feat(remote): match the server CDM to the client's DRM and read vaults first

A dual widevine/playready cdm entry now loads the device of the client's DRM system, for old clients too since they already send cdm_type. A new client hands a capped track to its own device for the track's DRM system, and raises the refusal only after its local vaults miss.

tests/remote/key_source.py

@@ -1,3 +1,4 @@
+import logging
 from types import SimpleNamespace
 from typing import Any, Iterable, Optional
 from uuid import UUID
@@ -17,7 +18,41 @@ def remote_keys(
     svc._server_cdm = server_cdm
     svc.server_cdm_type = server_cdm_type
     svc.client_licensed = set(client_licensed)
+    svc.deferred_refusals = {}
     svc.server_vault_keys = dict(server_vault_keys or {})
     svc.server_vault = ServerVault(svc)
-    svc.ctx = SimpleNamespace(obj=SimpleNamespace(cdm=local_cdm))
+    svc.ctx = SimpleNamespace(obj=SimpleNamespace(cdm=local_cdm, cdm_for=None))
     return svc
+
+
+CAPPED = {"keys": {}, "capped_tracks": {"vid": {"reason": "server_cdm_max_height", "max_height": 1080}}}
+PR_DEVICE = SimpleNamespace(is_playready=True, security_level=3000)
+
+
+def remote_session(local_cdm: Any, answer: dict) -> RemoteService:
+    """A server-CDM RemoteService whose every POST records its payload in ``posts`` and returns ``answer``."""
+    svc = remote_keys(server_cdm_type="playready", local_cdm=local_cdm)
+    svc._track_alias = {}
+    svc._title_alias = {}
+    svc._session_id = "sess"
+    svc.log = logging.getLogger("test-remote-session")
+    posts: list = []
+    svc.client = SimpleNamespace(post=lambda endpoint, payload, expect=(): posts.append(payload) or answer)
+    svc.drain_server_logs = lambda: None
+    svc.posts = posts
+    return svc
+
+
+class OneTrack(list):
+    @property
+    def videos(self) -> list:
+        return list(self)
+
+    @property
+    def audio(self) -> list:
+        return []
+
+
+def one_title(track: Any) -> SimpleNamespace:
+    """A title holding only ``track``, as a video."""
+    return SimpleNamespace(tracks=OneTrack([track]))