Import no-transaction substrings from dqlitewire instead of inlining

Replace the inline "no transaction is active" / "cannot rollback"
literals in _is_no_tx_rollback_error with the wire-layer constant
NO_TRANSACTION_MESSAGE_SUBSTRINGS. The client and dbapi now share
one source of truth, eliminating the silent-divergence risk when
a server-side wording change requires updating one but not the
other.

Pin via a unit test that exercises the recogniser with each
substring drawn from the wire constant.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

Author: antoineleclair

src/dqliteclient/connection.py

@@ -25,7 +25,7 @@
 )
 from dqlitewire import DEFAULT_MAX_CONTINUATION_FRAMES as _DEFAULT_MAX_CONTINUATION_FRAMES
 from dqlitewire import DEFAULT_MAX_TOTAL_ROWS as _DEFAULT_MAX_TOTAL_ROWS
-from dqlitewire import LEADER_ERROR_CODES
+from dqlitewire import LEADER_ERROR_CODES, NO_TRANSACTION_MESSAGE_SUBSTRINGS
 from dqlitewire import SQLITE_BUSY as _SQLITE_BUSY
 from dqlitewire import TX_AUTO_ROLLBACK_PRIMARY_CODES as _TX_AUTO_ROLLBACK_PRIMARY_CODES
 from dqlitewire import primary_sqlite_code as _primary_sqlite_code
@@ -341,24 +341,26 @@ def _is_no_tx_rollback_error(exc: BaseException) -> bool:
     reply from the server during a ROLLBACK.
 
     Recognised by SQLite primary code 1 (``SQLITE_ERROR``) plus the
-    "no transaction is active" or "cannot rollback" wording. Both
+    wording fragments listed in
+    :data:`dqlitewire.NO_TRANSACTION_MESSAGE_SUBSTRINGS`. Both
     conditions must hold so a disk-full / constraint / IO error whose
     message happens to include the magic substring is not silently
     treated as benign.
 
     Used by the ``transaction()`` context manager and by the pool's
     ``_reset_connection`` to distinguish "server already auto-rolled
     back; preserve the slot" from a real ROLLBACK failure that
-    requires invalidation. Centralising the check avoids drift if the
-    SQLite-error wording ever changes.
+    requires invalidation. The substring list lives in the wire layer
+    so this recogniser and the dbapi's ``_is_no_transaction_error``
+    cannot drift apart on a server-side wording change.
     """
     if not isinstance(exc, OperationalError):
         return False
     code = getattr(exc, "code", None)
     if code is None or _primary_sqlite_code(code) != 1:  # SQLITE_ERROR
         return False
     msg = str(exc).lower()
-    return "no transaction is active" in msg or "cannot rollback" in msg
+    return any(s in msg for s in NO_TRANSACTION_MESSAGE_SUBSTRINGS)
 
 
 # RFC 1035 hostname labels are ASCII letters, digits, and hyphen. We

tests/test_no_transaction_substrings_source_of_truth.py

@@ -0,0 +1,46 @@
+"""Pin: the client-layer ``_is_no_tx_rollback_error`` recogniser
+shares its substring list with ``dqlitewire.NO_TRANSACTION_MESSAGE_SUBSTRINGS``.
+
+A previous shape inlined the literal substrings in two places
+(client and dbapi). Centralising the source in the wire layer
+makes drift impossible at the literal level — both layers
+import the same tuple object.
+"""
+
+from __future__ import annotations
+
+from dqliteclient.connection import _is_no_tx_rollback_error
+from dqlitewire import NO_TRANSACTION_MESSAGE_SUBSTRINGS
+
+
+def test_recogniser_uses_wire_layer_substrings() -> None:
+    """Drive the recogniser with each substring (alongside the right
+    SQLite code) and verify it returns True. If a future maintainer
+    drops a substring on either side, this test detects it via the
+    wire constant."""
+    from dqliteclient.exceptions import OperationalError
+
+    for substr in NO_TRANSACTION_MESSAGE_SUBSTRINGS:
+        exc = OperationalError(1, f"prefix {substr} suffix")
+        assert _is_no_tx_rollback_error(exc), (
+            f"recogniser must accept the substring {substr!r} "
+            "from dqlitewire.NO_TRANSACTION_MESSAGE_SUBSTRINGS"
+        )
+
+
+def test_recogniser_rejects_unrelated_message() -> None:
+    from dqliteclient.exceptions import OperationalError
+
+    exc = OperationalError(1, "some unrelated SQLite error")
+    assert not _is_no_tx_rollback_error(exc)
+
+
+def test_substring_constant_has_expected_values() -> None:
+    """Pin the canonical substring list — both clauses must be
+    present so a server-version drift that drops one but not the
+    other still triggers the recogniser. If a server change requires
+    an update, the integration pin
+    ``test_no_transaction_error_wording.py`` (in dbapi) catches it
+    against a live cluster."""
+    assert "no transaction is active" in NO_TRANSACTION_MESSAGE_SUBSTRINGS
+    assert "cannot rollback" in NO_TRANSACTION_MESSAGE_SUBSTRINGS