch, which returned a
generic 400 and never restored the old container, leaving the service down.
Retrying then wedged: the failed new container still held the service name, so
the next attempt's rename to `<name>_old` collided with the leftover from the
first attempt and threw the same error every time.
- Wrap newContainer.start() so a start failure removes the half-created
container and rolls back to the previous one.
- Clear any stale `<name>_old` before renaming so retries can't collide.
- Dedupe the three rollback sites into a single rollbackToOld() helper (also
removes a non-null assertion in the create-failure path that could itself
throw when no `_old` existed).
Refs #949
Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>
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