chore(motion): document magic UI duration exceptions (#365)

docs/motion-and-high-refresh.md

@@ -142,11 +142,18 @@ Suggested order: A1 → A2 → A3 in parallel with A4; then A5; A6 closes the mi
 When reviewing PRs that touch animation:
 
 1. Reject bare `Duration(milliseconds: …)` / ad-hoc `Curves.*` in product UI unless
-   wired through `QueryaMotion` (or documented physics constants in `QueryaSpring`).
+   wired through `QueryaMotion` (or documented physics / choreography constants).
 2. Require Full / Reduced / Off + OS `disableAnimations` coverage for new transitions.
 3. Split / resize: no spring or lag mid-drag; settle only on release / focus chrome.
 4. Never stagger or fade virtualized result rows while scrolling.
 
+**Allowed named non-token durations** (named + documented — not magic literals at call sites):
+
+| Constant | Value | Where |
+|----------|-------|--------|
+| `kQueryaStaggerStep` | 30 ms | `QueryaStagger` first-paint choreography |
+| `kUpdateBadgePulsePeriod` | 1400 ms | Update title-bar chip pulse (chrome; see #363) |
+
 Checklist for 120 Hz verification: [perf-baseline.md](perf-baseline.md) § Fluid shell.
 
 ## 8. References

lib/core/motion/querya_stagger.dart

@@ -3,6 +3,10 @@ import 'package:flutter/material.dart';
 import 'querya_motion.dart';
 import 'querya_motion_context.dart';
 
+/// Default per-child delay for [QueryaStagger] (physics/choreography constant,
+/// not a surface morph token — see docs/motion-and-high-refresh.md).
+const Duration kQueryaStaggerStep = Duration(milliseconds: 30);
+
 /// Staggered fade-in for a fixed list — **first paint only**, capped at [maxStaggered].
 ///
 /// Do not wrap virtualized / scrolling grids; use for history lists, recent
@@ -12,7 +16,7 @@ class QueryaStagger extends StatefulWidget {
     super.key,
     required this.children,
     this.maxStaggered = 8,
-    this.step = const Duration(milliseconds: 30),
+    this.step = kQueryaStaggerStep,
   });
 
   final List<Widget> children;