refactor(GetFonts): tighten mapManagerToParams + add coverage

Collapse the three duplicated getGroup/map/length-guard chains into a
single selectedIn helper. Drop the unnecessary `as string[]` casts —
Property<TValue extends string>.value already yields string at the call
site.

Add unit tests covering empty query, populated query, missing group,
empty group, single + multi selection, unknown group ids, and the
combined param shape.

src/features/GetFonts/lib/mapper/mapManagerToParams.test.ts

@@ -0,0 +1,127 @@
+import type { Property } from '$shared/lib';
+import {
+    describe,
+    expect,
+    it,
+} from 'vitest';
+import { createFilterManager } from '../../model/store/filterManager/filterManager.svelte';
+import { mapManagerToParams } from './mapManagerToParams';
+
+/**
+ * Build a Property with explicit selection state.
+ */
+function prop(value: string, selected = false): Property<string> {
+    return { id: value, name: value, value, selected };
+}
+
+/**
+ * Build a filter group with a known id and a list of (value, selected) entries.
+ */
+function group(id: string, props: Array<[string, boolean]>) {
+    return {
+        id,
+        label: id,
+        properties: props.map(([value, selected]) => prop(value, selected)),
+    };
+}
+
+describe('mapManagerToParams', () => {
+    describe('search query', () => {
+        it('omits q when query is empty', () => {
+            const manager = createFilterManager({ queryValue: '', groups: [] });
+            expect(mapManagerToParams(manager).q).toBeUndefined();
+        });
+
+        it('passes the debounced query through as q', () => {
+            // Constructor seeds both immediate and debounced synchronously.
+            const manager = createFilterManager({ queryValue: 'roboto', groups: [] });
+            expect(mapManagerToParams(manager).q).toBe('roboto');
+        });
+    });
+
+    describe('group selections', () => {
+        it('omits a group entirely when no group with that id exists', () => {
+            const manager = createFilterManager({ queryValue: '', groups: [] });
+            const params = mapManagerToParams(manager);
+            expect(params.providers).toBeUndefined();
+            expect(params.categories).toBeUndefined();
+            expect(params.subsets).toBeUndefined();
+        });
+
+        it('omits a group when it exists but has no selections', () => {
+            const manager = createFilterManager({
+                queryValue: '',
+                groups: [group('providers', [['google', false], ['fontshare', false]])],
+            });
+            expect(mapManagerToParams(manager).providers).toBeUndefined();
+        });
+
+        it('returns the selected values for a single group', () => {
+            const manager = createFilterManager({
+                queryValue: '',
+                groups: [group('providers', [['google', true], ['fontshare', false]])],
+            });
+            expect(mapManagerToParams(manager).providers).toEqual(['google']);
+        });
+
+        it('returns multiple selected values in selection order', () => {
+            const manager = createFilterManager({
+                queryValue: '',
+                groups: [
+                    group('categories', [
+                        ['serif', true],
+                        ['sans-serif', false],
+                        ['display', true],
+                        ['monospace', true],
+                    ]),
+                ],
+            });
+            expect(mapManagerToParams(manager).categories).toEqual(['serif', 'display', 'monospace']);
+        });
+
+        it('maps each of the three recognized group ids independently', () => {
+            const manager = createFilterManager({
+                queryValue: '',
+                groups: [
+                    group('providers', [['google', true]]),
+                    group('categories', [['serif', true], ['sans-serif', true]]),
+                    group('subsets', [['latin', true]]),
+                ],
+            });
+            const params = mapManagerToParams(manager);
+            expect(params.providers).toEqual(['google']);
+            expect(params.categories).toEqual(['serif', 'sans-serif']);
+            expect(params.subsets).toEqual(['latin']);
+        });
+
+        it('ignores groups whose id does not match providers/categories/subsets', () => {
+            const manager = createFilterManager({
+                queryValue: '',
+                groups: [group('weights', [['400', true], ['700', true]])],
+            });
+            const params = mapManagerToParams(manager);
+            expect(params.providers).toBeUndefined();
+            expect(params.categories).toBeUndefined();
+            expect(params.subsets).toBeUndefined();
+        });
+    });
+
+    describe('combined output', () => {
+        it('produces a complete param object when query and selections coexist', () => {
+            const manager = createFilterManager({
+                queryValue: 'inter',
+                groups: [
+                    group('providers', [['google', true]]),
+                    group('categories', [['sans-serif', true]]),
+                    group('subsets', [['latin', false]]),
+                ],
+            });
+            expect(mapManagerToParams(manager)).toEqual({
+                q: 'inter',
+                providers: ['google'],
+                categories: ['sans-serif'],
+                subsets: undefined,
+            });
+        });
+    });
+});

src/features/GetFonts/lib/mapper/mapManagerToParams.ts

@@ -29,25 +29,20 @@ import type { FilterManager } from '../../model';
  * ```
  */
 export function mapManagerToParams(manager: FilterManager): Partial<ProxyFontsParams> {
-    const providers = manager.getGroup('providers')?.instance.selectedProperties.map(p => p.value);
-    const categories = manager.getGroup('categories')?.instance.selectedProperties.map(p => p.value);
-    const subsets = manager.getGroup('subsets')?.instance.selectedProperties.map(p => p.value);
+    /**
+     * Return the list of selected values for a group, or undefined when
+     * the group is missing or has no selection — matches the API's
+     * "omit empty filters" contract.
+     */
+    const selectedIn = (id: string): string[] | undefined => {
+        const values = manager.getGroup(id)?.instance.selectedProperties.map(p => p.value);
+        return values && values.length > 0 ? values : undefined;
+    };
 
     return {
-        // Search query (debounced)
         q: manager.debouncedQueryValue || undefined,
-
-        // NEW: Support arrays - send all selected values
-        providers: providers && providers.length > 0
-            ? providers as string[]
-            : undefined,
-
-        categories: categories && categories.length > 0
-            ? categories as string[]
-            : undefined,
-
-        subsets: subsets && subsets.length > 0
-            ? subsets as string[]
-            : undefined,
+        providers: selectedIn('providers'),
+        categories: selectedIn('categories'),
+        subsets: selectedIn('subsets'),
     };
 }