pre-commit: fail on trailing whitespace

pre-commit

@@ -14,3 +14,19 @@ if [ "$should_run" = "yes" ]; then
 else
     echo "No relevant changes; skipping Tailwind build."
 fi
+
+# Check for trailing whitespace in staged files, fail if found
+
+git diff --cached --name-only --diff-filter=ACM | while IFS= read -r file; do
+    [ -f "$file" ] || continue
+
+    case "$file" in
+        *.py|*.js|*.ts|*.sh|*.md|*.txt|*.html|*.css)
+            if grep -qE '[[:space:]]+$' "$file"; then
+                echo "Commit aborted due to trailing whitespace."
+                echo "Fix it manually or use tools/strip-trailing-whitespace.sh"
+                exit 1
+            fi
+            ;;
+    esac
+done

tools/strip-trailing-whitespace.sh

@@ -0,0 +1,30 @@
+#!/bin/bash
+#
+# Strip trailing whitespace from tracked files with specific extensions.
+# Usage: ./tools/strip-trailing-whitespace.sh
+# Works on macOS (BSD sed) or Linux (GNU sed), but not both at once.
+
+set -euo pipefail
+
+# Extensions to include
+EXT_REGEX='\.(py|js|ts|sh|md|txt|html|css)$'
+
+# Detect sed flavor
+if sed --version >/dev/null 2>&1; then
+    SED_CMD=(sed -i -e 's/[[:space:]]\+$//')
+elif sed -i '' testfile 2>/dev/null; then
+    SED_CMD=(sed -i '' -e 's/[[:space:]]\+$//')
+else
+    echo "Unsupported sed version. Must be GNU sed or BSD sed (macOS)." >&2
+    exit 1
+fi
+
+git ls-files -z | while IFS= read -r -d '' file; do
+    [[ -f "$file" ]] || continue
+    [[ "$file" =~ $EXT_REGEX ]] || continue
+
+    if grep -qE '[[:space:]]+$' "$file"; then
+        echo "Fixing: $file"
+        "${SED_CMD[@]}" "$file"
+    fi
+done