docs(22): add Task 4 for parameters API tests

- Add test to verify parameters field is passed to Replicate/fal.ai APIs
- Tests that UI settings (seed, steps, guidance) reach provider APIs
- Tests that dynamicInputs override parameters when both have same key

.planning/phases/22-generate-node-dynamic-input-tests/22-01-PLAN.md

@@ -24,11 +24,13 @@ Output: Complete test coverage for dynamic input flows in GenerateImageNode, Gen
 **Existing test files to extend:**
 @src/components/__tests__/GenerateImageNode.test.tsx
 @src/components/__tests__/GenerateVideoNode.test.tsx
+@src/app/api/generate/__tests__/route.test.ts
 
-**Component being tested:**
+**Components/routes being tested:**
 @src/components/nodes/GenerateImageNode.tsx (lines 464-580 for dynamic handles)
 @src/components/nodes/GenerateVideoNode.tsx
 @src/components/nodes/ModelParameters.tsx
+@src/app/api/generate/route.ts (lines 342-377 for parameters handling)
 
 **Prior Phase Summary (provides test patterns):**
 @.planning/phases/17-component-tests/17-03-SUMMARY.md
@@ -167,6 +169,63 @@ inputSchema: [
   <done>GenerateVideoNode tests match GenerateImageNode coverage for dynamic handles</done>
 </task>
 
+<task type="auto">
+  <name>Task 4: Add API route tests for parameters field</name>
+  <files>src/app/api/generate/__tests__/route.test.ts</files>
+  <action>
+Add tests to verify the `parameters` field (UI settings) is passed to provider APIs.
+
+**Replicate provider:**
+- Should pass parameters to prediction input
+- Should merge parameters with dynamicInputs (dynamicInputs take precedence)
+
+**fal.ai provider:**
+- Should pass parameters to fal.ai request body
+- Should merge parameters with dynamicInputs
+
+Test pattern:
+```typescript
+it("should pass parameters to prediction input", async () => {
+  // ... mock setup ...
+
+  const request = createMockPostRequest(
+    {
+      prompt: "Test prompt",
+      selectedModel: {
+        provider: "replicate",
+        modelId: "stability-ai/sdxl",
+        displayName: "SDXL",
+      },
+      parameters: {
+        seed: 42,
+        num_inference_steps: 30,
+        guidance_scale: 7.5,
+      },
+    },
+    { "X-Replicate-API-Key": "test-key" }
+  );
+
+  const response = await POST(request);
+
+  // Verify parameters were passed to prediction
+  const createPredictionCall = mockFetch.mock.calls[1];
+  const requestBody = JSON.parse(createPredictionCall[1].body);
+  expect(requestBody.input).toEqual(
+    expect.objectContaining({
+      seed: 42,
+      num_inference_steps: 30,
+      guidance_scale: 7.5,
+    })
+  );
+});
+```
+
+Also test that dynamicInputs override parameters when both have same key.
+  </action>
+  <verify>npm test -- src/app/api/generate/__tests__/route.test.ts --testNamePattern="parameters"</verify>
+  <done>API route tests verify parameters field is passed to Replicate and fal.ai</done>
+</task>
+
 </tasks>
 
 <verification>
@@ -174,10 +233,12 @@ Before declaring plan complete:
 - [ ] `npm test -- src/components/__tests__/ModelParameters.test.tsx` passes
 - [ ] `npm test -- src/components/__tests__/GenerateImageNode.test.tsx` passes
 - [ ] `npm test -- src/components/__tests__/GenerateVideoNode.test.tsx` passes
+- [ ] `npm test -- src/app/api/generate/__tests__/route.test.ts` passes
 - [ ] No TypeScript errors
 - [ ] Schema loading tested
 - [ ] Dynamic handle variations tested
 - [ ] Placeholder handles tested
+- [ ] Parameters passed to API tested
 </verification>
 
 <success_criteria>
@@ -186,6 +247,7 @@ Before declaring plan complete:
 - ModelParameters component fully tested
 - Dynamic input handle rendering fully tested
 - Placeholder handle behavior fully tested
+- Parameters field passed to provider APIs tested
 - Phase 22 complete
 </success_criteria>