Add regression tests for prop attachment, centering, and editor UX

- Implemented test_phase9a_prop_attach.gd to validate anchor schema, alignment math, and preview isolation.
- Implemented test_phase9b_prop_centering.gd to check canonical origin presentation, bounds, centering, and save threshold.
- Implemented test_phase9c_prop_editor_ux.gd to assess the user experience in the prop editor, including anchor renaming and UI responsiveness.
- Added corresponding .uid files for each test.
- Created sync_sources.py script to manage markdown file synchronization with the notebook.
- Added .gitignore for virtual environment files.

tools/.gitignore

@@ -0,0 +1 @@
+.venv/

tools/sync_doc/sync_sources.py

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+import asyncio
+from pathlib import Path
+from notebooklm import NotebookLMClient
+
+RELATIVE_TARGETS = [
+    "../../AGENTS.md",
+    "../../README.md",
+    "../../plans",
+    "../../docs"
+]
+
+NOTEBOOK_TITLE = "Stickman Studio"
+
+def gather_markdown_files(base_path: Path):
+    """Recursively collect all .md files from specified relative paths."""
+    files_to_upload = []
+    
+    for rel_path in RELATIVE_TARGETS:
+        target = (base_path / rel_path).resolve()
+        
+        if target.is_file() and target.suffix.lower() in [".md", ".markdown"]:
+            files_to_upload.append(target)
+        elif target.is_dir():
+            for md_file in target.rglob("*.md"):
+                files_to_upload.append(md_file)
+        else:
+            print(f"⚠️ Target path not found: {target}")
+
+    return list(dict.fromkeys(files_to_upload))
+
+
+async def main():
+    script_dir = Path(__file__).parent.resolve()
+
+    async with await NotebookLMClient.from_storage() as client:
+
+        # 1. Locate 'Stickman Studio'
+        print(f"🔍 Searching for notebook: '{NOTEBOOK_TITLE}'...")
+        notebooks = await client.notebooks.list()
+        
+        target_notebook = next(
+            (nb for nb in notebooks if getattr(nb, 'title', None) == NOTEBOOK_TITLE or getattr(nb, 'display_name', None) == NOTEBOOK_TITLE), 
+            None
+        )
+
+        if not target_notebook:
+            print(f"❌ Could not find notebook named '{NOTEBOOK_TITLE}'.")
+            return
+
+        notebook_id = getattr(target_notebook, 'id', None) or getattr(target_notebook, 'name', '')
+        print(f"✅ Found notebook ID: {notebook_id}")
+
+        # 2. Safely filter and delete ONLY non-chat file sources
+        existing_sources = await client.sources.list(notebook_id=notebook_id)
+        
+        sources_to_delete = []
+        for source in existing_sources:
+            # Check source properties to identify saved chats
+            mime_type = getattr(source, 'original_mime_type', None) or getattr(source, 'originalMimeType', '')
+            source_type = getattr(source, 'source_type', None) or getattr(source, 'type', '')
+            
+            # SAFEGUARD: Keep any source identified as a chat note
+            is_chat = 'chat' in str(mime_type).lower() or 'chat' in str(source_type).lower()
+            
+            if is_chat:
+                source_title = getattr(source, 'title', None) or getattr(source, 'display_name', 'Chat')
+                print(f"🛡️ Preserving past chat: '{source_title}'")
+            else:
+                sources_to_delete.append(source)
+
+        if sources_to_delete:
+            print(f"\n🗑️ Removing {len(sources_to_delete)} file sources (keeping chats intact)...")
+            for source in sources_to_delete:
+                source_id = getattr(source, 'id', None) or getattr(source, 'name', '')
+                source_title = getattr(source, 'title', None) or getattr(source, 'display_name', 'File Source')
+                await client.sources.delete(notebook_id=notebook_id, source_id=source_id)
+                print(f"   - Removed: {source_title}")
+        else:
+            print("ℹ️ No old file sources to remove.")
+
+        # 3. Collect target Markdown files
+        md_files = gather_markdown_files(script_dir)
+        print(f"\n📁 Found {len(md_files)} local markdown files to attach.")
+
+        # 4. Upload Markdown files
+        for md_path in md_files:
+            rel_display = md_path.relative_to(script_dir.parent.parent)
+            print(f"   ⬆️ Uploading: {rel_display}")
+            await client.sources.add_file(
+                notebook_id=notebook_id,
+                file_path=str(md_path)
+            )
+
+        print(f"\n🎉 Sync complete! All local docs updated without touching your chat notes.")
+
+
+if __name__ == "__main__":
+    asyncio.run(main())