fix: category slug-uniqueness check fails closed on API error

isSlugTaken previously caught network/API errors and returned false,
letting the save proceed as if the slug were free. Now the error
propagates and blocks save via a distinct slugCheckError state,
surfaced in the category form with its own hint.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>

src/app/features/admin/categories/components/admin-category-form.component.html

@@ -29,7 +29,7 @@
         <app-form-field [label]="'adminCategories.title' | translate" [required]="true">
           <app-input [ngModel]="category.title" (ngModelChange)="updateTitle($event)" />
         </app-form-field>
-        <app-form-field [label]="'adminCategories.slug' | translate" [required]="true" [hint]="'adminProducts.slugHint' | translate" [error]="slugTaken ? ('adminCategories.slugTaken' | translate) : null">
+        <app-form-field [label]="'adminCategories.slug' | translate" [required]="true" [hint]="'adminProducts.slugHint' | translate" [error]="slugCheckError ? ('adminCategories.slugCheckError' | translate) : (slugTaken ? ('adminCategories.slugTaken' | translate) : null)">
           <app-input [ngModel]="category.slug" (ngModelChange)="updateField('slug', $event)" />
         </app-form-field>
         <label><span>{{ 'adminCategories.parent' | translate }}</span>

src/app/features/admin/categories/components/admin-category-form.component.ts

@@ -41,6 +41,7 @@ export class AdminCategoryFormComponent {
   @Input() breadcrumb: string[] = [];
   @Input() children: AdminCategory[] = [];
   @Input() slugTaken = false;
+  @Input() slugCheckError = false;
   @Input() locales: string[] = ['en'];
   @Input() mode: 'create' | 'edit' = 'create';
   @Input() health!: AdminCategoryHealth;

src/app/features/admin/categories/facade/admin-categories.facade.ts

@@ -1,5 +1,5 @@
 import { Injectable, computed, inject, signal } from '@angular/core';
-import { take } from 'rxjs/operators';
+import { catchError, of, take } from 'rxjs';
 import { AdminCategory, AdminCategoryEditorMode, AdminCategoryListFilters } from '../models/admin-category.model';
 import { AdminCategoriesFormFactory } from '../services/admin-categories-form.factory';
 import { ADMIN_CATEGORIES_GATEWAY } from '../services/admin-categories-gateway.token';
@@ -135,6 +135,7 @@ export class AdminCategoriesFacade {
   readonly editorMode = signal<AdminCategoryEditorMode>('create');
   readonly dirty = signal(false);
   readonly slugTaken = signal(false);
+  readonly slugCheckError = signal(false);
   private savedSnapshot: string | null = null;
   private draftStorageKey: string | null = null;
 
@@ -305,15 +306,26 @@ export class AdminCategoriesFacade {
     const draft = this.draft();
     if (!draft || !draft.slug) {
       this.slugTaken.set(false);
+      this.slugCheckError.set(false);
       return;
     }
-    this.gateway.isSlugTaken(draft.slug, this.editorMode() === 'edit' ? draft.id : null).pipe(take(1))
-      .subscribe(taken => this.slugTaken.set(taken));
+    this.gateway.isSlugTaken(draft.slug, this.editorMode() === 'edit' ? draft.id : null).pipe(
+      take(1),
+      catchError(() => {
+        this.slugCheckError.set(true);
+        return of(true);
+      })
+    ).subscribe(taken => {
+      this.slugTaken.set(taken);
+      if (!taken) {
+        this.slugCheckError.set(false);
+      }
+    });
   }
 
   saveDraft(publish: boolean): void {
     const draft = this.draft();
-    if (!draft || this.slugTaken()) return;
+    if (!draft || this.slugTaken() || this.slugCheckError()) return;
 
     const toSave: AdminCategory = { ...draft, status: publish ? 'published' : 'draft', updatedAt: new Date().toISOString() };
     const request = this.editorMode() === 'create' ? this.gateway.createCategory(toSave) : this.gateway.updateCategory(toSave);

src/app/features/admin/categories/pages/admin-category-editor-page.component.ts

@@ -9,7 +9,7 @@ import { LanguageService } from '../../../../services/language.service';
   selector: 'app-admin-category-editor-page',
   standalone: true,
   imports: [AdminCategoryFormComponent, TranslatePipe],
-  template: `@if (facade.draft(); as draft) {<main class="editor-page"><header><h1>{{ title() | translate }}</h1></header><app-admin-category-form [category]="draft" [parentOptions]="parentOptions()" [breadcrumb]="facade.breadcrumbFor(draft.parentId)" [children]="facade.childrenOf(draft.id)" [slugTaken]="facade.slugTaken()" [locales]="facade.supportedLocales()" [mode]="facade.editorMode()" [health]="facade.health(draft)" (categoryChange)="facade.updateDraft($event)" (saveDraft)="save(false)" (publish)="save(true)" /></main>} @else {<main class="editor-page"><p>{{ 'common.loading' | translate }}</p></main>}`,
+  template: `@if (facade.draft(); as draft) {<main class="editor-page"><header><h1>{{ title() | translate }}</h1></header><app-admin-category-form [category]="draft" [parentOptions]="parentOptions()" [breadcrumb]="facade.breadcrumbFor(draft.parentId)" [children]="facade.childrenOf(draft.id)" [slugTaken]="facade.slugTaken()" [slugCheckError]="facade.slugCheckError()" [locales]="facade.supportedLocales()" [mode]="facade.editorMode()" [health]="facade.health(draft)" (categoryChange)="facade.updateDraft($event)" (saveDraft)="save(false)" (publish)="save(true)" /></main>} @else {<main class="editor-page"><p>{{ 'common.loading' | translate }}</p></main>}`,
   styles: [`.editor-page { max-width: 1120px; margin: 0 auto; padding: 24px; display: grid; gap: 16px; } .editor-page h1, .editor-page p { margin: 0; }`],
   changeDetection: ChangeDetectionStrategy.OnPush
 })

src/app/features/admin/categories/services/admin-categories-api.gateway.ts

@@ -59,8 +59,7 @@ export class AdminCategoriesApiGateway implements AdminCategoriesGateway {
       params = params.set('excludingId', excludingId);
     }
     return this.http.get<{ taken: boolean }>(`${this.baseUrl}/slug-taken`, { params }).pipe(
-      map(response => response.taken),
-      catchError(() => of(false))
+      map(response => response.taken)
     );
   }
 }