feat: set tools in State so its available to before_run hooks (#12376)

Co-authored-by: Stefano Fiorucci <[email protected]>

haystack/components/agents/agent.py

@@ -743,6 +743,7 @@ class Agent:
         state.set("tool_call_counts", {tool.name: 0 for tool in flat_tools})
         state.set("exit_reason", None)
         state.set("continue_run", False)
+        state.set("tools", flat_tools)
         state.set("hook_context", hook_context or {})
 
         streaming_callback = select_streaming_callback(  # type: ignore[call-overload]

releasenotes/notes/agent-before-run-tools-f5ee03eb231cfea2.yaml

@@ -0,0 +1,7 @@
+---
+enhancements:
+  - |
+    ``before_run`` hooks can now read ``state.data["tools"]``. The key was previously written only once the first step
+    had started, so a ``before_run`` hook hit a ``KeyError``. It holds a snapshot of the tools available at that point,
+    refreshed before every LLM call, so with a dynamic toolset such as ``SearchableToolset`` a ``before_run`` hook sees
+    only the tools discovered so far.

test/components/agents/test_agent_hooks.py

@@ -196,6 +196,16 @@ class TestAgentHooksValidation:
 
 
 class TestBeforeRunHook:
+    def test_tools_are_available_before_the_first_step(self):
+        available_tool_names: list[str] = []
+
+        def record_tools(state: State) -> None:
+            available_tool_names.extend(tool.name for tool in state.data["tools"])
+
+        agent = _agent(MockChatGenerator(), tools=[save], hooks={"before_run": [hook(record_tools)]})
+        agent.run(messages=[ChatMessage.from_user("hi")])
+        assert available_tool_names == ["save"]
+
     def test_runs_once_across_multi_step_run(self):
         agent = _agent(
             MockChatGenerator(),