feat(doctor): per-platform check sets + --platform flag

Replaces unconditional defaultDoctorChecks with doctorChecksFor(platform);
web-only users no longer see scary FAILs for adb/emulator/java/sidecar.

cmd/sanderling/doctor.go

@@ -11,6 +11,8 @@ import (
 	"strconv"
 	"time"
 
+	"github.com/chromedp/chromedp"
+
 	"github.com/priyanshujain/sanderling/internal/sidecar"
 )
 
@@ -19,7 +21,31 @@ type doctorCheck struct {
 	Run  func(ctx context.Context) error
 }
 
-func defaultDoctorChecks() []doctorCheck {
+// doctorChecksFor returns the host-readiness checks for a target platform.
+// "all" returns the union (deduped by name) so the legacy zero-arg `doctor`
+// behaviour keeps surfacing every platform's prerequisites.
+func doctorChecksFor(platform string) []doctorCheck {
+	switch platform {
+	case "web":
+		return webChecks()
+	case "android":
+		return androidChecks()
+	case "ios":
+		return iosChecks()
+	case "all":
+		return allChecks()
+	default:
+		return nil
+	}
+}
+
+func webChecks() []doctorCheck {
+	return []doctorCheck{
+		{Name: "headless chromium can launch", Run: checkChromiumLaunch},
+	}
+}
+
+func androidChecks() []doctorCheck {
 	return []doctorCheck{
 		{Name: "adb on PATH", Run: checkExecutableOnPath("adb")},
 		{Name: "emulator on PATH or under ANDROID_HOME", Run: checkEmulator},
@@ -28,6 +54,49 @@ func defaultDoctorChecks() []doctorCheck {
 	}
 }
 
+func iosChecks() []doctorCheck {
+	return []doctorCheck{
+		{Name: "xcrun on PATH", Run: checkExecutableOnPath("xcrun")},
+		{Name: "simctl on PATH", Run: checkExecutableOnPath("simctl")},
+		{Name: "java 17+ on PATH", Run: checkJavaVersion},
+		{Name: "sidecar JAR is real (not placeholder)", Run: checkSidecarJAR},
+	}
+}
+
+func allChecks() []doctorCheck {
+	seen := map[string]bool{}
+	var combined []doctorCheck
+	for _, group := range [][]doctorCheck{webChecks(), androidChecks(), iosChecks()} {
+		for _, c := range group {
+			if seen[c.Name] {
+				continue
+			}
+			seen[c.Name] = true
+			combined = append(combined, c)
+		}
+	}
+	return combined
+}
+
+// checkChromiumLaunch boots a headless chromium under chromedp's default
+// allocator, opens a blank tab, and tears down. Confirms the bundled CDP
+// surface plus a working Chromium binary path.
+func checkChromiumLaunch(ctx context.Context) error {
+	allocCtx, allocCancel := chromedp.NewExecAllocator(ctx,
+		append(chromedp.DefaultExecAllocatorOptions[:],
+			chromedp.Flag("headless", true),
+			chromedp.Flag("disable-gpu", true),
+		)...,
+	)
+	defer allocCancel()
+	tabCtx, tabCancel := chromedp.NewContext(allocCtx)
+	defer tabCancel()
+	if err := chromedp.Run(tabCtx, chromedp.Navigate("about:blank")); err != nil {
+		return fmt.Errorf("chromium launch: %w", err)
+	}
+	return nil
+}
+
 func checkSidecarJAR(_ context.Context) error {
 	if sidecar.IsPlaceholder() {
 		return fmt.Errorf("placeholder JAR embedded; run `make sidecar && make sanderling` to embed the real fat JAR")
@@ -38,6 +107,37 @@ func checkSidecarJAR(_ context.Context) error {
 	return nil
 }
 
+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)
+		}
+	}
+	switch options.platform {
+	case "web", "android", "ios", "all":
+		return options, nil
+	default:
+		return doctorOptions{}, fmt.Errorf("unsupported platform: %q (web, android, ios, all)", options.platform)
+	}
+}
+
 func runDoctorChecks(ctx context.Context, checks []doctorCheck, stdout io.Writer) error {
 	failures := 0
 	for _, check := range checks {

cmd/sanderling/doctor_test.go

@@ -81,3 +81,93 @@ func TestCheckExecutableOnPath_MissingCommand(t *testing.T) {
 		t.Errorf("expected error for missing command")
 	}
 }
+
+func TestDoctorChecksFor_Web_OmitsJava(t *testing.T) {
+	for _, c := range doctorChecksFor("web") {
+		if strings.Contains(c.Name, "java") || strings.Contains(c.Name, "sidecar") || strings.Contains(c.Name, "adb") {
+			t.Errorf("web checks should not include %q", c.Name)
+		}
+	}
+	if len(doctorChecksFor("web")) == 0 {
+		t.Error("web checks empty")
+	}
+}
+
+func TestDoctorChecksFor_Android_IncludesADB(t *testing.T) {
+	checks := doctorChecksFor("android")
+	found := false
+	for _, c := range checks {
+		if strings.Contains(c.Name, "adb") {
+			found = true
+		}
+	}
+	if !found {
+		t.Errorf("android checks missing adb: %+v", checks)
+	}
+}
+
+func TestDoctorChecksFor_iOS_IncludesXcrun(t *testing.T) {
+	checks := doctorChecksFor("ios")
+	found := false
+	for _, c := range checks {
+		if strings.Contains(c.Name, "xcrun") {
+			found = true
+		}
+	}
+	if !found {
+		t.Errorf("ios checks missing xcrun: %+v", checks)
+	}
+}
+
+func TestDoctorChecksFor_All_IsUnion(t *testing.T) {
+	all := doctorChecksFor("all")
+	names := map[string]int{}
+	for _, c := range all {
+		names[c.Name]++
+	}
+	for _, name := range []string{"adb on PATH", "xcrun on PATH", "headless chromium can launch"} {
+		if names[name] != 1 {
+			t.Errorf("expected %q in 'all' exactly once, got %d", name, names[name])
+		}
+	}
+}
+
+func TestDoctorChecksFor_UnknownPlatform(t *testing.T) {
+	if got := doctorChecksFor("fuchsia"); got != nil {
+		t.Errorf("expected nil for unknown platform, got %+v", got)
+	}
+}
+
+func TestParseDoctorArgs_DefaultAll(t *testing.T) {
+	options, err := parseDoctorArgs(nil)
+	if err != nil {
+		t.Fatal(err)
+	}
+	if options.platform != "all" {
+		t.Errorf("default platform: got %q, want all", options.platform)
+	}
+}
+
+func TestParseDoctorArgs_ExplicitPlatform(t *testing.T) {
+	for _, form := range [][]string{
+		{"--platform", "web"},
+		{"--platform=web"},
+	} {
+		options, err := parseDoctorArgs(form)
+		if err != nil {
+			t.Fatalf("%v: %v", form, err)
+		}
+		if options.platform != "web" {
+			t.Errorf("%v: got platform=%q, want web", form, options.platform)
+		}
+	}
+}
+
+func TestParseDoctorArgs_RejectsUnknown(t *testing.T) {
+	if _, err := parseDoctorArgs([]string{"--platform=fuchsia"}); err == nil {
+		t.Error("expected error for unsupported platform")
+	}
+	if _, err := parseDoctorArgs([]string{"--bogus"}); err == nil {
+		t.Error("expected error for unknown argument")
+	}
+}

cmd/sanderling/main.go

@@ -76,8 +76,16 @@ func runTest(options testOptions, stdout io.Writer) error {
 	return runTestPipeline(ctx, options, stdout)
 }
 
-func runDoctor(stdout io.Writer) error {
+func runDoctor(args []string, stdout io.Writer) error {
-	return runDoctorChecks(context.Background(), defaultDoctorChecks(), stdout)
+	options, err := parseDoctorArgs(args)
+	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)
 }
 
 func run(args []string, stdout, stderr io.Writer) error {
@@ -99,7 +107,7 @@ func run(args []string, stdout, stderr io.Writer) error {
 		}
 		return runInspect(options, stdout)
 	case "doctor":
-		return runDoctor(stdout)
+		return runDoctor(args[2:], stdout)
 	case "version", "-v", "--version":
 		fmt.Fprintln(stdout, Version)
 		return nil