feat(render): Classic 2D Highway parity — perspective falling-fret renderer (v0.1.16)

[ChrisBeWithYou]

Stacked on #9 (→ #8 → #7 → #6 → #5). Review only this diff.

What

The highway_2d view slot (added in #7) rendered our horizontal-lane tab scroller — not the 2D highway you meant. Clarified: Byron's "Classic 2D Highway" — the perspective falling-fret highway (X = fret, notes fall toward a strike line at y≈0.82 with project() depth scaling; the 2D cousin of the 3D highway). This PR ports it.

HOST CHECK (2026-07-10): that renderer is createHighway()'s private _defaultRenderer (static/highway.js + static/js/highway-{geometry,draw,state-primitives}.js) — core, closure-fed + websocket-fed, no viz factory → MIRROR (host issue got-feedBack/feedBack#835 asks for a bundle-driven feedBackViz_highway_2d, which would flip this to a clean borrow).

How

New makeClassic2DHighwayRenderer() reading our bundle, host constants/geometry lifted from source:

• #080810 BG, perspective project() (VISIBLE_SECONDS 3.0 / Z_CAM 2.2 / Z_MAX 10.0, strike at y=0.82), centered fretX() trapezoid, converging fret lines, beat sweep, DEFAULT_STRING_COLORS/DIM/BRIGHT palette, glowing now-line, falling perspective-scaled fret-number gems (body + dim glow + white number, open-string wide bar, dead-note X, technique glyphs), sustain trails, amber fret rail with the live anchor-window highlight.
• Fret window follows chart anchors via the host's smoothed displayMaxFret (0.4 rate), falls back to notes' max fret when a chart has no anchors. Lefty mirror + inverted string order honored.
• resolveRendererFactory highway_2d fallback → this (was makeBuiltin2DRenderer); the borrow-first vizFactoryFor('highway_2d') probe is unchanged, so the host factory still wins when #835 ships. makeBuiltin2DRenderer stays the Jumping-Tab (builtin_2d) + >8-string path, untouched.

Deliberate approximations (documented in the renderer header)

• Exotic host overlays our bundle doesn't feed — unison-bend connectors, strum-group brackets, master-difficulty phrase filtering, lyrics, chord frames — omitted.
• A credited hit keeps Virtuoso's green-gem grammar (#22c55e + glow — the cross-surface "a hit is unmistakable" guarantee from the 2026-07-09 tester fix) rather than the host's string-bright lit gem, so a hit reads as clearly here as on our Tab/Notation surfaces. Consume-the-judge: credit stays verifier-only; this is display.

Verification

Screenshot-confirmed static (receding trapezoid, fret lines, strike line, string palette, 0–8 amber rail) and playing (numbered gems falling with perspective scale + sustain trails, near gem landing on the strike line). Full smoke 16/19 — only the 3 pre-existing base reds; smoke-renderers' pixel-enforced highway_2d row green.

🤖 Generated with Claude Code

https://claude.ai/code/session_01MS2YFb6UUSwJVV6CmEa25i

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[ChrisBeWithYou]

Landed on virtuoso-dev via the 2026-07-14 batch integration (v0.2.2), not a GitHub merge event — these branches predate the main→dev reconcile (Byron's Gold-rung #11 took the line to 0.2.x) and were rebased, so their head SHAs don't match the commits that reached dev. All content is verified present in dev (incl. #5's 62fc72e tuningMidis, cherry-picked as f0c78c6). Closing to avoid a duplicate re-merge; the work ships to main via the dev→main PR #4 line. — automated