fix: make max table name length backend-specific (64 MySQL, 63 PostgreSQL)

MySQL allows 64-character identifiers; PostgreSQL allows 63
(NAMEDATALEN-1) and silently truncates longer names.

Add max_table_name_length property to the adapter ABC (default 64),
override to 63 in PostgreSQLAdapter. Replace the hardcoded
MAX_TABLE_NAME_LENGTH constant in declare.py.

No backward compatibility impact — MySQL keeps 64, PostgreSQL
gets the correct 63.

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

Author: dimitri-yatsenko

src/datajoint/adapters/base.py

@@ -259,6 +259,18 @@ def make_full_table_name(self, database: str, table_name: str) -> str:
         """
         return f"{self.quote_identifier(database)}.{self.quote_identifier(table_name)}"
 
+    @property
+    def max_table_name_length(self) -> int:
+        """
+        Maximum length of a table name for this backend.
+
+        Returns
+        -------
+        int
+            Maximum allowed characters in a table identifier.
+        """
+        return 64  # safe default (MySQL limit)
+
     # =========================================================================
     # Type Mapping
     # =========================================================================

src/datajoint/adapters/postgres.py

@@ -249,6 +249,11 @@ def quote_identifier(self, name: str) -> str:
         """
         return f'"{name}"'
 
+    @property
+    def max_table_name_length(self) -> int:
+        """PostgreSQL NAMEDATALEN-1 = 63."""
+        return 63
+
     def split_full_table_name(self, full_table_name: str) -> tuple[str, str]:
         """Split ``"schema"."table"`` into ``('schema', 'table')``."""
         schema, table = full_table_name.replace('"', "").split(".")

src/datajoint/declare.py

@@ -52,7 +52,6 @@
 # Get SQL mapping for core types
 CORE_TYPE_SQL = {name: sql_type for name, (_, sql_type) in CORE_TYPES.items()}
 
-MAX_TABLE_NAME_LENGTH = 63  # PostgreSQL NAMEDATALEN-1; MySQL allows 64 but 63 is safe for both
 CONSTANT_LITERALS = {
     "CURRENT_TIMESTAMP",
     "NULL",
@@ -435,10 +434,10 @@ def declare(
     # Parse table name using adapter (handles backend-specific quoting)
     schema_name, table_name = adapter.split_full_table_name(full_table_name)
 
-    if len(table_name) > MAX_TABLE_NAME_LENGTH:
+    if len(table_name) > adapter.max_table_name_length:
         raise DataJointError(
             "Table name `{name}` exceeds the max length of {max_length}".format(
-                name=table_name, max_length=MAX_TABLE_NAME_LENGTH
+                name=table_name, max_length=adapter.max_table_name_length
             )
         )