fix: better frontmatter errors

packages/opencode/src/config/markdown.ts

@@ -1,3 +1,7 @@
+import { NamedError } from "@/util/error"
+import matter from "gray-matter"
+import { z } from "zod"
+
 export namespace ConfigMarkdown {
   export const FILE_REGEX = /(?<![\w`])@(\.?[^\s`,.]*(?:\.[^\s`,.]+)*)/g
   export const SHELL_REGEX = /!`([^`]+)`/g
@@ -9,4 +13,29 @@ export namespace ConfigMarkdown {
   export function shell(template: string) {
     return Array.from(template.matchAll(SHELL_REGEX))
   }
+
+  export async function parse(filePath: string) {
+    const template = await Bun.file(filePath).text()
+
+    try {
+      const md = matter(template)
+      return md
+    } catch (err) {
+      throw new FrontmatterError(
+        {
+          path: filePath,
+          message: `Failed to parse YAML frontmatter: ${err instanceof Error ? err.message : String(err)}`,
+        },
+        { cause: err },
+      )
+    }
+  }
+
+  export const FrontmatterError = NamedError.create(
+    "ConfigFrontmatterError",
+    z.object({
+      path: z.string(),
+      message: z.string(),
+    }),
+  )
 }