Fix output() tool for forked agents: extract from AST after tool turns

The old dispatch_tools intercepted output() calls and stored them in
auto.outputs. The new Agent::turn() dispatches normally, so output()
was hitting the filesystem path (which fails without POC_AGENT_OUTPUT_DIR).

Now run_with_backend scans the conversation AST after each tool turn
and extracts output() call arguments into auto.outputs. collect_results
in dmn.rs reads these to surface memories and inject reflections.

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

src/agent/oneshot.rs

@@ -165,6 +165,28 @@ impl AutoAgent {
                 .map_err(|e| format!("{}: {}", self.name, e))?;
 
             if result.had_tool_calls {
+                // Extract output() calls from the conversation
+                let ctx = backend.0.context.lock().await;
+                for node in ctx.conversation() {
+                    if let super::context::AstNode::Branch { children, .. } = node {
+                        for child in children {
+                            if let Some(leaf) = child.leaf() {
+                                if let super::context::NodeBody::ToolCall { name, arguments } = leaf.body() {
+                                    if name == "output" {
+                                        if let Ok(args) = serde_json::from_str::<serde_json::Value>(arguments) {
+                                            let key = args["key"].as_str().unwrap_or("");
+                                            let value = args["value"].as_str().unwrap_or("");
+                                            if !key.is_empty() {
+                                                self.outputs.insert(key.to_string(), value.to_string());
+                                            }
+                                        }
+                                    }
+                                }
+                            }
+                        }
+                    }
+                }
+                drop(ctx);
                 continue;
             }