diff --git a/backend/src/platform/api/middleware.py b/backend/src/platform/api/middleware.py
index a19e61e..d364e6f 100644
--- a/backend/src/platform/api/middleware.py
+++ b/backend/src/platform/api/middleware.py
@@ -3,6 +3,7 @@
 import logging
 import time
 
+from starlette.exceptions import HTTPException
 from starlette.middleware.base import BaseHTTPMiddleware
 from starlette.requests import Request
 from starlette.responses import Response, JSONResponse
@@ -61,6 +62,8 @@ async def dispatch(self, request: Request, call_next) -> Response:
                 {"detail": str(exc)},
                 status_code=status.HTTP_503_SERVICE_UNAVAILABLE,
             )
+        except HTTPException:
+            raise  # Let Starlette handle route-level HTTP errors (e.g. 404)
         except Exception:
             logger.exception("Unhandled exception in PlatformMiddleware")
             return JSONResponse(
diff --git a/backend/src/platform/api/routes.py b/backend/src/platform/api/routes.py
index a98fe03..7ba1011 100644
--- a/backend/src/platform/api/routes.py
+++ b/backend/src/platform/api/routes.py
@@ -407,7 +407,11 @@ async def init_environment(request: Request) -> JSONResponse:
         logger.warning("Unauthorized template access in init_environment")
         return unauthorized()
     except ValueError as e:
-        logger.warning(f"Template resolution failed in init_environment: {e}")
+        logger.warning(
+            f"Template resolution failed in init_environment: {e} "
+            f"(service={body.templateService!r}, name={body.templateName!r}, "
+            f"testId={body.testId!r}, schema={body.templateSchema!r})"
+        )
         return bad_request(str(e))
 
     if not body.testId and not body.impersonateUserId and not body.impersonateEmail:
diff --git a/backend/src/platform/isolationEngine/environment.py b/backend/src/platform/isolationEngine/environment.py
index 010cd27..a7326ad 100644
--- a/backend/src/platform/isolationEngine/environment.py
+++ b/backend/src/platform/isolationEngine/environment.py
@@ -55,14 +55,35 @@ def migrate_schema(self, template_schema: str, target_schema: str) -> None:
         self._set_replica_identity(target_schema)
 
     def _ensure_box_columns(self, schema: str) -> None:
-        """Add columns that may be missing from older template snapshots."""
+        """Add columns that may be missing from older template snapshots.
+
+        Only runs against schemas that actually contain Box tables.  Each
+        ALTER TABLE is wrapped in a SAVEPOINT so that a single failure does
+        not poison the surrounding transaction (the same pattern used by
+        ``_copy_custom_indexes``).
+        """
         _columns = [
             # (table, column, SQL type, default)
             ("box_folders", "path", "VARCHAR(500)", "'/'"),
             ("box_files", "path", "VARCHAR(500)", "'/0/'"),
         ]
         with self.session_manager.base_engine.begin() as conn:
+            # Quick check: skip entirely when the schema has no Box tables.
+            has_box = conn.execute(
+                text(
+                    "SELECT EXISTS("
+                    "  SELECT 1 FROM information_schema.tables"
+                    "  WHERE table_schema = :schema"
+                    "    AND table_name = 'box_folders'"
+                    ")"
+                ),
+                {"schema": schema},
+            ).scalar()
+            if not has_box:
+                return
+
             for table, col, sql_type, default in _columns:
+                nested = conn.begin_nested()
                 try:
                     conn.execute(
                         text(
@@ -71,7 +92,9 @@ def _ensure_box_columns(self, schema: str) -> None:
                             f"DEFAULT {default}"
                         )
                     )
+                    nested.commit()
                 except Exception as exc:
+                    nested.rollback()
                     logger.warning(
                         f"Could not ensure column {schema}.{table}.{col}: {exc}"
                     )