fix: drop root frontmatter when building CopilotRule

Author: dyoshikawa

src/features/rules/copilot-rule.test.ts

@@ -304,15 +304,15 @@ describe("CopilotRule", () => {
         rulesyncRule: original,
       });
 
-      // Root Copilot file must have no applyTo when the rulesync rule had no globs.
-      expect(copilotRule.getFrontmatter().applyTo).toBeUndefined();
+      // Root Copilot file must have no frontmatter.
+      expect(copilotRule.getFrontmatter()).toEqual({});
 
       const reimported = copilotRule.toRulesyncRule();
       const rf = reimported.getFrontmatter();
 
       expect(rf.root).toBe(true);
       expect(rf.globs).toBeUndefined();
-      expect(rf.description).toBe("Project overview");
+      expect(rf.description).toBeUndefined();
       expect(reimported.getBody()).toBe("Overview content");
     });
 
@@ -407,10 +407,7 @@ describe("CopilotRule", () => {
         validate: true,
       });
 
-      expect(copilotRule.getFrontmatter()).toEqual({
-        description: "Root rule from rulesync",
-        applyTo: "**/*",
-      });
+      expect(copilotRule.getFrontmatter()).toEqual({});
       expect(copilotRule.getBody()).toBe("Root rulesync rule content");
       expect(copilotRule.getRelativeDirPath()).toBe(".github");
       expect(copilotRule.getRelativeFilePath()).toBe("copilot-instructions.md");
@@ -494,7 +491,7 @@ describe("CopilotRule", () => {
         validate: true,
       });
 
-      expect(copilotRule.getFrontmatter().excludeAgent).toBe("coding-agent");
+      expect(copilotRule.getFrontmatter()).toEqual({});
     });
 
     it("should use default baseDir when not provided", () => {

src/features/rules/copilot-rule.ts

@@ -171,7 +171,7 @@ export class CopilotRule extends ToolRule {
       // Root file: .github/copilot-instructions.md (no frontmatter for root file)
       return new CopilotRule({
         baseDir: baseDir,
-        frontmatter: copilotFrontmatter,
+        frontmatter: {},
         body,
         relativeDirPath: paths.root.relativeDirPath,
         relativeFilePath: paths.root.relativeFilePath,