refactor: workflow-as-agent outputs readable summary instead of raw hash

Extract can now work with the readable content directly, without
needing a special extractPrompt for DAG traversal.

Closes #182

packages/workflow-execute/src/workflow-as-agent.ts

@@ -108,7 +108,7 @@ export function workflowAsAgent(
         io,
         logger,
       );
-      return result.rootHash;
+      return `Child workflow "${workflowName}" completed (returnCode=${result.returnCode}).\n\nSummary: ${result.summary}\n\nChild thread root hash: ${result.rootHash}`;
     } catch (e) {
       const message = e instanceof Error ? e.message : String(e);
       return `ERROR: ${message}`;