Emit OnToolEnd hooks for interrupted and failed tools

executeSingleTool had three exit paths but only the success path
emitted all end signals. The interrupted path (nested agent
approval) skipped OnToolEnd and StreamEventToolEnd entirely,
leaving hook consumers with an unpaired OnToolStart. The error
path also missed StreamEventToolEnd and AgentHooks.OnToolEnd.

Signed-off-by: Bryan Frimin <bryan@getprobo.com>

pkg/agent/agent_test.go

@@ -134,10 +134,11 @@ func (g *outputBlocker) Check(_ context.Context, message llm.Message) (*agent.Gu
 
 type recordingHook struct {
 	agent.NoOpHooks
-	runStarted bool
-	runEnded   bool
-	toolNames  []string
-	handoffs   []string
+	runStarted     bool
+	runEnded       bool
+	toolStartNames []string
+	toolNames      []string
+	handoffs       []string
 }
 
 func (h *recordingHook) OnRunStart(_ context.Context, _ *agent.Agent, _ []llm.Message) {
@@ -148,6 +149,10 @@ func (h *recordingHook) OnRunEnd(_ context.Context, _ *agent.Agent, _ *agent.Res
 	h.runEnded = true
 }
 
+func (h *recordingHook) OnToolStart(_ context.Context, _ *agent.Agent, tool agent.Tool, _ string) {
+	h.toolStartNames = append(h.toolStartNames, tool.Name())
+}
+
 func (h *recordingHook) OnToolEnd(_ context.Context, _ *agent.Agent, tool agent.Tool, _ agent.ToolResult, _ error) {
 	h.toolNames = append(h.toolNames, tool.Name())
 }