feat(agent): add post-turn stop callback

packages/agent/README.md

@@ -112,6 +112,20 @@ The `beforeToolCall` hook runs after `tool_execution_start` and validated argume
 
 Tools can also return `terminate: true` to hint that the automatic follow-up LLM call should be skipped. The loop only stops early when every finalized tool result in that batch sets `terminate: true`. Mixed batches continue normally.
 
+Low-level loop callers can set `shouldStopAfterTurn` to stop gracefully after the current turn completes:
+
+```typescript
+const stream = agentLoop(prompts, context, {
+  model,
+  convertToLlm,
+  shouldStopAfterTurn: async ({ message, toolResults, context, newMessages }) => {
+    return shouldCompactBeforeNextTurn(context.messages);
+  },
+});
+```
+
+`shouldStopAfterTurn` runs after `turn_end` is emitted and after the assistant response and any tool executions have completed normally. If it returns `true`, the loop emits `agent_end` and exits before polling steering or follow-up queues, and before starting another LLM call. It does not abort the provider stream, does not cancel running tools, and does not alter the assistant message stop reason.
+
 When you use the `Agent` class, assistant `message_end` processing is treated as a barrier before tool preflight begins. That means `beforeToolCall` sees agent state that already includes the assistant message that requested the tool call.
 
 ### continue() Event Sequence