docs(mcp): align token-encryption + mint docstrings with oauth_obo

Startup key-enforcement counts ALL user-scoped auth types (oauth_user and oauth_obo, per is_user_scoped_auth), and the entra mint leg always carries scope=<audience>/.default (per-server oauth_scopes is ignored on that leg). The docstrings named only oauth_user / left the scope behavior ambiguous. Comment-only; no behavior change.

tests/test_mcp_obo_mint.py

@@ -8,8 +8,9 @@ BRIEFING.md ("Verified wire shapes") — every mock asserts the EXACT form
 payload posted to the IdP token endpoint (body-inspecting, not
 call-counting):
 
-- entra: ONE refresh-token grant carrying ``scope=<audience>/.default``
-  (or the per-server ``oauth_scopes`` override verbatim);
+- entra: ONE refresh-token grant always carrying
+  ``scope=<audience>/.default`` (per-server ``oauth_scopes`` is ignored
+  on this leg — a bare scope list would drop the audience);
 - rfc8693: a refresh grant (NO scope key) for a subject token, then a
   token-exchange grant with ``audience=<server oauth_audience>`` and the
   per-server scope only when configured.

turnstone/core/mcp_crypto.py

@@ -596,13 +596,14 @@ def initialize_mcp_crypto_state(app_state: object, *, node_id: str = "") -> None
     1. ``load_mcp_token_cipher_config()`` — wrapped in try/except. Raises
        :class:`SystemExit(1)` on :class:`MCPTokenKeyConfigError` after
        logging.
-    2. Counts ``mcp_servers`` rows with ``auth_type='oauth_user'``. If
+    2. Counts ``mcp_servers`` rows with a user-scoped ``auth_type``
+       (``oauth_user`` or ``oauth_obo``; see ``is_user_scoped_auth``). If
        any exist AND no key is configured, raises ``SystemExit(1)``.
        Same enforcement when ``[oidc] capture_user_credential`` is
        enabled (the captured IdP credential must be encrypted at rest).
     3. On success, sets ``app_state.mcp_token_cipher`` and
        ``app_state.mcp_token_store`` (both possibly ``None`` when no
-       key + no oauth_user rows).
+       key + no user-scoped rows).
 
     The helper is shared by ``turnstone/server.py:_lifespan`` and
     ``turnstone/console/server.py:_lifespan``.  A separate