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@@ -1,3 +1,106 @@
+<general_rules>
+This repository is a monorepo where each library lives in a subdirectory under `libs/`. When modifying code in any library, you must run the following commands in that library's directory before creating a pull request:
+
+- `make format` – run code formatters (ruff)
+- `make lint` – run the linter (ruff + mypy)
+- `make test` – execute the test suite (pytest)
+
+All libraries use `uv` as the package manager, not pip or poetry. Commands should be prefixed with `uv run` when executing tools like pytest, ruff, or mypy.
+
+When creating new functionality, always search the relevant library's directory structure first to see if similar functionality exists. For the main `langgraph` library, check these key directories:
+- `libs/langgraph/langgraph/channels/` - for channel-related functionality
+- `libs/langgraph/langgraph/graph/` - for graph construction and state management
+- `libs/langgraph/langgraph/pregel/` - for execution engine components
+- `libs/langgraph/langgraph/utils/` - for utility functions
+
+The root `Makefile` provides commands to run operations across all libraries:
+- `make install` - install all library dependencies using uv
+- `make format` - format code in all libraries
+- `make lint` - lint all libraries
+- `make test` - run tests in all libraries
+
+Follow the existing code style enforced by ruff and ensure type annotations are present for mypy validation. All libraries maintain consistent configuration for these tools in their `pyproject.toml` files.
+</general_rules>
+
+<repository_structure>
+This is a monorepo containing 8 main Python libraries under the `libs/` directory:
+
+**Core Libraries:**
+- `checkpoint` - base interfaces for LangGraph checkpointers
+- `langgraph` - core framework for building stateful, multi-actor agents
+- `prebuilt` - high-level APIs for creating and running agents and tools
+
+**Storage Implementations:**
+- `checkpoint-postgres` - PostgreSQL implementation of checkpoint saver
+- `checkpoint-sqlite` - SQLite implementation of checkpoint saver
+
+**Developer Tools:**
+- `cli` - official command-line interface for LangGraph
+- `sdk-py` - Python SDK for the LangGraph Platform API
+- `sdk-js` - JavaScript/TypeScript SDK for LangGraph REST API
+
+**Dependency Hierarchy:**
+```
+checkpoint
+├── checkpoint-postgres
+├── checkpoint-sqlite
+├── prebuilt
+└── langgraph
+
+prebuilt
+└── langgraph
+
+sdk-py
+├── langgraph
+└── cli
+```
+
+Each library follows a consistent structure with its own `pyproject.toml`, `Makefile`, `tests/` directory, and main package directory. The main `langgraph` library contains subdirectories for `channels/`, `func/`, `graph/`, `managed/`, `pregel/`, and `utils/`.
+
+Libraries use editable installs to reference each other during development via `[tool.uv.sources]` sections in their `pyproject.toml` files.
+</repository_structure>
+
+<dependencies_and_installation>
+This repository uses `uv` as the primary package manager. To set up the entire monorepo:
+
+```bash
+make install
+```
+
+This command creates a virtual environment and installs all libraries in editable mode using `uv pip install -e` for each library in `libs/`.
+
+Each library has its own `pyproject.toml` with:
+- Production dependencies in the `[project]` dependencies array
+- Development dependencies in `[dependency-groups]` dev array
+- Local library references in `[tool.uv.sources]` for editable installs
+
+Common development dependencies across all libraries include: `ruff`, `codespell`, `pytest`, `pytest-asyncio`, `pytest-mock`, `mypy`, and `pytest-watcher`.
+
+To work on a specific library, navigate to its directory under `libs/` and use `uv run` to execute commands within that library's environment.
+</dependencies_and_installation>
+
+<testing_instructions>
+All libraries use `pytest` as the testing framework with asyncio support enabled (`asyncio_mode = "auto"`). Tests are configured with strict markers and detailed output (`--strict-markers --strict-config --durations=5 -vv`).
+
+**Running Tests:**
+- Single library: `cd libs/<library> && make test`
+- All libraries: `make test` (from root)
+- Specific test file: `make test TEST=path/to/test.py`
+- Watch mode: `make test_watch` (in individual library directories)
+
+**PostgreSQL-dependent Libraries:**
+Some libraries (`langgraph`, `checkpoint-postgres`, `prebuilt`) require PostgreSQL for testing. These use Docker Compose with configuration files at `libs/*/tests/compose-postgres.yml`. The test commands automatically start/stop PostgreSQL containers.
+
+To skip Docker-dependent tests, set `NO_DOCKER=true` environment variable.
+
+**Test Structure:**
+- Test files are located in `libs/*/tests/` directories
+- Use `pytest-asyncio` for async test functions
+- Common test utilities and fixtures are shared via `conftest.py` files
+- Some libraries use `syrupy` for snapshot testing
+
+Tests should cover core functionality, error handling, and integration scenarios. Follow existing test patterns within each library for consistency.
+</testing_instructions>
 # AGENTS Instructions
 
 This repository is a monorepo. Each library lives in a subdirectory under `libs/`.
@@ -53,3 +156,4 @@ sdk-js (standalone)
 ```
 
 Changes to a library may impact all of its dependents shown above.
+