Validate type codes against ValueType in encode_row_header

Previously only checked that type codes fit in 4 bits (<=15). Now also
validates they are defined ValueType members, catching undefined codes
like 0, 6, 7, 8, etc. that would fail on decode.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

Author: antoineleclair

src/dqlitewire/tuples.py

@@ -163,9 +163,12 @@ def encode_row_header(types: Sequence[ValueType]) -> bytes:
     if not types:
         return b""
 
+    _valid_type_codes = frozenset(ValueType)
     for i, t in enumerate(types):
         if int(t) > 15:
             raise EncodeError(f"Value type {t} at index {i} exceeds 4-bit nibble range (max 15)")
+        if int(t) not in _valid_type_codes:
+            raise EncodeError(f"Invalid type code {int(t)} at index {i}: not a valid ValueType")
 
     header = bytearray()
     for i in range(0, len(types), 2):

tests/test_tuples.py

@@ -365,6 +365,26 @@ def test_decode_insufficient_data(self) -> None:
         with pytest.raises(DecodeError, match="Not enough data for row header"):
             decode_row_header(b"\x01\x02\x03\x04", 1)
 
+    def test_encode_rejects_type_code_zero(self) -> None:
+        """encode_row_header should reject type code 0, which is not a valid ValueType."""
+        import pytest
+
+        from dqlitewire.exceptions import EncodeError
+
+        with pytest.raises(EncodeError, match="[Ii]nvalid.*type"):
+            encode_row_header([0])
+
+    def test_encode_rejects_undefined_type_codes(self) -> None:
+        """encode_row_header should reject type codes not defined in ValueType."""
+        import pytest
+
+        from dqlitewire.exceptions import EncodeError
+
+        # Type codes 6, 7, 8 are undefined
+        for code in [6, 7, 8, 12, 13, 14, 15]:
+            with pytest.raises(EncodeError, match="[Ii]nvalid.*type"):
+                encode_row_header([code])
+
 
 class TestRowValuesBlob:
     def test_roundtrip_with_blob(self) -> None: