DM-38279: Do all spawning work in start

src/rsp_restspawner/errors.py

@@ -1,26 +1,18 @@
-from httpx import Response
+"""Exceptions for the RSP REST spawner.
 
+JupyterHub catches all exceptions derived from `Exception` and treats them the
+same, so the distinction between exceptions is just for better error reporting
+and improved code readability.
+"""
 
-class SpawnerError(Exception):
-    def __init__(self, response: Response) -> None:
-        self._response = response
 
-    def __str__(self) -> str:
-        r = self._response
-        sc = r.status_code
-        rp = r.reason_phrase
-        txt = r.text
-        url = r.url
-        return f"Request for {url}: status code {sc} ({rp}): '{txt}'"
+class InvalidAuthStateError(Exception):
+    """The JupyterHub auth state for the user contains no token."""
 
 
 class MissingFieldError(Exception):
-    pass
-
+    """The reply from the lab controller is missing a required field."""
 
-class EventError(Exception):
-    pass
 
-
-class InvalidAuthStateError(Exception):
-    """The JupyterHub auth state for the user contains no token."""
+class SpawnFailedError(Exception):
+    """The lab controller reports that the spawn failed."""