fix(core): floor adaptive precision at float resolution to let springs settle on sub-precision drift

[joshuaellis]

Closes #2208.

Summary

When a caller passes a target value to controller.start() that differs from the current value by less than the smallest difference doubles can represent at that magnitude, the spring entered animation with an adaptive precision the math could never satisfy — so the animation never finished and the awaited start() promise never resolved. The original repro is layout code computing positions with Math.cos(Math.PI / 2): JS returns 6.12e-17 instead of 0, so a "logical 160" target arrives as 159.99999999999997. isEqual(160, 159.99999999999997) is false, the spring sees a non-zero distance, and the adaptive precision (|to - from| * 0.001 ≈ 3.5e-18) is unrepresentable. The spring drifts forever; frameLoop never goes idle.

The fix floors the adaptive default at max(|to|, |from|, 1) * Number.EPSILON — the smallest meaningful precision for the values being animated. Caller-supplied config.precision and the from === to fast path are unchanged.

Repro

const ctrl = new Controller({ x: 160, y: 0, scale: 1 })
const driftedTarget = 160 * Math.cos(Math.PI + Math.PI / 2) + 160
// 159.99999999999997 — sub-precision drift from 160

await ctrl.start({ x: driftedTarget, y: 110, scale: 0 })
// previously never resolved

[changeset-bot]

🦋 Changeset detected

Latest commit: 6f96c9c

The changes in this PR will be included in the next version bump.

This PR includes changesets to release 12 packages

Name	Type
@react-spring/core	Patch
@react-spring/animated	Patch
@react-spring/mock-raf	Patch
@react-spring/parallax	Patch
@react-spring/rafz	Patch
@react-spring/shared	Patch
@react-spring/types	Patch
@react-spring/konva	Patch
@react-spring/native	Patch
@react-spring/three	Patch
@react-spring/web	Patch
@react-spring/zdog	Patch

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Project	Deployment	Actions	Updated (UTC)
react-spring	Error		May 23, 2026 2:29pm