feat(middleware): TodoListMiddleware should survive summarization

### Checked other resources - [x] This is a feature request, not a bug report or usage question. - [x] I added a clear and descriptive title that summarizes the feature request. - [x] I used the GitHub search to find a similar feature request and didn't find it. - [x] I checked the LangChain documentation and API reference to see if this feature already exists. - [x] This is not related to the langchain-community package. ### Package (Required) - [x] langchain - [ ] langchain-openai - [ ] langchain-anthropic - [ ] langchain-classic - [ ] langchain-core - [ ] langchain-model-profiles - [ ] langchain-tests - [ ] langchain-text-splitters - [ ] langchain-chroma - [ ] langchain-deepseek - [ ] langchain-exa - [ ] langchain-fireworks - [ ] langchain-groq - [ ] langchain-huggingface - [ ] langchain-mistralai - [ ] langchain-nomic - [ ] langchain-ollama - [ ] langchain-openrouter - [ ] langchain-perplexity - [ ] langchain-qdrant - [ ] langchain-xai - [ ] Other / not sure / general ### Feature Description TodoListMiddleware should re-inject the current todo list into the system prompt on every model call for immunity against summarization. Currently wrap_model_call only appends static instructions, it never reads state["todos"]. This means the agent's live plan is invisible to the model unless it happens to still be in message history. Proposed addition: inject_current_todos: bool = True parameter on TodoListMiddleware.__init__. When enabled, _build_system_content() reads state["todos"] and appends a <current_todos> block with status markers ([ ] pending, [~] in_progress, [x] completed) to the system prompt on every model call. ### Use Case This breaks silently when TodoListMiddleware is composed with SummarizationMiddleware in long-running / deep agent runs. SummarizationMiddleware compacts message history when the context window fills up. The ToolMessage echo of the last write_todos call is eligible for summarization once trimmed, the model loses visibility of its current …