test: major coverage expansion — 18 new test files, ~830 new tests

Unit tests: 1354 → 1781 (+427)
- 11 new AI bridge module tests (packages/ai/ from 2/13 → 13/13 files)
- files-page-store (0% → full), pdf-to-image-store, features-store expanded
- saturation and edit-metadata image-engine operations
- analytics route, features route, web analytics lib, api-extended

Integration tests: ~2070 → 2320 (+250)
- 31 integration files expanded with branch-coverage-targeted tests
- progress.ts SSE endpoints (28% → comprehensive, +18 tests)
- gif-tools all modes (+18), pdf-to-image format variants (+13)
- Cross-format matrix expanded to 17 tools × 17 formats (467 tests)
- Adversarial: concurrent, memory pressure, unicode filenames, pipeline limits

E2E-Docker: +1020 lines across 6 spec files
- Info, colors, sharpening, base64, QR read, JXL/ICO/SVG formats
- Strip-metadata, image-enhancement, content-aware-resize expanded
- Batch pipelines, multi-format batches, HEIC input coverage

tests/integration/bulk-rename.test.ts

@@ -347,6 +347,95 @@ describe("Bulk Rename", () => {
     expect(filenames).toContain("output-3.webp");
   });
 
+  it("skips empty file buffers (zero-length files)", async () => {
+    const { body, contentType } = createMultipartPayload([
+      { name: "file", filename: "real.png", contentType: "image/png", content: PNG },
+      { name: "file", filename: "empty.png", contentType: "image/png", content: Buffer.alloc(0) },
+      { name: "settings", content: JSON.stringify({ pattern: "item-{{index}}" }) },
+    ]);
+
+    const res = await app.inject({
+      method: "POST",
+      url: "/api/v1/tools/bulk-rename",
+      headers: {
+        authorization: `Bearer ${adminToken}`,
+        "content-type": contentType,
+      },
+      body,
+    });
+
+    expect(res.statusCode).toBe(200);
+    const filenames = zipEntryNames(res.rawPayload);
+    // Empty file is skipped, so only 1 file should be in the ZIP
+    expect(filenames).toHaveLength(1);
+    expect(filenames).toContain("item-1.png");
+  });
+
+  it("returns 400 for invalid settings JSON", async () => {
+    const { body, contentType } = createMultipartPayload([
+      { name: "file", filename: "test.png", contentType: "image/png", content: PNG },
+      { name: "settings", content: "not-json{{{" },
+    ]);
+
+    const res = await app.inject({
+      method: "POST",
+      url: "/api/v1/tools/bulk-rename",
+      headers: {
+        authorization: `Bearer ${adminToken}`,
+        "content-type": contentType,
+      },
+      body,
+    });
+
+    expect(res.statusCode).toBe(400);
+    const result = JSON.parse(res.body);
+    expect(result.error).toMatch(/json/i);
+  });
+
+  it("returns 400 for invalid settings values", async () => {
+    const { body, contentType } = createMultipartPayload([
+      { name: "file", filename: "test.png", contentType: "image/png", content: PNG },
+      { name: "settings", content: JSON.stringify({ pattern: "", startIndex: -1 }) },
+    ]);
+
+    const res = await app.inject({
+      method: "POST",
+      url: "/api/v1/tools/bulk-rename",
+      headers: {
+        authorization: `Bearer ${adminToken}`,
+        "content-type": contentType,
+      },
+      body,
+    });
+
+    expect(res.statusCode).toBe(400);
+    const result = JSON.parse(res.body);
+    expect(result.error).toMatch(/invalid settings/i);
+  });
+
+  it("handles files with no extension", async () => {
+    const { body, contentType } = createMultipartPayload([
+      { name: "file", filename: "noext", contentType: "application/octet-stream", content: PNG },
+      { name: "settings", content: JSON.stringify({ pattern: "renamed-{{index}}" }) },
+    ]);
+
+    const res = await app.inject({
+      method: "POST",
+      url: "/api/v1/tools/bulk-rename",
+      headers: {
+        authorization: `Bearer ${adminToken}`,
+        "content-type": contentType,
+      },
+      body,
+    });
+
+    expect(res.statusCode).toBe(200);
+    const filenames = zipEntryNames(res.rawPayload);
+    expect(filenames).toHaveLength(1);
+    // No extension to preserve
+    expect(filenames[0]).toBe("renamed-1");
+  });
+
   it("handles startIndex of 0", async () => {
     const { body, contentType } = createMultipartPayload([
       { name: "file", filename: "x.png", contentType: "image/png", content: PNG },