fix: auto-detect default branch when 'main' doesn't exist

- Uses git ls-remote --symref to detect default branch (main/master/etc)
- Falls back gracefully: try requested branch → detect → retry
- Fixes repos using 'master' or other non-main default branches
- Also fixes stale empty cache dirs from failed clones

Author: shreyas-lyzr

src/utils/git-cache.ts

@@ -1,4 +1,4 @@
-import { existsSync, mkdirSync, rmSync } from 'node:fs';
+import { existsSync, mkdirSync, rmSync, readdirSync } from 'node:fs';
 import { join } from 'node:path';
 import { createHash } from 'node:crypto';
 import { homedir, tmpdir } from 'node:os';
@@ -21,10 +21,35 @@ function cacheKey(url: string, branch: string): string {
   return createHash('sha256').update(`${url}#${branch}`).digest('hex').slice(0, 16);
 }
 
+function isDirEmpty(dir: string): boolean {
+  try {
+    return readdirSync(dir).length === 0;
+  } catch {
+    return true;
+  }
+}
+
+function detectDefaultBranch(url: string): string {
+  try {
+    const output = execSync(`git ls-remote --symref ${url} HEAD`, {
+      encoding: 'utf-8',
+      stdio: ['pipe', 'pipe', 'pipe'],
+      timeout: 15_000,
+    });
+    // Parse: ref: refs/heads/master	HEAD
+    const match = output.match(/ref: refs\/heads\/(\S+)\s+HEAD/);
+    if (match?.[1]) return match[1];
+  } catch {
+    // fallback
+  }
+  return 'main';
+}
+
 export function resolveRepo(url: string, options: ResolveRepoOptions = {}): ResolveRepoResult {
-  const branch = options.branch ?? 'main';
+  const requestedBranch = options.branch ?? 'main';
 
   if (options.noCache) {
+    const branch = requestedBranch === 'main' ? detectDefaultBranch(url) : requestedBranch;
     const dir = join(tmpdir(), `gitagent-${cacheKey(url, branch)}-${Date.now()}`);
     cloneRepo(url, branch, dir);
     return {
@@ -35,21 +60,33 @@ export function resolveRepo(url: string, options: ResolveRepoOptions = {}): Reso
     };
   }
 
-  const hash = cacheKey(url, branch);
+  const hash = cacheKey(url, requestedBranch);
   const dir = join(CACHE_BASE, hash);
 
-  if (existsSync(dir) && !options.refresh) {
+  // If cached dir exists, is non-empty, and no refresh requested — use it
+  if (existsSync(dir) && !isDirEmpty(dir) && !options.refresh) {
     return { dir };
   }
 
-  if (existsSync(dir) && options.refresh) {
-    // Nuke cached clone and re-clone fresh to avoid divergent branch issues
+  // Clean up stale/empty cache dir
+  if (existsSync(dir)) {
     rmSync(dir, { recursive: true, force: true });
-    cloneRepo(url, branch, dir);
-    return { dir };
   }
 
-  cloneRepo(url, branch, dir);
+  // Try cloning with requested branch first, fall back to auto-detect
+  try {
+    cloneRepo(url, requestedBranch, dir);
+  } catch {
+    // Branch not found — auto-detect default branch and retry
+    if (existsSync(dir)) rmSync(dir, { recursive: true, force: true });
+    const detectedBranch = detectDefaultBranch(url);
+    if (detectedBranch !== requestedBranch) {
+      cloneRepo(url, detectedBranch, dir);
+    } else {
+      throw new Error(`Could not clone ${url} — branch "${requestedBranch}" not found`);
+    }
+  }
+
   return { dir };
 }