fix: update formula handling in SKILL.md and frontmatter.ts (#11046)

- Changed "cask" to "formula" in SKILL.md for consistency.
- Enhanced formula parsing in frontmatter.ts to trim whitespace and fallback to cask if formula is not provided.

skills/model-usage/SKILL.md

@@ -13,7 +13,7 @@ metadata:
             {
               "id": "brew-cask",
               "kind": "brew",
-              "cask": "steipete/tap/codexbar",
+              "formula": "steipete/tap/codexbar",
               "bins": ["codexbar"],
               "label": "Install CodexBar (brew cask)",
             },

src/agents/skills/frontmatter.ts

@@ -45,8 +45,13 @@ function parseInstallSpec(input: unknown): SkillInstallSpec | undefined {
   if (osList.length > 0) {
     spec.os = osList;
   }
-  if (typeof raw.formula === "string") {
-    spec.formula = raw.formula;
+  const formula = typeof raw.formula === "string" ? raw.formula.trim() : "";
+  if (formula) {
+    spec.formula = formula;
+  }
+  const cask = typeof raw.cask === "string" ? raw.cask.trim() : "";
+  if (!spec.formula && cask) {
+    spec.formula = cask;
   }
   if (typeof raw.package === "string") {
     spec.package = raw.package;