# Engine playground — IX-85–120

Creator and inventor: Lars Rocha. Coding assistance supports implementation and testing; it does not imply ownership.

36 new interactive instruments, alongside the 73 existing labs. Each page has variable controls, a visual trace, sample inspection, a law statement, scope limits and versioned study replay. The 12 formerly proposed upgrades are separate companions.

The calculations use a pinned Rust adapter compiled to WebAssembly, with explicit browser extractions for the spotter, sampling and directory views. This is a bounded inspector, not a port of every game. The roof experiment, flat-ground traffic, shared mesh edges and CPU-only fleet measurements identify their limits on the page. No GPU performance is inferred.

## Start exploring

- [IX-85: Contract & parity](engine-contract.html) — Exact words. Visible witnesses.
- [IX-86: Car Law Garage](car-garage.html) — One address. A different silhouette.
- [IX-87: Ridge → roof](ridge-roof.html) — Let the mountain draw a roofline.
- [IX-88: Paint & plates](car-plates.html) — Keep the body. Change its expression.
- [IX-89: Word → range](word-ranges.html) — Type a word. Read its landscape.
- [IX-90: Ridge composition](ridge-composer.html) — Compose peaks, passes and water.
- [IX-91: Ruler fissures](fissures.html) — Find the deep cuts among shallow joints.
- [IX-92: River orders](river-orders.html) — Follow the ruler upstream.
- [IX-93: Settlement addresses](settlements.html) — Seek the next town without searching.
- [IX-94: City plot forge](city-plots.html) — A skyline you can visit in any order.
- [IX-95: Traffic & junctions](traffic.html) — Watch a lane become a journey.
- [IX-96: Sieve roads](sieve-roads.html) — Let an address decide the next bend.
- [IX-97: Tower coverage](tower-coverage.html) — Cover a line. Discover the gaps.
- [IX-98: Wave economy](wave-economy.html) — Same opening. Three spending decisions.
- [IX-99: Spotter influence](spotter.html) — Your position becomes a tower’s advantage.
- [IX-100: Race courses](race-courses.html) — Every metre has an address.
- [IX-101: Flight envelope](flight-envelope.html) — Feel the boundary between climb and stall.
- [IX-102: Arena contacts](arena-contacts.html) — Drop it. Bounce it. Find the goal mouth.
- [IX-103: Trajectory bench](trajectories.html) — Aim beyond a straight line.
- [IX-104: Terrain materials](terrain-materials.html) — One sample. Height, water, colour.
- [IX-105: Sampling blind spots](sampling-alias.html) — The sample can miss the whole law.
- [IX-106: Moving bake timeline](bake-timeline.html) — Fly the window. Watch the work arrive.
- [IX-107: Fleet detail](fleet-detail.html) — Spend detail where you can see it.
- [IX-108: Fixed-step replay](replay.html) — Change the display rate. Keep the tick.
- [IX-109: Engine Law Atlas](engine-atlas.html) — Trace an idea into a working instrument.
- [IX-110: Indexed hash streams](engine-indexed.html) — Reorder your visits. Keep the answers.
- [IX-111: Selection decisions](engine-selection.html) — Read every keep and rejection.
- [IX-112: One rank, three readings](engine-ranks.html) — A car, a settlement, a measured height.
- [IX-113: Shared mesh edges](engine-mesh.html) — Change detail. Inspect the common boundary.
- [IX-114: Horizon bounds](engine-horizons.html) — A gully sees a different sky.
- [IX-115: Support diagnostics](engine-support.html) — Give the same step two different bodies.
- [IX-116: Streaming identities](engine-streaming.html) — Move the window. Keep the ground.
- [IX-117: Valley song](engine-song.html) — Hear the columns you cross.
- [IX-118: Evidence cards](engine-evidence.html) — Make the claim inspectable.
- [IX-119: Generation budgets](engine-budgets.html) — Measure the work before raising the limit.
- [IX-120: Engine notebooks](engine-notebooks.html) — Keep a car, range or road as a recipe.

## Verification and memory

193 preserved source tests pass. The adapter checks 299 unchanged fixture rows against compiled Rust and independent JavaScript, plus 517 domain assertions. Browser tests cover all 36 pages, live edits, play/stop, valid replay, rejected tampering, mobile layouts, cancellation and the bounded main-thread fallback. Those are focused tests; historical whole-project counts are not rerun claims.

A job has at most a 64 × 64 field or 1,200 motion ticks. One worker runs at a time; cancellation terminates it and late results cannot replace a newer window. The worker is recycled after 24 requests. WASM linear memory is capped at 128 MiB; browser/JavaScript memory is additional. Thirty detailed cars reuse one mesh buffer; generated bytes are not resident bytes. The tested adapter workload used 9.25 MiB of WASM memory. This is measured workload evidence, not a bound on total tab memory.

Fissure sampling uses a footprint: coarse and fine cells at the same origin can deliberately differ. The ground-sharing tests use the ordinary ridge field; the fissure test explicitly checks the source footprint behavior.

[Source provenance](engine/provenance.json) · [Engine/dependency licenses](engine/licenses.json) · [Compile the original source](sources/index.html) · [Roadmap](roadmap.html)