fix: ensure newline before gitignore entry

ai_prompt_auto_commit/prepare_repository.py

@@ -56,9 +56,12 @@ def prepare_repository(
     # Add .prompts/ to the root .gitignore
     root_gitignore = repo_root / ".gitignore"
     pattern = f"/{prompts_directory}/"
-    existing = root_gitignore.read_text(encoding="utf-8").splitlines() if root_gitignore.exists() else []
+    existing_text = root_gitignore.read_text(encoding="utf-8") if root_gitignore.exists() else ""
+    existing = existing_text.splitlines()
     if pattern not in existing:
         with root_gitignore.open("a", encoding="utf-8") as fh:
+            if existing_text and not existing_text.endswith("\n"):
+                fh.write("\n")
             fh.write(f"{pattern}\n")
         print(f"Added '{pattern}' to {root_gitignore}")
     else:

tests/test_prepare_repository.py

@@ -44,6 +44,14 @@ def test_root_gitignore_existing_content_preserved(repo: Path) -> None:
     assert f"/{PROMPTS_DIRECTORY}/" in content
 
 
+def test_root_gitignore_newline_added_when_missing(repo: Path) -> None:
+    (repo / ".gitignore").write_text("*.pyc", encoding="utf-8")  # no trailing newline
+    prepare_repository()
+    lines = (repo / ".gitignore").read_text(encoding="utf-8").splitlines()
+    assert f"/{PROMPTS_DIRECTORY}/" in lines
+    assert lines[0] == "*.pyc"
+
+
 # ---------------------------------------------------------------------------
 # get_default_claude_settings
 # ---------------------------------------------------------------------------