Three fixes for the Desktop/TUI cold-start stall where the event loop
is blocked for ~14s between HERMES_BACKEND_READY and the first
prompt (#60800):
1. copilot_auth: skip subprocess fallback when any
Copilot env var is explicitly set (even if invalid). The user
expressed token intent via env var; silently substituting a CLI
token is surprising and the subprocess adds up to 5s on Windows.
2. tui_gateway/ws: run resolve_skin() via asyncio.to_thread so config
loading + skin engine init do not block the WS read loop during
the cold-start RPC burst.
3. web_server: extend _warm_gateway_module to pre-import the heavy
module chains (auth, copilot_auth, runtime_provider, skin_engine,
inventory, model_switch) that the first WS connection + RPC burst
would otherwise import on the loop thread. These trigger .pyc
compilation and Defender scans on Windows (15-30s per the existing
comment) and were not covered by the original gateway-only warm.
Tests: 5 new tests in test_cold_start_gil_stall.py + 2 new tests in
test_copilot_auth.py. All 36 copilot_auth tests + 16 ws/web_server
tests pass.
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