test: no test throws a response away; the stream session is narrowed, not baselined

The 7 baselined Optional accesses in plex/stream.py were one fact the type did not carry: the
initial spawn (replace_only=None) always supersedes, so only the fallback respawn can get None.
An assert at the call site says so; the pyright baseline drops 195 -> 188.

test_abuse_limits: the public-URL and YouTube enqueue tests stopped at the profile lookup
(400 no_profile) and passed on that unrelated refusal. They now send an inline spec and assert
the job is queued. The same shape — a request whose response is discarded — sat at 53 more
places across the suite (all returned what they should, measured with a TestClient probe);
each now asserts its status, and test_response_checked keeps it that way (seen red).

backend/tests/test_welcome_mail.py

@@ -229,7 +229,12 @@ def test_registering_again_does_not_create_a_second_account(db, client, monkeypa
     _smtp_on(monkeypatch)
     _capture(monkeypatch, "send_verify_email")
     for _ in range(2):
-        client.post("/auth/register", json={"email": "twice@example.com", "password": _PW})
+        assert (
+            client.post(
+                "/auth/register", json={"email": "twice@example.com", "password": _PW}
+            ).status_code
+            == 200
+        )
 
     db.expire_all()
     rows = db.execute(select(User).where(User.email == "twice@example.com")).scalars().all()