feat(android): detect foreground package via adb dumpsys

internal/android/android.go

@@ -8,6 +8,7 @@ import (
 	"os"
 	"os/exec"
 	"path/filepath"
+	"regexp"
 	"slices"
 	"strings"
 	"time"
@@ -236,6 +237,38 @@ func waitForBoot(ctx context.Context, timeout time.Duration) error {
 	}
 }
 
+// ForegroundPackage returns the package of the currently resumed activity on
+// the connected device, or "" when it cannot be determined.
+func ForegroundPackage(ctx context.Context) (string, error) {
+	adb, err := AdbBinary()
+	if err != nil {
+		return "", err
+	}
+	output, err := exec.CommandContext(ctx, adb, "shell", "dumpsys", "activity", "activities").Output()
+	if err != nil {
+		return "", err
+	}
+	return parseForegroundPackage(string(output)), nil
+}
+
+// resumedActivityPackage matches the "<package>/<activity>" component name that
+// dumpsys prints on ResumedActivity lines, capturing the package.
+var resumedActivityPackage = regexp.MustCompile(`([a-zA-Z][a-zA-Z0-9_.]*)/[a-zA-Z0-9_.$]+`)
+
+// parseForegroundPackage extracts the foreground package from `dumpsys activity
+// activities` output by reading the first ResumedActivity component name.
+func parseForegroundPackage(dumpsys string) string {
+	for line := range strings.SplitSeq(dumpsys, "\n") {
+		if !strings.Contains(line, "ResumedActivity") {
+			continue
+		}
+		if match := resumedActivityPackage.FindStringSubmatch(line); match != nil {
+			return match[1]
+		}
+	}
+	return ""
+}
+
 func bootCompleted(ctx context.Context) (bool, error) {
 	adb, err := AdbBinary()
 	if err != nil {

internal/android/android_test.go

@@ -91,3 +91,39 @@ func TestPathContains(t *testing.T) {
 		t.Error("did not expect /nope in PATH")
 	}
 }
+
+func TestParseForegroundPackage(t *testing.T) {
+	cases := []struct {
+		name    string
+		dumpsys string
+		want    string
+	}{
+		{
+			name:    "mResumedActivity folio",
+			dumpsys: "  Stack #0:\n    mResumedActivity: ActivityRecord{a1b2c3 u0 app.folio/.MainActivity t42}\n",
+			want:    "app.folio",
+		},
+		{
+			name:    "topResumedActivity chrome",
+			dumpsys: "ResumedActivity: ActivityRecord{ff u0 com.android.chrome/com.google.android.apps.chrome.Main t9}\n  topResumedActivity=ActivityRecord{ff u0 com.android.chrome/com.google.android.apps.chrome.Main}",
+			want:    "com.android.chrome",
+		},
+		{
+			name:    "launcher",
+			dumpsys: "    mResumedActivity: ActivityRecord{x u0 com.google.android.apps.nexuslauncher/.NexusLauncherActivity t1}",
+			want:    "com.google.android.apps.nexuslauncher",
+		},
+		{
+			name:    "no resumed activity",
+			dumpsys: "  some unrelated dumpsys output\n  with no resumed line\n",
+			want:    "",
+		},
+	}
+	for _, tc := range cases {
+		t.Run(tc.name, func(t *testing.T) {
+			if got := parseForegroundPackage(tc.dumpsys); got != tc.want {
+				t.Errorf("parseForegroundPackage = %q, want %q", got, tc.want)
+			}
+		})
+	}
+}