Add pre-commit git hook to run lintrunner on staged files

.gitattributes

@@ -11,3 +11,6 @@
 
 # make sure build.sh retains Unix line endings, even when checked out on windows.
 *.sh text eol=lf
+
+# Git hooks must have Unix line endings to work on all platforms
+.githooks/* text eol=lf

.githooks/pre-commit

@@ -0,0 +1,35 @@
+#!/bin/sh
+# .githooks/pre-commit — check staged files with lintrunner before commit
+#
+# Setup (one-time per clone):
+#   git config core.hooksPath .githooks
+#
+# Skip when needed:
+#   git commit --no-verify
+
+if ! command -v lintrunner >/dev/null 2>&1; then
+    echo "Warning: lintrunner not found - skipping pre-commit lint check."
+    echo "  To install: pip install -r requirements-lintrunner.txt && lintrunner init"
+    exit 0
+fi
+
+# Check if there are any staged files to lint (added, copied, modified, renamed)
+STAGED=$(git diff --cached --name-only --diff-filter=ACMR)
+if [ -z "$STAGED" ]; then
+    exit 0
+fi
+
+# Run lintrunner in check mode (no auto-fix) on staged files.
+# --paths-cmd lets lintrunner handle the file list safely, avoiding
+# shell quoting issues with special characters in filenames.
+lintrunner --paths-cmd='git diff --cached --name-only --diff-filter=ACMR'
+STATUS=$?
+
+if [ "$STATUS" -ne 0 ]; then
+    echo ""
+    echo "Pre-commit lint check failed."
+    echo "  To auto-fix:  lintrunner -a"
+    echo "  Then re-stage and commit again."
+    echo "  To skip:      git commit --no-verify"
+    exit 1
+fi

CONTRIBUTING.md

@@ -9,6 +9,20 @@ We're always looking for your help to improve the product (bug fixes, new featur
 * Make sure your PR adheres to the [PR Guidelines](./docs/PR_Guidelines.md) and [Coding Conventions and Standards](./docs/Coding_Conventions_and_Standards.md) established by the team.
 * If you're unsure about any of the above and want to contribute, you're welcome to [start a discussion](https://github.com/microsoft/onnxruntime/discussions) with the team.
 
+## Git hooks (recommended)
+
+This repository provides a pre-commit hook that runs [lintrunner](https://github.com/suo/lintrunner) on staged files before each commit. To enable it:
+
+```sh
+git config core.hooksPath .githooks
+```
+
+The hook checks staged files for lint issues and blocks the commit if any are found. To auto-fix issues, run `lintrunner -a`, re-stage the changes, and commit again.
+
+If you need to bypass the hook (e.g., for a work-in-progress commit), use `git commit --no-verify`.
+
+> **Note:** Setting `core.hooksPath` replaces Git's default hook directory (`.git/hooks/`). If you have existing custom hooks, you may need to integrate them manually.
+
 ## Propose a new public API
 
  ONNX Runtime has a collection of [public APIs](./README.md#api-documentation).  Some of these APIs make their way back into the Windows OS.  We make compatibility commitments for these APIs and follow a structured process when adding to them.  Please use the [Feature Request issue template](https://github.com/microsoft/onnxruntime/issues/new?template=feature_request.md) before starting any PRs that affect any of the public APIs.