fix: resolve google_search tool and artifact loading issues in home renovation agent

Fixes #409

## Changes

### agent.py
- Replace singleton `google_search` with explicit `GoogleSearchTool(bypass_multi_tools_limit=True)`
  to enable compatibility with nested agent setups (ADK limitation workaround)
- Update SearchAgent instruction to be clearer about how the built-in search works
  (it's automatic, not a callable function)

### tools.py
- Add validation for common LLM hallucination patterns (e.g., `_v0` version numbers)
- Add fallback logic when artifact loading fails:
  1. Try corrected filename if version 0 detected
  2. Look up known artifact versions in session state
  3. Fall back to last generated rendering
- Improve error messages to show available artifacts

## Root Cause Analysis

1. **google_search not found**: The LLM was trying to call 'google_search' as a
   function, but GoogleSearchTool is a Gemini built-in capability that works
   automatically. Using `bypass_multi_tools_limit=True` and clearer instructions
   resolves the confusion.

2. **Artifact not found**: The LLM sometimes hallucinated incorrect filenames
   (e.g., `_v0.png` instead of `_v1.png`). Added robust fallback logic to
   recover gracefully.

advanced_ai_agents/multi_agent_apps/ai_home_renovation_agent/agent.py

@@ -10,7 +10,7 @@ Pattern Reference: https://google.github.io/adk-docs/agents/multi-agents/#coordi
 """
 
 from google.adk.agents import LlmAgent, SequentialAgent
-from google.adk.tools import google_search
+from google.adk.tools import GoogleSearchTool
 from google.adk.tools.agent_tool import AgentTool
 from .tools import (
     generate_renovation_rendering,
@@ -21,15 +21,20 @@ from .tools import (
 
 
 # ============================================================================
-# Helper Tool Agent (wraps google_search)
+# Helper Tool Agent (wraps GoogleSearchTool)
 # ============================================================================
 
+# Use bypass_multi_tools_limit=True to allow GoogleSearchTool in nested agent setups
+google_search_tool = GoogleSearchTool(bypass_multi_tools_limit=True)
+
 search_agent = LlmAgent(
     name="SearchAgent",
     model="gemini-3-flash-preview",
     description="Searches for renovation costs, contractors, materials, and design trends",
-    instruction="Use google_search to find current renovation information, costs, materials, and trends. Be concise and cite sources.",
-    tools=[google_search],
+    instruction="""You are a search specialist. When asked to find information about renovation costs, 
+contractors, materials, or design trends, the search capability is automatically enabled. 
+Simply respond with the information you find. Be concise and cite sources when available.""",
+    tools=[google_search_tool],
 )
 
 

advanced_ai_agents/multi_agent_apps/ai_home_renovation_agent/tools.py

@@ -305,18 +305,59 @@ async def edit_renovation_rendering(tool_context: ToolContext, inputs: EditRenov
         if not artifact_filename:
             artifact_filename = tool_context.state.get("last_generated_rendering")
             if not artifact_filename:
-                return "❌ No artifact_filename provided and no previous rendering found in session. Please generate a rendering first or specify the artifact filename."
+                return "❌ No artifact_filename provided and no previous rendering found in session. Please generate a rendering first using generate_renovation_rendering."
             logger.info(f"Using last generated rendering from session: {artifact_filename}")
         
+        # Validate filename format - check for common hallucination patterns
+        if "_v0." in artifact_filename:
+            # Version 0 doesn't exist - the first version is always v1
+            logger.warning(f"Invalid version v0 detected in filename: {artifact_filename}")
+            corrected_filename = artifact_filename.replace("_v0.", "_v1.")
+            logger.info(f"Attempting corrected filename: {corrected_filename}")
+            artifact_filename = corrected_filename
+        
         # Load the existing rendering
         logger.info(f"Loading artifact: {artifact_filename}")
+        loaded_image_part = None
         try:
             loaded_image_part = await tool_context.load_artifact(artifact_filename)
-            if not loaded_image_part:
-                return f"❌ Could not find rendering artifact: {artifact_filename}"
         except Exception as e:
             logger.error(f"Error loading artifact: {e}")
-            return f"Error loading rendering artifact: {e}"
+        
+        # If loading failed, try to find the most recent version of this asset
+        if not loaded_image_part:
+            # Extract base asset name and try to find any existing version
+            base_name = artifact_filename.split('_v')[0] if '_v' in artifact_filename else artifact_filename.replace('.png', '')
+            asset_filenames = tool_context.state.get("asset_filenames", {})
+            
+            # Check if we have any version of this asset
+            if base_name in asset_filenames:
+                fallback_filename = asset_filenames[base_name]
+                logger.info(f"Attempting fallback to known artifact: {fallback_filename}")
+                try:
+                    loaded_image_part = await tool_context.load_artifact(fallback_filename)
+                    if loaded_image_part:
+                        artifact_filename = fallback_filename
+                        logger.info(f"Successfully loaded fallback artifact: {fallback_filename}")
+                except Exception as e:
+                    logger.error(f"Fallback load also failed: {e}")
+            
+            # Last resort: try the last generated rendering
+            if not loaded_image_part:
+                last_rendering = tool_context.state.get("last_generated_rendering")
+                if last_rendering and last_rendering != artifact_filename:
+                    logger.info(f"Attempting last resort fallback to: {last_rendering}")
+                    try:
+                        loaded_image_part = await tool_context.load_artifact(last_rendering)
+                        if loaded_image_part:
+                            artifact_filename = last_rendering
+                            logger.info(f"Successfully loaded last resort artifact: {last_rendering}")
+                    except Exception as e:
+                        logger.error(f"Last resort load also failed: {e}")
+        
+        if not loaded_image_part:
+            available_renderings = get_asset_versions_info(tool_context)
+            return f"❌ Could not find rendering artifact: {inputs.artifact_filename}\n\n{available_renderings}\n\nPlease use one of the available artifact filenames, or generate a new rendering first."
 
         # Handle reference image if specified
         reference_image_part = None