diff --git a/server/internal/store/devices_login_swap_test.go b/server/internal/store/devices_login_swap_test.go
new file mode 100644
index 0000000..723314e
--- /dev/null
+++ b/server/internal/store/devices_login_swap_test.go
@@ -0,0 +1,75 @@
+package store_test
+
+import (
+	"context"
+	"testing"
+
+	"github.com/wangjia/pangolin/server/internal/devices"
+)
+
+// TestSQLite_LoginRegistersSameDeviceForTwoAccounts reproduces the #27 (F3) fix
+// at the exact code path login drives: recordLogin → devReg.RegisterDevice →
+// devices.Service.RegisterIfAbsent{MaxDevices:0}. Two accounts on the SAME physical
+// device (same device uuid) must each get their own devices row.
+//
+// Under the old global UNIQUE(uuid) the second account's registration failed
+// (silently on login, best-effort) → the device row for account B never existed →
+// ConnectNode later reported DEVICE_NOT_REGISTERED (the 403 deadlock, F3).
+func TestSQLite_LoginRegistersSameDeviceForTwoAccounts(t *testing.T) {
+	ctx := context.Background()
+	db := openSQLite(t)
+
+	mkUser := func(u, email string) int64 {
+		res, err := db.ExecContext(ctx,
+			`INSERT INTO users (uuid, email, pw_hash, dp_uuid) VALUES (?, ?, 'h', ?)`,
+			u, email, "dp-"+u)
+		if err != nil {
+			t.Fatalf("user %s: %v", u, err)
+		}
+		id, _ := res.LastInsertId()
+		return id
+	}
+	userA := mkUser("u-a", "a@x.c")
+	userB := mkUser("u-b", "b@x.c")
+
+	svc := devices.NewService(devices.NewStore(db), nil)
+	const sharedUUID = "shared-install-uuid"
+
+	// Account A "logs in" on the device.
+	idA, _, apiErr := svc.RegisterIfAbsent(ctx, devices.RegisterInput{
+		UserID: userA, DeviceUUID: sharedUUID, Platform: "macos", MaxDevices: 0,
+	})
+	if apiErr != nil || idA == 0 {
+		t.Fatalf("A register: id=%d err=%v", idA, apiErr)
+	}
+
+	// Account B "logs in" on the SAME physical device (same uuid) — the F3 case.
+	idB, _, apiErr := svc.RegisterIfAbsent(ctx, devices.RegisterInput{
+		UserID: userB, DeviceUUID: sharedUUID, Platform: "macos", MaxDevices: 0,
+	})
+	if apiErr != nil {
+		t.Fatalf("B register on same device uuid must succeed (F3 fix), got %v", apiErr)
+	}
+	if idB == 0 || idB == idA {
+		t.Fatalf("B must get its own device row, idA=%d idB=%d", idA, idB)
+	}
+
+	// A logs in again → idempotent refresh of A's own row (not a new row).
+	idA2, _, apiErr := svc.RegisterIfAbsent(ctx, devices.RegisterInput{
+		UserID: userA, DeviceUUID: sharedUUID, Platform: "macos", MaxDevices: 0,
+	})
+	if apiErr != nil || idA2 != idA {
+		t.Fatalf("A re-register must refresh same row: id=%d (want %d) err=%v", idA2, idA, apiErr)
+	}
+
+	// Both rows coexist for the shared uuid, one per account.
+	var n int
+	if err := db.QueryRowContext(ctx,
+		`SELECT COUNT(*) FROM devices WHERE uuid=?`, sharedUUID).Scan(&n); err != nil {
+		t.Fatal(err)
+	}
+	if n != 2 {
+		t.Fatalf("shared uuid must have 2 rows (one per account), got %d", n)
+	}
+	t.Logf("OK: device uuid %q shared by account A (row #%d) + account B (row #%d)", sharedUUID, idA, idB)
+}