fix(context-bill): walk both links to one directory so the walk never depends on readdir order

Co-authored-by: capy-ai[bot] <230910855+capy-ai[bot]@users.noreply.github.com>

lib/context-bill.ts

@@ -233,8 +233,9 @@ function encloses(outer: string, inner: string): boolean {
  *
  * Symlinked files and directories are followed, and every returned path stays
  * the lexical path under `dir`, so buildBill and --exact key the same files.
- * Each real directory is walked once (cycle guard), and a link to a directory
- * that encloses `dir` is never followed.
+ * Two links to one directory are both walked (each is real scanner load), so
+ * the result never depends on readdir order. A directory that is already on
+ * the current walk (a loop) or that encloses `dir` is never entered.
  */
 export function walkMd(dir: string): string[] {
   const out: string[] = [];
@@ -244,8 +245,7 @@ export function walkMd(dir: string): string[] {
   } catch {
     return out;
   }
-  const visited = new Set([rootReal]);
-  const walk = (current: string) => {
+  const walk = (current: string, ancestors: string[]) => {
     let entries: fs.Dirent[];
     try {
       entries = fs.readdirSync(current, { withFileTypes: true });
@@ -267,12 +267,11 @@ export function walkMd(dir: string): string[] {
       } catch {
         continue;
       }
-      if (visited.has(real) || encloses(real, rootReal)) continue;
-      visited.add(real);
-      walk(p);
+      if (ancestors.includes(real) || encloses(real, rootReal)) continue;
+      walk(p, [...ancestors, real]);
     }
   };
-  walk(dir);
+  walk(dir, [rootReal]);
   return out;
 }
 

test/context-bill.test.ts

@@ -273,7 +273,9 @@ describe("upstream fix b: installed-tree layout (repo-checkout subdir skip)", ()
     }
     // Every path the bill (and --exact) keys on stays under the skills root.
     for (const file of walkMd(skills)) expect(file.startsWith(skills + path.sep)).toBe(true);
+    // dirlink/SKILL.md links to review/sections, so its file is walked under both names.
     expect(walkMd(skills).map((f) => path.relative(skills, f)).sort()).toEqual([
+      path.join("dirlink", "SKILL.md", "flow.md"),
       path.join("office-hours", "SKILL.md"),
       path.join("office-hours", "sections", "flow.md"),
       path.join("review", "SKILL.md"),