Clear programClusterRoutes when clusterRoutingMode is removed

[tomastigera]

Problem

Setting Installation.spec.calicoNetwork.clusterRoutingMode and then removing it leaves the cluster running whatever that mode last wrote, while the Installation looks exactly like one that never touched the field. Nothing is written, nothing is logged, and status.computed is empty.

The state it can strand is the deprecated BIRD-programs-IPIP configuration. A user who sets BIRD to opt out of the v3.33 default and then removes the field expecting the default back stays on the deprecated arm, with no indication anywhere.

kubectl patch installation default --type=merge \
  -p '{"spec":{"calicoNetwork":{"clusterRoutingMode":"BIRD"}}}'
#  -> FelixConfiguration=Disabled  BGPConfiguration=Enabled      (correct)

kubectl patch installation default --type=json \
  -p '[{"op":"remove","path":"/spec/calicoNetwork/clusterRoutingMode"}]'
#  -> both still set, status.computed empty, operator log silent for 76s

Why the early return is there

setClusterRoutingOnFelixConfiguration and setClusterRoutingOnBGPConfiguration return early when the mode is nil. That is correct for a field that was never set: writing there would pin the operator's idea of today's Calico defaults into the datastore, which is exactly what clusterRoutingMode() documents as the reason for the gate. What it cannot do is tell never-set from set-then-unset.

Change

Use status.computed as the record of what the operator last applied. It is persisted on the CR so it survives restarts, and it still holds the previous reconcile's value at the point the setters run. A mode there plus no mode in the spec is the set-to-unset transition.

On that transition, clear programClusterRoutes and let Calico's own defaults decide again — which is what the existing comment asks for. The gate is preserved: an unset field still never writes a value.

A value the operator never wrote belongs to the user and is left alone, so configuring programClusterRoutes directly on FelixConfiguration keeps working while the Installation field is unset.

Tests

Two specs in core_controller_test.go, both driving real reconciles against the fake client:

• set, then remove → both programClusterRoutes cleared
• never set, user writes programClusterRoutes directly → left alone

Mutation-tested: reverting either setter to return false, nil fails the first spec. The existing "should not patch FelixConfig and BGPConfig when ClusterRouteMode not set" spec is unchanged and still passes, which is the regression guard for the documented no-write-on-unset behaviour.

Suite: 311 passed / 22 failed. The 22 are all cel_validation_test.go [BeforeEach] envtest setup failures; a control run on unmodified upstream/master in the same worktree fails the identical 22 (309 passed / 22 failed), so they are pre-existing and environmental.

Found during the v3.33 test cycle, Zephyr OS-R232 / RT-3.

CORE-13588

AI assistance

This PR was written in part with the assistance of generative AI.

Release Note

Fix the operator leaving a stale programClusterRoutes value behind when clusterRoutingMode is removed from the Installation, which could strand a cluster on the deprecated BIRD-programs-IPIP configuration.