test(api validation): check query validation boundaries for ?layout= parameter (Variation 4) (JhaSourav07#1957)

## Description

Fixes JhaSourav07#1456

This PR adds query validation boundaries for the `?layout=` parameter in
`streakParamsSchema` to return a 400 Bad Request if an unsupported value
is supplied. It also adds unit tests and integration tests.

## Pillar

- [ ] 🎨 Pillar 1 — New Theme Design
- [ ] 📐 Pillar 2 — Geometric SVG Improvement
- [ ] 🕐 Pillar 3 — Timezone Logic Optimization
- [x] 🛠️ Other (Bug fix, refactoring, docs)

## Visual Preview

None (Validation changes)

## Checklist before requesting a review:

- [x] I have read the `CONTRIBUTING.md` file.
- [x] I have tested these changes locally.
- [x] I have run `npm run format` and `npm run lint` locally and
resolved all errors.
- [x] My commits follow the Conventional Commits format.
- [x] I have updated `README.md` if I added a new theme or URL
parameter.
- [x] I have started the repo.
- [x] I have made sure that i have only one commit to merge in this PR.
- [x] The SVG output matches the CommitPulse "premium quality" aesthetic
standard.

Author: JhaSourav07

app/api/streak/route.test.ts

@@ -149,7 +149,21 @@ describe('GET /api/streak', () => {
       expect(response.status).toBe(400);
       const body = await response.json();
       expect(body.error).toBe('Invalid parameters');
-      expect(body.details).not.toBeNull();
+    });
+
+    it('returns 400 Bad Request when ?layout= is set to an unsupported format (Variation 4)', async () => {
+      const response = await GET(
+        makeRequest({
+          user: 'octocat',
+          layout: 'unsupported_layout',
+        })
+      );
+
+      expect(response.status).toBe(400);
+      const body = await response.json();
+      expect(body.details.fieldErrors.layout[0]).toContain(
+        'Invalid layout format. Supported values: default, compact, full.'
+      );
     });
 
     it('returns 400 when the user parameter is missing', async () => {

lib/validations.test.ts

@@ -1182,3 +1182,71 @@ describe('streakParamsSchema — date query validation boundaries (Variation 4)'
     expect(result.success).toBe(true);
   });
 });
+
+/* ==========================================================================
+ * LAYOUT PARAMETER — QUERY VALIDATION BOUNDARIES (VARIATION 4)
+ * ========================================================================== */
+
+describe('streakParamsSchema — layout query validation boundaries (Variation 4)', () => {
+  it('rejects unsupported_layout and marks the parse as failed', () => {
+    const result = streakParamsSchema.safeParse({
+      user: 'octocat',
+      layout: 'unsupported_layout',
+    });
+
+    expect(result.success).toBe(false);
+  });
+
+  it('surfaces a meaningful error message for unsupported_layout', () => {
+    const result = streakParamsSchema.safeParse({
+      user: 'octocat',
+      layout: 'unsupported_layout',
+    });
+
+    expect(result.success).toBe(false);
+    if (!result.success) {
+      const messages = result.error.issues.map((i) => i.message).join(' ');
+      expect(messages).toContain(
+        'Invalid layout format. Supported values: default, compact, full.'
+      );
+    }
+  });
+
+  it('accepts "default" as a valid layout value', () => {
+    const result = streakParamsSchema.safeParse({
+      user: 'octocat',
+      layout: 'default',
+    });
+
+    expect(result.success).toBe(true);
+  });
+
+  it('accepts "compact" as a valid layout value', () => {
+    const result = streakParamsSchema.safeParse({
+      user: 'octocat',
+      layout: 'compact',
+    });
+
+    expect(result.success).toBe(true);
+  });
+
+  it('accepts "full" as a valid layout value', () => {
+    const result = streakParamsSchema.safeParse({
+      user: 'octocat',
+      layout: 'full',
+    });
+
+    expect(result.success).toBe(true);
+  });
+
+  it('treats omitted layout as undefined (no validation error)', () => {
+    const result = streakParamsSchema.safeParse({
+      user: 'octocat',
+    });
+
+    expect(result.success).toBe(true);
+    if (result.success) {
+      expect(result.data.layout).toBeUndefined();
+    }
+  });
+});