New server.engine_env_overrides (engine name → {VAR: val}), merged into
the engine's process env at spawn. Lets low-level driver knobs be set
without hardcoding — set radeon → RADV_DEBUG=syncshaders to serialize
RADV shader dispatch and test whether the Polaris compute-ring async
race (ring comp_x.y.z timeout) is what wedges the RX 580 under sustained
Vulkan compute.
Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_014S8VtAvG499SsCbeESRK7V