Two-car first release: contact feedback, rival braking and recovery foundation

[LumenHelixLab]

Purpose

The owner approved narrowing the first release to one player and one physical AI on one polished Cleveland course. This replaces the previous three-car target and prioritizes fair, readable contact and reliable rematches.

Changes

• Enforce a two-car grid, update HUD standings, and block race startup if grid creation fails.
• Classify car contact from relative motion and solver impulse; connect impact audio and expose scrape Niagara/Blueprint feedback and cosmetic wear hooks.
• Select one presentation owner per pair and rate-limit feedback.
• Restore target-speed braking and constrain AI commands, including recovery, when a rival is ahead.
• Remove the diagnostic 25-metre forward reset; share recovery clearance checks.
• Add the approved scope, handoff and acceptance checklist in docs/superpowers/specs/2026-10-06-two-car-first-release.md.

Verification

• Baseline: 263 Python tests passed, 5 skipped.
• Final: 264 passed, 5 skipped. New test compiles and executes the production C++ contact/following policy with g++.
• The five existing skips require missing akron_raw.osm.
• Independent source review performed; corrected duplicate pair feedback, recovery bypass of following controls, and startup failure handling.
• Published tree matches the tested local tree exactly.

Draft gates — Grok / Windows Unreal host

This is a source foundation, not a completed physics or visual acceptance.

• Compile with the installed UE 5.7 toolchain and retain logs.
• Verify exactly two cars, one possessed rival, start/results/rematch, and failed-spawn behavior.
• Bind and review collision sound, scrape sound/Niagara, cosmetic material response and optional reduced-motion-aware camera effects. Hooks alone are not finished presentation.
• Playtest sideswipes, rear taps, hard impacts, stopped rivals, rollover and blocked reset; verify no forward/lap advantage.
• Tune braking and passing room; current conservative following is not a completed overtaking strategy.
• Record a complete packaged race and visual review on named hardware.

Keep this draft until the engine and on-track gates pass. No Unreal compile or playtest was available in the Linux implementation environment. Existing unrelated Node CI failures are not claimed fixed.