fix: address a name collision risk in the MCS handling logic

[Chen Yu (michaelawyu)]

What type of PR is this?

/bug

What this PR does / why we need it:

This PR fixes a name collision situation that might lead to two MCS constantly overwriting the same derived service.

Which issue(s) this PR fixes:

N/A

Requirements:

• run make reviewable for basic local test
• Read and followed fleet-networking's Code of conduct.
• uses conventional commit messages
• [NA] includes documentation
• adds unit tests

How has this code been tested

• UTs
• ITs

Special notes for your reviewer

N/A

[codecov]

Codecov Report

❌ Patch coverage is 70.78652% with 26 lines in your changes missing coverage. Please review.
✅ Project coverage is 67.11%. Comparing base (556170b) to head (d2f3fe6).
⚠️ Report is 4 commits behind head on main.

Files with missing lines	Patch %	Lines
pkg/controllers/multiclusterservice/controller.go	64.51%	17 Missing and 5 partials ⚠️
pkg/controllers/multiclusterservice/uniquename.go	85.18%	2 Missing and 2 partials ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #397      +/-   ##
==========================================
- Coverage   67.11%   67.11%   -0.01%     
==========================================
  Files          33       34       +1     
  Lines        3783     3859      +76     
==========================================
+ Hits         2539     2590      +51     
- Misses       1070     1089      +19     
- Partials      174      180       +6     

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[Copilot]

Pull request overview

Adds collision-resistant derived Service naming while preserving compatibility with existing MCS resources.

Changes:

• Adds hash-suffixed derived Service names.
• Verifies ownership before updating or deleting Services.
• Adds unit and integration coverage for collision handling and migration.

Reviewed changes

Copilot reviewed 5 out of 5 changed files in this pull request and generated 1 comment.

Show a summary per file

File	Description
pkg/controllers/multiclusterservice/uniquename.go	Generates hash-suffixed Service names.
pkg/controllers/multiclusterservice/uniquename_test.go	Tests naming and truncation.
pkg/controllers/multiclusterservice/controller.go	Adds ownership checks and migration handling.
pkg/controllers/multiclusterservice/controller_test.go	Updates controller unit tests for new names.
pkg/controllers/multiclusterservice/controller_integration_test.go	Tests new, legacy, and colliding MCS scenarios.

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[Copilot]

Pull request overview

Copilot reviewed 5 out of 5 changed files in this pull request and generated 1 comment.

Suppressed comments (2)

Previously missed (1) — in code that hasn't changed since the last review.

pkg/controllers/multiclusterservice/uniquename_test.go:112

• These assertions accept any 12-character hex suffix, so they do not test that the suffix is actually keyed by MCS identity—the behavior that prevents this PR's collision. A constant suffix would pass every case. Add paired assertions that team-a/service and team/a-service differ, that distinct UIDs for the same namespace/name differ, and that identical inputs remain deterministic.

			wantPattern := "^" + regexp.QuoteMeta(tc.wantPrefix) + "-[0-9a-f]{12}$"
			matched, err := regexp.MatchString(wantPattern, got.Name)
			if err != nil {
				t.Fatalf("failed to match pattern %q: %v", wantPattern, err)
			}
			if !matched {
				t.Fatalf("uniqueDerivedServiceName() = %q, want match %q", got.Name, wantPattern)

pkg/controllers/multiclusterservice/controller.go:446

• Treating a Service with no owner-namespace label as orphaned authorizes the subsequent CreateOrUpdate to adopt and rewrite it. A mutable MCS derived-service label can therefore target an unrelated unlabeled fleet-system Service and change its ports, type, and labels. Missing either owner label means ownership is unproven; handle it as an unmanaged/colliding Service and assign the MCS a different derived name instead of overwriting it.

	case !foundOwnerNS:
		// The owner information is missing, this normally wouldn't happen, as the derived service is created in one go
		// with the owner information set as labels. Still, the controller handles this by letting the following createOrUpdate
		// step to overwrite the derived service with the correct owner information.
		return derivedSvcOwnerVeriResOrphaned, nil