refactor(packages): rename rules-core to rules-engine

Ultraworked with [Sisyphus](https://github.com/code-yeongyu/oh-my-openagent)

Co-authored-by: Sisyphus <clio-agent@sisyphuslabs.ai>

packages/rules-engine/src/scanner.ts

@@ -0,0 +1,58 @@
+import { existsSync, readdirSync, realpathSync, type Dirent } from "node:fs";
+import { isAbsolute, join, relative } from "node:path";
+import { EXCLUDED_DIRS, GITHUB_INSTRUCTIONS_PATTERN, RULE_EXTENSIONS } from "./constants";
+import type { DirectoryScanEntry } from "./types";
+
+function isGitHubInstructionsDir(dir: string): boolean {
+  return dir.includes(".github/instructions") || dir.endsWith(".github/instructions");
+}
+
+function isRuleFile(fileName: string, dir: string): boolean {
+  if (isGitHubInstructionsDir(dir)) return GITHUB_INSTRUCTIONS_PATTERN.test(fileName);
+  return RULE_EXTENSIONS.some((extension) => fileName.endsWith(extension));
+}
+
+export function safeRealpathSync(filePath: string): string {
+  try {
+    return realpathSync.native(filePath);
+  } catch {
+    return filePath;
+  }
+}
+
+function isPathWithinRoot(candidate: string, root: string): boolean {
+  const rel = relative(root, candidate);
+  return rel === "" || (!rel.startsWith("..") && !isAbsolute(rel));
+}
+
+export function findRuleFilesRecursive(
+  dir: string,
+  results: DirectoryScanEntry[],
+  visited = new Set<string>(),
+  boundaryRoot?: string,
+): void {
+  if (!existsSync(dir)) return;
+  const realDir = safeRealpathSync(dir);
+  const effectiveBoundary = boundaryRoot ?? realDir;
+  if (!isPathWithinRoot(realDir, effectiveBoundary)) return;
+  if (visited.has(realDir)) return;
+  visited.add(realDir);
+  let entries: Dirent<string>[] = [];
+  try {
+    entries = readdirSync(dir, { withFileTypes: true, encoding: "utf8" }).sort((left, right) => left.name.localeCompare(right.name));
+  } catch {
+    return;
+  }
+  for (const entry of entries) {
+    const fullPath = join(dir, entry.name);
+    if (entry.isDirectory()) {
+      if (!EXCLUDED_DIRS.has(entry.name)) findRuleFilesRecursive(fullPath, results, visited, effectiveBoundary);
+      continue;
+    }
+    if (entry.isFile() && isRuleFile(entry.name, dir)) {
+      const realPath = safeRealpathSync(fullPath);
+      if (!isPathWithinRoot(realPath, effectiveBoundary)) continue;
+      results.push({ path: fullPath, realPath, relativePath: entry.name });
+    }
+  }
+}