tests: fill macro-clips coverage gaps (+35 tests)

Refactor + new tests triggered by an explicit coverage audit of the
macro-clips feature set.

- extracted blendButtonStates into src/lib/buttonBlend.ts so it can be
  tested without mounting CanvasStage; the component now delegates to
  it. Behaviour unchanged.
- store coverage: removeMarker / setMarkerTime / setMarkerColor on
  unknown ids are no-ops, addMarker accepts an initial color,
  removeScriptFrame / setScriptFrameActions / setScriptFrameTime on
  unknown ids are no-ops, removeButtonInstance keeps the clip,
  addButtonInstance defaults x/y to stage center,
  setButtonInstancePosition writes through, setButtonInstanceLabel('')
  clears, setButtonClipTransitions stores + deletes.
- button runtime: applyButtonStateChange is a no-op when the target
  equals the current state, honors the persisted disabled flag as the
  from-state, reset() clears transitions alongside state/disabled.
  store.actionRuntime warns on unknown button refs.
- blendButtonStates: matched layer lerps props (incl. fill color),
  unmatched from-layer fades out, unmatched to-layer fades in,
  u=0/u=1 boundary conditions, missing asset id resolves are skipped.
- DSL edge cases: empty source, comments-only, trailing blank lines,
  wrong state ref prefix, disable without arg, jump @ without name.
- tick firing robustness: multi-track frames fire in time order,
  actions within a frame fire in list order, scriptFramesInRange
  open-closed boundary is exact.

Macro-clips suites now total 76 tests across 11 groups; grand total
277 tests in the runner.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

src/components/CanvasStage.vue

@@ -23,7 +23,7 @@ import {
   useButtonRuntime,
 } from '@/composables/useButtonRuntime'
 import { evalAction } from '@/lib/actions'
-import { lerpProps } from '@/lib/interpolate'
+import { blendButtonStates } from '@/lib/buttonBlend'
 import { t } from '@/i18n'
 import { useKfSelection } from '@/composables/useKfSelection'
 import { showLocked } from '@/composables/useShowLocked'
@@ -226,50 +226,15 @@ function sampleStateLayers(
   return out
 }
 
-/**
- * Blend the "from" state's layers into the "to" state's layers by layer
- * name. Matched pairs lerp their props; unmatched from-layers fade out,
- * unmatched to-layers fade in.
- */
 function blendStates(
   clip: ButtonClip,
   from: ButtonState,
   to: ButtonState,
   u: number,
 ): ButtonRenderItem['layers'] {
-  const fromLayers = clip.states[from] ?? []
-  const toLayers = clip.states[to] ?? []
-  const fromByName = new Map<string, Layer>()
-  const toByName = new Map<string, Layer>()
-  for (const l of fromLayers) fromByName.set(l.name, l)
-  for (const l of toLayers) toByName.set(l.name, l)
-  const seen = new Set<string>()
-  const out: ButtonRenderItem['layers'] = []
-  // Preserve to-state order primarily, with unmatched from-layers pinned
-  // underneath so the new state visually rises into place.
-  for (const l of fromLayers) {
-    if (toByName.has(l.name)) continue
-    const asset = store.scene.assets.find((a) => a.id === l.assetId)
-    if (!asset) continue
-    const base = sampleLayer(l, 0)
-    out.push({ layer: l, asset, props: { ...base, opacity: base.opacity * (1 - u) } })
-  }
-  for (const l of toLayers) {
-    const asset = store.scene.assets.find((a) => a.id === l.assetId)
-    if (!asset) continue
-    seen.add(l.name)
-    const fromLayer = fromByName.get(l.name)
-    if (fromLayer) {
-      const a = sampleLayer(fromLayer, 0)
-      const b = sampleLayer(l, 0)
-      out.push({ layer: l, asset, props: lerpProps(a, b, u) })
-    } else {
-      const base = sampleLayer(l, 0)
-      out.push({ layer: l, asset, props: { ...base, opacity: base.opacity * u } })
-    }
-  }
-  void seen
-  return out
+  return blendButtonStates(clip, from, to, u, (id) =>
+    store.scene.assets.find((a) => a.id === id),
+  )
 }
 
 const activeButtonInstances = computed<ButtonRenderItem[]>(() => {