fix: ENOBUFS in detect_changes by setting maxBuffer on git/rg execFileSync (#957)

* Initial plan

* Fix ENOBUFS in detect_changes by setting maxBuffer on git/rg execFileSync

Agent-Logs-Url: https://github.com/abhigyanpatwari/GitNexus/sessions/bb241ed0-3b39-431f-a242-b0c7ced9707b

Co-authored-by: magyargergo <11230420+magyargergo@users.noreply.github.com>

---------

Co-authored-by: copilot-swe-agent[bot] <198982749+Copilot@users.noreply.github.com>
Co-authored-by: magyargergo <11230420+magyargergo@users.noreply.github.com>

gitnexus/src/mcp/local/local-backend.ts

@@ -1765,7 +1765,14 @@ export class LocalBackend {
 
     let diffOutput: string;
     try {
-      diffOutput = execFileSync('git', diffArgs, { cwd: repo.repoPath, encoding: 'utf-8' });
+      // maxBuffer raised from Node's 1MB default to 256MB to avoid ENOBUFS on
+      // repos with large unstaged/untracked diffs (e.g. unignored build folders).
+      // See issue: spawnSync git ENOBUFS in detect_changes(scope="unstaged").
+      diffOutput = execFileSync('git', diffArgs, {
+        cwd: repo.repoPath,
+        encoding: 'utf-8',
+        maxBuffer: 256 * 1024 * 1024,
+      });
     } catch (err: any) {
       return { error: `Git diff failed: ${err.message}` };
     }
@@ -2039,6 +2046,8 @@ export class LocalBackend {
         cwd: repo.repoPath,
         encoding: 'utf-8',
         timeout: 5000,
+        // Avoid ENOBUFS on large repos: rg -l can list many files.
+        maxBuffer: 256 * 1024 * 1024,
       });
       const files = output
         .trim()

gitnexus/test/unit/local-backend-maxbuffer.test.ts

@@ -0,0 +1,48 @@
+/**
+ * Source-code regression: ENOBUFS on large git/rg output.
+ *
+ * Node's default maxBuffer for execFileSync is 1 MB, which is easily exceeded
+ * by `git diff` on repos with large unstaged changes (e.g. unignored build
+ * folders) — see the original bug report:
+ *
+ *   "spawnSync git ENOBUFS in gitnexus_detect_changes(scope=\"unstaged\")
+ *    due to missing maxBuffer".
+ *
+ * Every `execFileSync` call in `local-backend.ts` that captures stdout
+ * (i.e. sets `encoding`) MUST pass an explicit `maxBuffer`. This test is a
+ * lightweight static guard so the regression cannot silently come back.
+ *
+ * Kept as a standalone file (no LocalBackend import) so it does not depend
+ * on the LadybugDB native binding being available in the test environment.
+ */
+import { describe, it, expect } from 'vitest';
+import fs from 'fs';
+import path from 'path';
+
+const SOURCE_PATH = path.join(__dirname, '../../src/mcp/local/local-backend.ts');
+
+describe('local-backend: execFileSync maxBuffer regression', () => {
+  const source = fs.readFileSync(SOURCE_PATH, 'utf-8');
+
+  it('every stdout-capturing execFileSync call passes maxBuffer', () => {
+    // Match each `execFileSync(...)` call. The local-backend.ts call sites use
+    // a single trailing options object literal, so a non-greedy match up to the
+    // closing `)` of the statement is sufficient.
+    const callRe = /execFileSync\s*\(([\s\S]*?)\)\s*;/g;
+    const offenders: string[] = [];
+    let match: RegExpExecArray | null;
+    while ((match = callRe.exec(source)) !== null) {
+      const args = match[1];
+      // Only stdout-capturing calls (encoding set) are at risk of ENOBUFS.
+      if (!/encoding\s*:/.test(args)) continue;
+      if (!/maxBuffer\s*:/.test(args)) {
+        const lineNo = source.slice(0, match.index).split('\n').length;
+        offenders.push(`line ${lineNo}: ${args.replace(/\s+/g, ' ').slice(0, 160)}`);
+      }
+    }
+    expect(
+      offenders,
+      `execFileSync calls missing explicit maxBuffer (ENOBUFS risk):\n${offenders.join('\n')}`,
+    ).toEqual([]);
+  });
+});