diff --git a/frontend/src/app/features/hal/resources/work-package-resource.spec.ts b/frontend/src/app/features/hal/resources/work-package-resource.spec.ts
index 544ac937ebf..99f8fcef22b 100644
--- a/frontend/src/app/features/hal/resources/work-package-resource.spec.ts
+++ b/frontend/src/app/features/hal/resources/work-package-resource.spec.ts
@@ -110,7 +110,7 @@ describe('WorkPackage', () => {
     });
   });
 
-  describe('id getter', () => {
+  describe('displayId', () => {
     afterEach(() => {
       source = undefined;
     });
@@ -121,8 +121,12 @@ describe('WorkPackage', () => {
         createWorkPackage();
       });
 
-      it('should return the displayId', () => {
-        expect(workPackage.id).toEqual('PROJ-7');
+      it('should return the semantic identifier', () => {
+        expect(workPackage.displayId).toEqual('PROJ-7');
+      });
+
+      it('should not override the numeric id', () => {
+        expect(workPackage.id).toEqual('42');
       });
     });
 
@@ -133,7 +137,7 @@ describe('WorkPackage', () => {
       });
 
       it('should return the numeric displayId as string', () => {
-        expect(workPackage.id).toEqual('42');
+        expect(workPackage.displayId).toEqual('42');
       });
     });
 
@@ -144,11 +148,35 @@ describe('WorkPackage', () => {
       });
 
       it('should fall back to the numeric id', () => {
-        expect(workPackage.id).toEqual('42');
+        expect(workPackage.displayId).toEqual('42');
       });
     });
   });
 
+  describe('displayIdWithHash', () => {
+    afterEach(() => {
+      source = undefined;
+    });
+
+    it('should prefix displayId with # in semantic mode', () => {
+      source = { id: 42, displayId: 'PROJ-7' };
+      createWorkPackage();
+      expect(workPackage.displayIdWithHash).toEqual('#PROJ-7');
+    });
+
+    it('should prefix displayId with # in classic mode', () => {
+      source = { id: 42, displayId: '42' };
+      createWorkPackage();
+      expect(workPackage.displayIdWithHash).toEqual('#42');
+    });
+
+    it('should fall back to numeric id when displayId is absent', () => {
+      source = { id: 42 };
+      createWorkPackage();
+      expect(workPackage.displayIdWithHash).toEqual('#42');
+    });
+  });
+
   describe('when retrieving `canAddAttachment`', () => {
     beforeEach(createWorkPackage);
 
diff --git a/frontend/src/app/features/hal/resources/work-package-resource.ts b/frontend/src/app/features/hal/resources/work-package-resource.ts
index 2c466ce045d..45544542814 100644
--- a/frontend/src/app/features/hal/resources/work-package-resource.ts
+++ b/frontend/src/app/features/hal/resources/work-package-resource.ts
@@ -127,22 +127,27 @@ export class WorkPackageBaseResource extends HalResource {
 
   /**
    * Returns the user-facing work package identifier.
-   *
-   * The API always includes a `displayId` field: either `"PROJ-42"` in semantic
-   * mode or `"123"` in classic mode. This override means every consumer of `wp.id`
-   * (table rows, card views, URLs, cache keys) automatically gets the right value
-   * without per-view conditional logic.
-   *
-   * Note: `$source.id` (the numeric PK) is still available via `$source.id` and
-   * in `_links.self.href`, which always uses the numeric path. Only the
-   * user-facing identifier changes.
+   * "PROJ-42" in semantic mode, "123" in classic mode.
+   * Falls back to numeric id when displayId is not in the API response.
    */
-  public override get id():string|null {
+  public get displayId():string {
     if (this.$source.displayId) {
       return this.$source.displayId.toString();
     }
 
-    return super.id;
+    return this.id?.toString() ?? '';
+  }
+
+  /**
+   * Returns the work package identifier formatted for display in the UI,
+   * always prefixed with `#`: `#123` in classic mode, `#PROJ-42` in
+   * semantic mode.
+   */
+  public get displayIdWithHash():string {
+    const wpId = this.displayId;
+    if (!wpId) return '';
+
+    return `#${wpId}`;
   }
 
   public updatedAt:Date;
@@ -190,7 +195,7 @@ export class WorkPackageBaseResource extends HalResource {
   }
 
   /**
-   * Return "<type name>: <subject> (#<id>)" if type and id are known.
+   * Return "<type name>: <subject> (<displayIdWithHash>)" if type and id are known.
    */
   public subjectWithType(truncateSubject = 40):string {
     // eslint-disable-next-line @typescript-eslint/no-unsafe-member-access
@@ -198,10 +203,10 @@ export class WorkPackageBaseResource extends HalResource {
   }
 
   /**
-   * Return "<subject> (#<id>)" if the id is known.
+   * Return "<subject> (<displayIdWithHash>)" if the id is known.
    */
   public subjectWithId(truncateSubject = 40):string {
-    const id = isNewResource(this) ? '' : ` (#${this.id || ''})`;
+    const id = isNewResource(this) ? '' : ` (${this.displayIdWithHash})`;
 
     return `${this.truncatedSubject(truncateSubject)}${id}`;
   }
diff --git a/frontend/src/app/features/work-packages/components/wp-buttons/wp-share-button/wp-share-button.component.ts b/frontend/src/app/features/work-packages/components/wp-buttons/wp-share-button/wp-share-button.component.ts
index 6ff5ed52dbc..5928d5d01e2 100644
--- a/frontend/src/app/features/work-packages/components/wp-buttons/wp-share-button/wp-share-button.component.ts
+++ b/frontend/src/app/features/work-packages/components/wp-buttons/wp-share-button/wp-share-button.component.ts
@@ -91,7 +91,7 @@ export class WorkPackageShareButtonComponent extends UntilDestroyedMixin impleme
   private countShares():Observable<number> {
     const filters = new ApiV3FilterBuilder()
       .add('entityType', '=', ['WorkPackage'])
-      .add('entityId', '=', [this.workPackage.$source.id!.toString()]);
+      .add('entityId', '=', [this.workPackage.id!]);
 
     return this
       .apiV3Service
diff --git a/frontend/src/app/features/work-packages/components/wp-relations/embedded/wp-relation-query.base.ts b/frontend/src/app/features/work-packages/components/wp-relations/embedded/wp-relation-query.base.ts
index aefd5d1cbbe..890b0176532 100644
--- a/frontend/src/app/features/work-packages/components/wp-relations/embedded/wp-relation-query.base.ts
+++ b/frontend/src/app/features/work-packages/components/wp-relations/embedded/wp-relation-query.base.ts
@@ -104,7 +104,7 @@ export abstract class WorkPackageRelationQueryBase extends UntilDestroyedMixin {
       return this.queryUrlParamsHelper.buildV3GetQueryFromQueryResource(
         this.query,
         { valid_subset: true },
-        { id: this.workPackage.$source.id!.toString() },
+        { id: this.workPackage.id! },
       );
     }
     return this.query;
diff --git a/frontend/src/app/features/work-packages/components/wp-relations/wp-relations-hierarchy/wp-relations-hierarchy.directive.ts b/frontend/src/app/features/work-packages/components/wp-relations/wp-relations-hierarchy/wp-relations-hierarchy.directive.ts
index 5be188620b5..1249d28bbe7 100644
--- a/frontend/src/app/features/work-packages/components/wp-relations/wp-relations-hierarchy/wp-relations-hierarchy.directive.ts
+++ b/frontend/src/app/features/work-packages/components/wp-relations/wp-relations-hierarchy/wp-relations-hierarchy.directive.ts
@@ -86,7 +86,7 @@ export class WorkPackageRelationsHierarchyComponent extends UntilDestroyedMixin
     this.canAddRelation = !!this.workPackage.addRelation;
 
     this.childrenQueryProps = {
-      filters: JSON.stringify([{ parent: { operator: '=', values: [this.workPackage.$source.id!.toString()] } }]),
+      filters: JSON.stringify([{ parent: { operator: '=', values: [this.workPackage.id] } }]),
       'columns[]': ['id', 'type', 'subject', 'status'],
       showHierarchies: false,
     };
diff --git a/frontend/src/app/features/work-packages/components/wp-table/wp-table-hover-sync.ts b/frontend/src/app/features/work-packages/components/wp-table/wp-table-hover-sync.ts
index 8199915a9d8..eff7497b1a0 100644
--- a/frontend/src/app/features/work-packages/components/wp-table/wp-table-hover-sync.ts
+++ b/frontend/src/app/features/work-packages/components/wp-table/wp-table-hover-sync.ts
@@ -72,8 +72,8 @@ export class WpTableHoverSync {
     this.removeOldAndAddNewHoverClass(parentTableRow, parentTimelineRow);
   }
 
-  private extractWorkPackageId(row:Element):string {
-    return row.getAttribute('data-work-package-id')!;
+  private extractWorkPackageId(row:Element):number {
+    return parseInt(row.getAttribute('data-work-package-id')!);
   }
 
   private removeOldAndAddNewHoverClass(parentTableRow:Element | null, parentTimelineRow:Element | null) {
diff --git a/frontend/src/app/features/work-packages/routing/wp-view-base/work-package-single-view.base.ts b/frontend/src/app/features/work-packages/routing/wp-view-base/work-package-single-view.base.ts
index 7b7b1ac14f5..9e12b28fafb 100644
--- a/frontend/src/app/features/work-packages/routing/wp-view-base/work-package-single-view.base.ts
+++ b/frontend/src/app/features/work-packages/routing/wp-view-base/work-package-single-view.base.ts
@@ -195,9 +195,7 @@ export abstract class WorkPackageSingleViewBase extends UntilDestroyedMixin {
       );
 
     this.displayNotificationsButton$ = this.storeService.hasNotifications$;
-    // Use the numeric PK ($source.id) — the notification API's resourceId filter
-    // requires a database ID, not the user-facing display identifier.
-    this.storeService.setFilters(this.workPackage.$source.id!.toString());
+    this.storeService.setFilters(this.workPackage.id!);
 
     // Set authorisation data
     this.authorisationService.initModelAuth('work_package', this.workPackage.$links);
diff --git a/lib/api/v3/work_packages/work_package_sql_representer.rb b/lib/api/v3/work_packages/work_package_sql_representer.rb
index 84a7b89ec9a..8c2f52e7656 100644
--- a/lib/api/v3/work_packages/work_package_sql_representer.rb
+++ b/lib/api/v3/work_packages/work_package_sql_representer.rb
@@ -78,7 +78,7 @@ module API
 
         property :displayId,
                  representation: ->(*) {
-                   Setting::WorkPackageIdentifier.semantic_mode_active? ? "identifier" : "id::text"
+                   Setting::WorkPackageIdentifier.semantic_mode_active? ? "COALESCE(identifier, id::text)" : "id::text"
                  }
 
         property :subject