diff --git a/docs/autoflow/04-architecture/api/api-spec.md b/docs/autoflow/04-architecture/api/api-spec.md
index 0bdcece..ee0e47d 100644
--- a/docs/autoflow/04-architecture/api/api-spec.md
+++ b/docs/autoflow/04-architecture/api/api-spec.md
@@ -47,6 +47,46 @@
   }
   ```
 
+### POST `/api/pairing/exchange`（agent → 雲端；public、不走 AuthMiddleware）
+
+> 呼叫方是 **local agent**（不是瀏覽器前端）：agent 拿 Pairing Token 換 Session Token 時本身還沒有登入身份，故此端點註冊在 engine 層級、不套 auth。行為主文件見 `../visiona-agent-tdd.md` §4.3 / §7.1；本節記錄 contract 形狀與 WP-0（ADR-018）擴充。
+
+- **Request**（實作對齊 `visionA-backend/internal/api/pairing.go` `PairingExchangeRequest` 與 agent 端 `internal/tunnel/pairing.go` `exchangeRequest`）：
+  ```json
+  {
+    "pairing_token": "vAc_<32 hex>",
+    "devices": [
+      {
+        "serial_number": "0x1A2B3C4D",
+        "device_type": "KL520",
+        "firmware": "1.2.3"
+      }
+    ]
+  }
+  ```
+  - `pairing_token`（**required**）：一次性 Pairing Token。
+  - `devices`（**optional**、WP-0 / migration 0004 新增）：agent 在 exchange 前撈本地 `GET /api/devices` 上報的實體 USB 清單（含 Kneron kn_number 序號）。陣列因應「一 agent 多 USB」；`device_type` / `firmware` 為 optional 欄位（`omitempty`）。
+- **Response**（200，通用 envelope 的 `data`）：
+  ```json
+  {
+    "session_token": "vAs_...",
+    "account": "demo@visionA.local",
+    "relay_url": "wss://relay.visionA.cloud",
+    "expires_at": "2026-07-21T00:00:00Z"
+  }
+  ```
+- **錯誤碼**（走 `error.code`，對齊 TDD §7.1 四種 case）：`INVALID_PAIRING_TOKEN` / `PAIRING_TOKEN_EXPIRED` / `PAIRING_TOKEN_USED` / `PAIRING_TOKEN_REVOKED`。
+
+**`devices` 欄位的雲端行為（WP-0 序號地基，決策見 `../adr/adr-018-agent-device-model.md`）**：
+
+| 規則 | 行為 |
+|------|------|
+| R1（最小落地） | exchange 仍只落**一筆** device 記錄：從上報清單挑**第一顆序號可用**的裝置，把序號填進 `devices.serial_number`（agent 有帶 `device_type` 時一併填入）。多顆 USB 的完整模型（一 agent N device）屬 WP-B / migration 0005 範疇 |
+| R2（假序號） | 假序號 `0x00000000`（agent 端 pyusb fallback、無 Kneron SDK 時寫死上報）與空字串序號**視同無序號**、跳過不用 → `serial_number` 寫 NULL |
+| R4（同序號重配） | 同 owner 已存在同 serial 的未刪除 device → **復用既有 `device_id`**（只更新 `paired_at` / `updated_at`），不新建，避免撞 partial unique index `uq_devices_owner_serial_active` |
+
+**向下相容**：`devices` 欄位缺省（舊 agent、local server 未起、撈不到清單、0 顆裝置）→ 行為與舊版**完全一致**：自建一筆 `serial_number = NULL` 的 device。序號是加值資訊，配對本身不因撈不到 USB 而失敗。
+
 ### GET `/api/pairing/status`
 - 查詢當前 user 的 tunnel 連線狀態
 - Response:
diff --git a/local-agent/server/internal/device/manager.go b/local-agent/server/internal/device/manager.go
index 7a87f6d..4ceb000 100644
--- a/local-agent/server/internal/device/manager.go
+++ b/local-agent/server/internal/device/manager.go
@@ -10,21 +10,39 @@ import (
 	"visiona-agent/server/pkg/logger"
 )
 
+// fakeSerialNumber is the placeholder kn_number reported by the Python
+// bridge pyusb fallback when the Kneron SDK is unavailable (e.g. macOS
+// without the dylib). It is not a real hardware serial, so it must never be
+// used as a routing key (multiple devices could collide on it). Treated the
+// same as "no serial" (ADR-018 §2.2 / R2).
+const fakeSerialNumber = "0x00000000"
+
 type Manager struct {
-	registry       *DriverRegistry
-	sessions       map[string]*DeviceSession
-	eventBus       chan DeviceEvent
-	scriptPath     string
-	logBroadcaster *logger.Broadcaster
-	mu             sync.RWMutex
+	registry *DriverRegistry
+	sessions map[string]*DeviceSession
+	// serialToLocalID maps a device's hardware serial (Kneron kn_number,
+	// e.g. "0x1A2B3C4D") to its local synthetic session key ("kl520-0").
+	//
+	// Why it exists (ADR-018 serial routing): cloud-side requests arrive with
+	// an identifier that never matched the local sessions key (the cloud used
+	// its own DB UUID). The serial is the only identifier stable across both
+	// layers, so GetDevice does a dual lookup: sessions[id] first (backward
+	// compatible with local synthetic IDs), then serialToLocalID[id].
+	// Empty and fake ("0x00000000") serials are never indexed.
+	serialToLocalID map[string]string
+	eventBus        chan DeviceEvent
+	scriptPath      string
+	logBroadcaster  *logger.Broadcaster
+	mu              sync.RWMutex
 }
 
 func NewManager(registry *DriverRegistry, scriptPath string) *Manager {
 	return &Manager{
-		registry:   registry,
-		sessions:   make(map[string]*DeviceSession),
-		eventBus:   make(chan DeviceEvent, 100),
-		scriptPath: scriptPath,
+		registry:        registry,
+		sessions:        make(map[string]*DeviceSession),
+		serialToLocalID: make(map[string]string),
+		eventBus:        make(chan DeviceEvent, 100),
+		scriptPath:      scriptPath,
 	}
 }
 
@@ -60,6 +78,7 @@ func (m *Manager) Start() {
 		m.sessions[info.ID] = NewSession(d)
 		log.Printf("Registered Kneron device: %s (%s, type=%s)", info.Name, info.ID, info.Type)
 	}
+	m.rebuildSerialIndexLocked()
 }
 
 // Rescan re-detects connected Kneron devices. New devices are registered,
@@ -97,6 +116,8 @@ func (m *Manager) Rescan() []driver.DeviceInfo {
 		}
 	}
 
+	m.rebuildSerialIndexLocked()
+
 	// Return current list.
 	devices := make([]driver.DeviceInfo, 0, len(m.sessions))
 	for _, s := range m.sessions {
@@ -105,6 +126,31 @@ func (m *Manager) Rescan() []driver.DeviceInfo {
 	return devices
 }
 
+// rebuildSerialIndexLocked rebuilds serialToLocalID from the current
+// sessions. Caller must hold m.mu (write lock).
+//
+// Rebuilding (instead of incremental add/delete) keeps the index trivially
+// consistent with sessions across Start/Rescan, including device removal.
+// Empty serials are skipped; the fake serial "0x00000000" is skipped because
+// multiple SDK-less devices report the same value (routing would be
+// ambiguous). Real kn_numbers are unique per physical dongle; should a
+// duplicate ever appear it is logged and only one entry wins.
+func (m *Manager) rebuildSerialIndexLocked() {
+	idx := make(map[string]string, len(m.sessions))
+	for id, s := range m.sessions {
+		serial := s.Driver.Info().SerialNumber
+		if serial == "" || serial == fakeSerialNumber {
+			continue
+		}
+		if prev, dup := idx[serial]; dup {
+			log.Printf("WARNING: duplicate device serial %s (devices %s and %s); serial routing keeps one entry only", serial, prev, id)
+			continue
+		}
+		idx[serial] = id
+	}
+	m.serialToLocalID = idx
+}
+
 func (m *Manager) ListDevices() []driver.DeviceInfo {
 	m.mu.RLock()
 	defer m.mu.RUnlock()
@@ -115,14 +161,26 @@ func (m *Manager) ListDevices() []driver.DeviceInfo {
 	return devices
 }
 
+// GetDevice resolves a device session by identifier with a dual lookup
+// (ADR-018 serial routing, additive and backward compatible):
+//
+//  1. sessions[id] — the local synthetic key ("kl520-0"); every existing
+//     caller keeps working unchanged.
+//  2. serialToLocalID[id] — the hardware serial (kn_number, "0x1A2B3C4D");
+//     lets cloud-proxied requests (flash / inference / camera / connect /
+//     disconnect all converge here) address a physical dongle by serial.
 func (m *Manager) GetDevice(id string) (*DeviceSession, error) {
 	m.mu.RLock()
 	defer m.mu.RUnlock()
-	s, ok := m.sessions[id]
-	if !ok {
-		return nil, fmt.Errorf("device not found: %s", id)
+	if s, ok := m.sessions[id]; ok {
+		return s, nil
 	}
-	return s, nil
+	if localID, ok := m.serialToLocalID[id]; ok {
+		if s, ok := m.sessions[localID]; ok {
+			return s, nil
+		}
+	}
+	return nil, fmt.Errorf("device not found: %s", id)
 }
 
 func (m *Manager) Connect(id string) error {
diff --git a/local-agent/server/internal/device/manager_test.go b/local-agent/server/internal/device/manager_test.go
index 08364b7..ca6eb9b 100644
--- a/local-agent/server/internal/device/manager_test.go
+++ b/local-agent/server/internal/device/manager_test.go
@@ -11,9 +11,17 @@ type testDriver struct {
 	connected bool
 }
 
-func (d *testDriver) Info() driver.DeviceInfo                                { return d.info }
-func (d *testDriver) Connect() error                                         { d.connected = true; d.info.Status = driver.StatusConnected; return nil }
-func (d *testDriver) Disconnect() error                                      { d.connected = false; d.info.Status = driver.StatusDisconnected; return nil }
+func (d *testDriver) Info() driver.DeviceInfo { return d.info }
+func (d *testDriver) Connect() error {
+	d.connected = true
+	d.info.Status = driver.StatusConnected
+	return nil
+}
+func (d *testDriver) Disconnect() error {
+	d.connected = false
+	d.info.Status = driver.StatusDisconnected
+	return nil
+}
 func (d *testDriver) IsConnected() bool                                      { return d.connected }
 func (d *testDriver) Flash(_ string, _ chan<- driver.FlashProgress) error    { return nil }
 func (d *testDriver) StartInference() error                                  { return nil }
@@ -92,3 +100,114 @@ func TestManager_Connect(t *testing.T) {
 		t.Error("Connect() did not connect device")
 	}
 }
+
+// ==========================================================================
+// Serial routing (ADR-018 WP-0): serialToLocalID + GetDevice dual lookup
+// ==========================================================================
+
+// seedDevice registers a test driver session and rebuilds the serial index,
+// mimicking what Start()/Rescan() do after registration.
+func seedDevice(mgr *Manager, info driver.DeviceInfo) *testDriver {
+	td := &testDriver{info: info}
+	mgr.mu.Lock()
+	mgr.sessions[info.ID] = NewSession(td)
+	mgr.rebuildSerialIndexLocked()
+	mgr.mu.Unlock()
+	return td
+}
+
+func TestManager_GetDevice_BySerial(t *testing.T) {
+	mgr := NewManager(NewRegistry(), "")
+	seedDevice(mgr, driver.DeviceInfo{ID: "kl520-0", SerialNumber: "0x1A2B3C4D"})
+
+	t.Run("serial hits the physical device", func(t *testing.T) {
+		s, err := mgr.GetDevice("0x1A2B3C4D")
+		if err != nil {
+			t.Fatalf("GetDevice(serial) error = %v", err)
+		}
+		if got := s.Driver.Info().ID; got != "kl520-0" {
+			t.Errorf("GetDevice(serial) resolved ID = %q, want kl520-0", got)
+		}
+	})
+
+	t.Run("local synthetic id still works (backward compat)", func(t *testing.T) {
+		s, err := mgr.GetDevice("kl520-0")
+		if err != nil {
+			t.Fatalf("GetDevice(localID) error = %v", err)
+		}
+		if s == nil {
+			t.Fatal("GetDevice(localID) returned nil session")
+		}
+	})
+
+	t.Run("unknown id (e.g. cloud UUID) still misses", func(t *testing.T) {
+		if _, err := mgr.GetDevice("d76718a9-cf15-4795-914e-df5ae46ee536"); err == nil {
+			t.Error("GetDevice(UUID) expected error, got nil")
+		}
+	})
+}
+
+func TestManager_GetDevice_MultipleSerials(t *testing.T) {
+	mgr := NewManager(NewRegistry(), "")
+	mgr.mu.Lock()
+	mgr.sessions["kl520-0"] = NewSession(&testDriver{info: driver.DeviceInfo{ID: "kl520-0", SerialNumber: "0xAAAA0001"}})
+	mgr.sessions["kl720-0"] = NewSession(&testDriver{info: driver.DeviceInfo{ID: "kl720-0", SerialNumber: "0xBBBB0002"}})
+	mgr.rebuildSerialIndexLocked()
+	mgr.mu.Unlock()
+
+	s1, err := mgr.GetDevice("0xAAAA0001")
+	if err != nil {
+		t.Fatalf("GetDevice(0xAAAA0001) error = %v", err)
+	}
+	if got := s1.Driver.Info().ID; got != "kl520-0" {
+		t.Errorf("serial 0xAAAA0001 resolved to %q, want kl520-0", got)
+	}
+
+	s2, err := mgr.GetDevice("0xBBBB0002")
+	if err != nil {
+		t.Fatalf("GetDevice(0xBBBB0002) error = %v", err)
+	}
+	if got := s2.Driver.Info().ID; got != "kl720-0" {
+		t.Errorf("serial 0xBBBB0002 resolved to %q, want kl720-0", got)
+	}
+}
+
+func TestManager_SerialIndex_SkipsEmptyAndFakeSerial(t *testing.T) {
+	mgr := NewManager(NewRegistry(), "")
+	mgr.mu.Lock()
+	// Empty serial (bridge could not read kn_number).
+	mgr.sessions["kl520-0"] = NewSession(&testDriver{info: driver.DeviceInfo{ID: "kl520-0"}})
+	// Fake serial from pyusb fallback (no SDK) — must not be routable.
+	mgr.sessions["kl720-0"] = NewSession(&testDriver{info: driver.DeviceInfo{ID: "kl720-0", SerialNumber: fakeSerialNumber}})
+	mgr.rebuildSerialIndexLocked()
+	mgr.mu.Unlock()
+
+	if _, err := mgr.GetDevice(""); err == nil {
+		t.Error("GetDevice(\"\") expected error (empty serial must not be indexed)")
+	}
+	if _, err := mgr.GetDevice(fakeSerialNumber); err == nil {
+		t.Errorf("GetDevice(%s) expected error (fake serial must not be routable)", fakeSerialNumber)
+	}
+	// Devices themselves remain reachable by local id.
+	if _, err := mgr.GetDevice("kl520-0"); err != nil {
+		t.Errorf("GetDevice(kl520-0) error = %v", err)
+	}
+	if _, err := mgr.GetDevice("kl720-0"); err != nil {
+		t.Errorf("GetDevice(kl720-0) error = %v", err)
+	}
+}
+
+func TestManager_SerialIndex_RemovedDeviceUnroutable(t *testing.T) {
+	mgr := NewManager(NewRegistry(), "")
+	seedDevice(mgr, driver.DeviceInfo{ID: "kl520-0", SerialNumber: "0x1A2B3C4D"})
+
+	// Simulate Rescan removing the device: delete session + rebuild index.
+	mgr.mu.Lock()
+	delete(mgr.sessions, "kl520-0")
+	mgr.rebuildSerialIndexLocked()
+	mgr.mu.Unlock()
+
+	if _, err := mgr.GetDevice("0x1A2B3C4D"); err == nil {
+		t.Error("GetDevice(serial) expected error after device removal")
+	}
+}
diff --git a/local-agent/server/internal/driver/interface.go b/local-agent/server/internal/driver/interface.go
index 1a1ea9f..ae0cc2f 100644
--- a/local-agent/server/internal/driver/interface.go
+++ b/local-agent/server/internal/driver/interface.go
@@ -16,10 +16,16 @@ type DeviceDriver interface {
 }
 
 type DeviceInfo struct {
-	ID           string       `json:"id"`
-	Name         string       `json:"name"`
-	Type         string       `json:"type"`
-	Port         string       `json:"port"`
+	ID   string `json:"id"`
+	Name string `json:"name"`
+	Type string `json:"type"`
+	Port string `json:"port"`
+	// SerialNumber is the Kneron kn_number reported by the Python bridge
+	// (formatted "0x%08X"). Empty when the bridge cannot read it (e.g. the
+	// pyusb fallback reports the fake value 0x00000000, which callers should
+	// treat as "no serial"). Used as the stable cross-layer routing key
+	// (cloud devices.serial_number <-> local sessions key), see ADR-018.
+	SerialNumber string       `json:"serialNumber,omitempty"`
 	VendorID     uint16       `json:"vendorId,omitempty"`
 	ProductID    uint16       `json:"productId,omitempty"`
 	Status       DeviceStatus `json:"status"`
diff --git a/local-agent/server/internal/driver/kneron/detector.go b/local-agent/server/internal/driver/kneron/detector.go
index dc42c6a..9f5adb5 100644
--- a/local-agent/server/internal/driver/kneron/detector.go
+++ b/local-agent/server/internal/driver/kneron/detector.go
@@ -89,8 +89,8 @@ const KneronVendorID uint16 = 0x3231
 
 // Known Kneron product IDs.
 const (
-	ProductIDKL520 = "0x0100"
-	ProductIDKL720 = "0x0200"
+	ProductIDKL520    = "0x0100"
+	ProductIDKL720    = "0x0200"
 	ProductIDKL720Alt = "0x0720"
 )
 
@@ -198,6 +198,24 @@ func DetectDevices(scriptPath string) []driver.DeviceInfo {
 		return nil
 	}
 
+	return parseScanDevices(devicesRaw)
+}
+
+// parseScanDevices converts the raw `devices` array from the Python bridge
+// scan response into driver.DeviceInfo entries.
+//
+// Extracted from DetectDevices so the parsing logic is unit-testable without
+// spawning the Python bridge subprocess.
+//
+// Serial number (kn_number) handling:
+//   - The bridge reports kn_number formatted "0x%08X" (SDK scan branch).
+//   - A missing or non-string kn_number yields an empty SerialNumber; the
+//     device is still registered (serial is additive metadata — a device must
+//     never be dropped because its serial could not be read).
+//   - The synthetic ID ("kl520-0") stays untouched: it remains the local
+//     sessions routing key (flash/inference depend on it). The serial travels
+//     in the new SerialNumber field only (ADR-018 serial routing).
+func parseScanDevices(devicesRaw []interface{}) []driver.DeviceInfo {
 	// Track per-chip counters for naming (e.g. "KL520 #1", "KL720 #1").
 	chipCount := map[string]int{}
 
@@ -223,18 +241,24 @@ func DetectDevices(scriptPath string) []driver.DeviceInfo {
 			productID = p
 		}
 
+		serial := ""
+		if s, ok := dev["kn_number"].(string); ok {
+			serial = strings.TrimSpace(s)
+		}
+
 		chip, devType := chipFromProductID(productID)
 		chipCount[chip]++
 		idx := chipCount[chip]
 
 		info := driver.DeviceInfo{
-			ID:          fmt.Sprintf("%s-%d", strings.ToLower(chip), idx-1),
-			Name:        fmt.Sprintf("Kneron %s #%d", chip, idx),
-			Type:        devType,
-			Port:        port,
-			VendorID:    KneronVendorID,
-			Status:      driver.StatusDetected,
-			FirmwareVer: fw,
+			ID:           fmt.Sprintf("%s-%d", strings.ToLower(chip), idx-1),
+			Name:         fmt.Sprintf("Kneron %s #%d", chip, idx),
+			Type:         devType,
+			Port:         port,
+			SerialNumber: serial,
+			VendorID:     KneronVendorID,
+			Status:       driver.StatusDetected,
+			FirmwareVer:  fw,
 		}
 		devices = append(devices, info)
 	}
diff --git a/local-agent/server/internal/driver/kneron/detector_test.go b/local-agent/server/internal/driver/kneron/detector_test.go
new file mode 100644
index 0000000..a3bfa10
--- /dev/null
+++ b/local-agent/server/internal/driver/kneron/detector_test.go
@@ -0,0 +1,105 @@
+package kneron
+
+import (
+	"testing"
+)
+
+// TestParseScanDevices_WithKnNumber verifies the serial number (kn_number)
+// reported by the Python bridge is preserved into DeviceInfo.SerialNumber
+// while the synthetic local ID stays untouched (ADR-018 serial routing, WP-0).
+func TestParseScanDevices_WithKnNumber(t *testing.T) {
+	raw := []interface{}{
+		map[string]interface{}{
+			"port":       "1-2",
+			"firmware":   "KDP",
+			"kn_number":  "0x1A2B3C4D",
+			"product_id": "0x0100",
+		},
+		map[string]interface{}{
+			"port":       "1-3",
+			"firmware":   "KDP2",
+			"kn_number":  "0x0E5F6071",
+			"product_id": "0x0720",
+		},
+	}
+
+	devices := parseScanDevices(raw)
+	if len(devices) != 2 {
+		t.Fatalf("parseScanDevices() = %d devices, want 2", len(devices))
+	}
+
+	if devices[0].ID != "kl520-0" {
+		t.Errorf("devices[0].ID = %q, want kl520-0 (synthetic ID must not change)", devices[0].ID)
+	}
+	if devices[0].SerialNumber != "0x1A2B3C4D" {
+		t.Errorf("devices[0].SerialNumber = %q, want 0x1A2B3C4D", devices[0].SerialNumber)
+	}
+	if devices[1].ID != "kl720-0" {
+		t.Errorf("devices[1].ID = %q, want kl720-0", devices[1].ID)
+	}
+	if devices[1].SerialNumber != "0x0E5F6071" {
+		t.Errorf("devices[1].SerialNumber = %q, want 0x0E5F6071", devices[1].SerialNumber)
+	}
+}
+
+// TestParseScanDevices_MissingKnNumber verifies a payload without kn_number
+// still yields the full device list (serial empty, no panic, no device drop).
+func TestParseScanDevices_MissingKnNumber(t *testing.T) {
+	raw := []interface{}{
+		map[string]interface{}{
+			"port":       "1-2",
+			"firmware":   "KDP",
+			"product_id": "0x0100",
+		},
+	}
+
+	devices := parseScanDevices(raw)
+	if len(devices) != 1 {
+		t.Fatalf("parseScanDevices() = %d devices, want 1 (device must not be dropped)", len(devices))
+	}
+	if devices[0].SerialNumber != "" {
+		t.Errorf("SerialNumber = %q, want empty when kn_number absent", devices[0].SerialNumber)
+	}
+	if devices[0].ID != "kl520-0" {
+		t.Errorf("ID = %q, want kl520-0", devices[0].ID)
+	}
+}
+
+// TestParseScanDevices_NonStringKnNumber verifies a non-string kn_number
+// (e.g. raw number instead of formatted hex string) does not panic and the
+// device is still registered with an empty serial.
+func TestParseScanDevices_NonStringKnNumber(t *testing.T) {
+	raw := []interface{}{
+		map[string]interface{}{
+			"port":       "1-2",
+			"kn_number":  float64(123456), // JSON number decodes to float64
+			"product_id": "0x0200",
+		},
+	}
+
+	devices := parseScanDevices(raw)
+	if len(devices) != 1 {
+		t.Fatalf("parseScanDevices() = %d devices, want 1", len(devices))
+	}
+	if devices[0].SerialNumber != "" {
+		t.Errorf("SerialNumber = %q, want empty for non-string kn_number", devices[0].SerialNumber)
+	}
+}
+
+// TestParseScanDevices_WhitespaceTrimmed verifies kn_number whitespace is trimmed.
+func TestParseScanDevices_WhitespaceTrimmed(t *testing.T) {
+	raw := []interface{}{
+		map[string]interface{}{
+			"kn_number":  "  0x1A2B3C4D ",
+			"product_id": "0x0100",
+		},
+	}
+
+	devices := parseScanDevices(raw)
+	if len(devices) != 1 {
+		t.Fatalf("parseScanDevices() = %d devices, want 1", len(devices))
+	}
+	if devices[0].SerialNumber != "0x1A2B3C4D" {
+		t.Errorf("SerialNumber = %q, want trimmed 0x1A2B3C4D", devices[0].SerialNumber)
+	}
+}
diff --git a/local-agent/visiona-agent/app.go b/local-agent/visiona-agent/app.go
index 239e57c..3adca03 100644
--- a/local-agent/visiona-agent/app.go
+++ b/local-agent/visiona-agent/app.go
@@ -56,9 +56,9 @@ const (
 	// 乾淨 Windows 環境總和常常超過 60 秒，180 秒涵蓋 99% 情境。日常啟動
 	// server 幾百毫秒就能回應，放寬上限不影響正常情境；配合 pipeline pause
 	// 機制也不會讓 soft/hard timeout 誤觸。
-	healthCheckTimeout = 180 * time.Second
-	shutdownGracePeriod  = 5 * time.Second
-	appName              = "visiona-agent"
+	healthCheckTimeout  = 180 * time.Second
+	shutdownGracePeriod = 5 * time.Second
+	appName             = "visiona-agent"
 )
 
 // PythonMode 決定 Python runtime 的選擇策略。
@@ -189,12 +189,13 @@ func NewApp() *App {
 // startup 由 Wails 在 app 啟動時呼叫。
 //
 // M8-4b：整合 6 階段啟動 pipeline。流程：
-//   stage 1（init Wails console）→ seedUserDataDir 完成後 CompleteStage(1)
-//   stage 2（Python runtime）   ┐
-//   stage 3（spawn server）     ├─ 由 startServerV2 內部 hook
-//   stage 4（device probe）     ┘
-//   stage 5（open browser）     → ctrl.Start() return 後處理
-//   stage 6（wait WebSocket）   → watcher goroutine poll sentinel file
+//
+//	stage 1（init Wails console）→ seedUserDataDir 完成後 CompleteStage(1)
+//	stage 2（Python runtime）   ┐
+//	stage 3（spawn server）     ├─ 由 startServerV2 內部 hook
+//	stage 4（device probe）     ┘
+//	stage 5（open browser）     → ctrl.Start() return 後處理
+//	stage 6（wait WebSocket）   → watcher goroutine poll sentinel file
 //
 // pipeline 失敗時不再呼叫 reportFatal（會直接結束程式），而是進 Error state，
 // 讓使用者看到 Wails 控制台的 Retry 按鈕。
@@ -413,6 +414,11 @@ func (a *App) tryStartTunnel() {
 	exchanger := tunnel.NewHTTPPairingExchanger(cloudAPIURL)
 	exchanger.MockMode = mockMode
 	exchanger.InsecureSkipTLSVerify = insecureSkipTLSVerify
+	// WP-0（ADR-018 序號地基）：exchange 前撈本地 /api/devices 把 USB 序號
+	// （kn_number）塞進 payload，雲端據此填 devices.serial_number。
+	// 撈失敗不會中斷配對（見 tunnel.DeviceLister 註解）。port 在上方已確認 > 0。
+	exchanger.DeviceLister = tunnel.NewLocalDeviceLister(port)
+	exchanger.Logf = a.appLog
 
 	// Startup log 明確標示當前模式；mock=true 時用 WARN 級字眼讓 dev 一眼看到。
 	if mockMode {
diff --git a/local-agent/visiona-agent/internal/tunnel/pairing.go b/local-agent/visiona-agent/internal/tunnel/pairing.go
index cba7033..441b786 100644
--- a/local-agent/visiona-agent/internal/tunnel/pairing.go
+++ b/local-agent/visiona-agent/internal/tunnel/pairing.go
@@ -21,6 +21,7 @@ import (
 	"errors"
 	"fmt"
 	"io"
+	"log"
 	"net/http"
 	"regexp"
 	"strings"
@@ -110,10 +111,39 @@ type ExchangeResult struct {
 }
 
 // exchangeRequest 對應 TDD §4.3 定義的 request body。
+//
+// Devices 為 WP-0（ADR-018 序號地基）新增的 optional 欄位：exchange 前向本地
+// server 撈 `GET /api/devices` 取得實體 USB 清單（含 Kneron kn_number 序號），
+// 讓雲端把序號填進 devices.serial_number（serial 路由的資料來源）。
+// `omitempty` 保證舊行為相容：撈不到清單（local server 未起 / timeout / 0 裝置）
+// 時不送此欄位，雲端走現行「自建 serial=NULL device」路徑。
 type exchangeRequest struct {
-	PairingToken string `json:"pairing_token"`
+	PairingToken string           `json:"pairing_token"`
+	Devices      []exchangeDevice `json:"devices,omitempty"`
 }
 
+// exchangeDevice 是 exchange payload 中的單顆實體 USB 裝置。
+// 用陣列因應「一 agent 多 USB」（WP-0 只保證序號送達，多顆的完整模型是 WP-B）。
+type exchangeDevice struct {
+	SerialNumber string `json:"serial_number"`
+	DeviceType   string `json:"device_type,omitempty"`
+	Firmware     string `json:"firmware,omitempty"`
+}
+
+// LocalDevice 是 DeviceLister 回傳的本地 USB 裝置摘要（exchange payload 的來源）。
+type LocalDevice struct {
+	SerialNumber string
+	DeviceType   string
+	Firmware     string
+}
+
+// DeviceLister 回傳本地 server 目前偵測到的 USB 裝置清單。
+//
+// 由 app.go 組裝時注入（NewLocalDeviceLister(port)），Exchanger 不自己猜 port。
+// 回傳 error 或 nil 清單都不會讓 exchange 失敗——序號是加值資訊，配對本身
+// 不能因為撈不到 USB 而中斷（fallback 到不帶 devices 的現行行為）。
+type DeviceLister func() ([]LocalDevice, error)
+
 // exchangeResponse 對齊雲端 /api/pairing/exchange 的成功 envelope（api/errors.go WriteSuccess）：
 //
 //	{
@@ -200,6 +230,14 @@ type HTTPPairingExchanger struct {
 	// 僅在 Client == nil（走預設 client 建構）時生效；若呼叫者注入自訂 Client，
 	// 以該 Client 自帶的 Transport 為準。
 	InsecureSkipTLSVerify bool
+
+	// DeviceLister 供 exchange 前撈本地 USB 清單（含序號）塞進 payload。
+	// nil 或回傳失敗 → payload 不帶 devices（exchange 照常進行，見 DeviceLister 註解）。
+	DeviceLister DeviceLister
+
+	// Logf 為 optional 的 log 函式（app.go 注入 appLog）。nil 時 fallback 到
+	// 標準 log.Printf。撈裝置清單失敗屬「可恢復、不中斷」情況，必須留下紀錄。
+	Logf func(format string, args ...interface{})
 }
 
 // NewHTTPPairingExchanger 建立一個生產預設實例。
@@ -262,7 +300,10 @@ func (e *HTTPPairingExchanger) exchangeReal(pairingToken string) (ExchangeResult
 		client = &c
 	}
 
-	body, err := json.Marshal(exchangeRequest{PairingToken: pairingToken})
+	body, err := json.Marshal(exchangeRequest{
+		PairingToken: pairingToken,
+		Devices:      e.collectLocalDevices(),
+	})
 	if err != nil {
 		return ExchangeResult{}, err
 	}
@@ -310,6 +351,94 @@ func (e *HTTPPairingExchanger) exchangeReal(pairingToken string) (ExchangeResult
 	}
 }
 
+// collectLocalDevices 在 exchange 前撈本地 USB 清單、轉成 payload 形狀。
+//
+// 不弄壞守則（device-serial-task1-mapping.md §2 段 4a）：撈清單失敗（local
+// server 沒起 / timeout / 0 裝置）**不可讓 exchange 失敗**——回 nil 讓 payload
+// 省略 devices 欄位（`omitempty`），雲端走現行「serial=NULL」路徑。
+func (e *HTTPPairingExchanger) collectLocalDevices() []exchangeDevice {
+	if e.DeviceLister == nil {
+		return nil
+	}
+	devs, err := e.DeviceLister()
+	if err != nil {
+		e.logf("pairing: list local devices failed (exchange continues without serials): %v", err)
+		return nil
+	}
+	if len(devs) == 0 {
+		return nil
+	}
+	out := make([]exchangeDevice, 0, len(devs))
+	for _, d := range devs {
+		out = append(out, exchangeDevice{
+			SerialNumber: strings.TrimSpace(d.SerialNumber),
+			DeviceType:   d.DeviceType,
+			Firmware:     d.Firmware,
+		})
+	}
+	return out
+}
+
+// logf 走注入的 Logf（app.go 的 appLog）；未注入時 fallback 標準 log。
+func (e *HTTPPairingExchanger) logf(format string, args ...interface{}) {
+	if e.Logf != nil {
+		e.Logf(format, args...)
+		return
+	}
+	log.Printf(format, args...)
+}
+
+// localDeviceListTimeout 是撈本地 /api/devices 的 timeout。
+// 比照 server_control.go probe 的 2 秒——序號是加值資訊，不能拖慢配對。
+const localDeviceListTimeout = 2 * time.Second
+
+// localDevicesEnvelope 對齊 local server `GET /api/devices` 的回應 envelope：
+//
+//	{ "success": true, "data": { "devices": [ { "id", "serialNumber", "type", "firmwareVersion", ... } ] } }
+//
+// 只解需要的欄位（serialNumber / type / firmwareVersion）。
+type localDevicesEnvelope struct {
+	Success bool `json:"success"`
+	Data    struct {
+		Devices []struct {
+			SerialNumber    string `json:"serialNumber"`
+			Type            string `json:"type"`
+			FirmwareVersion string `json:"firmwareVersion"`
+		} `json:"devices"`
+	} `json:"data"`
+}
+
+// NewLocalDeviceLister 建立一個向本地 server（127.0.0.1:port）撈
+// `GET /api/devices` 的 DeviceLister。port 由 app.go 從 ServerController 取得
+// 後注入（Exchanger 不自己猜 port）。
+func NewLocalDeviceLister(port int) DeviceLister {
+	client := &http.Client{Timeout: localDeviceListTimeout}
+	url := fmt.Sprintf("http://127.0.0.1:%d/api/devices", port)
+	return func() ([]LocalDevice, error) {
+		resp, err := client.Get(url)
+		if err != nil {
+			return nil, fmt.Errorf("local device list: %w", err)
+		}
+		defer resp.Body.Close()
+		if resp.StatusCode != http.StatusOK {
+			return nil, fmt.Errorf("local device list: http %d", resp.StatusCode)
+		}
+		var env localDevicesEnvelope
+		if err := json.NewDecoder(resp.Body).Decode(&env); err != nil {
+			return nil, fmt.Errorf("local device list: decode: %w", err)
+		}
+		out := make([]LocalDevice, 0, len(env.Data.Devices))
+		for _, d := range env.Data.Devices {
+			out = append(out, LocalDevice{
+				SerialNumber: d.SerialNumber,
+				DeviceType:   d.Type,
+				Firmware:     d.FirmwareVersion,
+			})
+		}
+		return out, nil
+	}
+}
+
 // mapExchangeErrorCode 把雲端錯誤 envelope 的 error.code 映射成 agent 內部 sentinel error。
 //
 // code 為雲端的大寫常數（見 visionA-backend api.ErrCodeInvalidPairingToken 等）：
diff --git a/local-agent/visiona-agent/internal/tunnel/pairing_test.go b/local-agent/visiona-agent/internal/tunnel/pairing_test.go
index 79c659a..42d8383 100644
--- a/local-agent/visiona-agent/internal/tunnel/pairing_test.go
+++ b/local-agent/visiona-agent/internal/tunnel/pairing_test.go
@@ -4,8 +4,11 @@ package tunnel
 import (
 	"encoding/json"
 	"errors"
+	"io"
 	"net/http"
 	"net/http/httptest"
+	"net/url"
+	"strconv"
 	"strings"
 	"testing"
 )
@@ -374,3 +377,178 @@ func TestExchangeReal404HintsMockMode(t *testing.T) {
 		t.Errorf("err = %v — should hint mock_mode or AB11", err)
 	}
 }
+
+// ==========================================================================
+// WP-0（ADR-018 序號地基）：exchange payload 帶本地 USB 裝置清單
+// ==========================================================================
+
+// TestExchangeReal_PayloadIncludesDevices 驗證 DeviceLister 有清單時，
+// exchange request body 帶 devices（含 serial_number），序號得以上雲。
+func TestExchangeReal_PayloadIncludesDevices(t *testing.T) {
+	var gotBody map[string]interface{}
+	srv := httptest.NewServer(http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
+		_ = json.NewDecoder(r.Body).Decode(&gotBody)
+		w.Header().Set("Content-Type", "application/json")
+		_ = json.NewEncoder(w).Encode(exchangeResponse{
+			Success: true,
+			Data:    exchangeResponseData{SessionToken: "vAs_" + strings.Repeat("a", 64)},
+		})
+	}))
+	defer srv.Close()
+
+	ex := NewHTTPPairingExchanger(srv.URL)
+	ex.DeviceLister = func() ([]LocalDevice, error) {
+		return []LocalDevice{
+			{SerialNumber: "0x1A2B3C4D", DeviceType: "kneron_kl520", Firmware: "KDP"},
+			{SerialNumber: " 0x0E5F6071 ", DeviceType: "kneron_kl720"},
+		}, nil
+	}
+
+	if _, err := ex.Exchange("vAc_0123456789abcdef0123456789abcdef"); err != nil {
+		t.Fatalf("Exchange: %v", err)
+	}
+
+	devices, ok := gotBody["devices"].([]interface{})
+	if !ok {
+		t.Fatalf("request body 缺 devices 欄位：%v", gotBody)
+	}
+	if len(devices) != 2 {
+		t.Fatalf("devices 長度 = %d, want 2", len(devices))
+	}
+	d0 := devices[0].(map[string]interface{})
+	if d0["serial_number"] != "0x1A2B3C4D" {
+		t.Errorf("devices[0].serial_number = %v, want 0x1A2B3C4D", d0["serial_number"])
+	}
+	if d0["device_type"] != "kneron_kl520" {
+		t.Errorf("devices[0].device_type = %v, want kneron_kl520", d0["device_type"])
+	}
+	d1 := devices[1].(map[string]interface{})
+	if d1["serial_number"] != "0x0E5F6071" {
+		t.Errorf("devices[1].serial_number = %v（應 trim 空白）, want 0x0E5F6071", d1["serial_number"])
+	}
+}
+
+// TestExchangeReal_DeviceListerFails_ExchangeStillSucceeds 驗證不弄壞守則：
+// 撈本地清單失敗時 exchange 照常成功（payload 無 devices），且失敗有留 log。
+func TestExchangeReal_DeviceListerFails_ExchangeStillSucceeds(t *testing.T) {
+	var gotBody map[string]interface{}
+	srv := httptest.NewServer(http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
+		_ = json.NewDecoder(r.Body).Decode(&gotBody)
+		w.Header().Set("Content-Type", "application/json")
+		_ = json.NewEncoder(w).Encode(exchangeResponse{
+			Success: true,
+			Data:    exchangeResponseData{SessionToken: "vAs_" + strings.Repeat("b", 64)},
+		})
+	}))
+	defer srv.Close()
+
+	var logged []string
+	ex := NewHTTPPairingExchanger(srv.URL)
+	ex.DeviceLister = func() ([]LocalDevice, error) {
+		return nil, errors.New("local server unreachable")
+	}
+	ex.Logf = func(format string, args ...interface{}) {
+		logged = append(logged, format)
+	}
+
+	if _, err := ex.Exchange("vAc_0123456789abcdef0123456789abcdef"); err != nil {
+		t.Fatalf("Exchange 不應因撈清單失敗而失敗：%v", err)
+	}
+	if _, has := gotBody["devices"]; has {
+		t.Errorf("撈清單失敗時 payload 不應帶 devices：%v", gotBody["devices"])
+	}
+	if len(logged) == 0 {
+		t.Error("撈清單失敗應留 log（no silent failures）")
+	}
+}
+
+// TestExchangeReal_NoDeviceLister_NoDevicesField 驗證未注入 DeviceLister（舊行為）
+// 時 payload 完全不帶 devices 欄位（omitempty 相容性）。
+func TestExchangeReal_NoDeviceLister_NoDevicesField(t *testing.T) {
+	var rawBody []byte
+	srv := httptest.NewServer(http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
+		buf := new(strings.Builder)
+		_, _ = io.Copy(buf, r.Body)
+		rawBody = []byte(buf.String())
+		w.Header().Set("Content-Type", "application/json")
+		_ = json.NewEncoder(w).Encode(exchangeResponse{
+			Success: true,
+			Data:    exchangeResponseData{SessionToken: "vAs_" + strings.Repeat("c", 64)},
+		})
+	}))
+	defer srv.Close()
+
+	ex := NewHTTPPairingExchanger(srv.URL)
+	if _, err := ex.Exchange("vAc_0123456789abcdef0123456789abcdef"); err != nil {
+		t.Fatalf("Exchange: %v", err)
+	}
+	if strings.Contains(string(rawBody), "devices") {
+		t.Errorf("無 DeviceLister 時 payload 不應含 devices 欄位：%s", rawBody)
+	}
+}
+
+// TestNewLocalDeviceLister_ParsesEnvelope 驗證 NewLocalDeviceLister 能解析
+// local server GET /api/devices 的 envelope（success + data.devices）。
+func TestNewLocalDeviceLister_ParsesEnvelope(t *testing.T) {
+	srv := httptest.NewServer(http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
+		if r.URL.Path != "/api/devices" {
+			w.WriteHeader(404)
+			return
+		}
+		w.Header().Set("Content-Type", "application/json")
+		_, _ = w.Write([]byte(`{
+			"success": true,
+			"data": {
+				"devices": [
+					{"id":"kl520-0","name":"Kneron KL520 #1","type":"kneron_kl520","serialNumber":"0x1A2B3C4D","firmwareVersion":"KDP","status":"detected"},
+					{"id":"kl720-0","name":"Kneron KL720 #1","type":"kneron_kl720","status":"detected"}
+				]
+			}
+		}`))
+	}))
+	defer srv.Close()
+
+	port := portFromTestServerURL(t, srv.URL)
+	lister := NewLocalDeviceLister(port)
+	devs, err := lister()
+	if err != nil {
+		t.Fatalf("lister: %v", err)
+	}
+	if len(devs) != 2 {
+		t.Fatalf("devices = %d, want 2", len(devs))
+	}
+	if devs[0].SerialNumber != "0x1A2B3C4D" || devs[0].DeviceType != "kneron_kl520" || devs[0].Firmware != "KDP" {
+		t.Errorf("devs[0] = %+v", devs[0])
+	}
+	if devs[1].SerialNumber != "" {
+		t.Errorf("devs[1].SerialNumber = %q, want empty（serialNumber omitempty）", devs[1].SerialNumber)
+	}
+}
+
+// TestNewLocalDeviceLister_Unreachable 驗證 local server 不可達時回 error
+// （由 collectLocalDevices 轉為「不帶 devices、exchange 照常」）。
+func TestNewLocalDeviceLister_Unreachable(t *testing.T) {
+	// 先開再關，拿一個幾乎必然沒人聽的 port。
+	srv := httptest.NewServer(http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {}))
+	port := portFromTestServerURL(t, srv.URL)
+	srv.Close()
+
+	lister := NewLocalDeviceLister(port)
+	if _, err := lister(); err == nil {
+		t.Error("lister 對不可達的 local server 應回 error")
+	}
+}
+
+// portFromTestServerURL 從 httptest server URL（http://127.0.0.1:PORT）解出 port。
+func portFromTestServerURL(t *testing.T, rawURL string) int {
+	t.Helper()
+	u, err := url.Parse(rawURL)
+	if err != nil {
+		t.Fatalf("parse url %q: %v", rawURL, err)
+	}
+	port, err := strconv.Atoi(u.Port())
+	if err != nil {
+		t.Fatalf("parse port from %q: %v", rawURL, err)
+	}
+	return port
+}
diff --git a/visionA-backend/internal/api/pairing.go b/visionA-backend/internal/api/pairing.go
index ef7c252..a24ade0 100644
--- a/visionA-backend/internal/api/pairing.go
+++ b/visionA-backend/internal/api/pairing.go
@@ -336,8 +336,14 @@ func registerPairingPublicRoutes(r gin.IRouter, deps Deps) {
 }
 
 // PairingExchangeRequest 是 POST /api/pairing/exchange 的 request body。
+//
+// Devices 為 WP-0（ADR-018 序號地基）新增的 optional 欄位：agent 在 exchange 前
+// 撈本地 USB 清單（含 Kneron kn_number 序號）上報，雲端據此填
+// devices.serial_number。舊 agent 不送此欄位 → 行為與現行完全一致
+// （自建 serial=NULL device）。
 type PairingExchangeRequest struct {
-	PairingToken string `json:"pairing_token" binding:"required"`
+	PairingToken string                `json:"pairing_token" binding:"required"`
+	Devices      []ExchangeDeviceInput `json:"devices,omitempty"`
 }
 
 // PairingExchangeResponse 是 POST /api/pairing/exchange 成功時的 data payload。
@@ -439,7 +445,7 @@ func pairingExchangeHandler(deps Deps) gin.HandlerFunc {
 			deviceID    string
 		)
 		if deps.PairingExchanger != nil {
-			res, exErr := deps.PairingExchanger.Provision(ctx, info.UserID, info.TokenHash, auth.SessionTokenTTL)
+			res, exErr := deps.PairingExchanger.Provision(ctx, info.UserID, info.TokenHash, auth.SessionTokenTTL, req.Devices)
 			if exErr != nil {
 				logOrDefault(deps.Logger).Error("pairing exchange: provision device+session failed",
 					"error", exErr,
diff --git a/visionA-backend/internal/api/pairing_exchange.go b/visionA-backend/internal/api/pairing_exchange.go
index b3d4b89..29841b9 100644
--- a/visionA-backend/internal/api/pairing_exchange.go
+++ b/visionA-backend/internal/api/pairing_exchange.go
@@ -30,8 +30,10 @@ package api
 
 import (
 	"context"
+	"errors"
 	"fmt"
 	"log/slog"
+	"strings"
 	"time"
 
 	"github.com/google/uuid"
@@ -53,11 +55,41 @@ const (
 
 // ExchangeProvisionResult 回報 exchange 自建 device + 建 session token 的結果。
 type ExchangeProvisionResult struct {
-	DeviceID         string             // 本次自建的 device id
+	DeviceID         string             // 本次自建（或依 serial 復用）的 device id
 	SessionPlaintext string             // 新 session token 原文（caller 只此一次能拿到）
 	SessionInfo      *auth.SessionToken // session token 儲存層表示（含 ExpiresAt）
 }
 
+// ExchangeDeviceInput 是 exchange payload 中 agent 上報的單顆實體 USB 裝置
+// （WP-0 / ADR-018 序號地基，對齊 agent 端 tunnel.exchangeDevice 的 JSON）。
+type ExchangeDeviceInput struct {
+	SerialNumber string `json:"serial_number"`
+	DeviceType   string `json:"device_type,omitempty"`
+	Firmware     string `json:"firmware,omitempty"`
+}
+
+// fakeSerialNumber 是 agent 端 pyusb fallback（無 Kneron SDK，如 macOS 缺 dylib）
+// 寫死上報的假序號。多顆無 SDK 裝置會撞同一個值，不可當唯一鍵 / 路由鍵——
+// 視同「無序號」寫 NULL（ADR-018 §2.2 / task-1 mapping R2）。
+const fakeSerialNumber = "0x00000000"
+
+// firstUsableSerialDevice 從 agent 上報清單挑第一顆「序號可用」的裝置。
+//
+// WP-0 最小落地（task-1 mapping R1）：exchange 仍只落一筆 device，多顆 USB 的
+// 完整模型（一 agent N device）是 WP-B / migration 0005 的範疇。這裡取第一顆
+// 有效序號填入；空序號與假序號（0x00000000）跳過。
+func firstUsableSerialDevice(devices []ExchangeDeviceInput) (ExchangeDeviceInput, bool) {
+	for _, d := range devices {
+		serial := strings.TrimSpace(d.SerialNumber)
+		if serial == "" || strings.EqualFold(serial, fakeSerialNumber) {
+			continue
+		}
+		d.SerialNumber = serial
+		return d, true
+	}
+	return ExchangeDeviceInput{}, false
+}
+
 // PairingExchanger 把「自建 device + 建 session token」包成一個原子（Postgres tx）或
 // 一致（in-memory 依序）操作。
 //
@@ -67,14 +99,26 @@ type PairingExchanger interface {
 	// Provision 自建一筆 device（owner = userID）並建一筆綁該 device 的 session token。
 	//
 	// parentTokenHash 為來源 pairing token 的 hash（稽核鏈，寫進 session_tokens.parent_token_hash）。
-	Provision(ctx context.Context, userID, parentTokenHash string, ttl time.Duration) (ExchangeProvisionResult, error)
+	//
+	// devices 為 agent 上報的實體 USB 清單（WP-0 序號地基，可為 nil = 舊 agent /
+	// 撈不到清單，行為與現行完全一致）。序號可用時：
+	//   - 同 owner 已有同 serial 的未刪除 device → 復用既有 device_id（防
+	//     uq_devices_owner_serial_active 23505 炸裂；「同序號重配 = 復用」，R4）。
+	//   - 否則新建 device 並填 serial_number。
+	Provision(ctx context.Context, userID, parentTokenHash string, ttl time.Duration, devices []ExchangeDeviceInput) (ExchangeProvisionResult, error)
 }
 
 // ── Postgres 後端 ─────────────────────────────────────────────────────────────
 
-// pgDeviceSaver 是 device 在 tx 內 upsert 的能力（由 device.PostgresRepository 滿足）。
+// pgDeviceSaver 是 device 在 tx 內 upsert + 依 serial 查詢的能力
+// （由 device.PostgresRepository 滿足）。
+//
+// GetBySerial 用於 WP-0 序號防炸：serial 有值時 exchange 先查同 owner 是否已有
+// 同 serial 的未刪除 device，有則復用、不再自建（避免撞 partial unique
+// uq_devices_owner_serial_active → 23505 → exchange 500）。
 type pgDeviceSaver interface {
 	SaveTx(ctx context.Context, q db.Querier, d *device.Device) error
+	GetBySerial(ctx context.Context, ownerUserID, serial string) (*device.Device, error)
 }
 
 // pgSessionTokenCreator 是「在 tx 內建 session token」的能力（由 auth.PostgresSessionTokenStore 滿足）。
@@ -105,40 +149,66 @@ func NewPostgresPairingExchanger(
 	}
 }
 
-// Provision 在單一交易內：自建 device → 建綁該 device 的 session token。
+// Provision 在單一交易內：自建（或依 serial 復用）device → 建綁該 device 的 session token。
 //
 // 任一步失敗整筆 rollback（device 不會「已建但沒 token」殘留在 DB）。
+//
+// WP-0 序號地基（ADR-018）：agent 上報清單有可用序號時，先 GetBySerial 查同
+// owner 是否已有同 serial 的未刪除 device——有則復用既有 device_id（同序號重配
+// = 復用，R4），沒有才新建並填 serial_number。已知限制：GetBySerial 走 pool
+// （非 tx 內），與並發 exchange 之間有極小 race window；撞到時 SaveTx 會被
+// partial unique index 擋下（整筆 rollback、不產生重複 serial），同一顆 agent
+// 的配對操作實務上是序列的，可接受。
 func (e *pgPairingExchanger) Provision(
-	ctx context.Context, userID, parentTokenHash string, ttl time.Duration,
+	ctx context.Context, userID, parentTokenHash string, ttl time.Duration, devices []ExchangeDeviceInput,
 ) (ExchangeProvisionResult, error) {
 	var res ExchangeProvisionResult
-	deviceID := uuid.NewString()
 	now := time.Now().UTC()
 
-	err := db.WithTx(ctx, e.pool, func(q db.Querier) error {
-		dev := &device.Device{
-			ID:          deviceID,
-			OwnerUserID: userID,
-			Name:        defaultPairedDeviceName,
-			DeviceType:  defaultPairedDeviceType,
-			// serial_number 留空（agent 未帶）：SaveTx 把空 serial 寫成 SQL NULL，
-			// 故同 owner 多次 exchange 各建一筆 serial=NULL 的 distinct device，不撞
-			// partial unique uq_devices_owner_serial_active（每個 NULL 互不相等）。
-			RemoteStatus: device.RemoteStatusOffline,
-			Status:       device.USBStatusUnknown,
-			PairedAt:     &now,
-			CreatedAt:    now,
-			UpdatedAt:    now,
+	dev := &device.Device{
+		ID:          uuid.NewString(),
+		OwnerUserID: userID,
+		Name:        defaultPairedDeviceName,
+		DeviceType:  defaultPairedDeviceType,
+		// serial_number 預設留空（agent 未帶）：SaveTx 把空 serial 寫成 SQL NULL，
+		// 故同 owner 多次 exchange 各建一筆 serial=NULL 的 distinct device，不撞
+		// partial unique uq_devices_owner_serial_active（每個 NULL 互不相等）。
+		RemoteStatus: device.RemoteStatusOffline,
+		Status:       device.USBStatusUnknown,
+		PairedAt:     &now,
+		CreatedAt:    now,
+		UpdatedAt:    now,
+	}
+
+	if input, ok := firstUsableSerialDevice(devices); ok {
+		existing, gErr := e.devices.GetBySerial(ctx, userID, input.SerialNumber)
+		switch {
+		case gErr == nil:
+			// 復用既有 device：保留既有欄位，只更新配對時間。
+			dev = existing
+			dev.PairedAt = &now
+			dev.UpdatedAt = now
+		case errors.Is(gErr, device.ErrNotFound):
+			// 新建 device，填入序號（+ agent 上報的 device type 若有）。
+			dev.SerialNumber = input.SerialNumber
+			if input.DeviceType != "" {
+				dev.DeviceType = input.DeviceType
+			}
+		default:
+			return ExchangeProvisionResult{}, fmt.Errorf("exchange: get device by serial: %w", gErr)
 		}
+	}
+
+	err := db.WithTx(ctx, e.pool, func(q db.Querier) error {
 		if saveErr := e.devices.SaveTx(ctx, q, dev); saveErr != nil {
 			return fmt.Errorf("exchange: save device: %w", saveErr)
 		}
 
-		plaintext, info, createErr := e.sessionToken.CreateTx(ctx, q, userID, deviceID, parentTokenHash, ttl)
+		plaintext, info, createErr := e.sessionToken.CreateTx(ctx, q, userID, dev.ID, parentTokenHash, ttl)
 		if createErr != nil {
 			return fmt.Errorf("exchange: create session token: %w", createErr)
 		}
-		res.DeviceID = deviceID
+		res.DeviceID = dev.ID
 		res.SessionPlaintext = plaintext
 		res.SessionInfo = info
 		return nil
@@ -176,15 +246,15 @@ func NewInMemoryPairingExchanger(
 	}
 }
 
-// Provision 自建 device 後建綁該 device 的 session token（依序，非交易）。
+// Provision 自建（或依 serial 復用）device 後建綁該 device 的 session token
+// （依序，非交易）。serial 處理邏輯與 pgPairingExchanger 對齊（WP-0）。
 func (e *memPairingExchanger) Provision(
-	ctx context.Context, userID, parentTokenHash string, ttl time.Duration,
+	ctx context.Context, userID, parentTokenHash string, ttl time.Duration, devices []ExchangeDeviceInput,
 ) (ExchangeProvisionResult, error) {
-	deviceID := uuid.NewString()
 	now := time.Now().UTC()
 
 	dev := &device.Device{
-		ID:           deviceID,
+		ID:           uuid.NewString(),
 		OwnerUserID:  userID,
 		Name:         defaultPairedDeviceName,
 		DeviceType:   defaultPairedDeviceType,
@@ -194,16 +264,34 @@ func (e *memPairingExchanger) Provision(
 		CreatedAt:    now,
 		UpdatedAt:    now,
 	}
+
+	if input, ok := firstUsableSerialDevice(devices); ok {
+		existing, gErr := e.devices.GetBySerial(ctx, userID, input.SerialNumber)
+		switch {
+		case gErr == nil:
+			dev = existing
+			dev.PairedAt = &now
+			dev.UpdatedAt = now
+		case errors.Is(gErr, device.ErrNotFound):
+			dev.SerialNumber = input.SerialNumber
+			if input.DeviceType != "" {
+				dev.DeviceType = input.DeviceType
+			}
+		default:
+			return ExchangeProvisionResult{}, fmt.Errorf("exchange: get device by serial: %w", gErr)
+		}
+	}
+
 	if err := e.devices.Save(ctx, dev); err != nil {
 		return ExchangeProvisionResult{}, fmt.Errorf("exchange: save device: %w", err)
 	}
 
-	plaintext, info, err := e.sessionToken.Create(ctx, userID, deviceID, parentTokenHash, ttl)
+	plaintext, info, err := e.sessionToken.Create(ctx, userID, dev.ID, parentTokenHash, ttl)
 	if err != nil {
 		return ExchangeProvisionResult{}, fmt.Errorf("exchange: create session token: %w", err)
 	}
 	return ExchangeProvisionResult{
-		DeviceID:         deviceID,
+		DeviceID:         dev.ID,
 		SessionPlaintext: plaintext,
 		SessionInfo:      info,
 	}, nil
diff --git a/visionA-backend/internal/api/pairing_exchange_db_test.go b/visionA-backend/internal/api/pairing_exchange_db_test.go
index e33285d..a86bea6 100644
--- a/visionA-backend/internal/api/pairing_exchange_db_test.go
+++ b/visionA-backend/internal/api/pairing_exchange_db_test.go
@@ -58,7 +58,7 @@ func TestPGExchange_ProvisionCreatesDeviceAndSession(t *testing.T) {
 	tdb, exchanger, devRepo, sessions, owner := pgExchangeFixture(t)
 
 	parentHash := auth.HashToken("vAc_" + uuid.NewString()[:32])
-	res, err := exchanger.Provision(ctx, owner, parentHash, auth.SessionTokenTTL)
+	res, err := exchanger.Provision(ctx, owner, parentHash, auth.SessionTokenTTL, nil)
 	require.NoError(t, err)
 	require.NotEmpty(t, res.DeviceID, "應自建一筆 device")
 	require.NotEmpty(t, res.SessionPlaintext, "應建一個 session token")
@@ -94,7 +94,7 @@ func TestPGExchange_Provision_RollbackOnBadOwner(t *testing.T) {
 	tdb, exchanger, _, _, _ := pgExchangeFixture(t)
 
 	badOwner := uuid.NewString() // 不在 users 表
-	_, err := exchanger.Provision(ctx, badOwner, "", auth.SessionTokenTTL)
+	_, err := exchanger.Provision(ctx, badOwner, "", auth.SessionTokenTTL, nil)
 	require.Error(t, err, "owner 不存在 → device.owner_user_id FK violation")
 
 	// device 不應殘留（整筆交易 rollback）
@@ -108,11 +108,79 @@ func TestPGExchange_Provision_MultipleCreatesDistinctDevices(t *testing.T) {
 	ctx := context.Background()
 	_, exchanger, _, _, owner := pgExchangeFixture(t)
 
-	res1, err := exchanger.Provision(ctx, owner, "", auth.SessionTokenTTL)
+	res1, err := exchanger.Provision(ctx, owner, "", auth.SessionTokenTTL, nil)
 	require.NoError(t, err)
-	res2, err := exchanger.Provision(ctx, owner, "", auth.SessionTokenTTL)
+	res2, err := exchanger.Provision(ctx, owner, "", auth.SessionTokenTTL, nil)
 	require.NoError(t, err)
 
 	assert.NotEqual(t, res1.DeviceID, res2.DeviceID, "兩次 exchange 應各自建不同 device")
 	assert.NotEqual(t, res1.SessionPlaintext, res2.SessionPlaintext, "兩次 session token 應不同")
 }
+
+// ==========================================================================
+// WP-0（ADR-018 序號地基）：exchange 收 agent 上報序號（真 DB）
+// ==========================================================================
+
+// TestPGExchange_Provision_FillsSerialNumber 驗證序號真的寫進 devices.serial_number
+// （非 NULL），且 device_type 取 agent 上報值。
+func TestPGExchange_Provision_FillsSerialNumber(t *testing.T) {
+	ctx := context.Background()
+	tdb, exchanger, devRepo, _, owner := pgExchangeFixture(t)
+
+	res, err := exchanger.Provision(ctx, owner, "", auth.SessionTokenTTL,
+		[]ExchangeDeviceInput{{SerialNumber: "0x1A2B3C4D", DeviceType: "kneron_kl520"}})
+	require.NoError(t, err)
+
+	dev, err := devRepo.Get(ctx, res.DeviceID)
+	require.NoError(t, err)
+	assert.Equal(t, "0x1A2B3C4D", dev.SerialNumber)
+	assert.Equal(t, "kneron_kl520", dev.DeviceType)
+
+	// 直接查 DB 確認 serial_number 非 NULL（不是空字串寫入）
+	var serialIsNull bool
+	require.NoError(t, tdb.Pool.QueryRow(ctx,
+		`SELECT serial_number IS NULL FROM devices WHERE id = $1`, res.DeviceID).Scan(&serialIsNull))
+	assert.False(t, serialIsNull, "devices.serial_number 不應為 NULL")
+}
+
+// TestPGExchange_Provision_SameSerialReusesDevice 驗證同序號重複 exchange 不撞
+// partial unique uq_devices_owner_serial_active（23505）——復用既有 device、
+// 不 500、devices 表不長出第二筆。
+func TestPGExchange_Provision_SameSerialReusesDevice(t *testing.T) {
+	ctx := context.Background()
+	tdb, exchanger, _, sessions, owner := pgExchangeFixture(t)
+	input := []ExchangeDeviceInput{{SerialNumber: "0x1A2B3C4D"}}
+
+	res1, err := exchanger.Provision(ctx, owner, "", auth.SessionTokenTTL, input)
+	require.NoError(t, err)
+	res2, err := exchanger.Provision(ctx, owner, "", auth.SessionTokenTTL, input)
+	require.NoError(t, err, "同序號重配不可撞 23505 炸 500（防炸守則）")
+
+	assert.Equal(t, res1.DeviceID, res2.DeviceID, "同序號重配應復用既有 device")
+	assert.Equal(t, 1, tdb.CountRows(t, "devices"), "同序號重配不應多建 device")
+
+	// 兩個 session token 都存在、都綁同一顆 device
+	tok2, err := sessions.Get(ctx, res2.SessionPlaintext)
+	require.NoError(t, err)
+	assert.Equal(t, res1.DeviceID, tok2.DeviceID)
+}
+
+// TestPGExchange_Provision_FakeSerialWritesNull 驗證假序號 0x00000000 視同無序號
+// → serial_number 寫 NULL、不進復用分支（NULL 互不相等，各建 distinct device）。
+func TestPGExchange_Provision_FakeSerialWritesNull(t *testing.T) {
+	ctx := context.Background()
+	tdb, exchanger, _, _, owner := pgExchangeFixture(t)
+	input := []ExchangeDeviceInput{{SerialNumber: "0x00000000"}}
+
+	res1, err := exchanger.Provision(ctx, owner, "", auth.SessionTokenTTL, input)
+	require.NoError(t, err)
+	res2, err := exchanger.Provision(ctx, owner, "", auth.SessionTokenTTL, input)
+	require.NoError(t, err, "假序號寫 NULL、NULL 互不相等 → 不撞 unique")
+
+	assert.NotEqual(t, res1.DeviceID, res2.DeviceID)
+
+	var serialIsNull bool
+	require.NoError(t, tdb.Pool.QueryRow(ctx,
+		`SELECT serial_number IS NULL FROM devices WHERE id = $1`, res1.DeviceID).Scan(&serialIsNull))
+	assert.True(t, serialIsNull, "假序號應寫 NULL")
+}
diff --git a/visionA-backend/internal/api/pairing_exchange_test.go b/visionA-backend/internal/api/pairing_exchange_test.go
index 094ef12..5c04c10 100644
--- a/visionA-backend/internal/api/pairing_exchange_test.go
+++ b/visionA-backend/internal/api/pairing_exchange_test.go
@@ -22,7 +22,7 @@ func TestMemExchange_ProvisionCreatesDeviceAndSession(t *testing.T) {
 	sessions := auth.NewInMemorySessionTokenStore()
 	exchanger := NewInMemoryPairingExchanger(devRepo, sessions)
 
-	res, err := exchanger.Provision(ctx, "owner-1", "parent-hash", auth.SessionTokenTTL)
+	res, err := exchanger.Provision(ctx, "owner-1", "parent-hash", auth.SessionTokenTTL, nil)
 	require.NoError(t, err)
 	require.NotEmpty(t, res.DeviceID)
 	require.NotEmpty(t, res.SessionPlaintext)
@@ -49,11 +49,96 @@ func TestMemExchange_Provision_DistinctDevices(t *testing.T) {
 	exchanger := NewInMemoryPairingExchanger(
 		device.NewInMemoryRepository(), auth.NewInMemorySessionTokenStore())
 
-	res1, err := exchanger.Provision(ctx, "owner-1", "", auth.SessionTokenTTL)
+	res1, err := exchanger.Provision(ctx, "owner-1", "", auth.SessionTokenTTL, nil)
 	require.NoError(t, err)
-	res2, err := exchanger.Provision(ctx, "owner-1", "", auth.SessionTokenTTL)
+	res2, err := exchanger.Provision(ctx, "owner-1", "", auth.SessionTokenTTL, nil)
 	require.NoError(t, err)
 
 	assert.NotEqual(t, res1.DeviceID, res2.DeviceID)
 	assert.NotEqual(t, res1.SessionPlaintext, res2.SessionPlaintext)
 }
+
+// ==========================================================================
+// WP-0（ADR-018 序號地基）：exchange 收 agent 上報序號
+// ==========================================================================
+
+// TestMemExchange_Provision_FillsSerialNumber 驗證 agent 上報序號時，自建 device
+// 的 serial_number 有值（+ device_type 若有上報）。
+func TestMemExchange_Provision_FillsSerialNumber(t *testing.T) {
+	ctx := context.Background()
+	devRepo := device.NewInMemoryRepository()
+	exchanger := NewInMemoryPairingExchanger(devRepo, auth.NewInMemorySessionTokenStore())
+
+	res, err := exchanger.Provision(ctx, "owner-1", "", auth.SessionTokenTTL,
+		[]ExchangeDeviceInput{{SerialNumber: "0x1A2B3C4D", DeviceType: "kneron_kl520", Firmware: "KDP"}})
+	require.NoError(t, err)
+
+	dev, err := devRepo.Get(ctx, res.DeviceID)
+	require.NoError(t, err)
+	assert.Equal(t, "0x1A2B3C4D", dev.SerialNumber, "serial_number 應填入 agent 上報值")
+	assert.Equal(t, "kneron_kl520", dev.DeviceType, "device_type 有上報時應覆蓋預設")
+}
+
+// TestMemExchange_Provision_SameSerialReusesDevice 驗證同序號重複 exchange
+// 復用既有 device（防唯一約束炸裂；「同序號重配 = 復用」，R4）——不新建、
+// 不報錯、session token 各自獨立。
+func TestMemExchange_Provision_SameSerialReusesDevice(t *testing.T) {
+	ctx := context.Background()
+	devRepo := device.NewInMemoryRepository()
+	exchanger := NewInMemoryPairingExchanger(devRepo, auth.NewInMemorySessionTokenStore())
+	input := []ExchangeDeviceInput{{SerialNumber: "0x1A2B3C4D"}}
+
+	res1, err := exchanger.Provision(ctx, "owner-1", "", auth.SessionTokenTTL, input)
+	require.NoError(t, err)
+	res2, err := exchanger.Provision(ctx, "owner-1", "", auth.SessionTokenTTL, input)
+	require.NoError(t, err, "同序號重配不可失敗（防 23505 的行為對齊）")
+
+	assert.Equal(t, res1.DeviceID, res2.DeviceID, "同序號重配應復用既有 device")
+	assert.NotEqual(t, res1.SessionPlaintext, res2.SessionPlaintext, "session token 應各自獨立")
+
+	devices, err := devRepo.List(ctx, "owner-1")
+	require.NoError(t, err)
+	assert.Len(t, devices, 1, "同序號重配不應多建 device")
+}
+
+// TestMemExchange_Provision_FakeSerialTreatedAsEmpty 驗證假序號 0x00000000
+// （macOS 無 SDK 的 pyusb fallback）視同無序號：serial 留空、行為與不帶序號一致
+// （每次 exchange 各建一筆 distinct device）。
+func TestMemExchange_Provision_FakeSerialTreatedAsEmpty(t *testing.T) {
+	ctx := context.Background()
+	devRepo := device.NewInMemoryRepository()
+	exchanger := NewInMemoryPairingExchanger(devRepo, auth.NewInMemorySessionTokenStore())
+	input := []ExchangeDeviceInput{{SerialNumber: "0x00000000"}}
+
+	res1, err := exchanger.Provision(ctx, "owner-1", "", auth.SessionTokenTTL, input)
+	require.NoError(t, err)
+	res2, err := exchanger.Provision(ctx, "owner-1", "", auth.SessionTokenTTL, input)
+	require.NoError(t, err)
+
+	dev1, err := devRepo.Get(ctx, res1.DeviceID)
+	require.NoError(t, err)
+	assert.Empty(t, dev1.SerialNumber, "假序號應視同無序號（寫 NULL）")
+	assert.NotEqual(t, res1.DeviceID, res2.DeviceID, "假序號不進復用分支，各建 distinct device")
+}
+
+// TestMemExchange_Provision_PicksFirstUsableSerial 驗證多顆上報時取第一顆
+// 可用序號（空序號 / 假序號跳過）——WP-0 最小落地（R1：多顆完整模型是 WP-B）。
+func TestMemExchange_Provision_PicksFirstUsableSerial(t *testing.T) {
+	ctx := context.Background()
+	devRepo := device.NewInMemoryRepository()
+	exchanger := NewInMemoryPairingExchanger(devRepo, auth.NewInMemorySessionTokenStore())
+
+	res, err := exchanger.Provision(ctx, "owner-1", "", auth.SessionTokenTTL,
+		[]ExchangeDeviceInput{
+			{SerialNumber: ""},           // 空序號跳過
+			{SerialNumber: "0x00000000"}, // 假序號跳過
+			{SerialNumber: " 0x0E5F6071 ", DeviceType: "kneron_kl720"},
+			{SerialNumber: "0xFFFF0001"},
+		})
+	require.NoError(t, err)
+
+	dev, err := devRepo.Get(ctx, res.DeviceID)
+	require.NoError(t, err)
+	assert.Equal(t, "0x0E5F6071", dev.SerialNumber, "應取第一顆可用序號（trim 空白）")
+	assert.Equal(t, "kneron_kl720", dev.DeviceType)
+}