fix: commit migration session setup

Assistant: codex
Assistant-Model: gpt-5.6-sol
Assistant-Session: 01a053ff-1d6f-7fe2-ac1c-a6eb40a42a0c

hub_core/migrations/roles.py

@@ -1,6 +1,13 @@
 from __future__ import annotations
 
 import re
+from typing import Protocol
+
+
+class MigrationConnection(Protocol):
+    def exec_driver_sql(self, statement: str) -> object: ...
+
+    def commit(self) -> None: ...
 
 
 def migration_role_statement(role: str | None) -> str | None:
@@ -19,3 +26,27 @@ def migration_schema_statement(schema: str | None) -> str | None:
     if not re.fullmatch(r"[a-z_][a-z0-9_]{0,62}", schema):
         raise ValueError("HUB_CORE_MIGRATION_SCHEMA is not a safe PostgreSQL schema name")
     return f'SET search_path TO "{schema}", public'
+
+
+def configure_migration_session(
+    connection: MigrationConnection,
+    *,
+    role: str | None,
+    schema: str | None,
+) -> None:
+    """Apply and commit session settings before Alembic opens its transaction."""
+    statements = tuple(
+        statement
+        for statement in (
+            migration_role_statement(role),
+            migration_schema_statement(schema),
+        )
+        if statement is not None
+    )
+    for statement in statements:
+        connection.exec_driver_sql(statement)
+    if statements:
+        # SQLAlchemy 2 autobegins on exec_driver_sql().  Without this commit,
+        # Alembic joins the setup transaction and its DDL is rolled back when
+        # the connection closes.
+        connection.commit()