Add comprehensive error handling for API device attachment

- Add explicit 429 rate limit handling with RATE_LIMITED error code
- Add 6 new test cases for edge scenarios:
  - 403 Forbidden handling
  - 429 Rate Limit handling
  - JSON parse error handling
  - WellNuo API failure when fetching beneficiary
  - Timeout error detection
  - MAC address uppercase normalization verification

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude <noreply@anthropic.com>

__tests__/services/api-sensor-attachment-errors.test.ts

@@ -382,5 +382,175 @@ describe('API - Sensor Attachment Error Handling', () => {
       // Token will be URL encoded in the body, so just check it contains the token
       expect(bodyString).toContain('token=');
     });
+
+    it('should handle 403 Forbidden from Legacy API', async () => {
+      // Mock successful beneficiary lookup
+      (global.fetch as jest.Mock)
+        .mockResolvedValueOnce({
+          ok: true,
+          json: async () => ({
+            id: 123,
+            firstName: 'Maria',
+            deploymentId: mockDeploymentId
+          })
+        })
+        // Mock 403 response from Legacy API
+        .mockResolvedValueOnce({
+          ok: false,
+          status: 403,
+          json: async () => ({ message: 'Access denied' })
+        });
+
+      const result = await api.attachDeviceToBeneficiary(
+        mockBeneficiaryId,
+        mockWellId,
+        mockDeviceMac
+      );
+
+      expect(result.ok).toBe(false);
+      expect(result.error?.code).toBe('UNAUTHORIZED');
+      expect(result.error?.message).toMatch(/Authentication expired/);
+      expect(result.error?.status).toBe(403);
+    });
+
+    it('should handle 429 Rate Limit from Legacy API', async () => {
+      // Mock successful beneficiary lookup
+      (global.fetch as jest.Mock)
+        .mockResolvedValueOnce({
+          ok: true,
+          json: async () => ({
+            id: 123,
+            firstName: 'Maria',
+            deploymentId: mockDeploymentId
+          })
+        })
+        // Mock 429 response from Legacy API
+        .mockResolvedValueOnce({
+          ok: false,
+          status: 429,
+          json: async () => ({ message: 'Too many requests' })
+        });
+
+      const result = await api.attachDeviceToBeneficiary(
+        mockBeneficiaryId,
+        mockWellId,
+        mockDeviceMac
+      );
+
+      expect(result.ok).toBe(false);
+      expect(result.error?.code).toBe('RATE_LIMITED');
+      expect(result.error?.message).toContain('Too many requests');
+      expect(result.error?.status).toBe(429);
+    });
+
+    it('should handle JSON parse errors gracefully', async () => {
+      // Mock successful beneficiary lookup
+      (global.fetch as jest.Mock)
+        .mockResolvedValueOnce({
+          ok: true,
+          json: async () => ({
+            id: 123,
+            firstName: 'Maria',
+            deploymentId: mockDeploymentId
+          })
+        })
+        // Mock response with invalid JSON
+        .mockResolvedValueOnce({
+          ok: true,
+          status: 200,
+          json: async () => { throw new SyntaxError('Unexpected token'); }
+        });
+
+      const result = await api.attachDeviceToBeneficiary(
+        mockBeneficiaryId,
+        mockWellId,
+        mockDeviceMac
+      );
+
+      expect(result.ok).toBe(false);
+      expect(result.error?.code).toBe('EXCEPTION');
+    });
+
+    it('should handle WellNuo API failure when getting beneficiary', async () => {
+      // Mock failed beneficiary lookup from WellNuo API
+      (global.fetch as jest.Mock)
+        .mockResolvedValueOnce({
+          ok: false,
+          status: 500,
+          json: async () => ({ message: 'Internal error' })
+        });
+
+      const result = await api.attachDeviceToBeneficiary(
+        mockBeneficiaryId,
+        mockWellId,
+        mockDeviceMac
+      );
+
+      expect(result.ok).toBe(false);
+      expect(result.error?.code).toBe('DEPLOYMENT_NOT_FOUND');
+      expect(result.error?.status).toBe(404);
+    });
+
+    it('should handle timeout errors', async () => {
+      // Mock successful beneficiary lookup
+      (global.fetch as jest.Mock)
+        .mockResolvedValueOnce({
+          ok: true,
+          json: async () => ({
+            id: 123,
+            firstName: 'Maria',
+            deploymentId: mockDeploymentId
+          })
+        })
+        // Mock timeout error
+        .mockRejectedValueOnce(
+          new Error('network request failed: timeout')
+        );
+
+      const result = await api.attachDeviceToBeneficiary(
+        mockBeneficiaryId,
+        mockWellId,
+        mockDeviceMac
+      );
+
+      expect(result.ok).toBe(false);
+      expect(result.error?.code).toBe('NETWORK_ERROR');
+      expect(result.error?.message).toContain('No internet connection');
+    });
+
+    it('should uppercase device MAC address in request', async () => {
+      const lowercaseMac = '142b2f81a14c';
+
+      // Mock successful beneficiary lookup
+      (global.fetch as jest.Mock)
+        .mockResolvedValueOnce({
+          ok: true,
+          json: async () => ({
+            id: 123,
+            firstName: 'Maria',
+            deploymentId: mockDeploymentId
+          })
+        })
+        // Mock successful device_form response
+        .mockResolvedValueOnce({
+          ok: true,
+          status: 200,
+          json: async () => ({
+            status: '200 OK'
+          })
+        });
+
+      await api.attachDeviceToBeneficiary(
+        mockBeneficiaryId,
+        mockWellId,
+        lowercaseMac
+      );
+
+      // Verify MAC is uppercased
+      const secondCall = (global.fetch as jest.Mock).mock.calls[1];
+      const bodyString = secondCall[1].body;
+      expect(bodyString).toContain(`device_mac=${lowercaseMac.toUpperCase()}`);
+      expect(bodyString).not.toContain(`device_mac=${lowercaseMac}`);
+    });
   });
 });

services/api.ts

@@ -2048,6 +2048,9 @@ class ApiService {
         } else if (attachResponse.status === 404) {
           errorMessage = 'Sensor or deployment not found.';
           errorCode = 'NOT_FOUND';
+        } else if (attachResponse.status === 429) {
+          errorMessage = 'Too many requests. Please wait a moment and try again.';
+          errorCode = 'RATE_LIMITED';
         } else if (attachResponse.status === 500) {
           errorMessage = 'Server error. Please try again later.';
           errorCode = 'SERVER_ERROR';