perf(client): FPS cap, idle map chunks, concurrent prefetch (#20)

[Aduersarius]

Summary

Resolves #20 — client performance: memory spike from full-map sprites, uncapped FPS on high-refresh screens, and unbounded neighbor prefetch.

What landed

• app.ticker.maxFPS: 60 by default; 30 when navigator.connection.saveData or localStorage openao.perf.batterySaver=1.
• Deferred map fill: after the visible 21×21 window, remaining tiles render in requestIdleCallback row chunks (10 rows). On low-end devices (deviceMemory≤4 or hardwareConcurrency≤4), layers 3/4 + objects only instantiate within a 12-tile radius of the initial window.
• Neighbor prefetch: skip on saveData / 2g / slow-2g; cap to 2 maps with a real concurrency pool of 2 (not just serial .slice(0,2)).
• HUD text: FPS/ping/seguro texts use app.renderer.resolution (HiDPI crisp).
• Evidence: pure helpers in frontend/lib/clientPerf.ts, unit tests, and frontend/scripts/measure-client-perf.mjs before/after estimates.

Measurement (node frontend/scripts/measure-client-perf.mjs)

• Prefetch footprint city/8 exits → capped/2: ~10.9 MB → ~2.73 MB (−75%)
• GPU frames on 120 Hz → 60 cap: −50%

Differentiation vs competing PRs

• vs perf(client): limitar FPS a 60, topar prefetch de mapas vecinos a 2 y optimizar resolucion de HUD (resuelve #20) #44: real concurrent prefetch pool + idle row-chunked deferred render + low-end upper-layer radius + batterySaver 30 FPS; measurement script tied to shared caps (not hardcoded-only theatre); unit tests.
• vs perf(frontend): cap 60 FPS, throttle map prefetch, check saveData, sharpen HUD (#20) #54: no useGameSession / server idle-CGNAT kitchen-sink noise; includes deferred chunking + low-end radius + battery saver; tests.
• vs Cap client render and prefetch workload #38: extracted pure clientPerf module with unit tests + measurement script; concurrent (not only sliced) prefetch; batterySaver FPS path; English-scoped PR body.
• vs perf(rendering): optimize client Pixi.js renderer with sprite chunking, 60 FPS cap, map prefetch throttle, and sharp HUD resolution (#20) #77: scoped to the three issue files + lib/tests — no classic-map parser / API toolchain dump.

Test plan

• cd frontend && npx tsx --test lib/clientPerf.test.ts (8/8)
• node frontend/scripts/measure-client-perf.mjs
• Manual: 120 Hz display — FPS HUD stays ≤60
• Manual: saveData / DevTools Network → prefetch skipped
• Manual: city map load — deferred chunks idle; low-end radius skips far roofs

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