Stream Phase 1 artifacts from container tmpfs

Co-authored-by: codegirl007 <codegirl-007@users.noreply.github.com>

agentbox/internal/phase1/run_test.go

@@ -0,0 +1,54 @@
+package phase1
+
+import (
+	"image"
+	"image/color"
+	"image/png"
+	"os"
+	"path/filepath"
+	"testing"
+)
+
+func TestSquareCentroid(t *testing.T) {
+	path := filepath.Join(t.TempDir(), "screenshot.png")
+	img := image.NewRGBA(image.Rect(0, 0, 200, 100))
+	green := color.RGBA{R: 0, G: 255, B: 102, A: 255}
+	for y := 20; y < 60; y++ {
+		for x := 80; x < 120; x++ {
+			img.Set(x, y, green)
+		}
+	}
+	writePNG(t, path, img)
+
+	got, err := squareCentroid(path)
+	if err != nil {
+		t.Fatalf("squareCentroid() error = %v", err)
+	}
+	if got.X != 99.5 || got.Y != 39.5 {
+		t.Fatalf("squareCentroid() = (%.1f, %.1f), want (99.5, 39.5)", got.X, got.Y)
+	}
+}
+
+func TestSquareCentroidRejectsMissingSquare(t *testing.T) {
+	path := filepath.Join(t.TempDir(), "empty.png")
+	writePNG(t, path, image.NewRGBA(image.Rect(0, 0, 200, 100)))
+
+	if _, err := squareCentroid(path); err == nil {
+		t.Fatal("squareCentroid() error = nil, want missing-square error")
+	}
+}
+
+func writePNG(t *testing.T, path string, img image.Image) {
+	t.Helper()
+	file, err := os.Create(path)
+	if err != nil {
+		t.Fatal(err)
+	}
+	if err := png.Encode(file, img); err != nil {
+		_ = file.Close()
+		t.Fatal(err)
+	}
+	if err := file.Close(); err != nil {
+		t.Fatal(err)
+	}
+}