refactor(rust): move credential inheritance and SDK limits into a driver preflight

litellm-rust/crates/callbacks-legacy-python/AGENTS.md

@@ -1,19 +1,19 @@
 - Target invariants, not completion claims
-- Keep this crate the legacy `@client` wrapper as the native call sees it, and nothing else: the `Logging` contract (`function_setup`, the deployment hooks, `pre_call`/`post_call`, the sync and async success and failure fan-out, the deferred proxy release, the argument sharing those callbacks rely on) plus the kwargs rewrites the wrapper makes on the way in (credential-name inheritance, the budget and retry-count limits)
+- This crate is the legacy `@client` wrapper as the native call sees it, and nothing else: the `Logging` contract (`function_setup`, the deployment hooks, `pre_call`/`post_call`, the sync and async success and failure fan-out, the deferred proxy release, the argument sharing those callbacks rely on)
+  - Smell test: if a future callback host (`callbacks-v1-python`, WASM, in-process Rust) could share a piece of this crate, it does not belong here
+  - SDK request policy (credential inheritance, the budget and retry-count limits) is the driver's preflight, supplied by `python-bridge`; this crate only adopts the keyword view it produces
   - The driver in `litellm-host-python`, the routes and core see one `PythonLifecycle`; they never learn which Python objects consume a call
-- Rust drives the call; every litellm Python internal it still borrows is a variant of `LegacyPython`, grouped by subsystem (`Wrapper`, `Logging`, `DeploymentHooks`)
+- Every litellm Python internal Rust still borrows is a variant of `LegacyPython`, grouped by subsystem, with its signature pinned in `python_contract.json`
   - The enum only shrinks: when Rust owns a subsystem, delete its group rather than adding a Rust path beside it
   - Calling a user's own callback directly is permanent Python surface and gets its own type outside `LegacyPython`
-  - `PublicCall` is the caller's call as `Logging` sees it: the positional arguments, the keyword view as the legacy path rewrites it (setup, deployment hook, prepare) and the bound request object whose attributes back keywords the caller omitted; routes hand it over through `run_legacy_call` and keep no copy
-- `setup` reuses a `Logging` the caller passed as `litellm_logging_obj` (the proxy and Router are the live cases) and otherwise builds one through `function_setup`, as `@client` does
-  - Either way every phase calls the same `Logging` method the Python path calls; which callbacks run is `Logging`'s decision, never this crate's
+- `PublicCall` is the caller's call as `Logging` sees it: the positional arguments, the keyword view as the call rewrites it (setup, deployment hook, preflight) and the bound request object backing omitted keywords; routes hand it over through `run_legacy_call` and keep no copy
+- `setup` reuses a `Logging` passed as `litellm_logging_obj` (the proxy and Router) and otherwise builds one through `function_setup`; which callbacks run is `Logging`'s decision, never this crate's
 - Callbacks receive the caller's own objects and may mutate them; this crate alone carries that obligation
-  - Retain complete boundary arguments, opaque unknown values, aliases, omitted/default distinctions and deliberate copies; preserve the established deployment-hook kwargs view
-  - Before `pre_call`, re-alias every body key whose value equals the caller's argument to the caller's own object; this crate compares the two itself, and the argument is resolved by `litellm_host_python::lookup`
-  - Retain independently captured body/header roots from `pre_call` to `post_call`; in-place mutation reaches the wire, envelope field replacement is visible to later callbacks only
-  - A later kind of callback host (WASM, in-process Rust) has none of these obligations, so they stay out of `litellm-host`, `litellm-host-python` and the bridge; the only fact that crosses from the route is the prepared keyword view
-- Success and failure handlers receive the exact selected public response or exception; logging projections, redaction and snapshots keep their own copy contracts
-  - Ordinary failure-handler errors cannot suppress the other eligible family or replace the mapped provider error; a cancellation ends the call with no further dispatch
-  - Dispatch errors never replay provider work or trigger the opposite outcome; the proxy's acceptance or rejection releases deferred success at most once
+  - Retain complete boundary arguments, opaque values, aliases, omitted/default distinctions and deliberate copies; preserve the deployment-hook kwargs view
+  - Before `pre_call`, re-alias every body key whose value equals the caller's argument to the caller's own object, resolved through `litellm_host_python::lookup`
+  - Retain body/header roots from `pre_call` to `post_call`; in-place mutation reaches the wire, envelope field replacement is visible to later callbacks only
+- Success and failure handlers receive the exact selected public response or exception
+  - A failure-handler error cannot suppress the other eligible family or replace the mapped provider error; a cancellation ends the call with no further dispatch
+  - Dispatch errors never replay provider work or trigger the opposite outcome; the proxy releases deferred success at most once
   - Delivery follows the registry, not the callable's type: direct, awaited, executor-submitted, logging-worker and deferred paths stay distinct
 - Traverse every retained Python edge; `close` is idempotent and restores the correlation context once

litellm-rust/crates/callbacks-legacy-python/python_contract.json

@@ -6,9 +6,6 @@
     "start_time",
     "asynchronous"
   ],
-  "check_limits": [
-    "kwargs"
-  ],
   "finalize": [
     "response",
     "logger",
@@ -76,11 +73,6 @@
   ],
   "custom_pricing_fields": [],
   "is_internal_call": [],
-  "credential_list": [],
-  "warn_unknown_credential": [
-    "name",
-    "loaded"
-  ],
   "before_deployment_call": [
     "kwargs",
     "call_type"

litellm-rust/crates/callbacks-legacy-python/src/adapter.rs

@@ -19,7 +19,7 @@ use serde_json::Value;
 use crate::{
     DeploymentHooks, LegacyCallbacks, PublicCall, PythonLogger,
     deferred::{PendingLogging, PendingSuccess},
-    finalize, is_internal_call, prepare,
+    finalize, is_internal_call,
     python::Streaming,
     setup,
 };
@@ -117,9 +117,13 @@ impl LegacyLogging {
         })
     }
 
+    /// The keyword view the rest of the call reads: a copy, so the deployment hook's own
+    /// dict is left as the hook returned it, carrying the logger as `@client` injects it.
+    /// The driver's preflight rewrites this same dict before the host projects from it.
     fn prepare(&mut self, py: Python<'_>) -> PyResult<LifecycleStep> {
-        let prepared = prepare(py, self.call.kwargs().bind(py), self.logger()?)?.unbind();
-        self.call.set_kwargs(prepared);
+        let prepared = self.call.kwargs().bind(py).copy()?;
+        prepared.set_item("litellm_logging_obj", self.logger()?.object(py))?;
+        self.call.set_kwargs(prepared.unbind());
         Ok(LifecycleStep::Arguments(self.call.kwargs().clone_ref(py)))
     }
 
@@ -580,8 +584,6 @@ assert prepared['document'] is replacement
 assert prepared['pages'] is replaced_kwargs['pages']
 assert prepared['litellm_logging_obj'] is logger
 assert 'litellm_logging_obj' not in replaced_kwargs
-[checked] = [value for name, value in logger.calls if name == 'check_limits']
-assert checked is prepared
 ",
             );
         });
@@ -616,8 +618,6 @@ kwargs = {'logger': logger, 'vendor_extension': opaque}
                 &locals,
                 c"
 assert prepared['vendor_extension'] is opaque
-[checked] = [value for name, value in logger.calls if name == 'check_limits']
-assert checked['vendor_extension'] is opaque
 assert hooked == ([opaque] if asynchronous else []), hooked
 ",
             );
@@ -733,45 +733,6 @@ assert all(value is failure for name, value in logger.calls if name.endswith('_h
             );
         });
     }
-
-    #[rstest]
-    #[case::synchronous(false)]
-    #[case::asynchronous(true)]
-    fn a_limit_rejected_before_the_call_surfaces_as_the_callers_error(#[case] asynchronous: bool) {
-        Python::initialize();
-        Python::attach(|py| {
-            let locals = namespace(
-                py,
-                c"
-class BudgetExceeded(Exception):
-    pass
-
-rejection = BudgetExceeded('over budget')
-
-class LimitedLogger(StubLogger):
-    def check_limits(self, arguments):
-        raise rejection
-
-logger = LimitedLogger()
-logger.hooks = {'pre': lambda kwargs: kwargs}
-kwargs = {'logger': logger}
-",
-            );
-            let mut logging = legacy_call(py, &locals, asynchronous);
-            let kwargs = local(&locals, "kwargs")
-                .cast_into::<PyDict>()
-                .unwrap()
-                .unbind();
-            let result = logging.begin(py, kwargs, 0.0).and_then(|step| match step {
-                LifecycleStep::Await(_) => {
-                    logging.resume(py, Ok(local(&locals, "kwargs").unbind()))
-                }
-                step => Ok(step),
-            });
-            let error = result.err().unwrap();
-            assert!(error.value(py).is(local(&locals, "rejection")));
-        });
-    }
 }
 
 #[cfg(test)]

litellm-rust/crates/callbacks-legacy-python/src/call.rs

@@ -4,7 +4,7 @@
 //! this crate holds them.
 
 use litellm_host::{machine::Machine, protocol::Protocol};
-use litellm_host_python::{ProtocolHost, lookup, run_call};
+use litellm_host_python::{Preflight, ProtocolHost, lookup, run_call};
 use pyo3::{
     gc::{PyTraverseError, PyVisit},
     prelude::*,
@@ -39,7 +39,8 @@ impl PublicCall {
     }
 
     /// The keyword view the legacy path currently reads: the caller's copy until
-    /// `function_setup`, then each rewrite (setup, deployment hook, prepare) in turn.
+    /// `function_setup`, then each rewrite (setup, deployment hook, the driver's preflight)
+    /// in turn.
     pub(crate) fn kwargs(&self) -> &Py<PyDict> {
         &self.kwargs
     }
@@ -64,13 +65,15 @@ impl PublicCall {
 }
 
 /// Runs one native call under the legacy `Logging` contract: the protocol host projects from
-/// the keyword view the contract prepares, and the contract observes the call.
+/// the keyword view the contract prepares and `preflight` rewrites, and the contract
+/// observes the call.
 pub fn run_legacy_call<H, M>(
     py: Python<'_>,
     surface: LegacySurface,
     call: PublicCall,
     machine: M,
     host: H,
+    preflight: Preflight,
     asynchronous: bool,
 ) -> PyResult<Py<PyAny>>
 where
@@ -83,6 +86,7 @@ where
         machine,
         host,
         Box::new(LegacyLogging::new(py, surface, call, asynchronous)),
+        preflight,
         arguments,
         asynchronous,
     )

litellm-rust/crates/callbacks-legacy-python/src/lib.rs

@@ -1,9 +1,10 @@
 //! The legacy `@client` wrapper as the native call sees it: litellm's `Logging` object, the
-//! sync and async callback registries it fans out to, the deployment hooks, the deferred
-//! proxy release, and the kwargs rewrites the wrapper makes on the way in (credential-name
-//! inheritance, budget and retry-count limits). All of it sits behind one
+//! sync and async callback registries it fans out to, the deployment hooks and the deferred
+//! proxy release. All of it sits behind one
 //! [`PythonLifecycle`](litellm_host_python::PythonLifecycle), so the driver, the routes and
-//! core never learn which Python object is on the other end.
+//! core never learn which Python object is on the other end. The SDK's own request policy
+//! (credential inheritance, the budget and retry limits) is the driver's preflight, not this
+//! crate's.
 //!
 //! Legacy callbacks receive the caller's own objects and may mutate them. [`PublicCall`]
 //! is where those objects live, and [`run_legacy_call`] is how a route hands them over
@@ -14,14 +15,12 @@ mod call;
 mod callbacks;
 mod deferred;
 mod logger;
-mod preparation;
 mod python;
 pub(crate) use adapter::LegacyLogging;
 pub use adapter::{LegacySurface, PassThroughStream};
 pub use call::{PublicCall, run_legacy_call};
 pub(crate) use callbacks::{LegacyCallbacks, is_internal_call};
 pub(crate) use logger::{DeploymentHooks, PythonLogger, finalize, setup};
-pub(crate) use preparation::prepare;
 
 #[cfg(test)]
 mod test_support {
@@ -77,7 +76,6 @@ FAKES = {
         logger=kwargs['logger_factory'](kwargs) if 'logger_factory' in kwargs else kwargs['logger'],
         kwargs=kwargs,
     ),
-    'check_limits': lambda arguments: arguments['logger'].check_limits(arguments),
     'finalize': lambda response, logger, kwargs, start, end: logger.record('finalize', response),
     'update_logging': lambda logger, kwargs, model, optional_params, litellm_params, provider: logger.update_from_kwargs(
         kwargs=kwargs,
@@ -104,8 +102,6 @@ FAKES = {
     'restore_context': lambda logger: logger.record('restore', None),
     'custom_pricing_fields': lambda: ('ocr_cost_per_page',),
     'is_internal_call': lambda: legacy.is_internal.get(),
-    'credential_list': lambda: [],
-    'warn_unknown_credential': lambda name, loaded: None,
     'before_deployment_call': lambda kwargs, call_type: kwargs['logger'].hook('pre', kwargs, call_type),
     'after_deployment_success': lambda kwargs, response, call_type: kwargs['logger'].hook(
         'success', response, call_type
@@ -162,9 +158,6 @@ class StubLogger:
         self.record(phase + '_hook', call_type)
         return self.hooks.get(phase, lambda value: 'awaitable')(value)
 
-    def check_limits(self, arguments):
-        self.record('check_limits', arguments)
-
     def failure_handler(self, error, trace, start, end):
         self.record('failure_handler', error)
 

litellm-rust/crates/callbacks-legacy-python/src/python.rs

@@ -19,18 +19,12 @@ pub(crate) enum LegacyPython {
     Streaming(Streaming),
 }
 
-/// The `@client` wrapper around the call: `function_setup`, limits, credentials,
-/// response metadata and the correlation context.
+/// The `@client` wrapper around the call: `function_setup`, response metadata and the
+/// correlation context.
 #[derive(Clone, Copy, Debug, IntoStaticStr, PartialEq, Eq, VariantArray)]
 pub(crate) enum Wrapper {
     #[strum(serialize = "setup")]
     Setup,
-    #[strum(serialize = "check_limits")]
-    CheckLimits,
-    #[strum(serialize = "credential_list")]
-    CredentialList,
-    #[strum(serialize = "warn_unknown_credential")]
-    WarnUnknownCredential,
     #[strum(serialize = "is_internal_call")]
     IsInternalCall,
     #[strum(serialize = "finalize")]

litellm-rust/crates/host-python/AGENTS.md

@@ -2,7 +2,7 @@
 - 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)
+  - `ProtocolHost::project` receives the keyword view the adapter's `begin` returned, rewritten in place by the route's `Preflight`, not the caller's dict; a protocol host that projects from it inherits the adapter's rewrites (for the legacy adapter: setup, deployment hooks) and the preflight's (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

litellm-rust/crates/host-python/src/adapter.rs

@@ -9,6 +9,12 @@ pub fn missing_state() -> PyErr {
     PyRuntimeError::new_err("missing native call state")
 }
 
+/// The SDK's request policy, run by the driver on the keyword view `begin` returned and
+/// before the protocol host projects from it. It rewrites that view in place, so the
+/// lifecycle that returned it sees the rewrite too; a rejection fails the call as a host
+/// failure, so the lifecycle still observes it.
+pub type Preflight = fn(Python<'_>, &Bound<'_, PyDict>) -> PyResult<()>;
+
 /// What an adapter step produced: either the value the driver asked for, or a Python
 /// awaitable the driver hands back to the caller's task before asking again.
 pub enum LifecycleStep {