fix: break infinite status reconciliation loop in notebook controller

[Raakshass]

Summary

Fixes the infinite reconciliation loop in the notebook controller where updateNotebookStatus issues a Status().Update() PUT on every reconcile even when nothing has changed.

Root Cause

Three-link causal chain:

1. PodCondToNotebookCond (line 330) — kubelet never sets LastProbeTime on pod conditions, so the else branch injects metav1.Now() on every reconcile, producing a different timestamp each time.

2. updateNotebookStatus (line 238-240) — unconditional r.Status().Update(ctx, nb) with no comparison guard.

3. SetupWithManager (line 713-714) — For(&v1beta1.Notebook{}) with no GenerationChangedPredicate, so the status write bumps resourceVersion, emits a watch event, and re-enqueues.

Changes

File	Change
controllers/notebook_controller.go	Reorder PodCondToNotebookCond to resolve LastTransitionTime first, fall back LastProbeTime to condition.LastTransitionTime instead of metav1.Now(), add reflect.DeepEqual guard in updateNotebookStatus

Design Decisions

• LastProbeTime falls back to LastTransitionTime, not zero — the CRD schema declares lastProbeTime as type: string, format: date-time without nullable: true, and omitempty on metav1.Time (a struct) does not suppress the zero value.
• Block reorder — LastTransitionTime resolved first so LastProbeTime can reference it without a second metav1.Now() call.
• Both changes needed — DeepEqual guard alone does not break the loop because metav1.Now() makes it return false every time. The timestamp fix makes the status deterministic; the guard eliminates the residual no-op PUT.
• No new imports — reflect already used at line 257.

Test Results

All 5 TestCreateNotebookStatus subtests pass. go vet and go build clean.

Follow-up

• Add test case with LastProbeTime omitted asserting fallback equals LastTransitionTime
• CopyStatefulSetFields secondary loop is a separate concern

Contributor Checklist

• DCO sign-off
• All existing tests pass
• go vet clean
• go build clean
• Single file, minimal diff

[google-oss-prow]

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[Raakshass]

@juliusvonkohout