fix: cache canonical tools to avoid multiple calls when streaming

Merge https://github.com/google/adk-python/pull/3299
Fixes https://github.com/google/adk-python/issues/3237

Co-authored-by: Xuan Yang <xygoogle@google.com>
COPYBARA_INTEGRATE_REVIEW=https://github.com/google/adk-python/pull/3299 from hcadioli:fix/cache-tools de02bd3e4533c3741edf05788a5e8b2d3d38bae4
PiperOrigin-RevId: 829499299

src/google/adk/agents/invocation_context.py

@@ -32,6 +32,7 @@ from ..memory.base_memory_service import BaseMemoryService
 from ..plugins.plugin_manager import PluginManager
 from ..sessions.base_session_service import BaseSessionService
 from ..sessions.session import Session
+from ..tools.base_tool import BaseTool
 from .active_streaming_tool import ActiveStreamingTool
 from .base_agent import BaseAgent
 from .base_agent import BaseAgentState
@@ -202,6 +203,9 @@ class InvocationContext(BaseModel):
   plugin_manager: PluginManager = Field(default_factory=PluginManager)
   """The manager for keeping track of plugins in this invocation."""
 
+  canonical_tools_cache: Optional[list[BaseTool]] = None
+  """The cache of canonical tools for this invocation."""
+
   _invocation_cost_manager: _InvocationCostManager = PrivateAttr(
       default_factory=_InvocationCostManager
   )

src/google/adk/flows/llm_flows/base_llm_flow.py

@@ -855,7 +855,10 @@ class BaseLlmFlow(ABC):
         response: Optional[LlmResponse] = None,
     ) -> Optional[LlmResponse]:
       readonly_context = ReadonlyContext(invocation_context)
-      tools = await agent.canonical_tools(readonly_context)
+      if (tools := invocation_context.canonical_tools_cache) is None:
+        tools = await agent.canonical_tools(readonly_context)
+        invocation_context.canonical_tools_cache = tools
+
       if not any(tool.name == 'google_search_agent' for tool in tools):
         return response
       ground_metadata = invocation_context.session.state.get(