diff --git a/docs/architecture/delivery-ownership.md b/docs/architecture/delivery-ownership.md
index dbd9989..357f2a4 100644
--- a/docs/architecture/delivery-ownership.md
+++ b/docs/architecture/delivery-ownership.md
@@ -2,8 +2,8 @@
 
 ## Status
 
-This is the approved target architecture. The current source-owned onboarding
-implementation is being migrated and must not be used for new applications.
+This is the approved target architecture. Central onboarding is available for
+new applications; existing source-owned registrations remain migration work.
 
 ## Trust Boundary
 
@@ -24,6 +24,10 @@ operators and approved automation may push or merge into it. Flux must track
 only that branch for chart content. Flux must never track an application `main`
 branch or `maidn/delivery-*` branch.
 
+Onboarding requires an existing `maidn/platform-<app>` branch and verifies its
+no-direct-push protection before it opens the central registration PR. It never
+seeds a platform branch from developer-controlled `main`.
+
 ## Resource Flow
 
 ```mermaid
diff --git a/docs/operations.md b/docs/operations.md
index 8938b85..1432518 100644
--- a/docs/operations.md
+++ b/docs/operations.md
@@ -46,8 +46,9 @@ go run . bootstrap init --config <private-bootstrap-config> --organization <owne
 The source-owned onboarding implementation is retired. Central onboarding
 creates a reviewed cluster registration only; it never writes `.tekton` or
 `.maidn` resources to an application repository. Before merging that
-registration, a platform operator must create and protect the corresponding
-`maidn/platform-<app>` package through a reviewed platform PR. See [Delivery
+registration, a platform operator must create the corresponding
+`maidn/platform-<app>` package through a reviewed platform PR; onboarding
+verifies its existence and enforces its protection. See [Delivery
 Ownership](architecture/delivery-ownership.md) for the approved architecture
 and migration rules.
 
diff --git a/internal/bootstrap/onboard.go b/internal/bootstrap/onboard.go
index 4970a3a..227e9c0 100644
--- a/internal/bootstrap/onboard.go
+++ b/internal/bootstrap/onboard.go
@@ -57,6 +57,9 @@ func OnboardApp(cfg config.Config, sourceDir string) error {
 	if err := sourceManager.EnsureProtectedBranch(repository, resolved.Delivery.ProductionBranch); err != nil {
 		return fmt.Errorf("protect Forgejo production branch: %w", err)
 	}
+	if err := ensurePlatformBranch(sourceManager, repository, resolved.Delivery.AppRepoURL, resolved.Delivery.AppName); err != nil {
+		return err
+	}
 	registrationBranch := "maidn/register-" + resolved.Delivery.AppName
 	clusterManager := newOnboardingRepoManager(resolved.Git.BaseURL, resolved.Git.Token, resolved.Git.Owner, resolved.Git.Username, "", "", resolved.Flux.Branch, "")
 	if _, err := clusterManager.PublishRepositoryPullRequest(resolved.Flux.RepoName, "feat: register "+resolved.Delivery.AppName+" delivery", registrationBranch, resolved.Flux.Branch, func(dir string) error {
@@ -83,6 +86,25 @@ func OnboardApp(cfg config.Config, sourceDir string) error {
 	return nil
 }
 
+func platformBranch(appName string) string {
+	return "maidn/platform-" + appName
+}
+
+func ensurePlatformBranch(manager onboardingRepoManager, repository, repositoryURL, appName string) error {
+	branch := platformBranch(appName)
+	revision, err := manager.RemoteBranchRevision(repositoryURL, branch)
+	if err != nil {
+		return fmt.Errorf("read Forgejo platform branch: %w", err)
+	}
+	if revision == "" {
+		return fmt.Errorf("approved Forgejo platform branch %q must exist before central registration", branch)
+	}
+	if err := manager.EnsureProtectedBranch(repository, branch); err != nil {
+		return fmt.Errorf("protect Forgejo platform branch: %w", err)
+	}
+	return nil
+}
+
 // publishInitialAppBranches establishes the immutable source baseline before central registration.
 func publishInitialAppBranches(manager onboardingRepoManager, sourceDir, targetURL, sourceBranch, targetBranch, productionBranch string) error {
 	sourceRevision, err := forgejo.BranchRevision(sourceDir, sourceBranch)
@@ -209,8 +231,8 @@ spec:
   secretRef:
     name: forgejo-flux-credentials
   ref:
-    branch: maidn/platform-%s
-`, cfg.Delivery.AppName, cfg.Delivery.AppRepoURL, cfg.Delivery.AppName)
+    branch: %s
+`, cfg.Delivery.AppName, cfg.Delivery.AppRepoURL, platformBranch(cfg.Delivery.AppName))
 	if len(secretAccess) != 0 {
 		content += "---\n" + string(secretAccess)
 	}
diff --git a/internal/bootstrap/onboard_test.go b/internal/bootstrap/onboard_test.go
index 7d90a79..f68036e 100644
--- a/internal/bootstrap/onboard_test.go
+++ b/internal/bootstrap/onboard_test.go
@@ -158,8 +158,9 @@ func TestPublishInitialAppBranchesCreatesAndPreservesProduction(t *testing.T) {
 }
 
 type onboardingManagerFake struct {
-	owner string
-	calls []string
+	owner           string
+	calls           []string
+	remoteRevisions map[string]string
 }
 
 func (m *onboardingManagerFake) EnsureRepository(repo, _ string) (bool, error) {
@@ -169,6 +170,9 @@ func (m *onboardingManagerFake) EnsureRepository(repo, _ string) (bool, error) {
 
 func (m *onboardingManagerFake) RemoteBranchRevision(targetURL, branch string) (string, error) {
 	m.calls = append(m.calls, "remote "+targetURL+":"+branch)
+	if m.remoteRevisions != nil {
+		return m.remoteRevisions[branch], nil
+	}
 	return "existing", nil
 }
 
@@ -255,6 +259,8 @@ func TestOnboardAppUsesCanonicalSourceAndCentralClusterManagers(t *testing.T) {
 		"remote https://git.example.test/Maidn/maidn-e2e-web.git:main",
 		"remote https://git.example.test/Maidn/maidn-e2e-web.git:production",
 		"protect Maidn/maidn-e2e-web:production",
+		"remote https://git.example.test/Maidn/maidn-e2e-web.git:maidn/platform-web-ui",
+		"protect Maidn/maidn-e2e-web:maidn/platform-web-ui",
 	} {
 		if !strings.Contains(sourceCalls, want) {
 			t.Fatalf("source manager calls = %q, missing %q", sourceCalls, want)
@@ -267,3 +273,14 @@ func TestOnboardAppUsesCanonicalSourceAndCentralClusterManagers(t *testing.T) {
 		t.Fatalf("cluster manager calls = %q", got)
 	}
 }
+
+func TestEnsurePlatformBranchRequiresExistingBranch(t *testing.T) {
+	manager := &onboardingManagerFake{owner: "Maidn", remoteRevisions: map[string]string{}}
+	err := ensurePlatformBranch(manager, "maidn-e2e-web", "https://git.example.test/Maidn/maidn-e2e-web.git", "web-ui")
+	if err == nil || !strings.Contains(err.Error(), "maidn/platform-web-ui") {
+		t.Fatalf("ensurePlatformBranch() error = %v", err)
+	}
+	if strings.Contains(strings.Join(manager.calls, "\n"), "protect") {
+		t.Fatalf("missing platform branch was protected: %q", manager.calls)
+	}
+}
diff --git a/internal/forgejo/repo.go b/internal/forgejo/repo.go
index 88606b5..be10d33 100644
--- a/internal/forgejo/repo.go
+++ b/internal/forgejo/repo.go
@@ -780,10 +780,10 @@ func (rm *RepoManager) TriggerWebhookTest(repo, webhookURL, branch string) error
 	return nil
 }
 
-// EnsureProtectedBranch disables direct pushes to the configured production branch.
+// EnsureProtectedBranch disables direct pushes to a managed branch.
 func (rm *RepoManager) EnsureProtectedBranch(repo, branch string) error {
 	if repo == "" || branch == "" {
-		return errors.New("Forgejo repository and production branch are required")
+		return errors.New("Forgejo repository and branch are required")
 	}
 	endpoint := fmt.Sprintf("%s/api/v1/repos/%s/%s/branch_protections", rm.BaseURL, rm.Owner, repo)
 	var protections []branchProtection
@@ -801,11 +801,11 @@ func (rm *RepoManager) EnsureProtectedBranch(repo, branch string) error {
 		}
 	}
 	if len(matching) > 1 {
-		return fmt.Errorf("multiple Forgejo branch protections match production branch %q", branch)
+		return fmt.Errorf("multiple Forgejo branch protections match branch %q", branch)
 	}
 	if len(matching) == 1 {
 		if matching[0].EnablePush || matching[0].EnablePushWhitelist {
-			return fmt.Errorf("Forgejo production branch %q permits direct pushes", branch)
+			return fmt.Errorf("Forgejo branch %q permits direct pushes", branch)
 		}
 		return nil
 	}