feat(FontStore): add fetchAllPagesTo for parallel batch page loading

src/entities/Font/model/store/fontStore/fontStore.svelte.spec.ts

@@ -561,4 +561,67 @@ describe('FontStore', () => {
             store.destroy();
         });
     });
+
+    describe('fetchAllPagesTo', () => {
+        beforeEach(() => {
+            fetch.mockReset();
+            queryClient.clear();
+        });
+
+        it('fetches all missing pages in parallel up to targetIndex', async () => {
+            // First page already loaded (offset 0, limit 10, total 50)
+            const firstFonts = generateMockFonts(10);
+            fetch.mockResolvedValueOnce(makeResponse(firstFonts, { total: 50, limit: 10, offset: 0 }));
+            const store = makeStore();
+            await store.refetch();
+            flushSync();
+
+            expect(store.fonts).toHaveLength(10);
+
+            // Mock remaining pages
+            for (let offset = 10; offset < 50; offset += 10) {
+                fetch.mockResolvedValueOnce(
+                    makeResponse(generateMockFonts(10), { total: 50, limit: 10, offset }),
+                );
+            }
+
+            await store.fetchAllPagesTo(40);
+            flushSync();
+
+            expect(store.fonts).toHaveLength(50);
+        });
+
+        it('skips pages that fail and still merges successful ones', async () => {
+            const firstFonts = generateMockFonts(10);
+            fetch.mockResolvedValueOnce(makeResponse(firstFonts, { total: 30, limit: 10, offset: 0 }));
+            const store = makeStore();
+            await store.refetch();
+            flushSync();
+
+            // offset=10 fails, offset=20 succeeds
+            fetch.mockRejectedValueOnce(new Error('network error'));
+            fetch.mockResolvedValueOnce(
+                makeResponse(generateMockFonts(10), { total: 30, limit: 10, offset: 20 }),
+            );
+
+            await store.fetchAllPagesTo(25);
+            flushSync();
+
+            // Page at offset=20 merged, page at offset=10 missing — 20 total
+            expect(store.fonts).toHaveLength(20);
+        });
+
+        it('is a no-op when target is within already-loaded data', async () => {
+            const firstFonts = generateMockFonts(10);
+            fetch.mockResolvedValueOnce(makeResponse(firstFonts, { total: 50, limit: 10, offset: 0 }));
+            const store = makeStore();
+            await store.refetch();
+            flushSync();
+
+            const callsBefore = fetch.mock.calls.length;
+            await store.fetchAllPagesTo(5);
+
+            expect(fetch.mock.calls.length).toBe(callsBefore);
+        });
+    });
 });

src/entities/Font/model/store/fontStore/fontStore.svelte.ts

@@ -242,6 +242,80 @@ export class FontStore {
     async nextPage(): Promise<void> {
         await this.#observer.fetchNextPage();
     }
+
+    #isCatchingUp = false;
+    #inFlightOffsets = new Set<number>();
+
+    /**
+     * Fetch all pages between the current loaded count and targetIndex in parallel.
+     * Pages are merged into the cache as they arrive (sorted by offset).
+     * Failed pages are silently skipped — normal scroll will re-fetch them on demand.
+     */
+    async fetchAllPagesTo(targetIndex: number): Promise<void> {
+        if (this.#isCatchingUp) {
+            return;
+        }
+
+        const pageSize = typeof this.#params.limit === 'number' ? this.#params.limit : 50;
+        const key = this.buildQueryKey(this.#params);
+        const existing = this.#qc.getQueryData<InfiniteData<ProxyFontsResponse, PageParam>>(key);
+
+        if (!existing) {
+            return;
+        }
+
+        const loadedOffsets = new Set(existing.pageParams.map(p => p.offset));
+
+        // Collect offsets for all missing and not-in-flight pages
+        const missingOffsets: number[] = [];
+        for (let offset = 0; offset <= targetIndex; offset += pageSize) {
+            if (!loadedOffsets.has(offset) && !this.#inFlightOffsets.has(offset)) {
+                missingOffsets.push(offset);
+            }
+        }
+
+        if (missingOffsets.length === 0) {
+            return;
+        }
+
+        this.#isCatchingUp = true;
+
+        // Sorted merge buffer — flush in offset order as pages arrive
+        const buffer = new Map<number, ProxyFontsResponse>();
+        const failed = new Set<number>();
+        let nextFlushOffset = (existing.pageParams.at(-1)?.offset ?? -pageSize) + pageSize;
+
+        const flush = () => {
+            while (buffer.has(nextFlushOffset) || failed.has(nextFlushOffset)) {
+                if (buffer.has(nextFlushOffset)) {
+                    this.#appendPageToCache(buffer.get(nextFlushOffset)!);
+                    buffer.delete(nextFlushOffset);
+                }
+                failed.delete(nextFlushOffset);
+                nextFlushOffset += pageSize;
+            }
+        };
+
+        try {
+            await Promise.allSettled(
+                missingOffsets.map(async offset => {
+                    this.#inFlightOffsets.add(offset);
+                    try {
+                        const page = await this.fetchPage({ ...this.#params, offset });
+                        buffer.set(offset, page);
+                    } catch {
+                        failed.add(offset);
+                    } finally {
+                        this.#inFlightOffsets.delete(offset);
+                    }
+                    flush();
+                }),
+            );
+        } finally {
+            this.#isCatchingUp = false;
+        }
+    }
+
     /**
      * Backward pagination (no-op: infinite scroll accumulates forward only)
      */
@@ -289,6 +363,34 @@ export class FontStore {
         return this.fonts.filter(f => f.category === 'monospace');
     }
 
+    /**
+     * Merge a single page into the InfiniteQuery cache in offset order.
+     * Called by fetchAllPagesTo as each parallel fetch resolves.
+     */
+    #appendPageToCache(page: ProxyFontsResponse): void {
+        const key = this.buildQueryKey(this.#params);
+        const existing = this.#qc.getQueryData<InfiniteData<ProxyFontsResponse, PageParam>>(key);
+        if (!existing) {
+            return;
+        }
+
+        // Guard against duplicates
+        const loadedOffsets = new Set(existing.pageParams.map(p => p.offset));
+        if (loadedOffsets.has(page.offset)) {
+            return;
+        }
+
+        const allPages = [...existing.pages, page].sort((a, b) => a.offset - b.offset);
+        const allParams = [...existing.pageParams, { offset: page.offset }].sort(
+            (a, b) => a.offset - b.offset,
+        );
+
+        this.#qc.setQueryData<InfiniteData<ProxyFontsResponse, PageParam>>(key, {
+            pages: allPages,
+            pageParams: allParams,
+        });
+    }
+
     private buildQueryKey(params: FontStoreParams): readonly unknown[] {
         const filtered: Record<string, any> = {};