fix(noderesource): clear Status.StatefulSet when SyncStatefulSet deletes an impostor

[bdchatham]

Summary

Closes a cross-reconcile churn loop in the impostor-recovery path introduced by #345. Cursor review caught it.

The bug

SyncStatefulSet's impostor branch deletes the live StatefulSet and returns (nil, nil), expecting the next reconcile to observe NotFound and Apply fresh. The controller wrapper sees nil and returns without updating Status.StatefulSet.

But reconcile N continues past the wrapper into ExecutePlan. The apply-statefulset task calls SyncStatefulSet again. Status.StatefulSet still tracks the stale UID, the live object is gone, the impostor check falls through (NotFound case), and Apply creates fresh with a new UID. End of reconcile N: live STS exists, but Status.StatefulSet still points at the original stale UID.

Reconcile N+1: wrapper sees stale UID ≠ new live UID, deletes the fresh STS as another impostor, the task creates another, loop. Brief pod outage on every cycle.

The fix

When SyncStatefulSet deletes an impostor, also clear node.Status.StatefulSet. Any subsequent SyncStatefulSet call — same reconcile or the next — routes through the adopt-on-observe path that already exists (Status.StatefulSet == nil → Get live STS → adopt → Apply idempotent → caller stamps Status). No misclassification, no loop.

~2 lines of code + a focused unit test.

Test plan

• go build ./... clean
• go test ./... — all unit tests pass
• make test-integration — envtest 56s green
• Extended TestSyncStatefulSet_ImpostorThenApply: asserts Status.StatefulSet == nil after the impostor delete
• New TestSyncStatefulSet_ImpostorClearPreventsChurn: directly exercises the cross-reconcile scenario — impostor delete, fresh Apply within the same pass, then a third Sync call adopts rather than re-deleting

🤖 Generated with Claude Code

[cursor]

PR Summary

Medium Risk
Medium risk because it changes reconciliation state handling for StatefulSet impostor recovery; bugs here can cause unintended deletes or reconcile loops, though the change is small and covered by targeted tests.

Overview
Prevents a cross-reconcile churn loop in SyncStatefulSet by clearing node.Status.StatefulSet when an impostor StatefulSet (UID mismatch) is deleted, so subsequent syncs take the adopt/apply path instead of repeatedly re-deleting newly applied objects.

Updates unit tests to assert the status ref is cleared after impostor deletion and adds a new test that simulates multiple SyncStatefulSet calls across and within reconciles to ensure the freshly applied StatefulSet is adopted rather than treated as another impostor.

^{Reviewed by Cursor Bugbot for commit bad5aaa. Bugbot is set up for automated code reviews on this repo. Configure here.}