Add SyncStatus field to RelatedResourceSpec

[iakmc]

Summary

Adds a syncStatus field to RelatedResourceSpec. When set to true, the status subresource of a related object is synced in the same direction as its spec:

• origin: kcp -> status flows kcp -> service cluster
• origin: service -> status flows service cluster -> kcp

This is independent of the existing syncStatusBack behavior on primary resources (which always syncs status in the reverse direction).

Example

related:
  - identifier: subnet
    origin: kcp
    group: kcp.example.com
    version: v1
    resource: subnets
    syncStatus: true   # kcp status -> service cluster

Changes

• sdk/apis/syncagent/v1alpha1/published_resource.go - new SyncStatus bool on RelatedResourceSpec; doc comment recommends configuring Watch when origin: service to ensure status changes trigger reconciliation
• internal/sync/object_syncer.go - new syncStatusForward field and syncObjectStatusForward() method; called unconditionally from syncObjectContents() so a simultaneous spec+status change doesn't defer the status sync by one reconciliation cycle; includes a 404 guard that emits a Warning event instead of error-looping when the destination CRD has no status subresource
• internal/sync/object_syncer_test.go - unit tests for syncObjectStatusForward() (5 sub-tests covering no-op conditions, happy path, and 404 guard) and syncObjectContents() status-runs-even-on-spec-requeue invariant
• internal/sync/syncer_related.go - wires SyncStatus into objectSyncer: sets syncStatusForward and adds "status" to subresources
• deploy/crd/kcp.io/syncagent.kcp.io_publishedresources.yaml - regenerated CRD
• test/crds/subnet.yaml - new test CRD with status subresource
• test/e2e/sync/related_status_test.go - three e2e tests

Testing

Unit tests (make test) — all pass, including 6 new sub-tests in TestSyncObjectStatusForward and TestSyncObjectContentsForwardStatusRunsEvenOnSpecRequeue

Focused e2e — three new tests covering the happy paths and the default-off behavior:

go test -tags e2e -run "TestSyncRelatedObjectStatus" ./test/e2e/sync/

--- PASS: TestSyncRelatedObjectStatusFromKcp     (29s)
--- PASS: TestSyncRelatedObjectStatusFromService (18s)
--- PASS: TestSyncRelatedObjectStatusNotSyncedByDefault (27s)

Full e2e (make test-e2e) — 38/39 pass; the one failure (TestAPIExportEndpointSliceDifferentCluster) is pre-existing and unrelated to this change.

What Type of PR Is This?

/kind feature

Related Issue(s)

Fixes #173

Release Notes

Status sync for related resources: set syncStatus: true on a RelatedResourceSpec to sync the status subresource in the same direction as the spec. For origin: kcp status flows kcp -> service cluster; for origin: service it flows service cluster -> kcp.

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[iakmc]

/test pull-api-syncagent-verify

[embik]

This feels rather noisy, since status subresources tend to change frequently due to e.g. timestamps. I think it doesn't make sense to emit this event?

[embik]

This only ever returns false for requeue and the call site doesn't use it, so I think it can safely be dropped.