[pando85]

Summary

• Expose native topologySpreadConstraints in the Helm Deployment pod template with backward-compatible [] default.
• Support an optional strategy override (defaulting to Kubernetes behavior), allowing a delete-first initial migration from required anti-affinity on a saturated cluster.
• Replace the README HA example with revision-scoped hostname spreading using matchLabelKeys: [pod-template-hash].
• Add Helm unit tests for default omission, revision-aware topology spread, coexistence with affinity, and migration rollout strategy.

Why

Required pod anti-affinity is enforced in both directions: old RobotLB pods can reject incoming pods regardless of their pod-template-hash. Topology spread provides per-revision scheduling, so updated replicas can share nodes with the old revision. The first rollout still needs to account for old hard anti-affinity rules, hence the optional rollout strategy.

Verification

• Added four helm-unittest cases, executed by the existing helm-unittest CI job.
• No chart or app version bump; release versioning remains separate.

Upgrade note

On a 3-node/3-replica cluster currently using required anti-affinity, remove affinity.podAntiAffinity, set topologySpreadConstraints as documented, and temporarily set strategy.rollingUpdate.maxSurge: 0 and maxUnavailable: 1. Restore Kubernetes default strategy after all old pods have terminated.