fix(models): review feedback — separator vocabulary, constraints stub, import style

The scopes sanitize now shares the registry guard's separator
vocabulary: tab/newline/CR read as spaces, and every other C0 byte —
including the U+001C–U+001F block str.split() would silently promote to
separators — strips like the control it is, so a control byte inside a
token can never split it into two valid-looking scopes (pinned
alongside the registry's refusal).

The livepass auth-constraints stub serves the new
app_identity_auth_modes field so the pass exercises the served-data
path for the model list's auth badge, and the session-module import in
the mint tests drops to the string-path monkeypatch spelling
(single-style imports).

tests/test_model_provider_obo.py

@@ -1640,9 +1640,7 @@ class TestModelOboToken:
         """A delegated mode with no registered grant-profile pairing cannot
         pin a leg, so the dispatch refuses loudly before the mint bridge —
         minting with leg=None would run the pre-dedicated-mode overload."""
-        import turnstone.core.session as session_module
-
-        monkeypatch.setattr(session_module, "MODEL_AUTH_MODE_PROFILES", {})
+        monkeypatch.setattr("turnstone.core.session.MODEL_AUTH_MODE_PROFILES", {})
         reg = _registry_with(self._obo_cfg())
         sess = _fake_session(registry=reg, user_id=USER, mint_token="never")
         with pytest.raises(BackendAuthUnavailableError, match="grant-profile pairing"):

tests/test_model_registry.py

@@ -2982,14 +2982,17 @@ def test_obo_scopes_normalizers_agree_across_modules() -> None:
     assert mr_module.sanitize_backend_auth_scopes(dirty) == "aud-gwopenid"
     # The C0 separator block counts as Python whitespace, so a bare
     # str.split() would swallow it before the guard could refuse; the
-    # registry must refuse it like every other control byte, while the
-    # sanctioned separators (tab/newline/CR, blessed in the corpus above)
-    # keep collapsing.
+    # registry must refuse it like every other control byte, and the
+    # SANITIZE must strip it like every other control — never promote it to
+    # a separator that splits one token into two valid-looking scopes —
+    # while the sanctioned separators (tab/newline/CR, blessed in the
+    # corpus above) keep collapsing.
     for sep_byte in (chr(0x1C), chr(0x1D), chr(0x1E), chr(0x1F)):
         with pytest.raises(mr_module.ModelAuthConfigError):
             mr_module._normalize_auth_mode(
                 "gw", "rfc8693_obo", "api://gw", f"aud-gw{sep_byte}openid"
             )
+        assert mr_module.sanitize_backend_auth_scopes(f"aud-gw{sep_byte}openid") == "aud-gwopenid"
 
 
 def test_control_bearing_alias_refuses_to_load() -> None: