feat(observatory): reduced-motion + persistent pause control for the field

Closes the launch guardrail: the field's ambient orbit + force-sim drift
run >5s, so WCAG needs a persistent pause control and prefers-reduced-
motion must be honored.

- engine.setPaused(): freezes the deterministic clock so the orbit + sim
  drift hold still, while the frame still renders and the live preFrameHook
  still runs — discrete event pulses (firewall, decay, dream) are
  information, not decoration, so they land even when motion is reduced.
- ObservatoryStage: a persistent ❚❚ PAUSE / ▶ RESUME control on the live
  field; auto-pauses under prefers-reduced-motion (user can override).

Verified live: the pause button toggles engine.isPaused (frozen drift,
pulses still land); check 0 err, 1043 tests, build green.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

apps/dashboard/src/lib/observatory/ObservatoryStage.svelte

@@ -96,6 +96,32 @@
 	let projectionDays = $state(0);
 	let liveBridge: LiveBridge | null = null;
 	let liveDecayReady = $state(false);
+
+	// Motion control (WCAG): the field's ambient orbit/sim drift runs >5s, so it
+	// needs a persistent pause control AND must honor prefers-reduced-motion.
+	// When paused the clock freezes (drift stops) but live event pulses still
+	// land — they are information, not decoration. Auto-pauses under
+	// reduced-motion; the user can still override with the button.
+	let paused = $state(false);
+	let userSetPause = $state(false);
+	function initReducedMotion() {
+		if (typeof window === 'undefined') return;
+		const mq = window.matchMedia('(prefers-reduced-motion: reduce)');
+		if (mq.matches && !userSetPause) paused = true;
+		const onChange = (e: MediaQueryListEvent) => {
+			if (!userSetPause) paused = e.matches;
+		};
+		mq.addEventListener('change', onChange);
+		return () => mq.removeEventListener('change', onChange);
+	}
+	function togglePause() {
+		userSetPause = true;
+		paused = !paused;
+	}
+	// Push the pause state to the engine whenever either changes.
+	$effect(() => {
+		engine?.setPaused(paused);
+	});
 	// Live contradiction-firewall verdict — set when a real MemorySuppressed /
 	// contradiction event quarantines a memory on camera. Held ~7s then fades.
 	let liveFirewallLabel = $state('');
@@ -354,6 +380,7 @@
 
 	onMount(() => {
 		loadGraph();
+		return initReducedMotion();
 	});
 </script>
 
@@ -409,6 +436,23 @@
 			</div>
 		{/if}
 
+		<!-- Motion pause control (WCAG: persistent, for >5s ambient motion). Live
+		     field only. Pausing freezes ambient drift; live event pulses persist.
+		     Auto-on under prefers-reduced-motion. -->
+		{#if live}
+			<button
+				onclick={togglePause}
+				class="absolute bottom-4 right-4 pointer-events-auto flex items-center gap-2 px-3 py-1.5
+					rounded-xl border border-[#22C7DE]/25 bg-[#05060a]/80 backdrop-blur-sm
+					font-mono text-[11px] tracking-wide text-[#22C7DE]/80 hover:text-[#22C7DE]
+					hover:border-[#22C7DE]/50 transition-colors"
+				title={paused ? 'Resume field motion' : 'Pause field motion (event pulses stay live)'}
+				aria-pressed={paused}
+			>
+				{paused ? '▶ RESUME' : '❚❚ PAUSE'}
+			</button>
+		{/if}
+
 		<!-- v2.3 living field — forward-projection scrubber. Real per-memory FSRS
 		     decay drifts too slowly to watch in one session, so this projects the
 		     field N days forward on the SAME true forgetting curve (honest, not

apps/dashboard/src/lib/observatory/engine.ts

@@ -110,6 +110,15 @@ export class ObservatoryEngine {
 	private accumulatorMs = 0;
 	private static readonly FIXED_DT_MS = 1000 / 60;
 
+	/**
+	 * Paused (prefers-reduced-motion or the on-page control): the deterministic
+	 * clock stops advancing so the ambient orbit + force-sim drift FREEZE, but
+	 * the frame still renders and the live preFrameHook still runs — discrete
+	 * event pulses (firewall, decay, dream) are information, not decoration, so
+	 * they must land even when motion is reduced (WCAG-friendly).
+	 */
+	private paused = false;
+
 	constructor(opts: EngineOptions) {
 		this.canvas = opts.canvas;
 		this.demo = opts.demo;
@@ -178,6 +187,19 @@ export class ObservatoryEngine {
 		return this.clock.state.totalFrames;
 	}
 
+	/**
+	 * Freeze/unfreeze the ambient motion (prefers-reduced-motion or the on-page
+	 * pause control). Frozen = the clock stops advancing, so the orbit + force
+	 * sim hold still; live event pulses (via the preFrameHook) still land.
+	 */
+	setPaused(paused: boolean): void {
+		this.paused = paused;
+	}
+
+	get isPaused(): boolean {
+		return this.paused;
+	}
+
 	/**
 	 * Wall-clock now in ms. The ONE sanctioned wall-clock read (never for sim
 	 * state — the DemoClock owns that). The live FSRS decay field legitimately
@@ -317,8 +339,10 @@ export class ObservatoryEngine {
 		// on every display; only the scheduling reads the wall clock.
 		this.accumulatorMs += Math.min(deltaMs, 250);
 		let ticked = false;
+		// When paused, the clock is frozen (ambient/sim drift stops) — but we
+		// keep draining the accumulator so it doesn't fast-forward on resume.
 		while (this.accumulatorMs >= ObservatoryEngine.FIXED_DT_MS) {
-			this.clock.tick();
+			if (!this.paused) this.clock.tick();
 			this.accumulatorMs -= ObservatoryEngine.FIXED_DT_MS;
 			ticked = true;
 		}