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/watermark-image.test.ts

@@ -186,4 +186,153 @@ describe("watermark-image", () => {
 
     expect(res.statusCode).toBe(400);
   });
+
+  // ── Branch coverage: lines 44-48 (multipart parse error) ──────────
+
+  it("returns 400 for invalid Zod settings (scale out of range)", async () => {
+    const { body, contentType } = createMultipartPayload([
+      { name: "file", filename: "main.png", contentType: "image/png", content: PNG },
+      { name: "watermark", filename: "wm.png", contentType: "image/png", content: SMALL_PNG },
+      { name: "settings", content: JSON.stringify({ scale: 200 }) },
+    ]);
+
+    const res = await app.inject({
+      method: "POST",
+      url: "/api/v1/tools/watermark-image",
+      headers: { authorization: `Bearer ${adminToken}`, "content-type": contentType },
+      body,
+    });
+
+    expect(res.statusCode).toBe(400);
+    const json = JSON.parse(res.body);
+    expect(json.error).toContain("Invalid settings");
+  });
+
+  // ── Branch coverage: lines 164-168 (processing failure) ───────────
+
+  it("returns 422 when processing fails on corrupted main image", async () => {
+    // A buffer that passes multipart parsing but fails Sharp processing
+    const corruptedBuffer = Buffer.alloc(100, 0xff);
+    const { body, contentType } = createMultipartPayload([
+      { name: "file", filename: "main.png", contentType: "image/png", content: corruptedBuffer },
+      { name: "watermark", filename: "wm.png", contentType: "image/png", content: SMALL_PNG },
+      { name: "settings", content: JSON.stringify({}) },
+    ]);
+
+    const res = await app.inject({
+      method: "POST",
+      url: "/api/v1/tools/watermark-image",
+      headers: { authorization: `Bearer ${adminToken}`, "content-type": contentType },
+      body,
+    });
+
+    expect(res.statusCode).toBe(422);
+    const json = JSON.parse(res.body);
+    expect(json.error).toContain("Processing failed");
+  });
+
+  // ── HEIC input handling ───────────────────────────────────────────
+
+  it("processes HEIC main image", async () => {
+    const HEIC = readFileSync(join(FIXTURES, "test-200x150.heic"));
+    const { body, contentType } = createMultipartPayload([
+      { name: "file", filename: "photo.heic", contentType: "image/heic", content: HEIC },
+      { name: "watermark", filename: "wm.png", contentType: "image/png", content: SMALL_PNG },
+      { name: "settings", content: JSON.stringify({}) },
+    ]);
+
+    const res = await app.inject({
+      method: "POST",
+      url: "/api/v1/tools/watermark-image",
+      headers: { authorization: `Bearer ${adminToken}`, "content-type": contentType },
+      body,
+    });
+
+    expect(res.statusCode).toBe(200);
+    const json = JSON.parse(res.body);
+    expect(json.downloadUrl).toBeDefined();
+    expect(json.processedSize).toBeGreaterThan(0);
+  });
+
+  // ── Full opacity watermark (opacity=100 skips opacity mask) ───────
+
+  it("applies watermark at full opacity (100)", async () => {
+    const { body, contentType } = createMultipartPayload([
+      { name: "file", filename: "main.png", contentType: "image/png", content: PNG },
+      { name: "watermark", filename: "wm.png", contentType: "image/png", content: SMALL_PNG },
+      { name: "settings", content: JSON.stringify({ opacity: 100, scale: 25 }) },
+    ]);
+
+    const res = await app.inject({
+      method: "POST",
+      url: "/api/v1/tools/watermark-image",
+      headers: { authorization: `Bearer ${adminToken}`, "content-type": contentType },
+      body,
+    });
+
+    expect(res.statusCode).toBe(200);
+    const json = JSON.parse(res.body);
+    expect(json.downloadUrl).toBeDefined();
+  });
+
+  // ── Stress: large file ────────────────────────────────────────────
+
+  it("processes stress-large.jpg as main image", async () => {
+    const LARGE = readFileSync(join(FIXTURES, "content", "stress-large.jpg"));
+    const { body, contentType } = createMultipartPayload([
+      { name: "file", filename: "large.jpg", contentType: "image/jpeg", content: LARGE },
+      { name: "watermark", filename: "wm.jpg", contentType: "image/jpeg", content: JPG },
+      { name: "settings", content: JSON.stringify({ scale: 10 }) },
+    ]);
+
+    const res = await app.inject({
+      method: "POST",
+      url: "/api/v1/tools/watermark-image",
+      headers: { authorization: `Bearer ${adminToken}`, "content-type": contentType },
+      body,
+    });
+
+    expect(res.statusCode).toBe(200);
+    const json = JSON.parse(res.body);
+    expect(json.processedSize).toBeGreaterThan(0);
+  });
+
+  // ── Tiny main image with larger watermark ───────────────────────
+
+  it("handles small main image with watermark", async () => {
+    const { body, contentType } = createMultipartPayload([
+      { name: "file", filename: "main.png", contentType: "image/png", content: PNG },
+      { name: "watermark", filename: "wm.jpg", contentType: "image/jpeg", content: JPG },
+      { name: "settings", content: JSON.stringify({ scale: 1 }) },
+    ]);
+
+    const res = await app.inject({
+      method: "POST",
+      url: "/api/v1/tools/watermark-image",
+      headers: { authorization: `Bearer ${adminToken}`, "content-type": contentType },
+      body,
+    });
+
+    expect(res.statusCode).toBe(200);
+  });
+
+  // ── No settings field (defaults applied) ──────────────────────────
+
+  it("works when no settings field is provided at all", async () => {
+    const { body, contentType } = createMultipartPayload([
+      { name: "file", filename: "main.png", contentType: "image/png", content: PNG },
+      { name: "watermark", filename: "wm.png", contentType: "image/png", content: SMALL_PNG },
+    ]);
+
+    const res = await app.inject({
+      method: "POST",
+      url: "/api/v1/tools/watermark-image",
+      headers: { authorization: `Bearer ${adminToken}`, "content-type": contentType },
+      body,
+    });
+
+    expect(res.statusCode).toBe(200);
+    const json = JSON.parse(res.body);
+    expect(json.downloadUrl).toBeDefined();
+  });
 });