Prevent file overwrite on duplicate PDF downloads

- Add unique_path() helper to append number suffix when file exists
- Apply to both cmd_process and cmd_download functions
- Follow macOS Finder naming convention (e.g., slides 2.pdf)
- Update documentation to reflect duplicate handling behavior

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

Author: Saqoosha

CLAUDE.md

@@ -64,6 +64,7 @@ AutoMeetsSlide/
 - Commands: `login`, `check-auth`, `process` (supports `--system-prompt` flag)
 - Communicates via JSON on stdout
 - Uses `notebooklm-py` library for NotebookLM API
+- Duplicate file handling: automatically appends a number suffix (e.g., `_slides 2.pdf`) when output file already exists
 
 ### Data Flow
 1. User drops file → FileItem added to queue (pending)

python-sidecar/notebooklm_sidecar.py

@@ -19,6 +19,24 @@
 from pathlib import Path
 
 
+def unique_path(path: Path) -> Path:
+    """Return a unique file path by appending a number if the file already exists.
+
+    Example: slides.pdf -> slides 2.pdf -> slides 3.pdf
+    """
+    if not path.exists():
+        return path
+    stem = path.stem
+    suffix = path.suffix
+    parent = path.parent
+    counter = 2
+    while True:
+        candidate = parent / f"{stem} {counter}{suffix}"
+        if not candidate.exists():
+            return candidate
+        counter += 1
+
+
 def emit(status: str, message: str, **kwargs):
     """Emit a JSON status message to stdout."""
     data = {"status": status, "message": message, **kwargs}
@@ -197,7 +215,7 @@ async def cmd_process(file_path: str, output_dir: str, system_prompt: str | None
                 emit("progress", "Slide generation complete!")
 
             # Download PDF
-            output_file = output_dir / f"{file_path.stem}_slides.pdf"
+            output_file = unique_path(output_dir / f"{file_path.stem}_slides.pdf")
             emit("progress", f"Downloading PDF to: {output_file}")
 
             downloaded_path = await client.artifacts.download_slide_deck(
@@ -282,7 +300,7 @@ async def cmd_download(notebook_id: str, output_dir: str, name: str | None = Non
     try:
         async with await NotebookLMClient.from_storage() as client:
             file_name = f"{name}_slides.pdf" if name else "slides.pdf"
-            output_file = output_dir / file_name
+            output_file = unique_path(output_dir / file_name)
             downloaded_path = await client.artifacts.download_slide_deck(
                 notebook_id,
                 str(output_file),