diff --git a/packages/git/src/diff.ts b/packages/git/src/diff.ts
index b13a9f2..52177e1 100644
--- a/packages/git/src/diff.ts
+++ b/packages/git/src/diff.ts
@@ -1,7 +1,22 @@
 import { exec, execLarge, execLines, execWithStdin } from './exec.js';
 
+/**
+ * Flags that neutralize user git config which would otherwise alter the diff
+ * format and break parsing:
+ * - `--no-color` guards against `color.ui=always` / `color.diff=always`
+ * - `--no-ext-diff` guards against a configured `diff.external` driver
+ * - `--src-prefix`/`--dst-prefix` force the standard `a/`/`b/` prefixes,
+ *   overriding `diff.mnemonicPrefix`, `diff.noprefix` and custom prefixes
+ */
+const DIFF_FORMAT_ARGS = [
+  '--no-color',
+  '--no-ext-diff',
+  '--src-prefix=a/',
+  '--dst-prefix=b/',
+];
+
 export function getDiff(args: string[] = []): string {
-  const cmd = ['git', 'diff', ...args].join(' ');
+  const cmd = ['git', 'diff', ...DIFF_FORMAT_ARGS, ...args].join(' ');
   return execLarge(cmd);
 }
 
@@ -14,7 +29,7 @@ export function getUntrackedDiff(files: string[]): string {
 
   for (const file of files) {
     try {
-      execLarge(`git diff --no-index -- /dev/null "${file}"`);
+      execLarge(`git diff ${DIFF_FORMAT_ARGS.join(' ')} --no-index -- /dev/null "${file}"`);
     } catch (err: unknown) {
       const error = err as { stdout?: string; status?: number };
       if (error.status === 1 && error.stdout) {
@@ -38,7 +53,11 @@ export function resolveDiffArgs(ref: string): RefDiffArgs {
     case 'work':
       return { type: 'args', args: ['HEAD'], includeUntracked: true };
     default:
-      return { type: 'args', args: [normalizeRef(ref)], includeUntracked: true };
+      // Bare refs (`diffity main`) diff against the working tree, so untracked
+      // files are part of the change set (#10). Ranges (`A..B`) pin both
+      // endpoints — the working tree isn't involved, so untracked files must
+      // be excluded or the diff won't match `git diff A..B`.
+      return { type: 'args', args: [normalizeRef(ref)], includeUntracked: !ref.includes('..') };
   }
 }
 
@@ -58,7 +77,7 @@ export function resolveRef(ref: string, extraArgs: string[] = []): string {
 export function getDiffFiles(ref: string): string[] {
   const resolved = resolveDiffArgs(ref);
 
-  const tracked = execLines(`git diff --name-only ${resolved.args.join(' ')}`.trim());
+  const tracked = execLines(`git diff ${DIFF_FORMAT_ARGS.join(' ')} --name-only ${resolved.args.join(' ')}`.trim());
   if (resolved.includeUntracked) {
     const untracked = getUntrackedFiles();
     return [...new Set([...tracked, ...untracked])];
@@ -67,7 +86,7 @@ export function getDiffFiles(ref: string): string[] {
 }
 
 export function getDiffStat(args: string[] = []): string {
-  const cmd = ['git', 'diff', '--stat', ...args].join(' ');
+  const cmd = ['git', 'diff', ...DIFF_FORMAT_ARGS, '--stat', ...args].join(' ');
   try {
     return execLarge(cmd);
   } catch {
diff --git a/packages/git/src/exec.ts b/packages/git/src/exec.ts
index 623726e..68927ad 100644
--- a/packages/git/src/exec.ts
+++ b/packages/git/src/exec.ts
@@ -1,13 +1,24 @@
-import { execSync, type StdioOptions } from 'node:child_process';
+import {
+  execFileSync,
+  execSync,
+  type StdioOptions,
+} from 'node:child_process';
 
 const STDIO: StdioOptions = ['pipe', 'pipe', 'pipe'];
 
+/**
+ * Node's default is 1 MB, which is smaller than a large repository's file
+ * listing: `git ls-files` in a ~29k-file monorepo emits over 2 MB and the child
+ * process dies with ENOBUFS.
+ */
+const MAX_BUFFER = 50 * 1024 * 1024;
+
 export function execWithStdin(cmd: string, input: string): string {
   return execSync(cmd, {
     encoding: 'utf-8',
     stdio: STDIO,
     input,
-    maxBuffer: 50 * 1024 * 1024,
+    maxBuffer: MAX_BUFFER,
   });
 }
 
@@ -22,10 +33,23 @@ export function execLarge(cmd: string): string {
   return execSync(cmd, {
     encoding: 'utf-8',
     stdio: STDIO,
-    maxBuffer: 50 * 1024 * 1024,
+    maxBuffer: MAX_BUFFER,
   });
 }
 
+/**
+ * The argv form of `execLarge`, for commands whose arguments come from user
+ * input — a path with a space or a quote in it cannot be passed safely through
+ * a shell string.
+ */
+export function execFileLarge(command: string, args: string[]): string {
+  return execFileSync(command, args, {
+    encoding: 'utf-8',
+    stdio: STDIO,
+    maxBuffer: MAX_BUFFER,
+  }).trim();
+}
+
 export function execLines(cmd: string): string[] {
   const output = exec(cmd);
   if (!output) {
diff --git a/packages/git/src/tree.ts b/packages/git/src/tree.ts
index b6a22ef..dec7055 100644
--- a/packages/git/src/tree.ts
+++ b/packages/git/src/tree.ts
@@ -1,7 +1,8 @@
-import { execFileSync } from 'node:child_process';
 import { readFileSync } from 'node:fs';
 import { join } from 'node:path';
 
+import { execFileLarge } from './exec';
+
 export interface TreeEntry {
   type: 'blob' | 'tree';
   path: string;
@@ -11,19 +12,16 @@ export interface TreeEntry {
 function getWorkingTreeFiles(dirPath?: string): string[] {
   const pathArgs = dirPath ? [dirPath + '/'] : [];
 
-  const tracked = execFileSync('git', ['ls-files', ...pathArgs], {
-    encoding: 'utf-8',
-  }).trim();
+  const tracked = execFileLarge('git', ['ls-files', ...pathArgs]);
 
-  const deleted = execFileSync('git', ['ls-files', '--deleted', ...pathArgs], {
-    encoding: 'utf-8',
-  }).trim();
+  const deleted = execFileLarge('git', ['ls-files', '--deleted', ...pathArgs]);
 
-  const untracked = execFileSync(
-    'git',
-    ['ls-files', '--others', '--exclude-standard', ...pathArgs],
-    { encoding: 'utf-8' },
-  ).trim();
+  const untracked = execFileLarge('git', [
+    'ls-files',
+    '--others',
+    '--exclude-standard',
+    ...pathArgs,
+  ]);
 
   const deletedSet = new Set(deleted ? deleted.split('\n') : []);
   const files = new Set<string>();
@@ -71,30 +69,20 @@ export function getTreeEntries(_ref = 'HEAD', dirPath?: string): TreeEntry[] {
 }
 
 export function getTreeFingerprint(): string {
-  const tracked = execFileSync('git', ['ls-files'], {
-    encoding: 'utf-8',
-  }).trim();
+  const tracked = execFileLarge('git', ['ls-files']);
 
-  const statOutput = execFileSync(
-    'git',
-    ['status', '--porcelain', '-u'],
-    { encoding: 'utf-8' },
-  ).trim();
+  const statOutput = execFileLarge('git', ['status', '--porcelain', '-u']);
 
   return `${tracked.length}:${statOutput}`;
 }
 
 export function getWorkingTreeFileContent(filePath: string): string {
-  const root = execFileSync('git', ['rev-parse', '--show-toplevel'], {
-    encoding: 'utf-8',
-  }).trim();
+  const root = execFileLarge('git', ['rev-parse', '--show-toplevel']);
   return readFileSync(join(root, filePath), 'utf-8');
 }
 
 export function getWorkingTreeRawFile(filePath: string): { data: Buffer; fullPath: string } {
-  const root = execFileSync('git', ['rev-parse', '--show-toplevel'], {
-    encoding: 'utf-8',
-  }).trim();
+  const root = execFileLarge('git', ['rev-parse', '--show-toplevel']);
   const fullPath = join(root, filePath);
   return { data: readFileSync(fullPath), fullPath };
 }
diff --git a/packages/git/tests/diff-format.test.ts b/packages/git/tests/diff-format.test.ts
new file mode 100644
index 0000000..97617ff
--- /dev/null
+++ b/packages/git/tests/diff-format.test.ts
@@ -0,0 +1,94 @@
+import { describe, it, expect, beforeAll, afterAll } from 'vitest';
+import { execSync } from 'node:child_process';
+import { mkdtempSync, writeFileSync, rmSync } from 'node:fs';
+import { join } from 'node:path';
+import { tmpdir } from 'node:os';
+
+let repoDir: string;
+let origCwd: string;
+
+function git(cmd: string) {
+  execSync(`git ${cmd}`, { cwd: repoDir, stdio: 'pipe' });
+}
+
+function writeFile(name: string, content: string) {
+  writeFileSync(join(repoDir, name), content);
+}
+
+beforeAll(() => {
+  origCwd = process.cwd();
+  repoDir = mkdtempSync(join(tmpdir(), 'diffity-format-test-'));
+
+  git('init -b main');
+  git('config user.email "test@test.com"');
+  git('config user.name "Test"');
+
+  // git config that alters the default diff format and previously broke parsing
+  git('config diff.mnemonicprefix true');
+  git('config color.ui always');
+
+  writeFile('base.txt', 'a\nb\n');
+  git('add .');
+  git('commit -m "initial commit"');
+
+  process.chdir(repoDir);
+});
+
+afterAll(() => {
+  process.chdir(origCwd);
+  rmSync(repoDir, { recursive: true, force: true });
+});
+
+describe('diff format neutralization', () => {
+  it('emits standard a/ b/ prefixes despite diff.mnemonicprefix', async () => {
+    const { resolveRef } = await import('../src/diff.js');
+    writeFile('base.txt', 'a\nc\n');
+
+    const raw = resolveRef('unstaged');
+
+    expect(raw).toContain('diff --git a/base.txt b/base.txt');
+    expect(raw).toContain('--- a/base.txt');
+    expect(raw).toContain('+++ b/base.txt');
+    // no ANSI color escapes even with color.ui=always
+    expect(raw).not.toMatch(/\x1b\[/);
+
+    git('checkout -- base.txt');
+  });
+
+  it('lists file names without color escapes despite color.ui', async () => {
+    const { getDiffFiles } = await import('../src/diff.js');
+    writeFile('base.txt', 'a\nd\n');
+
+    const files = getDiffFiles('unstaged');
+
+    expect(files).toEqual(['base.txt']);
+    expect(files.join('')).not.toMatch(/\x1b\[/);
+
+    git('checkout -- base.txt');
+  });
+
+  it('emits a diffstat without color escapes despite color.ui', async () => {
+    const { getDiffStatForRef } = await import('../src/diff.js');
+    writeFile('base.txt', 'a\ne\n');
+
+    const stat = getDiffStatForRef('unstaged');
+
+    expect(stat).toContain('base.txt');
+    expect(stat).not.toMatch(/\x1b\[/);
+
+    git('checkout -- base.txt');
+  });
+
+  it('emits standard prefixes for untracked files', async () => {
+    const { resolveRef } = await import('../src/diff.js');
+    writeFile('untracked.txt', 'x\ny\n');
+
+    const raw = resolveRef('work');
+
+    expect(raw).toContain('diff --git a/untracked.txt b/untracked.txt');
+    expect(raw).toContain('+++ b/untracked.txt');
+    expect(raw).not.toMatch(/\x1b\[/);
+
+    execSync(`rm "${join(repoDir, 'untracked.txt')}"`, { stdio: 'pipe' });
+  });
+});
diff --git a/packages/git/tests/get-diff-files.test.ts b/packages/git/tests/get-diff-files.test.ts
index ec3684d..0b1ad05 100644
--- a/packages/git/tests/get-diff-files.test.ts
+++ b/packages/git/tests/get-diff-files.test.ts
@@ -86,6 +86,28 @@ describe('getDiffFiles', () => {
     git('checkout -- base.txt');
   });
 
+  it('includes untracked files for bare refs (diff against working tree)', async () => {
+    const { getDiffFiles } = await import('../src/diff.js');
+    writeFile('untracked-file.txt', 'untracked\n');
+
+    const files = getDiffFiles('main');
+    expect(files).toContain('untracked-file.txt');
+
+    execSync(`rm "${join(repoDir, 'untracked-file.txt')}"`, { stdio: 'pipe' });
+  });
+
+  it('excludes untracked files for range refs (both endpoints pinned)', async () => {
+    const { getDiffFiles } = await import('../src/diff.js');
+    writeFile('untracked-file.txt', 'untracked\n');
+
+    const files = getDiffFiles('main..feature');
+    expect(files).toContain('feature.txt');
+    expect(files).toContain('base.txt');
+    expect(files).not.toContain('untracked-file.txt');
+
+    execSync(`rm "${join(repoDir, 'untracked-file.txt')}"`, { stdio: 'pipe' });
+  });
+
   it('returns working tree files for work ref', async () => {
     const { getDiffFiles } = await import('../src/diff.js');
     writeFile('untracked-file.txt', 'untracked\n');
diff --git a/packages/git/tests/get-tree-large-repo.test.ts b/packages/git/tests/get-tree-large-repo.test.ts
new file mode 100644
index 0000000..6eca7b2
--- /dev/null
+++ b/packages/git/tests/get-tree-large-repo.test.ts
@@ -0,0 +1,67 @@
+import { describe, it, expect, beforeAll, afterAll } from 'vitest';
+import { execSync } from 'node:child_process';
+import { mkdtempSync, mkdirSync, writeFileSync, rmSync } from 'node:fs';
+import { join } from 'node:path';
+import { tmpdir } from 'node:os';
+
+import { getTree, getTreeFingerprint } from '../src/tree';
+
+/**
+ * Node's default maxBuffer is 1 MB. A repository whose file listing is larger
+ * than that used to kill `git ls-files` with ENOBUFS, which surfaced as
+ * "Failed to get tree" for every large repo.
+ */
+const DEFAULT_MAX_BUFFER = 1024 * 1024;
+
+let repoDir: string;
+let origCwd: string;
+
+function git(cmd: string) {
+  // This fixture is deliberately larger than the default 1 MB buffer, and
+  // `git commit` names every file it creates — so the setup needs the same
+  // headroom the code under test does.
+  execSync(`git ${cmd}`, {
+    cwd: repoDir,
+    stdio: 'pipe',
+    maxBuffer: 50 * 1024 * 1024,
+  });
+}
+
+beforeAll(() => {
+  origCwd = process.cwd();
+  repoDir = mkdtempSync(join(tmpdir(), 'diffity-large-tree-'));
+
+  git('init -b main');
+  git('config user.email "test@test.com"');
+  git('config user.name "Test"');
+
+  // Enough path bytes to exceed the default buffer: names are padded so the
+  // listing crosses 1 MB without needing tens of thousands of files.
+  const padding = 'p'.repeat(180);
+  mkdirSync(join(repoDir, 'many'));
+  for (let i = 0; i < 6000; i += 1) {
+    writeFileSync(join(repoDir, 'many', `f${i}-${padding}.txt`), '');
+  }
+  git('add .');
+  git('commit -m "many files"');
+
+  process.chdir(repoDir);
+});
+
+afterAll(() => {
+  process.chdir(origCwd);
+  rmSync(repoDir, { recursive: true, force: true });
+});
+
+describe('a repository whose listing exceeds the default buffer', () => {
+  it('lists every file rather than throwing ENOBUFS', () => {
+    const paths = getTree();
+
+    expect(paths).toHaveLength(6000);
+    expect(paths.join('\n').length).toBeGreaterThan(DEFAULT_MAX_BUFFER);
+  });
+
+  it('still fingerprints the tree', () => {
+    expect(getTreeFingerprint()).toMatch(/^\d+:/);
+  });
+});