feat(client): add AI agent detection to user agent

docs/ARCHITECTURE.md

@@ -137,6 +137,23 @@ Based on [RFC 6749](https://tools.ietf.org/html/rfc6749) and [RFC 7636](https://
 **Fallback:**
 - If refresh fails, prompt user to re-authenticate
 
+## User Agent
+
+Custom user agent identifies pup CLI and detects AI coding assistants:
+
+**Format:**
+```
+pup/v0.1.0 (go go1.25.0; os darwin; arch arm64)              # Without agent
+pup/v0.1.0 (go go1.25.0; os darwin; arch arm64) claude-code  # With agent
+```
+
+**AI Agent Detection:**
+- `CLAUDECODE=1` or `CLAUDE_CODE=1` → appends `claude-code`
+- `CURSOR_AGENT=true` or `CURSOR_AGENT=1` → appends `cursor`
+- Precedence: CLAUDECODE > CURSOR_AGENT
+
+**Implementation:** `pkg/useragent` - Separate package for reusability and testing.
+
 ## API Client Wrapper
 
 ### Design Pattern

pkg/client/client.go

@@ -10,13 +10,12 @@ import (
 	"fmt"
 	"io"
 	"net/http"
-	"runtime"
 	"time"
 
 	"github.com/DataDog/datadog-api-client-go/v2/api/datadog"
-	"github.com/DataDog/pup/internal/version"
 	"github.com/DataDog/pup/pkg/auth/storage"
 	"github.com/DataDog/pup/pkg/config"
+	"github.com/DataDog/pup/pkg/useragent"
 )
 
 // Client wraps the Datadog API client
@@ -74,7 +73,7 @@ func New(cfg *config.Config) (*Client, error) {
 	configuration.Host = fmt.Sprintf("api.%s", cfg.Site)
 
 	// Set custom user agent to identify requests as coming from pup CLI
-	configuration.UserAgent = getUserAgent()
+	configuration.UserAgent = useragent.Get()
 
 	// Enable all unstable operations to suppress warnings
 	// These are beta/preview features that we want to use
@@ -136,7 +135,7 @@ func (c *Client) RawRequest(method, path string, body io.Reader) (*http.Response
 
 	req.Header.Set("Content-Type", "application/json")
 	req.Header.Set("Accept", "application/json")
-	req.Header.Set("User-Agent", getUserAgent())
+	req.Header.Set("User-Agent", useragent.Get())
 
 	// Set auth headers from context
 	if token, ok := c.ctx.Value(datadog.ContextAccessToken).(string); ok && token != "" {
@@ -159,13 +158,3 @@ func (c *Client) RawRequest(method, path string, body io.Reader) (*http.Response
 	return resp, nil
 }
 
-// getUserAgent returns a custom user agent string identifying the pup CLI
-func getUserAgent() string {
-	return fmt.Sprintf(
-		"pup/%s (go %s; os %s; arch %s)",
-		version.Version,
-		runtime.Version(),
-		runtime.GOOS,
-		runtime.GOARCH,
-	)
-}

pkg/client/client_test.go

@@ -10,14 +10,14 @@ import (
 	"io"
 	"net/http"
 	"net/http/httptest"
-	"runtime"
 	"strings"
 	"testing"
 
 	"github.com/DataDog/datadog-api-client-go/v2/api/datadog"
 	datadogV1 "github.com/DataDog/datadog-api-client-go/v2/api/datadogV1"
 	"github.com/DataDog/pup/internal/version"
 	"github.com/DataDog/pup/pkg/config"
+	"github.com/DataDog/pup/pkg/useragent"
 )
 
 func TestNew_WithAPIKeys(t *testing.T) {
@@ -494,7 +494,7 @@ func TestClient_APIConfiguration(t *testing.T) {
 }
 
 func TestGetUserAgent(t *testing.T) {
-	userAgent := getUserAgent()
+	userAgent := useragent.Get()
 
 	// Check that it starts with "pup/"
 	if !strings.HasPrefix(userAgent, "pup/") {
@@ -506,21 +506,6 @@ func TestGetUserAgent(t *testing.T) {
 		t.Errorf("User-Agent should contain version '%s', got: %s", version.Version, userAgent)
 	}
 
-	// Check that it contains Go version
-	if !strings.Contains(userAgent, runtime.Version()) {
-		t.Errorf("User-Agent should contain Go version '%s', got: %s", runtime.Version(), userAgent)
-	}
-
-	// Check that it contains OS
-	if !strings.Contains(userAgent, runtime.GOOS) {
-		t.Errorf("User-Agent should contain OS '%s', got: %s", runtime.GOOS, userAgent)
-	}
-
-	// Check that it contains architecture
-	if !strings.Contains(userAgent, runtime.GOARCH) {
-		t.Errorf("User-Agent should contain arch '%s', got: %s", runtime.GOARCH, userAgent)
-	}
-
 	// Verify format: pup/<version> (go <version>; os <os>; arch <arch>)
 	if !strings.Contains(userAgent, "(go ") {
 		t.Errorf("User-Agent should contain '(go ', got: %s", userAgent)
@@ -614,7 +599,7 @@ func TestClient_IntegrationUserAgentInAPIClient(t *testing.T) {
 		t.Errorf("User-Agent should start with 'pup/', got: %s", userAgent)
 	}
 
-	expectedUA := getUserAgent()
+	expectedUA := useragent.Get()
 	if userAgent != expectedUA {
 		t.Errorf("User-Agent = %q, want %q", userAgent, expectedUA)
 	}

pkg/useragent/useragent.go

@@ -0,0 +1,62 @@
+// Unless explicitly stated otherwise all files in this repository are licensed
+// under the Apache License Version 2.0.
+// This product includes software developed at Datadog (https://www.datadoghq.com/).
+// Copyright 2024-present Datadog, Inc.
+
+package useragent
+
+import (
+	"fmt"
+	"os"
+	"runtime"
+	"strings"
+
+	"github.com/DataDog/pup/internal/version"
+)
+
+// Get returns the user agent string for pup CLI with optional AI agent detection.
+//
+// Format without agent:
+//
+//	pup/v0.1.0 (go go1.25.0; os darwin; arch arm64)
+//
+// Format with agent:
+//
+//	pup/v0.1.0 (go go1.25.0; os darwin; arch arm64) claude-code
+//
+// AI agents are detected via environment variables:
+//   - CLAUDECODE=1 or CLAUDE_CODE=1 → appends "claude-code"
+//   - CURSOR_AGENT=true or CURSOR_AGENT=1 → appends "cursor"
+//
+// If multiple agents are detected, CLAUDECODE takes precedence.
+func Get() string {
+	base := fmt.Sprintf(
+		"pup/%s (go %s; os %s; arch %s)",
+		version.Version,
+		runtime.Version(),
+		runtime.GOOS,
+		runtime.GOARCH,
+	)
+
+	if agent := detectAgent(); agent != "" {
+		return base + " " + agent
+	}
+	return base
+}
+
+// detectAgent detects AI coding assistant from environment variables.
+// Returns empty string if no agent is detected.
+func detectAgent() string {
+	// Check Claude Code (CLAUDECODE or CLAUDE_CODE)
+	if os.Getenv("CLAUDECODE") == "1" || os.Getenv("CLAUDE_CODE") == "1" {
+		return "claude-code"
+	}
+
+	// Check Cursor (CURSOR_AGENT=true or CURSOR_AGENT=1)
+	cursorAgent := strings.ToLower(os.Getenv("CURSOR_AGENT"))
+	if cursorAgent == "true" || cursorAgent == "1" {
+		return "cursor"
+	}
+
+	return ""
+}