fix: Remove charset setting - let server control encoding

Database charset/encoding should be configured on the server,
not the client. Removes:
- charset from ConnectionSettings
- charset from connection template
- charset parameter from adapter connect calls
- charset from thread-safe mode spec

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

Author: dimitri-yatsenko

docs/design/thread-safe-mode.md

@@ -52,7 +52,6 @@ All settings become connection-scoped and are accessed via `conn.config` (read/w
 | `stores` | dict | {} | Blob storage configuration |
 | `cache` | Path | None | Local cache directory |
 | `query_cache` | Path | None | Query cache directory |
-| `charset` | str | "" | Connection charset |
 | `reconnect` | bool | True | Auto-reconnect on lost connection |
 | `display_limit` | int | 12 | Max rows to display |
 | `display_width` | int | 14 | Column width for display |
@@ -365,7 +364,7 @@ class Connection:
     def from_config(cls, cfg=None, *, host=None, user=None, password=None,
                     port=None, backend=None, safemode=None, stores=None,
                     database_prefix=None, cache=None, query_cache=None,
-                    charset=None, reconnect=None, init_fun=None,
+                    reconnect=None, init_fun=None,
                     use_tls=None) -> "Connection":
         """
         Create connection with explicit configuration.
@@ -388,7 +387,6 @@ class Connection:
             **({"database_prefix": database_prefix} if database_prefix is not None else {}),
             **({"cache": cache} if cache is not None else {}),
             **({"query_cache": query_cache} if query_cache is not None else {}),
-            **({"charset": charset} if charset is not None else {}),
             **({"reconnect": reconnect} if reconnect is not None else {}),
         )
 
@@ -421,7 +419,6 @@ class ConnectionConfig:
         "stores": {},
         "cache": None,
         "query_cache": None,
-        "charset": "",
         "reconnect": True,
         "display_limit": 12,
         "display_width": 14,

src/datajoint/adapters/mysql.py

@@ -78,7 +78,6 @@ def connect(
             - init_command: SQL initialization command
             - ssl: TLS/SSL configuration dict (deprecated, use use_tls)
             - use_tls: bool or dict - DataJoint's SSL parameter (preferred)
-            - charset: Character set (default from kwargs)
 
         Returns
         -------
@@ -91,7 +90,6 @@ def connect(
         # Convert boolean True to dict for PyMySQL (PyMySQL expects dict or SSLContext)
         if ssl_config is True:
             ssl_config = {}  # Enable SSL with default settings
-        charset = kwargs.get("charset", "")
 
         # Prepare connection parameters
         conn_params = {
@@ -102,7 +100,6 @@ def connect(
             "init_command": init_command,
             "sql_mode": "NO_ZERO_DATE,NO_ZERO_IN_DATE,ERROR_FOR_DIVISION_BY_ZERO,"
             "STRICT_ALL_TABLES,NO_ENGINE_SUBSTITUTION,ONLY_FULL_GROUP_BY",
-            "charset": charset,
             "autocommit": True,  # DataJoint manages transactions explicitly
         }
 

src/datajoint/connection.py

@@ -222,8 +222,6 @@ def __init__(
         self._conn = None
         self._query_cache = None
         self._is_closed = True  # Mark as closed until connect() succeeds
-        # Store charset to avoid global config access in connect()
-        self._charset = "" if config.thread_safe else config.connection.charset
         # Store reconnect setting for query() method
         self._reconnect = True if config.thread_safe else config.database.reconnect
 
@@ -414,7 +412,6 @@ def connect(self) -> None:
                     user=self.conn_info["user"],
                     password=self.conn_info["passwd"],
                     init_command=self.init_fun,
-                    charset=self._charset,
                     use_tls=self.conn_info.get("ssl"),
                 )
             except Exception as ssl_error:
@@ -431,7 +428,6 @@ def connect(self) -> None:
                         user=self.conn_info["user"],
                         password=self.conn_info["passwd"],
                         init_command=self.init_fun,
-                        charset=self._charset,
                         use_tls=False,  # Explicitly disable SSL for fallback
                     )
                 else:

src/datajoint/settings.py

@@ -225,7 +225,6 @@ class ConnectionSettings(BaseSettings):
     model_config = SettingsConfigDict(extra="forbid", validate_assignment=True)
 
     init_function: str | None = None
-    charset: str = ""  # pymysql uses '' as default
 
 
 class DisplaySettings(BaseSettings):
@@ -825,7 +824,6 @@ def save_template(
                 },
                 "connection": {
                     "init_function": None,
-                    "charset": "",
                 },
                 "display": {
                     "limit": 12,