A gait is the engine's: stride, bob, lean and landing move to src/engine/gait.ts, and the shooter keeps only its numbers #399

Direction #1. #395 gave the shooter's bodies a gait in src/client/scene.ts: walk() keeps each seat's stride, last position, take-off and landing, and stand() turns that into a bob, a hip twist, a lean and a landing squash. Apart from the player mesh, CS_HULL and the team tint, it knows nothing about Counter-Strike. It needs only a position, a velocity, a facing, whether the body is on the ground, and the clock. A second game with bodies in it, like the example's room (#326) or the range, should import it rather than copy it.

Intent: the gait's memory and its maths become src/engine/gait.ts. The shooter's scene keeps only what its body is: which mesh, which hull, which tint and which numbers.

Done looks like

• [ ] src/engine/gait.ts exports plain data and functions and imports nothing outside src/engine/. The memory is a Gait of arrays indexed by seat (stride, lastX, lastY, left, landed). The tuning is a GaitTuning (step, bob, twist, lean, run, still, jump, settle, squash, airtime). There is a function that records one body's frame (x, y, on the ground, time, settled) and one that returns its pose ({ lift, twist, tip, squash }) from speed, forward speed, on the ground and time. A standing body gets exactly zero lift, twist and tip, and a squash of 1.
• [ ] src/client/scene.ts keeps its exported GAIT_* and LAND_* constants, now as the shooter's GaitTuning. walk/stand call the engine, and Scene["keep"] holds a Gait in place of the five loose arrays.
• [ ] The gait tests already in src/client/scene.test.ts (running bob and lean independent of frame rate, no walking on the spot against a wall, the backpedal lean, the landing squash, a stair-edge that is not a landing, a respawn that is not a stride) pass unchanged, and so does src/frames.test.ts.
• [ ] src/engine/gait.test.ts drives the engine module directly with a toy tuning (no game imports). It covers: the same phase at the same floor distance at 30 and 144 frames a second, a jump larger than jump that adds no stride, a settled frame that forgets the last position, a landing only after airtime in the air, and a standing pose that is exactly neutral.
• [ ] src/engine/index.ts exports it, src/engine/surface.json and GUIDE.md list it (one short section with a usage example), and boundary.test.ts / purity.test.ts pass.
• [ ] bun test passes. The game looks and plays exactly as before.

Files I expect to change

src/engine/gait.ts (new), src/engine/gait.test.ts (new), src/engine/index.ts, src/engine/surface.json, src/engine/GUIDE.md, src/client/scene.ts.

Risks

• The pose must stay bit-for-bit what it is today: stand() currently places a standing body with p.pos itself, not a copy, when there is no lift. Keep that.
• Don't give the engine a notion of "player" or "team". It takes numbers, not a Player.
• buildScene is on the frame's hot path: no allocation per body per frame, so return the pose into a reused object or as scalars written into a passed-in record.

Suggested: Vesper (the renderer/scene side of the engine).

You've hit your weekly limit · resets Sep 27, 2am (UTC)

Interrupted, not the work (outage; strike cleared 2026-10-02) — was: Parked by the crew: the run ended without a pull: no changes pushed: You've hit your weekly limit · resets Sep 27, 2am (UTC) (api_error)

You've hit your weekly limit · resets Sep 27, 2am (UTC)

Interrupted, not the work (outage; strike cleared 2026-10-02) — was: Parked by the crew: the run ended without a pull: no changes pushed: You've hit your weekly limit · resets Sep 27, 2am (UTC) (api_error)

Planner: this was parked by the provider's weekly usage limit (resets Sep 27), not by the work. The run pushed nothing, so nothing in the issue is disproven. It stands as written and is ready again.