diff --git a/src/main/AryxAppService.ts b/src/main/AryxAppService.ts
index 69ec61e..bed3c93 100644
--- a/src/main/AryxAppService.ts
+++ b/src/main/AryxAppService.ts
@@ -710,13 +710,15 @@ export class AryxAppService extends EventEmitter<AppServiceEvents> {
   }
 
   async deletePattern(patternId: string): Promise<WorkspaceState> {
-    if (isBuiltinPattern(patternId)) {
-      throw new Error('Built-in patterns cannot be deleted.');
-    }
-
     const workspace = await this.loadWorkspace();
     workspace.patterns = workspace.patterns.filter((pattern) => pattern.id !== patternId);
 
+    if (isBuiltinPattern(patternId)) {
+      const deletedIds = new Set(workspace.deletedBuiltinPatternIds ?? []);
+      deletedIds.add(patternId);
+      workspace.deletedBuiltinPatternIds = [...deletedIds];
+    }
+
     if (workspace.selectedPatternId === patternId) {
       workspace.selectedPatternId = workspace.patterns[0]?.id;
     }
diff --git a/src/main/persistence/workspaceRepository.ts b/src/main/persistence/workspaceRepository.ts
index 7ef5f36..624a222 100644
--- a/src/main/persistence/workspaceRepository.ts
+++ b/src/main/persistence/workspaceRepository.ts
@@ -30,13 +30,16 @@ import {
 } from '@main/persistence/appPaths';
 import { readJsonFile, writeJsonFile } from '@main/persistence/jsonStore';
 
-function mergePatterns(existingPatterns: PatternDefinition[]): PatternDefinition[] {
+function mergePatterns(existingPatterns: PatternDefinition[], deletedBuiltinIds: string[]): PatternDefinition[] {
   const builtinTimestamp = nowIso();
   const builtinPatterns = createBuiltinPatterns(builtinTimestamp);
   const builtinIds = new Set(builtinPatterns.map((pattern) => pattern.id));
+  const deletedSet = new Set(deletedBuiltinIds);
   const existingMap = new Map(existingPatterns.map((pattern) => [pattern.id, pattern]));
 
-  const mergedBuiltins = builtinPatterns.map((builtin) => {
+  const mergedBuiltins = builtinPatterns
+    .filter((builtin) => !deletedSet.has(builtin.id))
+    .map((builtin) => {
     const existing = existingMap.get(builtin.id);
     if (!existing) {
       return builtin;
@@ -108,9 +111,11 @@ export class WorkspaceRepository {
     }));
     const settings = normalizeWorkspaceSettings(stored.settings);
 
+    const deletedBuiltinPatternIds = stored.deletedBuiltinPatternIds ?? [];
+
     const workspace: WorkspaceState = {
       ...stored,
-      patterns: mergePatterns(stored.patterns ?? []).map((pattern) => ({
+      patterns: mergePatterns(stored.patterns ?? [], deletedBuiltinPatternIds).map((pattern) => ({
         ...pattern,
         approvalPolicy: applyDefaultToolApprovalPolicy(pattern.approvalPolicy),
         graph: resolvePatternGraph(pattern),
@@ -118,6 +123,7 @@ export class WorkspaceRepository {
       projects,
       sessions,
       settings,
+      deletedBuiltinPatternIds,
       selectedProjectId: projects.some((project) => project.id === stored.selectedProjectId)
         ? stored.selectedProjectId
         : projects[0]?.id,
diff --git a/src/renderer/components/PatternEditor.tsx b/src/renderer/components/PatternEditor.tsx
index 6602191..0f43b7c 100644
--- a/src/renderer/components/PatternEditor.tsx
+++ b/src/renderer/components/PatternEditor.tsx
@@ -311,7 +311,7 @@ export function PatternEditor({
           </div>
         </div>
         <div className="no-drag flex items-center gap-2">
-          {!isBuiltin && onDelete && (
+          {onDelete && (
             <button
               className="flex items-center gap-1.5 rounded-lg px-3 py-1.5 text-[13px] text-[var(--color-status-error)] transition-all duration-200 hover:bg-[var(--color-status-error)]/10"
               onClick={onDelete}
diff --git a/src/renderer/components/SettingsPanel.tsx b/src/renderer/components/SettingsPanel.tsx
index fa796fe..dd00e33 100644
--- a/src/renderer/components/SettingsPanel.tsx
+++ b/src/renderer/components/SettingsPanel.tsx
@@ -165,12 +165,10 @@ export function SettingsPanel({
           onBack={() => setEditingPattern(null)}
           onChange={setEditingPattern}
           onDelete={
-            isBuiltin
-              ? undefined
-              : async () => {
-                  await onDeletePattern(editingPattern.id);
-                  setEditingPattern(null);
-                }
+            async () => {
+              await onDeletePattern(editingPattern.id);
+              setEditingPattern(null);
+            }
           }
           onSave={async () => {
             await onSavePattern(editingPattern);
diff --git a/src/shared/domain/workspace.ts b/src/shared/domain/workspace.ts
index 4cf5323..c290673 100644
--- a/src/shared/domain/workspace.ts
+++ b/src/shared/domain/workspace.ts
@@ -10,6 +10,8 @@ export interface WorkspaceState {
   patterns: PatternDefinition[];
   sessions: SessionRecord[];
   settings: WorkspaceSettings;
+  /** IDs of built-in patterns the user has deleted. Prevents re-adding on load. */
+  deletedBuiltinPatternIds?: string[];
   /** Runtime-only MCP probe progress for live UI updates. */
   mcpProbingServerIds?: string[];
   selectedProjectId?: string;
diff --git a/tests/main/appServicePattern.test.ts b/tests/main/appServicePattern.test.ts
index aa16c40..511a995 100644
--- a/tests/main/appServicePattern.test.ts
+++ b/tests/main/appServicePattern.test.ts
@@ -59,6 +59,47 @@ function requirePattern(workspace: WorkspaceState, mode: PatternDefinition['mode
   return pattern;
 }
 
+describe('AryxAppService deletePattern', () => {
+  test('deletes a built-in pattern and tracks its ID', async () => {
+    const workspace = createWorkspaceSeed();
+    const builtinPattern = requirePattern(workspace, 'sequential');
+    const service = createService(workspace);
+
+    const result = await service.deletePattern(builtinPattern.id);
+
+    expect(result.patterns.find((p) => p.id === builtinPattern.id)).toBeUndefined();
+    expect(result.deletedBuiltinPatternIds).toContain(builtinPattern.id);
+  });
+
+  test('deletes a custom pattern without tracking its ID', async () => {
+    const workspace = createWorkspaceSeed();
+    const customPattern: PatternDefinition = {
+      ...requirePattern(workspace, 'single'),
+      id: 'custom-pattern',
+      name: 'My Custom Pattern',
+    };
+    workspace.patterns.push(customPattern);
+    const service = createService(workspace);
+
+    const result = await service.deletePattern('custom-pattern');
+
+    expect(result.patterns.find((p) => p.id === 'custom-pattern')).toBeUndefined();
+    expect(result.deletedBuiltinPatternIds ?? []).not.toContain('custom-pattern');
+  });
+
+  test('selects first remaining pattern when the active pattern is deleted', async () => {
+    const workspace = createWorkspaceSeed();
+    const targetPattern = requirePattern(workspace, 'single');
+    workspace.selectedPatternId = targetPattern.id;
+    const service = createService(workspace);
+
+    const result = await service.deletePattern(targetPattern.id);
+
+    expect(result.selectedPatternId).toBe(result.patterns[0]?.id);
+    expect(result.selectedPatternId).not.toBe(targetPattern.id);
+  });
+});
+
 describe('AryxAppService savePattern', () => {
   test('preserves a provided custom graph instead of re-syncing it', async () => {
     const workspace = createWorkspaceSeed();