Add critical instructions and hooks for Claude Code (#8715)

Co-Authored-By: dapplion <35266934+dapplion@users.noreply.github.com>

.claude/settings.json

@@ -0,0 +1,15 @@
+{
+  "hooks": {
+    "PostToolUse": [
+      {
+        "matcher": "Edit|Write",
+        "hooks": [
+          {
+            "type": "command",
+            "command": "echo '\n[Reminder] Run: cargo fmt --all && make lint-fix'"
+          }
+        ]
+      }
+    ]
+  }
+}

.githooks/pre-commit

@@ -0,0 +1,5 @@
+#!/bin/sh
+# Pre-commit hook: runs cargo fmt --check
+# Install with: make install-hooks
+
+exec cargo fmt --check

CLAUDE.md

@@ -2,6 +2,14 @@
 
 This file provides guidance for AI assistants (Claude Code, Codex, etc.) working with Lighthouse.
 
+## CRITICAL - Always Follow
+
+After completing ANY code changes:
+1. **MUST** run `cargo fmt --all && make lint-fix` to format and fix linting issues
+2. **MUST** run `cargo check` to verify compilation before considering task complete
+
+Run `make install-hooks` if you have not already to install git hooks. Never skip git hooks. If cargo is not available install the toolchain.
+
 ## Quick Reference
 
 ```bash

Makefile

@@ -361,3 +361,9 @@ clean:
 	cargo clean
 	make -C $(EF_TESTS) clean
 	make -C $(STATE_TRANSITION_VECTORS) clean
+
+# Installs git hooks from .githooks/ directory
+install-hooks:
+	@ln -sf ../../.githooks/pre-commit .git/hooks/pre-commit
+	@chmod +x .githooks/pre-commit
+	@echo "Git hooks installed. Pre-commit hook runs 'cargo fmt --check'."