Pick the frame's outline when adding a collider to a sprite (#218)

"Add collider" on a sprite always made a box of the sprite's size,
even when the sprite's picture is a frame that has a collision outline.
The outline then had to be picked by hand as "Frame collision".

- newColliderProps in colliderCommands.ts is the rule as a pure
  function. A sprite whose picture is a frame with an outline gets a
  collider with shape "frame" and that frame. Anything else keeps the
  box of the sprite's size.
- The frame is the one the sprite shows when the collider is added,
  also when only this placement overrides it.
- Decided here, the issue says nothing about size: a frame collider is
  as big as its frame, so a sprite drawn bigger or smaller with the
  same proportions gets the collider's scale set to match.
- Decided here as well: a sprite stretched out of the frame's
  proportions keeps the box, because an outline cannot be stretched
  in one direction.

Tests:
- Gate: 198 files, 2914 tests (2911 + 3), exit 0
- e2e 8,42: 46 checks passed (42: +1 for 42e-ii)
- Three new unit tests in tests/core/collider-parts.test.ts: the
  frame with undo, the scale with an overridden frame, and the cases
  that keep the box
- 42e-ii goes through the context menu: "Frame collision" with scale
  2 on the sprite wearing the wedge frame, a box on a sprite without
  a picture
- Five unit counter-probes fail, 1 to 2 tests each. They ran on
  stein2, not in the container.
- The browser counter-probe fails 42e-ii with shape "box"
- The e2e sum of 1617 is calculated (1616 + 1). Neither the full
  suite nor the smokes ran for this state.
- Vector art has no test of its own, it takes the same branch as a
  whole texture.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

src/core/commands/colliderCommands.ts

@@ -2,9 +2,11 @@ import { newId } from '../ids';
 import { findObject } from '../model/hierarchy';
 import { isLiveInstance, type ObjectRef, resolvedHolder } from '../model/instance';
 import type { Asset } from '../model/Asset';
-import type { PropertyBag } from '../model/Properties';
+import { frameOutline } from '../model/frameOutline';
+import { type PropertyBag, textOf } from '../model/Properties';
 import { findAsset, type ObjectHolder, type Project } from '../model/Project';
 import { createSceneObject, objectName, type SceneObject } from '../model/SceneObject';
+import { matchesAspect } from '../properties/aspect';
 import { resolveSceneObjectProps } from '../properties/resolve';
 import { transformOfObject } from '../properties/transform';
 import { removeById } from '../util/list';
@@ -74,7 +76,23 @@ export function colliderRefusal(project: Project, holder: ObjectHolder, target:
   return null;
 }
 
-/** A new collider asset is sized like the object (sprites: width × height; anything else: schema defaults). */
+/**
+ * What a new collider on `target` starts with. A sprite gets a box of its width × height – or, when
+ * its picture is a frame with a collision outline, that outline (#218): a frame collider is the
+ * frame's size, so it is scaled up to the sprite, and a sprite stretched out of the frame's
+ * proportions keeps the box, since an outline cannot be stretched. Anything else: schema defaults.
+ */
+export function newColliderProps(project: Project, targetAsset: Asset, target: SceneObject): PropertyBag {
+  if (targetAsset.type !== 'sprite') return {};
+  const size = spriteSize(project, targetAsset, target);
+  const frame = textOf(resolveSceneObjectProps(project, targetAsset, target).texture ?? '');
+  const outline = frameOutline(project, frame);
+  if (!outline || outline.pieces.length === 0 || !matchesAspect(outline, size)) return size;
+  const scale = size.width / outline.w;
+  return { shape: 'frame', frame, width: outline.w, height: outline.h, ...(scale === 1 ? {} : { scale }) };
+}
+
+/** A new collider asset starts with `newColliderProps`. */
 export class AddColliderCommand extends AddPartCommand {
   readonly label = 'Add collider';
   protected readonly partType = 'collider';
@@ -85,7 +103,7 @@ export class AddColliderCommand extends AddPartCommand {
 
   protected build(project: Project, target: SceneObject, targetAsset: Asset, owner: string): Asset {
     const asset = buildAsset('collider', nextAssetName(project, `${owner} collider`), this.assetId);
-    if (targetAsset.type === 'sprite') Object.assign(asset.props, spriteSize(project, targetAsset, target));
+    Object.assign(asset.props, newColliderProps(project, targetAsset, target));
     return asset;
   }
 }