Docs: record MyGo path-cache order dependence for snapshots

AGENTS.md

@@ -52,6 +52,7 @@ testdata/snapshots/  <os>/<name>-<light|dark>.png
 - `ui.NewTester` drives click, keys, typing. Assert values, not existence.
 - Every component: one `snapshot(t, name, w, h, view)` call (light and dark). Refresh with `go test -run <Name> -update .`
 - Run `go vet ./... && go test ./...` before reporting done.
+- Snapshots assume the default test order. MyGo shares its path-mask cache across a process, and its own chevrons are not snapped, so `-shuffle` can shift a few pixels (docs/upstream.md).
 
 ## Gallery page
 

docs/upstream.md

@@ -35,4 +35,4 @@ PRD 第 2 节要求公开接口不足时向上游提交扩展。以下缺口在
 | `SelectBase` 高亮无设置接口 | `ui/base.go:260` | Select |
 | `TextInputBase` 无只读开关与占位符 | `ui/editor.go:139,734,811` | TextInput 只读模式、CommandPalette |
 | `ui.Stepper` 禁用时仍可步进，固定 9 位取整 | `ui/indicators.go:216`、`ui/widgets.go` `snap` | NumberInput（已改为自绘） |
-| 路径遮罩缓存按四分之一像素取键 | `ui/path.go:189-210` | 全部自绘路径（以 `internal.Snap` 对齐网格） |
+| 路径遮罩缓存按四分之一像素取键，进程内共享 | `ui/path.go:189-210` | 自绘路径以 `internal.Snap` 对齐；MyGo 自绘的箭头（Outline 等）无法对齐，快照依赖测试运行顺序，`-shuffle` 下 TreeTable 快照会出现 6 像素差异 |