Add thread-safe Add/Del methods and refactor client locking

- Add Add and Del methods to Client for dynamic host management.
- Add RWMutex to Client to protect the devices map.
- Add Transport to Config to allow mocking HTTP transport in tests.
- Add getDeviceByHost helper to centralize device lookup locking.
- Refactor GetAll* methods to snapshot host keys before iteration to avoid concurrent map read/write panic.
- Add tests for thread safety and Add/Del functionality.

pkg/edgeos/client_test.go

@@ -0,0 +1,109 @@
+package edgeos
+
+import (
+	"bytes"
+	"context"
+	"fmt"
+	"io"
+	"net/http"
+	"sync"
+	"testing"
+)
+
+type mockTransport struct {
+	RoundTripFunc func(req *http.Request) (*http.Response, error)
+}
+
+func (m *mockTransport) RoundTrip(req *http.Request) (*http.Response, error) {
+	if m.RoundTripFunc != nil {
+		return m.RoundTripFunc(req)
+	}
+	// Default mock response
+	return &http.Response{
+		StatusCode: 200,
+		Body:       io.NopCloser(bytes.NewBufferString("{}")),
+		Header:     make(http.Header),
+	}, nil
+}
+
+func TestClient_ThreadSafety(t *testing.T) {
+	ctx := context.Background()
+	client := MustNew(ctx, []Config{})
+
+	var wg sync.WaitGroup
+	start := make(chan struct{})
+
+	// Writer: Adds and deletes hosts
+	wg.Add(1)
+	go func() {
+		defer wg.Done()
+		<-start
+		for i := 0; i < 100; i++ {
+			host := fmt.Sprintf("host-%d", i)
+			cfg := &Config{
+				Host:      host,
+				Transport: &mockTransport{},
+			}
+			if err := client.Add(cfg); err != nil {
+				// verify we don't error on valid add
+				t.Logf("Add error: %v", err)
+			}
+
+			// We invoke Del immediately.
+			if err := client.Del(host); err != nil {
+				t.Logf("Del error: %v", err)
+			}
+		}
+	}()
+
+	// Reader: Iterates hosts
+	wg.Add(1)
+	go func() {
+		defer wg.Done()
+		<-start
+		for i := 0; i < 10; i++ {
+			// GetAllInterfaces iterates keys.
+			// With mock transport, this will succeed (returning empty structs)
+			// checking for race conditions.
+			_, _ = client.GetAllInterfaces(ctx)
+		}
+	}()
+
+	close(start)
+	wg.Wait()
+}
+
+func TestClient_AddDel(t *testing.T) {
+	ctx := context.Background()
+	client := MustNew(ctx, []Config{})
+
+	cfg := &Config{
+		Host:      "test-host",
+		Transport: &mockTransport{},
+	}
+	if err := client.Add(cfg); err != nil {
+		t.Fatalf("Add failed: %v", err)
+	}
+
+	if err := client.Add(cfg); err == nil {
+		t.Fatal("Expected error adding duplicate host, got nil")
+	}
+
+	// Verify we can retrieve it
+	// Mock transport returns 200 OK with empty body, so GetInterfaces should return empty slice (or error decoding if empty body is not valid JSON array? actually "{}" is valid object, but GetInterfaces expects array for /interfaces?)
+	// Let's check api.go: GetInterfaces calls /interfaces.
+	// We can customize the mock if we want to test success return.
+	// For this test, we just care that it doesn't return "device not found".
+	_, err := client.GetInterfaces(ctx, "test-host")
+	if err != nil && err.Error() == "device not found: test-host" {
+		t.Fatal("Device should exist")
+	}
+
+	if err := client.Del("test-host"); err != nil {
+		t.Fatalf("Del failed: %v", err)
+	}
+
+	if err := client.Del("test-host"); err == nil {
+		t.Fatal("Expected error deleting non-existent host, got nil")
+	}
+}