Show tool call arguments in F2 context tree

tool_call labels now show the arguments truncated to 80 chars:
  tool: memory_render({"key":"identity"})
instead of just:
  tool_call: memory_render

Co-Authored-By: Proof of Concept <poc@bcachefs.org>

src/agent/context.rs

@@ -353,7 +353,7 @@ impl AstNode {
             Self::Leaf(leaf) => match &leaf.body {
                 NodeBody::Content(t) => truncate_preview(t, 60),
                 NodeBody::Thinking(t) => format!("thinking: {}", truncate_preview(t, 60)),
-                NodeBody::ToolCall { name, .. } => format!("tool_call: {}", name),
+                NodeBody::ToolCall { name, arguments } => format!("tool: {}({})", name, truncate_preview(arguments, 80)),
                 NodeBody::ToolResult(_) => "tool_result".into(),
                 NodeBody::Memory { key, score, .. } => match score {
                     Some(s) => format!("mem: {} score:{:.1}", key, s),