diff --git a/docs/accessibility/baseline.md b/docs/accessibility/baseline.md
index b5ab2d3..5abe2bf 100644
--- a/docs/accessibility/baseline.md
+++ b/docs/accessibility/baseline.md
@@ -34,3 +34,9 @@ These are environment controls. A persisted setting would change the public conf
 ## Screen readers
 
 NMSh redraws full-screen frames in the alternate screen. Terminals expose that to assistive technology inconsistently, so NMSh cannot guarantee screen-reader-friendly output. What it does provide is text-carried state and no pointer requirement; behavior with a specific terminal and reader has not been verified.
+
+## Motion
+
+`motion/motion.ts` is a pure engine: profiles per semantic state (`waiting`, `processing`, `streaming`, `transition`, `completion`, `failure`) sampled at an elapsed time. Reduced motion holds every profile still. It never schedules timers, changes width or touches PTY output.
+
+The shimmer (`status/shimmer.ts`) samples the `processing`/`streaming` profiles. The one existing activity timer is already bounded (100 ms), cleared on exit, and its renders are suppressed during passthrough, so no shared scheduler was added; one should arrive with a second animated consumer. `waiting`, `transition`, `completion` and `failure` have no consumer yet.
diff --git a/src/motion/motion.ts b/src/motion/motion.ts
new file mode 100644
index 0000000..5b4110c
--- /dev/null
+++ b/src/motion/motion.ts
@@ -0,0 +1,78 @@
+import {applyCurve, type Curve} from '../chroma/chroma.js';
+import {isReducedMotion} from '../presentation/environment.js';
+
+/**
+ * Restrained, pure motion: given elapsed time (from whichever clock the caller
+ * owns) a profile yields a 0..1 intensity for a cell. Chroma turns intensity
+ * into color; UI code decides where cells are. Nothing here changes width,
+ * schedules timers, or touches PTY output.
+ */
+export type MotionShape =
+  | 'sine' // symmetric breathing / traveling shimmer
+  | 'comet' // slow rise, fast fall
+  | 'tail' // fast rise, long tail
+  | 'pulse'; // quick rise, then settle to rest
+
+export type MotionSpread =
+  | 'uniform' // every cell moves together
+  | 'travel'; // the crest moves across cells
+
+export interface MotionProfile {
+  shape: MotionShape;
+  spread: MotionSpread;
+  /** Time for one full cycle (or the whole gesture when not repeating). */
+  cycleMs: number;
+  /** Repeating profiles loop; the rest settle at 0 once the gesture ends. */
+  repeat: boolean;
+  /** Cells per wavelength for `travel`. */
+  wavelength?: number;
+  /** Shapes the finished waveform; linear when omitted. */
+  curve?: Curve;
+}
+
+export type MotionState = 'waiting' | 'processing' | 'streaming' | 'transition' | 'completion' | 'failure';
+
+/** Which motion communicates which NMSh state. Reduced motion holds every one still. */
+export const MOTION_PROFILES: Readonly<Record<MotionState, MotionProfile>> = {
+  waiting: {shape: 'sine', spread: 'uniform', cycleMs: 3200, repeat: true},
+  processing: {shape: 'sine', spread: 'travel', cycleMs: 1800, repeat: true, wavelength: 12},
+  streaming: {shape: 'sine', spread: 'travel', cycleMs: 1200, repeat: true, wavelength: 12},
+  transition: {shape: 'pulse', spread: 'uniform', cycleMs: 300, repeat: false, curve: 'ease-out'},
+  completion: {shape: 'tail', spread: 'uniform', cycleMs: 700, repeat: false},
+  failure: {shape: 'pulse', spread: 'uniform', cycleMs: 450, repeat: false},
+};
+
+export function wrappedPhase(elapsedMs: number, cycleMs: number): number {
+  if (cycleMs <= 0) return 0;
+  return ((elapsedMs % cycleMs) + cycleMs) % cycleMs / cycleMs;
+}
+
+/** Waveform value for a phase in [0,1). */
+function waveform(shape: MotionShape, phase: number): number {
+  switch (shape) {
+    case 'sine': return (1 + Math.cos(2 * Math.PI * phase)) / 2;
+    case 'comet': return phase < 0.8 ? phase / 0.8 : 1 - (phase - 0.8) / 0.2;
+    case 'tail': return phase < 0.15 ? phase / 0.15 : 1 - (phase - 0.15) / 0.85;
+    case 'pulse': return phase < 0.25 ? applyCurve('ease-out', phase / 0.25) : 1 - applyCurve('ease-in-out', (phase - 0.25) / 0.75);
+  }
+}
+
+export interface SampleOptions {
+  /** Hold the profile still. Defaults to the user's reduced-motion setting. */
+  reduced?: boolean;
+}
+
+/**
+ * Intensity 0..1 of `cell` (its index along the text or bar) after `elapsedMs`.
+ * Reduced motion samples the profile at time zero for every call, so output is
+ * stable frame to frame.
+ */
+export function sampleMotion(profile: MotionProfile, elapsedMs: number, cell = 0, options: SampleOptions = {}): number {
+  const reduced = options.reduced ?? isReducedMotion();
+  const elapsed = reduced ? 0 : elapsedMs;
+  if (!profile.repeat && !reduced && (elapsed < 0 || elapsed >= profile.cycleMs)) return 0;
+  const clock = profile.repeat ? wrappedPhase(elapsed, profile.cycleMs) : Math.max(0, Math.min(1, elapsed / profile.cycleMs));
+  const shift = profile.spread === 'travel' ? cell / (profile.wavelength ?? 12) : 0;
+  const phase = ((clock - shift) % 1 + 1) % 1;
+  return applyCurve(profile.curve ?? 'linear', waveform(profile.shape, phase));
+}
diff --git a/src/status/shimmer.ts b/src/status/shimmer.ts
index 1e13a19..625ef85 100644
--- a/src/status/shimmer.ts
+++ b/src/status/shimmer.ts
@@ -1,31 +1,28 @@
 import {graphemes} from '../input/inputLayout.js';
 import {mixRgb} from '../chroma/chroma.js';
+import {MOTION_PROFILES, sampleMotion, wrappedPhase} from '../motion/motion.js';
 import {foreground, UI_COLORS, type RgbColor} from '../ui/palette.js';
 
 /** Time for the wave to travel one wavelength; independent of text length. */
-export const SHIMMER_CYCLE_MS = 1800;
+export const SHIMMER_CYCLE_MS = MOTION_PROFILES.processing.cycleMs;
 /** Recent output quickens the wave slightly instead of pulsing the whole line. */
-export const ACTIVE_SHIMMER_CYCLE_MS = 1200;
+export const ACTIVE_SHIMMER_CYCLE_MS = MOTION_PROFILES.streaming.cycleMs;
 /** Glyphs per wavelength: neighbours differ by 1/12 of a cycle. */
-export const SHIMMER_WAVELENGTH = 12;
+export const SHIMMER_WAVELENGTH = MOTION_PROFILES.processing.wavelength!;
 /** Luminance stays inside this band so the effect reads as a soft sheen. */
 const SHIMMER_FLOOR = 0.12;
 const SHIMMER_CEILING = 0.9;
 
-export function wrappedPhase(elapsedMs: number, cycleMs: number): number {
-  if (cycleMs <= 0) return 0;
-  return ((elapsedMs % cycleMs) + cycleMs) % cycleMs / cycleMs;
-}
+export {wrappedPhase};
 
 /**
  * Per-glyph luminance (0 base … 1 peak) of a smooth wave travelling left to
- * right. Each glyph is phase-shifted from its neighbour by 1/wavelength, and
- * the crest advances wavelength/cycle glyphs per millisecond, so a 100 ms
+ * right: the `processing` profile, or `streaming` while output is arriving.
+ * The crest advances wavelength/cycle glyphs per millisecond, so a 100 ms
  * frame moves it well under one glyph whatever the text length.
  */
 export function shimmerIntensity(elapsedMs: number, glyphIndex: number, _textLength: number, isActive: boolean): number {
-  const phase = wrappedPhase(elapsedMs, isActive ? ACTIVE_SHIMMER_CYCLE_MS : SHIMMER_CYCLE_MS);
-  const wave = (1 + Math.cos(2 * Math.PI * (glyphIndex / SHIMMER_WAVELENGTH - phase))) / 2;
+  const wave = sampleMotion(MOTION_PROFILES[isActive ? 'streaming' : 'processing'], elapsedMs, glyphIndex);
   return SHIMMER_FLOOR + (SHIMMER_CEILING - SHIMMER_FLOOR) * wave;
 }
 
diff --git a/tests/motion.test.ts b/tests/motion.test.ts
new file mode 100644
index 0000000..57a7cdc
--- /dev/null
+++ b/tests/motion.test.ts
@@ -0,0 +1,77 @@
+import assert from 'node:assert/strict';
+import test from 'node:test';
+import {MOTION_PROFILES, sampleMotion, wrappedPhase, type MotionProfile, type MotionState} from '../src/motion/motion.js';
+import {shimmerIntensity} from '../src/status/shimmer.js';
+
+const STILL = {reduced: false};
+
+test('every profile stays within 0..1 for any time and cell', () => {
+  for (const [state, profile] of Object.entries(MOTION_PROFILES) as Array<[MotionState, MotionProfile]>) {
+    for (let time = -500; time < 5000; time += 37) {
+      for (const cell of [0, 3, 11, 40]) {
+        const value = sampleMotion(profile, time, cell, STILL);
+        assert.ok(value >= 0 && value <= 1, `${state} t=${time} cell=${cell} -> ${value}`);
+      }
+    }
+  }
+});
+
+test('breathing is symmetric and uniform across cells', () => {
+  const waiting = MOTION_PROFILES.waiting;
+  const half = waiting.cycleMs / 2;
+  assert.equal(sampleMotion(waiting, 0, 0, STILL), 1);
+  assert.ok(Math.abs(sampleMotion(waiting, half, 0, STILL)) < 1e-9);
+  assert.ok(Math.abs(sampleMotion(waiting, 400, 0, STILL) - sampleMotion(waiting, waiting.cycleMs - 400, 0, STILL)) < 1e-9);
+  assert.equal(sampleMotion(waiting, 700, 0, STILL), sampleMotion(waiting, 700, 25, STILL));
+});
+
+test('traveling shimmer moves its crest across cells over time', () => {
+  const crest = (time: number) => {
+    let best = 0;
+    for (let cell = 0; cell < 12; cell += 1) if (sampleMotion(MOTION_PROFILES.processing, time, cell, STILL) > sampleMotion(MOTION_PROFILES.processing, time, best, STILL)) best = cell;
+    return best;
+  };
+  assert.ok(crest(0) !== crest(600));
+});
+
+test('comet rises slowly and falls fast; tail rises fast and decays slowly', () => {
+  const comet: MotionProfile = {shape: 'comet', spread: 'uniform', cycleMs: 1000, repeat: true};
+  const peak = sampleMotion(comet, 800, 0, STILL);
+  assert.equal(peak, 1);
+  assert.ok(sampleMotion(comet, 400, 0, STILL) < peak && sampleMotion(comet, 900, 0, STILL) < peak);
+  assert.ok(sampleMotion(comet, 900, 0, STILL) - sampleMotion(comet, 1000 - 1, 0, STILL) > 0.4, 'falls within the last 20%');
+  const tail = MOTION_PROFILES.completion;
+  assert.equal(Math.round(sampleMotion(tail, 0.15 * tail.cycleMs, 0, STILL) * 1000), 1000);
+  assert.ok(sampleMotion(tail, 0.5 * tail.cycleMs, 0, STILL) > 0.5, 'long tail is still lit at half time');
+});
+
+test('one-shot profiles settle at rest and do not repeat', () => {
+  for (const state of ['transition', 'completion', 'failure'] as const) {
+    const profile = MOTION_PROFILES[state];
+    assert.equal(sampleMotion(profile, 0, 0, STILL), 0);
+    assert.equal(sampleMotion(profile, profile.cycleMs, 0, STILL), 0);
+    assert.equal(sampleMotion(profile, profile.cycleMs * 3.3, 0, STILL), 0);
+    assert.equal(sampleMotion(profile, -10, 0, STILL), 0);
+  }
+  const pulse = MOTION_PROFILES.failure;
+  assert.ok(sampleMotion(pulse, pulse.cycleMs * 0.25, 0, STILL) > 0.95);
+});
+
+test('reduced motion holds every profile still and is deterministic', () => {
+  for (const profile of Object.values(MOTION_PROFILES)) {
+    const first = sampleMotion(profile, 0, 4, {reduced: true});
+    for (const time of [1, 250, 999, 12345]) assert.equal(sampleMotion(profile, time, 4, {reduced: true}), first);
+  }
+  const saved = process.env.NMSH_REDUCED_MOTION;
+  try {
+    process.env.NMSH_REDUCED_MOTION = '1';
+    assert.equal(shimmerIntensity(777, 3, 10, false), shimmerIntensity(12345, 3, 10, false));
+  } finally {
+    if (saved === undefined) delete process.env.NMSH_REDUCED_MOTION; else process.env.NMSH_REDUCED_MOTION = saved;
+  }
+});
+
+test('phase wraps and the shimmer is periodic', () => {
+  assert.equal(wrappedPhase(-250, 1000), 0.75);
+  assert.equal(shimmerIntensity(300, 2, 10, false), shimmerIntensity(300 + MOTION_PROFILES.processing.cycleMs, 2, 10, false));
+});