diff --git a/migrations/0023_gate_quality_modes.sql b/migrations/0023_gate_quality_modes.sql
index 98b2876caf..a7b8bb1ad1 100644
--- a/migrations/0023_gate_quality_modes.sql
+++ b/migrations/0023_gate_quality_modes.sql
@@ -1,4 +1,4 @@
-ALTER TABLE repository_settings ADD COLUMN linked_issue_gate_mode TEXT NOT NULL DEFAULT 'advisory';
-ALTER TABLE repository_settings ADD COLUMN duplicate_pr_gate_mode TEXT NOT NULL DEFAULT 'advisory';
+ALTER TABLE repository_settings ADD COLUMN linked_issue_gate_mode TEXT NOT NULL DEFAULT 'block';
+ALTER TABLE repository_settings ADD COLUMN duplicate_pr_gate_mode TEXT NOT NULL DEFAULT 'block';
 ALTER TABLE repository_settings ADD COLUMN quality_gate_mode TEXT NOT NULL DEFAULT 'advisory';
 ALTER TABLE repository_settings ADD COLUMN quality_gate_min_score INTEGER;
diff --git a/migrations/0025_restore_gate_blocking_modes.sql b/migrations/0025_restore_gate_blocking_modes.sql
new file mode 100644
index 0000000000..5c5ea0a073
--- /dev/null
+++ b/migrations/0025_restore_gate_blocking_modes.sql
@@ -0,0 +1,5 @@
+UPDATE repository_settings
+SET
+  linked_issue_gate_mode = CASE WHEN linked_issue_gate_mode = 'advisory' THEN 'block' ELSE linked_issue_gate_mode END,
+  duplicate_pr_gate_mode = CASE WHEN duplicate_pr_gate_mode = 'advisory' THEN 'block' ELSE duplicate_pr_gate_mode END
+WHERE gate_check_mode = 'enabled';
diff --git a/src/api/routes.ts b/src/api/routes.ts
index 311b2aa6c1..9c7b2e0726 100644
--- a/src/api/routes.ts
+++ b/src/api/routes.ts
@@ -445,8 +445,8 @@ const repositorySettingsSchema = z.object({
   checkRunMode: z.enum(["off", "enabled"]).default("off"),
   checkRunDetailLevel: z.enum(["minimal", "standard", "deep"]).default("standard"),
   gateCheckMode: z.enum(["off", "enabled"]).default("off"),
-  linkedIssueGateMode: z.enum(["off", "advisory", "block"]).default("advisory"),
-  duplicatePrGateMode: z.enum(["off", "advisory", "block"]).default("advisory"),
+  linkedIssueGateMode: z.enum(["off", "advisory", "block"]).default("block"),
+  duplicatePrGateMode: z.enum(["off", "advisory", "block"]).default("block"),
   qualityGateMode: z.enum(["off", "advisory", "block"]).default("advisory"),
   qualityGateMinScore: z.number().int().min(0).max(100).nullable().optional(),
   autoLabelEnabled: z.boolean().default(true),
diff --git a/src/db/repositories.ts b/src/db/repositories.ts
index 74c6bdba80..bfe3dcd735 100644
--- a/src/db/repositories.ts
+++ b/src/db/repositories.ts
@@ -386,8 +386,8 @@ export async function getRepositorySettings(env: Env, fullName: string): Promise
       checkRunMode: "off",
       checkRunDetailLevel: "minimal",
       gateCheckMode: "off",
-      linkedIssueGateMode: "advisory",
-      duplicatePrGateMode: "advisory",
+      linkedIssueGateMode: "block",
+      duplicatePrGateMode: "block",
       qualityGateMode: "advisory",
       qualityGateMinScore: null,
       autoLabelEnabled: true,
@@ -436,8 +436,8 @@ export async function upsertRepositorySettings(env: Env, settings: Partial<Repos
     checkRunMode: settings.checkRunMode ?? "off",
     checkRunDetailLevel: settings.checkRunDetailLevel ?? "minimal",
     gateCheckMode: settings.gateCheckMode ?? "off",
-    linkedIssueGateMode: settings.linkedIssueGateMode ?? "advisory",
-    duplicatePrGateMode: settings.duplicatePrGateMode ?? "advisory",
+    linkedIssueGateMode: settings.linkedIssueGateMode ?? "block",
+    duplicatePrGateMode: settings.duplicatePrGateMode ?? "block",
     qualityGateMode: settings.qualityGateMode ?? "advisory",
     qualityGateMinScore: normalizeQualityGateMinScore(settings.qualityGateMinScore),
     autoLabelEnabled: settings.autoLabelEnabled ?? true,
diff --git a/src/db/schema.ts b/src/db/schema.ts
index 5f2b3dc5d8..326a4f028d 100644
--- a/src/db/schema.ts
+++ b/src/db/schema.ts
@@ -41,8 +41,8 @@ export const repositorySettings = sqliteTable("repository_settings", {
   checkRunMode: text("check_run_mode").notNull().default("off"),
   checkRunDetailLevel: text("check_run_detail_level").notNull().default("minimal"),
   gateCheckMode: text("gate_check_mode").notNull().default("off"),
-  linkedIssueGateMode: text("linked_issue_gate_mode").notNull().default("advisory"),
-  duplicatePrGateMode: text("duplicate_pr_gate_mode").notNull().default("advisory"),
+  linkedIssueGateMode: text("linked_issue_gate_mode").notNull().default("block"),
+  duplicatePrGateMode: text("duplicate_pr_gate_mode").notNull().default("block"),
   qualityGateMode: text("quality_gate_mode").notNull().default("advisory"),
   qualityGateMinScore: integer("quality_gate_min_score"),
   autoLabelEnabled: integer("auto_label_enabled", { mode: "boolean" }).notNull().default(true),
diff --git a/src/github/app.ts b/src/github/app.ts
index 1630f53cd7..b6231f2533 100644
--- a/src/github/app.ts
+++ b/src/github/app.ts
@@ -114,7 +114,7 @@ export async function createOrUpdatePendingGateCheckRun(
     output: {
       title: "Gittensory Gate is evaluating",
       summary: "Gittensory is running deterministic public PR hygiene checks.",
-      text: "The Gate is advisory-first unless this repository explicitly configures a rule to block merge.",
+      text: "The Gate preserves legacy linked-issue and duplicate-PR blockers unless this repository explicitly sets those rules to advisory or off.",
     },
   });
 }
diff --git a/src/rules/advisory.ts b/src/rules/advisory.ts
index 4e521731fe..226a06b3ef 100644
--- a/src/rules/advisory.ts
+++ b/src/rules/advisory.ts
@@ -385,8 +385,8 @@ function isEvaluationBlocker(code: string): boolean {
 }
 
 function isConfiguredGateBlocker(code: string, policy: GateCheckPolicy): boolean {
-  if (code === "missing_linked_issue") return gateMode(policy.linkedIssueGateMode) === "block";
-  if (code === "duplicate_pr_risk") return gateMode(policy.duplicatePrGateMode) === "block";
+  if (code === "missing_linked_issue") return gateMode(policy.linkedIssueGateMode ?? "block") === "block";
+  if (code === "duplicate_pr_risk") return gateMode(policy.duplicatePrGateMode ?? "block") === "block";
   return false;
 }
 
diff --git a/test/unit/github-app.test.ts b/test/unit/github-app.test.ts
index f76b502e59..2a7e3b7e31 100644
--- a/test/unit/github-app.test.ts
+++ b/test/unit/github-app.test.ts
@@ -226,7 +226,7 @@ describe("GitHub check runs", () => {
       output: { title: "Gittensory Gate is evaluating" },
     });
     expect(capturedBody).not.toHaveProperty("conclusion");
-    expect(capturedBody.output?.text).toContain("advisory-first");
+    expect(capturedBody.output?.text).toContain("preserves legacy linked-issue and duplicate-PR blockers");
   });
 
   it("finalizes a known pending Gate check by id without listing check runs first", async () => {
diff --git a/test/unit/queue.test.ts b/test/unit/queue.test.ts
index 28d51b71cb..50dbfe8fcf 100644
--- a/test/unit/queue.test.ts
+++ b/test/unit/queue.test.ts
@@ -690,7 +690,7 @@ describe("queue processors", () => {
     );
   });
 
-  it("publishes an opt-in gate check without requiring comment output", async () => {
+  it("publishes an opt-in gate check without requiring comment output while preserving linked-issue blockers", async () => {
     const env = createTestEnv({ GITHUB_APP_PRIVATE_KEY: await generatePrivateKeyPem() });
     await persistRegistrySnapshot(
       env,
@@ -728,7 +728,7 @@ describe("queue processors", () => {
       }
       if (url.includes("/check-runs/900") && (init?.method ?? "GET") === "PATCH") {
         const body = JSON.parse(String(init?.body ?? "{}")) as { name?: string; status?: string; conclusion?: string; output?: { title?: string } };
-        expect(body).toMatchObject({ name: "Gittensory Gate", status: "completed", conclusion: "success", output: { title: "Gittensory Gate passed" } });
+        expect(body).toMatchObject({ name: "Gittensory Gate", status: "completed", conclusion: "failure", output: { title: "Gittensory Gate is blocking merge" } });
         calls.gateChecks += 1;
         return Response.json({ id: 900 });
       }
diff --git a/test/unit/rules.test.ts b/test/unit/rules.test.ts
index a1ec630333..b4b5cd3da7 100644
--- a/test/unit/rules.test.ts
+++ b/test/unit/rules.test.ts
@@ -181,7 +181,7 @@ describe("advisory rules", () => {
     expect(output.text).not.toMatch(/reward|wallet|trust score|score estimate/i);
   });
 
-  it("keeps missing linked issue and duplicate PR findings advisory unless their gate modes block", () => {
+  it("keeps legacy Gate blockers by default while honoring explicit advisory or off modes", () => {
     const pr: PullRequestRecord = {
       repoFullName: repo.fullName,
       number: 21,
@@ -195,7 +195,7 @@ describe("advisory rules", () => {
     };
     const missingIssueAdvisory = buildPullRequestAdvisory(repo, pr, { requireLinkedIssue: true });
 
-    expect(evaluateGateCheck(missingIssueAdvisory).conclusion).toBe("success");
+    expect(evaluateGateCheck(missingIssueAdvisory).conclusion).toBe("failure");
     expect(evaluateGateCheck(missingIssueAdvisory, { linkedIssueGateMode: "advisory" }).conclusion).toBe("success");
     expect(evaluateGateCheck(missingIssueAdvisory, { linkedIssueGateMode: "off" }).conclusion).toBe("success");
     expect(evaluateGateCheck(missingIssueAdvisory, { linkedIssueGateMode: "block" }).conclusion).toBe("failure");
@@ -206,6 +206,7 @@ describe("advisory rules", () => {
     });
 
     expect(duplicateAdvisory.findings.map((finding) => finding.code)).toContain("duplicate_pr_risk");
+    expect(evaluateGateCheck(duplicateAdvisory).conclusion).toBe("failure");
     expect(evaluateGateCheck(duplicateAdvisory, { duplicatePrGateMode: "advisory" }).conclusion).toBe("success");
     expect(evaluateGateCheck(duplicateAdvisory, { duplicatePrGateMode: "off" }).conclusion).toBe("success");
     expect(evaluateGateCheck(duplicateAdvisory, { duplicatePrGateMode: "block" }).conclusion).toBe("failure");