Fix [Errno 22] Invalid argument by adding filename sanitization and long path support. Improved error reporting and folder path cleaning for Windows compatibility.

GEMINI.md

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+# SharePoint Download Tool
+
+A Python-based utility designed to recursively download folders and files from a specific SharePoint Online Site using the Microsoft Graph API.
+
+## Project Overview
+
+*   **Purpose:** Automates the synchronization of specific SharePoint document library folders to a local directory.
+*   **Technologies:** 
+    *   **Python 3.x**
+    *   **Microsoft Graph API:** Used for robust data access.
+    *   **MSAL (Microsoft Authentication Library):** Handles Entra ID (Azure AD) authentication using Client Credentials flow.
+    *   **Requests:** Manages HTTP streaming for large file downloads.
+*   **Architecture:**
+    *   `download_sharepoint.py`: The core script that orchestrates authentication, site/drive discovery, and recursive folder traversal.
+    *   `connection_info.txt`: Centralized configuration file for credentials and target paths.
+    *   `requirements.txt`: Defines necessary Python dependencies.
+
+## Building and Running
+
+### Prerequisites
+*   Python 3.x installed.
+*   A registered application in Microsoft Entra ID with `Sites.Read.All` (or higher) application permissions.
+
+### Setup
+1.  **Install Dependencies:**
+    ```bash
+    pip install -r requirements.txt
+    ```
+2.  **Configure Connection:**
+    Edit `connection_info.txt` with your specific details:
+    *   `TENANT_ID`, `CLIENT_ID`, `CLIENT_SECRET`
+    *   `SITE_URL`: Full URL to the SharePoint site.
+    *   `DOCUMENT_LIBRARY`: The name of the target library (e.g., "Documents").
+    *   `FOLDERS_TO_DOWNLOAD`: Comma-separated list of folder names to sync.
+    *   `LOCAL_PATH`: The destination path on your local machine.
+
+### Execution
+Run the main download script:
+```bash
+python download_sharepoint.py
+```
+
+### Validation
+After execution, a CSV report named `download_report_YYYYMMDD_HHMMSS.csv` is generated, detailing any failed downloads or size mismatches for verification.
+
+## Development Conventions
+
+*   **Authentication:** Always use the Graph API with MSAL for app-only authentication.
+*   **Error Handling:** All file and folder operations should be wrapped in try-except blocks, with errors logged to the generated CSV report.
+*   **Verification:** Post-download verification is performed by comparing the local file size against the `size` property returned by the Graph API.
+*   **Security:** Never commit `connection_info.txt` or any file containing secrets. Use the provided `.gitignore`.