The initial fix added ~16 lines to server.py, tripping test_server_py_under_750_lines
(server.py must stay a thin dispatcher; logic belongs in api/). Moved the whole
preflight-response into apply_cors_preflight_headers(handler) in api/routes.py;
server.py's do_OPTIONS is now a 4-line dispatcher. server.py 764 -> 746 lines.
Same security behavior (same-origin/allowlist echo, Vary: Origin, no wildcard,
header-less denial); test rewritten to the header-emitting API + added Vary and
no-header-on-denial assertions and a routes.py wildcard regression guard.
nesquena-hermes
8da96a84d3