feat(skills): add retry mechanism for HTTP requests

Implement a retry mechanism with exponential backoff for HTTP requests in the skill installer. This improves reliability when fetching skills from GitHub by automatically retrying failed requests up to 3 times.

Add comprehensive tests to verify retry behavior under different scenarios including success on different attempts and proper delay between retries.

pkg/skills/installer.go

@@ -30,6 +30,23 @@ type BuiltinSkill struct {
 	Enabled bool   `json:"enabled"`
 }
 
+const maxRetries = 3
+
+func doRequestWithRetry(client *http.Client, req *http.Request) (*http.Response, error) {
+	var resp *http.Response
+	var err error
+	for i := range maxRetries {
+		resp, err = client.Do(req)
+		if err == nil && resp.StatusCode == http.StatusOK {
+			break
+		}
+		if i < maxRetries-1 {
+			time.Sleep(time.Second * time.Duration(i+1))
+		}
+	}
+	return resp, err
+}
+
 func NewSkillInstaller(workspace string) *SkillInstaller {
 	return &SkillInstaller{
 		workspace: workspace,
@@ -51,7 +68,7 @@ func (si *SkillInstaller) InstallFromGitHub(ctx context.Context, repo string) er
 		return fmt.Errorf("failed to create request: %w", err)
 	}
 
-	resp, err := client.Do(req)
+	resp, err := doRequestWithRetry(client, req)
 	if err != nil {
 		return fmt.Errorf("failed to fetch skill: %w", err)
 	}
@@ -101,7 +118,7 @@ func (si *SkillInstaller) ListAvailableSkills(ctx context.Context) ([]AvailableS
 		return nil, fmt.Errorf("failed to create request: %w", err)
 	}
 
-	resp, err := client.Do(req)
+	resp, err := doRequestWithRetry(client, req)
 	if err != nil {
 		return nil, fmt.Errorf("failed to fetch skills list: %w", err)
 	}

pkg/skills/installer_test.go

@@ -0,0 +1,133 @@
+package skills
+
+import (
+	"net/http"
+	"net/http/httptest"
+	"testing"
+	"time"
+
+	"github.com/stretchr/testify/assert"
+)
+
+func TestDoRequestWithRetry(t *testing.T) {
+	testcases := []struct {
+		name           string
+		serverBehavior func(*httptest.Server) int
+		wantSuccess    bool
+		wantAttempts   int
+	}{
+		{
+			name: "success-on-first-attempt",
+			serverBehavior: func(server *httptest.Server) int {
+				return 0
+			},
+			wantSuccess:  true,
+			wantAttempts: 1,
+		},
+		{
+			name: "success-on-second-attempt",
+			serverBehavior: func(server *httptest.Server) int {
+				return 1
+			},
+			wantSuccess:  true,
+			wantAttempts: 2,
+		},
+		{
+			name: "success-on-third-attempt",
+			serverBehavior: func(server *httptest.Server) int {
+				return 2
+			},
+			wantSuccess:  true,
+			wantAttempts: 3,
+		},
+		{
+			name: "fail-all-attempts",
+			serverBehavior: func(server *httptest.Server) int {
+				return 4
+			},
+			wantSuccess:  false,
+			wantAttempts: 3,
+		},
+		{
+			name: "non-ok-status-code",
+			serverBehavior: func(server *httptest.Server) int {
+				return 4
+			},
+			wantSuccess:  false,
+			wantAttempts: 3,
+		},
+	}
+
+	for _, tc := range testcases {
+		t.Run(tc.name, func(t *testing.T) {
+			attempts := 0
+			server := httptest.NewServer(http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
+				attempts++
+				if attempts <= tc.serverBehavior(nil) {
+					w.WriteHeader(http.StatusInternalServerError)
+					return
+				}
+				w.WriteHeader(http.StatusOK)
+				w.Write([]byte("success"))
+			}))
+
+			defer server.Close()
+
+			client := &http.Client{Timeout: 5 * time.Second}
+			req, err := http.NewRequest("GET", server.URL, nil)
+			assert.NoError(t, err)
+
+			resp, err := doRequestWithRetry(client, req)
+
+			if tc.wantSuccess {
+				assert.NoError(t, err)
+				assert.NotNil(t, resp)
+				assert.Equal(t, http.StatusOK, resp.StatusCode)
+				resp.Body.Close()
+			} else {
+				assert.NotNil(t, resp)
+				assert.Equal(t, http.StatusInternalServerError, resp.StatusCode)
+				resp.Body.Close()
+			}
+
+			assert.Equal(t, tc.wantAttempts, attempts)
+		})
+	}
+}
+
+func TestDoRequestWithRetry_Delay(t *testing.T) {
+	var start time.Time
+	delays := []time.Duration{}
+	server := httptest.NewServer(http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
+		if len(delays) == 0 {
+			delays = append(delays, 0)
+			w.WriteHeader(http.StatusInternalServerError)
+			return
+		}
+		if len(delays) == 1 {
+			start = time.Now()
+			delays = append(delays, 0)
+			w.WriteHeader(http.StatusInternalServerError)
+			return
+		}
+		if len(delays) == 2 {
+			elapsed := time.Since(start)
+			delays = append(delays, elapsed)
+			w.WriteHeader(http.StatusOK)
+			w.Write([]byte("success"))
+		}
+	}))
+	defer server.Close()
+
+	client := &http.Client{Timeout: 10 * time.Second}
+	req, err := http.NewRequest("GET", server.URL, nil)
+	assert.NoError(t, err)
+
+	resp, err := doRequestWithRetry(client, req)
+	assert.NoError(t, err)
+	assert.NotNil(t, resp)
+	assert.Equal(t, http.StatusOK, resp.StatusCode)
+	resp.Body.Close()
+
+	assert.GreaterOrEqual(t, delays[2], time.Second)
+}