Fix: Prevent Silent Failures by Propagating KRM Function Errors in Specializers

[pulkitvats2007-crypto]

Summary

Previously, errors from KRM function pipelines (IPAM, VLAN, Generic specializers) were logged but ignored.
This caused the controller to continue reconciliation and commit partially processed or invalid resources to Porch, while incorrectly reporting success.

This PR fixes the issue by returning errors from r.krmfn.Process(rl) directly to controller-runtime, ensuring failed reconciliations are retried and no corrupted state is committed.

---

Root Cause

• Errors from KRM functions were swallowed instead of returned.
• Controller continued execution with incomplete/invalid resources.
• ctrl.Result{}, nil prevented retries, causing silent failures.

---

Fix

• Propagate errors by returning them immediately:

_, err = r.krmfn.Process(rl)
if err != nil {
    log.Error(err, "function run failed")
    return ctrl.Result{}, errors.Wrap(err, "function run failed")
}

Applied Across

• ipam-specializer
• vlan-specializer
• generic-specializer
• specializer-reconciler

Ensures

• No partial state is committed
• Reconciliation stops on failure
• controller-runtime retries with backoff

---

Tests

• Added error-path unit tests for:
  • IPAM specializer
  • VLAN specializer
• Verified:
  • Errors are returned correctly
  • No updates are made to Porch on failure
• All tests passing: go test ./...

---

Impact

• Eliminates silent failures in KRM pipelines
• Prevents corrupted/partial GitOps state from being committed
• Enables automatic retries for transient failures (e.g., IPAM/VLAN backend issues)
• Improves reliability and correctness of Nephio deployments

---

Fixes kptdev/porch#807

[nephio-prow]

Hi @pulkitvats2007-crypto. Thanks for your PR.

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[efiacor]

/approve
/lgtm

[nephio-prow]

[APPROVALNOTIFIER] This PR is APPROVED

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