refactor: update loadRuleFiles to return single rule file content

- Modified loadRuleFiles function to return content from the first available rule file instead of combining multiple rule files.
- Updated tests to reflect the new behavior of loading only the .roorules file content when available, ensuring clarity in rule file handling.

Author: upamune

src/core/prompts/sections/__tests__/custom-instructions.test.ts

@@ -14,9 +14,7 @@ describe("loadRuleFiles", () => {
 		mockedFs.readFile.mockResolvedValue("  content with spaces  ")
 		const result = await loadRuleFiles("/fake/path")
 		expect(mockedFs.readFile).toHaveBeenCalled()
-		expect(result).toBe(
-			"\n# Rules from .roorules:\ncontent with spaces\n" + "\n# Rules from .clinerules:\ncontent with spaces\n",
-		)
+		expect(result).toBe("\n# Rules from .roorules:\ncontent with spaces\n")
 	})
 
 	it("should handle ENOENT error", async () => {
@@ -47,7 +45,7 @@ describe("loadRuleFiles", () => {
 		jest.clearAllMocks()
 	})
 
-	it("should combine content from multiple rule files when they exist", async () => {
+	it("should not combine content from multiple rule files when they exist", async () => {
 		mockedFs.readFile.mockImplementation(((filePath: string | Buffer | URL | number) => {
 			if (filePath.toString().endsWith(".roorules")) {
 				return Promise.resolve("roo rules content")
@@ -59,9 +57,7 @@ describe("loadRuleFiles", () => {
 		}) as any)
 
 		const result = await loadRuleFiles("/fake/path")
-		expect(result).toBe(
-			"\n# Rules from .roorules:\nroo rules content\n" + "\n# Rules from .clinerules:\ncline rules content\n",
-		)
+		expect(result).toBe("\n# Rules from .roorules:\nroo rules content\n")
 	})
 
 	it("should handle when no rule files exist", async () => {

src/core/prompts/sections/custom-instructions.ts

@@ -18,16 +18,15 @@ async function safeReadFile(filePath: string): Promise<string> {
 
 export async function loadRuleFiles(cwd: string): Promise<string> {
 	const ruleFiles = [".roorules", ".clinerules"]
-	let combinedRules = ""
 
 	for (const file of ruleFiles) {
 		const content = await safeReadFile(path.join(cwd, file))
 		if (content) {
-			combinedRules += `\n# Rules from ${file}:\n${content}\n`
+			return `\n# Rules from ${file}:\n${content}\n`
 		}
 	}
 
-	return combinedRules
+	return ""
 }
 
 export async function addCustomInstructions(