litellm/litellm-rust/crates/host-python/AGENTS.md
devin-ai-integration[bot] 1f8997398e
refactor(rust): extract the host coroutine into its own crate (#43129)
Move the generic async coroutine out of the host crate into litellm-coroutine,
with its requirements documented in the crate's AGENTS.md. RouteMachine becomes
CallMachine on top of it, host protocol ops move to host/src/protocol.rs, and
the messages, OCR, host-python, python-bridge and legacy callbacks crates adopt
the new types. Adds error definition rules to litellm-rust/AGENTS.md.

Co-authored-by: Yujong Lee <yujong@berri.ai>
2026-09-25 04:20:06 +00:00

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- Target invariants; implementation and runtime validation may lag these rules
- Keep this crate the CPython runtime adapter and nothing more: Serde marshalling, interpreter detachment, tokio/asyncio glue, the `Execution` handle, the call driver and the `PythonLifecycle`/`ProtocolHost` traits
- No LiteLLM domain dependencies beyond `litellm-host`: no route types, no `Logging` policy, no public API registration, no cdylib build features
- The driver emits `Succeeded` or `Failed` exactly once and never dispatches after a cancellation; which Python objects consume those events is the adapter's business
- `ProtocolHost::project` receives the keyword view the adapter's `begin` returned, not the caller's dict; a protocol host that projects from it inherits that adapter's rewrites (for the legacy adapter: setup, deployment hooks, credential inheritance)
- A native failure, including one a host op returns as `InvokeError::Native`, is classified exactly once through the route's `classify`; a Python exception raised inside the call, and a failure in `begin` or `after_success`, is raised as is
- A failing `classify` is raised with the native error's text as its `__context__`, never swallowed
- Use standard PyO3 ownership and conversion APIs
- Prefer `Bound<'py, T>` for attached operations/results, `Py<T>` for retention; binding/unbinding does not copy payloads
- Use `pythonize` for selected Serde data, never a JSON-text round trip; share conversion with `Pythonized<T>`
- Preserve `PythonizeError`'s standard conversion into `PyErr`; do not stringify original Python exceptions into new `ValueError`s
- Keep serializer-panic containment in `Pythonized<T>`: async output conversion can run in an unjoined blocking task and otherwise strand delivery
- Use `Python::detach` for Rust-only work; Python operations require attachment
- Keep diagnostic counters in the consumer; wrapper invocations do not measure every interpreter release
- Release exclusive class borrows/locks before Python calls or decrements that can invoke finalizers; expose retained Python edges to GC without calling Python during traversal
- Keep coroutine driving in the shared Python driver and the native handle
- Driver: `litellm/rust_bridge/lifecycle.py`; handle: `src/handle.rs`; call driver: `src/driver.rs`; native-backed behavior tests: `tests/lifecycle.py`
- Every adapter suspension is awaited inline in the caller's task; `into_future` creates a separate task and cannot satisfy this contract
- References: [ownership](https://pyo3.rs/v0.29.2/types.html), [conversions](https://pyo3.rs/v0.29.2/conversions/traits.html), [pythonize errors](https://docs.rs/pythonize/0.29.0/src/pythonize/error.rs.html)
- [GC](https://pyo3.rs/v0.29.2/class/protocols.html#garbage-collector-integration), [re-entry](https://pyo3.rs/v0.29.2/class/call.html), [parallelism](https://pyo3.rs/v0.29.2/parallelism.html), [async delivery source](https://docs.rs/pyo3-async-runtimes/0.29.0/src/pyo3_async_runtimes/generic.rs.html)