diff --git a/pkg/mount/coverage_more_test.go b/pkg/mount/coverage_more_test.go
index 65d1f0b..1805c42 100644
--- a/pkg/mount/coverage_more_test.go
+++ b/pkg/mount/coverage_more_test.go
@@ -47,3 +47,84 @@ func TestSetupAndTeardownWithFakeCommands(t *testing.T) {
 		t.Fatalf("partitionPath /dev = %q", got)
 	}
 }
+
+func TestSetupReportsLoopAndTempDirFailures(t *testing.T) {
+	dir := t.TempDir()
+	scripts := filepath.Join(dir, "bin")
+	if err := os.MkdirAll(scripts, 0o755); err != nil {
+		t.Fatal(err)
+	}
+	write := func(name, body string) {
+		path := filepath.Join(scripts, name)
+		if err := os.WriteFile(path, []byte("#!/usr/bin/env bash\nset -eu\n"+body+"\n"), 0o755); err != nil {
+			t.Fatalf("write %s: %v", name, err)
+		}
+	}
+	write("losetup", `exit 2`)
+	write("mount", `exit 0`)
+	write("umount", `exit 0`)
+	t.Setenv("PATH", scripts+string(os.PathListSeparator)+os.Getenv("PATH"))
+	if _, err := Setup(filepath.Join(dir, "image.img")); err == nil {
+		t.Fatal("expected losetup failure")
+	}
+
+	tmpFile := filepath.Join(dir, "tmp-file")
+	if err := os.WriteFile(tmpFile, []byte("not-a-dir"), 0o644); err != nil {
+		t.Fatal(err)
+	}
+	t.Setenv("TMPDIR", tmpFile)
+	if _, err := Setup("/dev/loop9"); err == nil {
+		t.Fatal("expected temp-dir creation failure")
+	}
+}
+
+func TestSetupReportsMountFailures(t *testing.T) {
+	t.Run("boot", func(t *testing.T) {
+		dir := t.TempDir()
+		scripts := filepath.Join(dir, "bin")
+		if err := os.MkdirAll(scripts, 0o755); err != nil {
+			t.Fatal(err)
+		}
+		write := func(name, body string) {
+			path := filepath.Join(scripts, name)
+			if err := os.WriteFile(path, []byte("#!/usr/bin/env bash\nset -eu\n"+body+"\n"), 0o755); err != nil {
+				t.Fatalf("write %s: %v", name, err)
+			}
+		}
+		write("mount", `exit 3`)
+		write("umount", `exit 0`)
+		write("losetup", `exit 0`)
+		t.Setenv("PATH", scripts+string(os.PathListSeparator)+os.Getenv("PATH"))
+		if _, err := Setup("/dev/loop9"); err == nil {
+			t.Fatal("expected boot mount failure")
+		}
+	})
+
+	t.Run("root", func(t *testing.T) {
+		dir := t.TempDir()
+		scripts := filepath.Join(dir, "bin")
+		if err := os.MkdirAll(scripts, 0o755); err != nil {
+			t.Fatal(err)
+		}
+		state := filepath.Join(dir, "mount-count")
+		write := func(name, body string) {
+			path := filepath.Join(scripts, name)
+			if err := os.WriteFile(path, []byte("#!/usr/bin/env bash\nset -eu\n"+body+"\n"), 0o755); err != nil {
+				t.Fatalf("write %s: %v", name, err)
+			}
+		}
+		write("mount", `state="`+state+`"
+count=0
+if [[ -f "$state" ]]; then count="$(cat "$state")"; fi
+count=$((count + 1))
+printf '%s' "$count" > "$state"
+if [[ "$count" == "2" ]]; then exit 4; fi
+exit 0`)
+		write("umount", `exit 0`)
+		write("losetup", `exit 0`)
+		t.Setenv("PATH", scripts+string(os.PathListSeparator)+os.Getenv("PATH"))
+		if _, err := Setup("/dev/loop9"); err == nil {
+			t.Fatal("expected root mount failure")
+		}
+	})
+}
diff --git a/pkg/writer/coverage_more_test.go b/pkg/writer/coverage_more_test.go
index c74552c..335d8b8 100644
--- a/pkg/writer/coverage_more_test.go
+++ b/pkg/writer/coverage_more_test.go
@@ -39,3 +39,39 @@ func TestWriteImageWithProgressBranches(t *testing.T) {
 		t.Fatal("expected missing source error")
 	}
 }
+
+func TestCopyFileErrorBranches(t *testing.T) {
+	dir := t.TempDir()
+	src := filepath.Join(dir, "src.img")
+	if err := os.WriteFile(src, []byte("writer-errors"), 0o644); err != nil {
+		t.Fatal(err)
+	}
+
+	blockedParent := filepath.Join(dir, "blocked-parent")
+	if err := os.WriteFile(blockedParent, []byte("not-a-dir"), 0o644); err != nil {
+		t.Fatal(err)
+	}
+	if err := copyFile(context.Background(), src, filepath.Join(blockedParent, "dest.img"), 0, nil); err == nil {
+		t.Fatal("expected destination parent mkdir failure")
+	}
+	if err := copyFile(context.Background(), filepath.Join(dir, "missing.img"), filepath.Join(dir, "dest.img"), 0, nil); err == nil {
+		t.Fatal("expected source open failure")
+	}
+	if err := copyFile(context.Background(), src, dir, 0, nil); err == nil {
+		t.Fatal("expected destination create failure")
+	}
+
+	sourceDir := filepath.Join(dir, "source-dir")
+	if err := os.Mkdir(sourceDir, 0o755); err != nil {
+		t.Fatal(err)
+	}
+	if err := copyFile(context.Background(), sourceDir, filepath.Join(dir, "dir-read.img"), 0, nil); err == nil {
+		t.Fatal("expected directory read failure")
+	}
+	if _, err := os.Stat("/dev/full"); err != nil {
+		t.Skip("/dev/full is required for deterministic write-error coverage")
+	}
+	if err := copyFile(context.Background(), src, "/dev/full", int64(len("writer-errors")), nil); err == nil {
+		t.Fatal("expected /dev/full write failure")
+	}
+}