Compare admin token as UTF-8 bytes to avoid TypeError on non-ASCII input (B-46)

secrets.compare_digest raises TypeError instead of returning False when a
str argument contains non-ASCII characters, turning a bad admin token into
an unhandled 500 instead of the expected 403. Encode both sides before
comparing.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>

tests/unit/test_admin.py

@@ -67,6 +67,15 @@ async def test_admin_rejects_wrong_token(client):
     assert resp.status_code == 403
 
 
+async def test_admin_rejects_non_ascii_token_with_403_not_500(client):
+    """B-46: secrets.compare_digest raises TypeError on a non-ASCII str, which
+    used to bubble up as a 500 instead of the expected 403. httpx encodes str
+    header values as ASCII client-side, so the raw UTF-8 bytes are passed
+    directly to reproduce what a real non-ASCII header on the wire looks like."""
+    resp = await client.get("/admin/config", headers={"X-Admin-Token": "café".encode("utf-8")})
+    assert resp.status_code == 403
+
+
 async def test_admin_reads_and_updates_config(client):
     headers = {"X-Admin-Token": "test-admin-token"}