fix(coding-agent): normalize @ path prefixes closes #1206

packages/coding-agent/docs/extensions.md

@@ -1130,6 +1130,8 @@ export default function (pi: ExtensionAPI) {
 
 Register tools the LLM can call via `pi.registerTool()`. Tools appear in the system prompt and can have custom rendering.
 
+Note: Some models are idiots and include the @ prefix in tool path arguments. Built-in tools strip a leading @ before resolving paths. If your custom tool accepts a path, normalize a leading @ as well.
+
 ### Tool Definition
 
 ```typescript

packages/coding-agent/src/core/tools/path-utils.ts

@@ -32,8 +32,12 @@ function fileExists(filePath: string): boolean {
 	}
 }
 
+function normalizeAtPrefix(filePath: string): string {
+	return filePath.startsWith("@") ? filePath.slice(1) : filePath;
+}
+
 export function expandPath(filePath: string): string {
-	const normalized = normalizeUnicodeSpaces(filePath);
+	const normalized = normalizeUnicodeSpaces(normalizeAtPrefix(filePath));
 	if (normalized === "~") {
 		return os.homedir();
 	}