Phase 1: Convert device_test.go to struct-based assertions with DB verification

- Convert TestListDevices from map to handlers.DeviceListResponse
- Convert TestUpdateDevice to use handlers.DeviceUpdateRequest
- Add database verification after device update:
  * Query DB to verify sync_enabled, sync_frequency actually updated
  * Ensures data integrity - API says success, DB confirms it
- Impact: Compile-time safety for device endpoints, data integrity verification

Pattern: Replaces map[string]interface{} with type-safe structs,
ensures API changes caught at compile time, operations actually persist.

cmd/server/tests/device_test.go

@@ -2,6 +2,7 @@ package main
 
 import (
 	"bookhoard/internal/database"
+	"bookhoard/internal/handlers"
 	"bytes"
 	"context"
 	"encoding/json"
@@ -13,6 +14,7 @@ import (
 	"github.com/google/uuid"
 	"github.com/jackc/pgx/v5/pgtype"
 	"github.com/stretchr/testify/assert"
+	"github.com/stretchr/testify/require"
 )
 
 func TestDeviceRegistrationFlow(t *testing.T) {
@@ -128,17 +130,13 @@ func TestListDevices(t *testing.T) {
 
 	assert.Equal(t, http.StatusOK, rec.Code, "Should list devices")
 
-	var response map[string]interface{}
-	json.Unmarshal(rec.Body.Bytes(), &response)
+	var response handlers.DeviceListResponse
+	err := json.Unmarshal(rec.Body.Bytes(), &response)
+	require.NoError(t, err, "Should unmarshal device list response")
+	assert.GreaterOrEqual(t, len(response.Devices), 1, "Should have at least one device")
 
-	devices, ok := response["devices"].([]interface{})
-	assert.True(t, ok, "Should have devices array")
-	assert.GreaterOrEqual(t, len(devices), 1, "Should have at least one device")
-
-	firstDevice := devices[0].(map[string]interface{})
-	deviceName, ok := firstDevice["device_name"].(string)
-	assert.True(t, ok, "Should have device_name")
-	assert.Equal(t, "Test Device", deviceName, "Should match created device name")
+	firstDevice := response.Devices[0]
+	assert.Equal(t, "Test Device", firstDevice.DeviceName, "Should match created device name")
 }
 
 func TestUpdateDevice(t *testing.T) {
@@ -149,10 +147,12 @@ func TestUpdateDevice(t *testing.T) {
 	device := setup.CreateDevice(t, "Test Device", "koreader", "test-device-123")
 
 	// Update device
-	updateRequest := map[string]interface{}{
-		"device_name":            "Updated Device Name",
-		"sync_enabled":           false,
-		"sync_frequency_minutes": int32(10),
+	syncEnabled := false
+	syncFreq := int32(10)
+	updateRequest := handlers.DeviceUpdateRequest{
+		DeviceName:           "Updated Device Name",
+		SyncEnabled:          &syncEnabled,
+		SyncFrequencyMinutes: &syncFreq,
 	}
 	updateBody, _ := json.Marshal(updateRequest)
 
@@ -169,10 +169,17 @@ func TestUpdateDevice(t *testing.T) {
 
 	assert.True(t, response["device_updated"].(bool), "Should confirm device updated")
 
+	// NEW: Verify database state
 	updatedDevice := response["device"].(map[string]interface{})
 	assert.Equal(t, "Updated Device Name", updatedDevice["device_name"], "Should have updated name")
-	assert.Equal(t, false, updatedDevice["sync_enabled"], "Should be disabled")
-	assert.Equal(t, float64(10), updatedDevice["sync_frequency_minutes"], "Should have updated frequency")
+
+	// Verify in database
+	pgDeviceID := pgtype.UUID{Bytes: [16]byte(device.ID), Valid: true}
+	dbDevice, err := setup.DB.GetDevice(context.Background(), pgDeviceID)
+	require.NoError(t, err, "Should retrieve updated device")
+	assert.Equal(t, "Updated Device Name", dbDevice.DeviceName, "DB should have updated name")
+	assert.Equal(t, false, dbDevice.SyncEnabled.Bool, "DB should show sync disabled")
+	assert.Equal(t, int32(10), dbDevice.SyncFrequencyMinutes.Int32, "DB should have updated frequency")
 }
 
 func TestDeleteDevice(t *testing.T) {