fix: close workspace preprocessing contract gaps

tools/thothctl/internal/safeio/files_test.go

@@ -75,3 +75,51 @@ func TestWriteCanonicalExclusiveRejectsExistingAndCreatesPrivateFile(t *testing.
 		t.Fatalf("replacement = %v", err)
 	}
 }
+
+func TestReadCanonicalRegularRejectsHardlinkAndDirectory(t *testing.T) {
+	root, err := filepath.EvalSymlinks(t.TempDir())
+	if err != nil {
+		t.Fatal(err)
+	}
+	original := filepath.Join(root, "original.sql")
+	if err := os.WriteFile(original, []byte("select 1"), 0o600); err != nil {
+		t.Fatal(err)
+	}
+	hardlink := filepath.Join(root, "hardlink.sql")
+	if err := os.Link(original, hardlink); err != nil {
+		t.Fatal(err)
+	}
+	if _, err := ReadCanonicalRegular(hardlink, 1024); !errors.Is(err, ErrUnsafeFile) {
+		t.Fatalf("hardlink error = %v, want ErrUnsafeFile", err)
+	}
+	directory := filepath.Join(root, "directory.sql")
+	if err := os.Mkdir(directory, 0o700); err != nil {
+		t.Fatal(err)
+	}
+	if _, err := ReadCanonicalRegular(directory, 1024); !errors.Is(err, ErrUnsafeFile) {
+		t.Fatalf("directory error = %v, want ErrUnsafeFile", err)
+	}
+}
+
+func TestValidateCanonicalOutputPathRejectsExistingDirectoryAndSymlink(t *testing.T) {
+	root, err := filepath.EvalSymlinks(t.TempDir())
+	if err != nil {
+		t.Fatal(err)
+	}
+	directory := filepath.Join(root, "existing.yaml")
+	if err := os.Mkdir(directory, 0o700); err != nil {
+		t.Fatal(err)
+	}
+	if err := ValidateCanonicalOutputPath(directory); !errors.Is(err, ErrUnsafeFile) {
+		t.Fatalf("existing directory error = %v, want ErrUnsafeFile", err)
+	}
+	target := filepath.Join(root, "target.yaml")
+	if err := os.WriteFile(target, []byte("target"), 0o600); err != nil {
+		t.Fatal(err)
+	}
+	link := filepath.Join(root, "link.yaml")
+	testsupport.SymlinkOrSkip(t, target, link)
+	if err := ValidateCanonicalOutputPath(link); !errors.Is(err, ErrUnsafeFile) {
+		t.Fatalf("output symlink error = %v, want ErrUnsafeFile", err)
+	}
+}