feat: add lint-changed.sh shell script

Author: iennae

.github/scripts/lint-changed.sh

@@ -0,0 +1,47 @@
+#!/usr/bin/env bash
+
+# Exit immediately if a command fails, or if an unset variable is used
+set -euo pipefail
+
+EVENT_NAME="${1:-local}"
+BASE_REF="${2:-main}"
+BEFORE_SHA="${3:-}"
+
+echo "Configuring target diff for event: $EVENT_NAME"
+
+# Determine the base branch/commit to diff against
+if [ "$EVENT_NAME" = "pull_request" ]; then
+    # Ensure we have the target branch metadata fetched.
+    # Note: If this fails due to shallow clone issues, the script will exit safely via set -e
+    git fetch origin "$BASE_REF" --depth=1 --quiet
+    BASE_SHA="origin/$BASE_REF"
+else
+    BASE_SHA="$BEFORE_SHA"
+    # Fallback if it's a direct push without a prior SHA, or a local run
+    if [ "$BASE_SHA" = "0000000000000000000000000000000000000000" ] || [ -z "$BASE_SHA" ]; then
+        BASE_SHA="HEAD~1"
+    fi
+fi
+
+# Extract changed Python files into a Bash array
+mapfile -t CHANGED_FILES < <(git diff --name-only --diff-filter=d "$BASE_SHA" -- '*.py' 2>/dev/null || true)
+
+# Execute linters if files exist
+if [ ${#CHANGED_FILES[@]} -gt 0 ]; then
+    echo "Files to lint:"
+    printf ' - %s\n' "${CHANGED_FILES[@]}"
+
+    # Track execution success manually so both tools get a chance to run
+    BLACK_EXIT=0
+    LINT_EXIT=0
+
+    # Pass the array safely using "${CHANGED_FILES[@]}"
+    nox -s blacken -- "${CHANGED_FILES[@]}" || BLACK_EXIT=$?
+    nox -s lint -- "${CHANGED_FILES[@]}" || LINT_EXIT=$?
+
+    if [ $BLACK_EXIT -ne 0 ] || [ $LINT_EXIT -ne 0 ]; then
+        echo "❌ One or more linting checks failed."
+        exit 1
+    fi
+else
+    echo "✅ No Python files changed in this scope. Skipping checks."