chore: tag User-Agent with mode=agent|interactive

Per PR review, re-add an interface identifier to the User-Agent but in a
parseable, analytics-friendly form. The UA now always carries a
mode=agent|interactive token (present in both modes, no client prefix) so
traffic can be grouped by interface across clients. The token reflects
only the interface, never the end user, so the value stays a stable
client identifier.

Author: claude

README.md

@@ -92,6 +92,7 @@ that is cheap to parse and free of decoration:
 - Default `--output` becomes `toon` (compact, token-efficient) instead of `table`
 - No color, spinners, or other terminal decoration
 - Banners, tips, and status chatter go to **stderr**, leaving **stdout** for data only
+- The request `User-Agent` carries `mode=agent` (human invocations carry `mode=interactive`) so API traffic can be segmented by interface
 
 ### How agent mode is detected
 

main.go

@@ -207,7 +207,8 @@ func run() (exitCode int) {
 	customerContextFlagValue = ""
 
 	// Resolve agent mode once up front. Downstream behavior — color, default
-	// output format, and stderr routing — all key off this.
+	// output format, stderr routing, and the User-Agent mode token — all key off
+	// this.
 	agentEnvDetected = detectedAgentEnv()
 	if v := strings.TrimSpace(os.Getenv("DCI_AGENT_MODE")); v != "" {
 		if _, ok := parseBoolish(v); !ok {
@@ -258,10 +259,11 @@ func run() (exitCode int) {
 	os.Setenv("RSH_PROFILE", "default")
 	viper.Set("rsh-profile", "default")
 
-	// Hardcode user-agent so the DCI API can identify CLI traffic. The value is
-	// stable across invocations, independent of agent mode or the end user.
-	// Restish picks this up via rsh-header and skips its own default.
-	viper.Set("rsh-header", []string{"user-agent:" + buildUserAgent()})
+	// Hardcode user-agent so the DCI API can identify CLI traffic. It carries a
+	// mode=agent|interactive token (never the end user) so traffic can be
+	// segmented by interface. Restish picks this up via rsh-header and skips its
+	// own default.
+	viper.Set("rsh-header", []string{"user-agent:" + buildUserAgent(agentMode)})
 
 	cli.Load("dci", cli.Root)
 	applyAPIKeyAuth()
@@ -609,10 +611,16 @@ func parseBoolish(v string) (bool, bool) {
 }
 
 // buildUserAgent returns the User-Agent header value identifying CLI traffic to
-// the DCI API. It is constant for a given build, independent of agent mode or
-// the end user, so the API always sees a stable client identifier.
-func buildUserAgent() string {
-	return fmt.Sprintf("dci-cli/%s (%s; %s/%s)", version, runtime.Version(), runtime.GOOS, runtime.GOARCH)
+// the DCI API. It always carries a mode=agent|interactive token so API traffic
+// can be segmented by interface (agent- vs human-driven) in analytics. The
+// token reflects only the interface, never the end user, so the value stays a
+// stable client identifier.
+func buildUserAgent(agent bool) string {
+	mode := "interactive"
+	if agent {
+		mode = "agent"
+	}
+	return fmt.Sprintf("dci-cli/%s (%s; %s/%s; mode=%s)", version, runtime.Version(), runtime.GOOS, runtime.GOARCH, mode)
 }
 
 // defaultOutputFormat is the output format used when --output is not given.

main_test.go

@@ -460,14 +460,26 @@ func TestAgentFlagOverride(t *testing.T) {
 }
 
 func TestBuildUserAgent(t *testing.T) {
-	ua := buildUserAgent()
-	if !strings.HasPrefix(ua, "dci-cli/") {
-		t.Fatalf("unexpected User-Agent prefix: %q", ua)
-	}
-	// The User-Agent must be a stable client identifier — it must not vary with
-	// agent mode or the end user.
-	if strings.Contains(ua, "agent=1") {
-		t.Fatalf("User-Agent must not carry agent-mode tag: %q", ua)
+	human := buildUserAgent(false)
+	if !strings.HasPrefix(human, "dci-cli/") {
+		t.Fatalf("unexpected User-Agent prefix: %q", human)
+	}
+	// The mode token is always present and self-describing so analytics can
+	// segment by interface; human mode is explicitly mode=interactive.
+	if !strings.Contains(human, "mode=interactive") {
+		t.Fatalf("human User-Agent must carry mode=interactive: %q", human)
+	}
+	if strings.Contains(human, "mode=agent") {
+		t.Fatalf("human User-Agent must not carry mode=agent: %q", human)
+	}
+
+	agent := buildUserAgent(true)
+	if !strings.Contains(agent, "mode=agent") {
+		t.Fatalf("agent User-Agent must carry mode=agent: %q", agent)
+	}
+	// Guard against the legacy opaque tag regressing.
+	if strings.Contains(agent, "agent=1") {
+		t.Fatalf("User-Agent must use mode=agent, not the legacy agent=1 tag: %q", agent)
 	}
 }