When a song loads without an explicit arrangement, highway_ws now reads the
player's selected `instrument` from config.json (the same file it already reads
for the default-arrangement preference) and picks the arrangement that matches:
bass -> the Bass part. Guitar — and any unknown/future instrument (drums, keys)
— falls through to the existing preference/most-notes default, which already
lands on a guitar part.
Previously the instrument selector only fed the tuner, so a bass player was
handed the default Lead/guitar chart, and the working-tuning coverage check then
compared a 4-string bass against a 6-string part (always "can't cover"). This is
the instrument->chart routing the working-tuning series leans on.
Server-only (every launch path flows through the WS, so no client change). An
explicit arrangement request always wins, so only the default part chosen on
load changes. Tests: tests/test_highway_ws_instrument_routing.py (bass->Bass,
guitar->default, explicit-wins) — 3 new, existing highway WS tests still green.
Claude-Session: https://claude.ai/code/session_01QbexxfTt8q2tAn436MqGWF
Co-authored-by: Claude Opus 4.8 <noreply@anthropic.com>
