fix: preserve linear target no-space failures

full_linux_test.go

@@ -0,0 +1,36 @@
+//go:build linux
+
+package acp
+
+import (
+	"context"
+	"errors"
+	"os"
+	"path/filepath"
+	"testing"
+)
+
+func TestRunStreamMapsDeviceFullToTargetNoSpace(t *testing.T) {
+	// Route a disposable target symlink to Linux's deterministic ENOSPC device.
+	root := t.TempDir()
+	input := filepath.Join(root, "source")
+	target := filepath.Join(root, "target")
+	if err := os.WriteFile(input, []byte("fixture"), 0o644); err != nil {
+		t.Fatal(err)
+	}
+	if err := os.Symlink("/dev/full", target); err != nil {
+		t.Fatal(err)
+	}
+	source := &sliceStreamSource{requests: []*StreamRequest{{
+		ID: 1, Source: input, Targets: []string{target},
+	}}}
+
+	// The synchronous stream boundary must preserve the portable no-space sentinel.
+	err := RunStream(
+		context.Background(), source, new(collectingStreamSink),
+		Overwrite(true), SetToDevice(LinearDevice(true)),
+	)
+	if !errors.Is(err, ErrTargetNoSpace) {
+		t.Fatalf("RunStream() error = %v, want %v", err, ErrTargetNoSpace)
+	}
+}