feat: Generate a fallback report upon recursion limit hit (#838)

* finish handle_recursion_limit_fallback

* fix

* renmae test file

* fix

* doc

---------

Co-authored-by: lxl0413 <lixinling2021@gmail.com>

docs/configuration_guide.md

@@ -305,6 +305,31 @@ Or via API request parameter:
 
 ---
 
+## Recursion Fallback Configuration
+
+When agents hit the recursion limit, DeerFlow can gracefully generate a summary of accumulated findings instead of failing (enabled by default).
+
+### Configuration
+
+In `conf.yaml`:
+```yaml
+ENABLE_RECURSION_FALLBACK: true
+```
+
+### Recursion Limit
+
+Set the maximum recursion limit via environment variable:
+```bash
+export AGENT_RECURSION_LIMIT=50  # default: 25
+```
+
+Or in `.env`:
+```ini
+AGENT_RECURSION_LIMIT=50
+```
+
+---
+
 ## RAG (Retrieval-Augmented Generation) Configuration
 
 DeerFlow supports multiple RAG providers for document retrieval. Configure the RAG provider by setting environment variables.