fix(cli): -h/--help exits 0 instead of error code

parseDoctorArgs hand-rolled its own flag loop and surfaced help text
as an error; parseTestArgs used flag.ContinueOnError but propagated
flag.ErrHelp to main() which printed "error: flag: help requested"
and exited 1.

Switch parseDoctorArgs to flag.NewFlagSet matching parseTestArgs, then
recognise flag.ErrHelp in main() so all subcommands exit 0 on -h.

cmd/sanderling/doctor.go

@@ -2,6 +2,7 @@ package main
 
 import (
 	"context"
+	"flag"
 	"fmt"
 	"io"
 	"os"
@@ -111,24 +112,13 @@ type doctorOptions struct {
 	platform string
 }
 
-func parseDoctorArgs(args []string) (doctorOptions, error) {
-	options := doctorOptions{platform: "all"}
-	for index := 0; index < len(args); index++ {
-		argument := args[index]
-		switch {
-		case argument == "--platform":
-			index++
-			if index >= len(args) {
-				return doctorOptions{}, fmt.Errorf("--platform requires a value")
-			}
-			options.platform = args[index]
-		case len(argument) > len("--platform=") && argument[:len("--platform=")] == "--platform=":
-			options.platform = argument[len("--platform="):]
-		case argument == "-h" || argument == "--help":
-			return doctorOptions{}, fmt.Errorf("doctor [--platform=web|android|ios|all]")
-		default:
-			return doctorOptions{}, fmt.Errorf("unknown doctor argument: %q", argument)
-		}
+func parseDoctorArgs(args []string, stderr io.Writer) (doctorOptions, error) {
+	flagSet := flag.NewFlagSet("doctor", flag.ContinueOnError)
+	flagSet.SetOutput(stderr)
+	var options doctorOptions
+	flagSet.StringVar(&options.platform, "platform", "all", "target platform: web, android, ios, all")
+	if err := flagSet.Parse(args); err != nil {
+		return doctorOptions{}, err
 	}
 	switch options.platform {
 	case "web", "android", "ios", "all":

cmd/sanderling/doctor_test.go

@@ -4,6 +4,8 @@ import (
 	"bytes"
 	"context"
 	"errors"
+	"flag"
+	"io"
 	"strings"
 	"testing"
 )
@@ -139,7 +141,7 @@ func TestDoctorChecksFor_UnknownPlatform(t *testing.T) {
 }
 
 func TestParseDoctorArgs_DefaultAll(t *testing.T) {
-	options, err := parseDoctorArgs(nil)
+	options, err := parseDoctorArgs(nil, io.Discard)
 	if err != nil {
 		t.Fatal(err)
 	}
@@ -153,7 +155,7 @@ func TestParseDoctorArgs_ExplicitPlatform(t *testing.T) {
 		{"--platform", "web"},
 		{"--platform=web"},
 	} {
-		options, err := parseDoctorArgs(form)
+		options, err := parseDoctorArgs(form, io.Discard)
 		if err != nil {
 			t.Fatalf("%v: %v", form, err)
 		}
@@ -164,10 +166,19 @@ func TestParseDoctorArgs_ExplicitPlatform(t *testing.T) {
 }
 
 func TestParseDoctorArgs_RejectsUnknown(t *testing.T) {
-	if _, err := parseDoctorArgs([]string{"--platform=fuchsia"}); err == nil {
+	if _, err := parseDoctorArgs([]string{"--platform=fuchsia"}, io.Discard); err == nil {
 		t.Error("expected error for unsupported platform")
 	}
-	if _, err := parseDoctorArgs([]string{"--bogus"}); err == nil {
+	if _, err := parseDoctorArgs([]string{"--bogus"}, io.Discard); err == nil {
 		t.Error("expected error for unknown argument")
 	}
 }
+
+func TestParseDoctorArgs_HelpReturnsErrHelp(t *testing.T) {
+	if _, err := parseDoctorArgs([]string{"-h"}, io.Discard); !errors.Is(err, flag.ErrHelp) {
+		t.Errorf("expected flag.ErrHelp for -h, got %v", err)
+	}
+	if _, err := parseDoctorArgs([]string{"--help"}, io.Discard); !errors.Is(err, flag.ErrHelp) {
+		t.Errorf("expected flag.ErrHelp for --help, got %v", err)
+	}
+}

cmd/sanderling/main.go

@@ -76,15 +76,12 @@ func runTest(options testOptions, stdout io.Writer) error {
 	return runTestPipeline(ctx, options, stdout)
 }
 
-func runDoctor(args []string, stdout io.Writer) error {
-	options, err := parseDoctorArgs(args)
+func runDoctor(args []string, stdout, stderr io.Writer) error {
+	options, err := parseDoctorArgs(args, stderr)
 	if err != nil {
 		return err
 	}
 	checks := doctorChecksFor(options.platform)
-	if checks == nil {
-		return fmt.Errorf("no checks for platform %q", options.platform)
-	}
 	return runDoctorChecks(context.Background(), checks, stdout)
 }
 
@@ -107,7 +104,7 @@ func run(args []string, stdout, stderr io.Writer) error {
 		}
 		return runInspect(options, stdout)
 	case "doctor":
-		return runDoctor(args[2:], stdout)
+		return runDoctor(args[2:], stdout, stderr)
 	case "version", "-v", "--version":
 		fmt.Fprintln(stdout, Version)
 		return nil
@@ -118,6 +115,11 @@ func run(args []string, stdout, stderr io.Writer) error {
 
 func main() {
 	if err := run(os.Args, os.Stdout, os.Stderr); err != nil {
+		// flag.ErrHelp means -h/--help was requested; flag already printed
+		// usage to stderr, so exit 0 rather than treating it as a failure.
+		if errors.Is(err, flag.ErrHelp) {
+			return
+		}
 		fmt.Fprintf(os.Stderr, "error: %v\n", err)
 		os.Exit(1)
 	}