docs(skill): correct the shape spellings and the motion-path claim (#193)

Two lines in SKILL.md made the generator write scenarios the schema rejects.

`ShapeType` is externally tagged, but the skill described the parameterised
variants as "star (with points, default 5)", which reads as a sibling field.
`"shape": "star"` fails with `invalid type: unit variant, expected struct
variant`; the correct spelling is `{"star": {"points": 6}}`. Show the literal
JSON for all eight variants instead of prose.

The skill also still stated that motion-path does not exist and that there is
no path-following mechanism. That stopped being true with #177. Point at
rules/motion-path.md and spell out the trap the old note should now be
preventing: `motion-path` in `style` is dropped, `motion_path` in `animation`
is the effect.

A test pins the eight documented spellings and keeps a bare `star` rejected,
so the wording cannot drift back.

Author: LeadcodeDev

.claude/skills/rustmotion/SKILL.md

@@ -919,7 +919,14 @@ Animates each character or word independently with staggered timing. Use `char_*
 | --------------- | ------------------ | ----------- |
 | `border-radius` | f32                | `null`      |
 
-**Shape types:** `rect`, `circle`, `rounded_rect`, `ellipse`, `triangle`, `star` (with `points`, default 5), `polygon` (with `sides`, default 6), `path` (with `data` SVG path string)
+**Shape types.** `ShapeType` is externally tagged: the plain variants are strings, the parameterised ones are single-key objects. Writing `"shape": "star"` fails with `invalid type: unit variant, expected struct variant`.
+
+```json
+"shape": "rect"                              // also: circle, rounded_rect, ellipse, triangle
+"shape": { "star": { "points": 6 } }         // default 5
+"shape": { "polygon": { "sides": 6 } }       // default 6
+"shape": { "path": { "data": "M0 0 L10 10" } }
+```
 
 **Gradient fill (root field):**
 ```json
@@ -2350,7 +2357,9 @@ New style fields available on all components:
 | ----------------- | ------ | ------- | -------------------------------------------------------- |
 | `gradient-border` | object | `null`  | `{ "colors": ["#f00", "#00f"], "width": 2, "angle": 0 }` — gradient-colored border ring, border-radius aware, painted instead of `border` when both are set |
 
-`stagger` and `timeline` are **root fields** (siblings of `style`), not style fields — see [rules/component-field-placement.md](rules/component-field-placement.md). `motion-path` does not exist in the current schema (leftover from the pre-CSS `LayerStyle` model) — there is no motion-path-following mechanism today.
+`stagger` and `timeline` are **root fields** (siblings of `style`), not style fields — see [rules/component-field-placement.md](rules/component-field-placement.md).
+
+There is no `motion-path` *style* property — that name is a leftover from the pre-CSS `LayerStyle` model and was removed. To move a component along a path, use the **`motion_path` animation effect** (snake_case), which takes SVG path data and can orient the component along the tangent — see [rules/motion-path.md](rules/motion-path.md). The two spellings are one character apart and mean different things: `motion-path` in `style` is dropped, `motion_path` in `animation` works.
 
 **Deprecated (accepted but never rendered — the validator warns):**
 

crates/rustmotion/src/tests.rs

@@ -163,6 +163,41 @@ mod component_smoke {
     const COMPONENT_ALIASES: &[(&str, &str)] =
         &[("container", "div"), ("progress_bar", "progress")];
 
+    /// The exact `shape` spellings SKILL.md documents must parse.
+    ///
+    /// `ShapeType` is externally tagged, and the skill used to describe the
+    /// parameterised variants as `star` "(with `points`)", which reads as a
+    /// sibling field and fails with `invalid type: unit variant, expected
+    /// struct variant`. The generator writes what the skill says, so a wrong
+    /// line there is not a documentation nit — it is a stream of invalid
+    /// scenarios. Pin the spellings.
+    #[test]
+    fn skill_documented_shape_spellings_parse() {
+        use rustmotion_core::schema::ShapeType;
+
+        for spelling in [
+            r#""rect""#,
+            r#""circle""#,
+            r#""rounded_rect""#,
+            r#""ellipse""#,
+            r#""triangle""#,
+            r#"{ "star": { "points": 6 } }"#,
+            r#"{ "polygon": { "sides": 6 } }"#,
+            r#"{ "path": { "data": "M0 0 L10 10" } }"#,
+        ] {
+            serde_json::from_str::<ShapeType>(spelling).unwrap_or_else(|e| {
+                panic!("SKILL.md documents `{spelling}`, which does not parse: {e}")
+            });
+        }
+
+        // …and the shape the skill used to imply must still be rejected, so a
+        // future edit cannot quietly reintroduce it.
+        assert!(
+            serde_json::from_str::<ShapeType>(r#""star""#).is_err(),
+            "a bare `star` must stay an error: it is what the old wording produced"
+        );
+    }
+
     #[test]
     fn all_components_serde_round_trip() {
         // deserialize → serialize → deserialize → serialize: the canonical