refactor(rust): isolate legacy callback contract

litellm-rust/Cargo.toml

@@ -9,8 +9,9 @@ license = "MIT"
 repository = "https://github.com/BerriAI/litellm"
 
 [workspace.dependencies]
-bytes = "1"
 litellm-core = { path = "crates/core" }
+litellm-callbacks = { path = "crates/callbacks" }
+litellm-callbacks-legacy = { path = "crates/callbacks-legacy" }
 litellm-framing = { path = "crates/framer" }
 litellm-auth = { path = "crates/auth" }
 litellm-auth-aws = { path = "crates/auth-aws" }
@@ -20,13 +21,16 @@ litellm-providers = { path = "crates/providers" }
 litellm-cache = { path = "crates/cache" }
 litellm-cache-memory = { path = "crates/cache-memory" }
 litellm-token-counter = { path = "crates/token-counter" }
-litellm-python-interop = { path = "crates/python-interop" }
+litellm-host-python = { path = "crates/host-python" }
+
+bytes = "1"
 pyo3 = "0.29.2"
 pyo3-async-runtimes = { version = "0.29.0", features = ["tokio-runtime"] }
 pythonize = "0.29.0"
 rand = "0.8"
 reqwest = { version = "0.12", default-features = false, features = ["blocking", "json", "multipart", "rustls-tls", "http2", "stream"] }
 rstest = "0.26.1"
+rstest_reuse = "0.7.0"
 rustls = { version = "0.23", default-features = false, features = ["ring", "std", "tls12"] }
 rustls-native-certs = "0.8"
 serde = { version = "1.0", features = ["derive"] }

litellm-rust/crates/auth-azure/src/resolve.rs

@@ -657,4 +657,49 @@ mod tests {
 
         assert!(matches!(error, Error::CredentialChain(errors) if errors.len() == 2));
     }
+
+    #[derive(Debug)]
+    struct CallerToken(&'static str);
+
+    impl litellm_auth::TokenProvider for CallerToken {
+        fn acquire(&self) -> litellm_auth::TokenFuture<'_> {
+            Box::pin(async move {
+                Ok(ResolvedCredential::AccessToken {
+                    token: SecretValue::new(self.0),
+                    expires_on: None,
+                })
+            })
+        }
+    }
+
+    fn caller_inputs(token: &'static str) -> AzureAuthInputs {
+        let params = json!({"azure_ad_token": "static-token"});
+        AzureAuthInputs {
+            azure_ad_token_provider: Some(litellm_auth::TokenProviderHandle::new(Arc::new(
+                CallerToken(token),
+            ))),
+            ..AzureAuthInputs::from_optional_params(params.as_object().unwrap()).unwrap()
+        }
+    }
+
+    #[tokio::test]
+    async fn caller_token_is_chosen_over_supplied_static_token() {
+        let credential = AzureAuthService::default()
+            .get_azure_ad_token(&caller_inputs("caller-token"), &|_| None)
+            .await
+            .unwrap()
+            .unwrap();
+
+        assert_eq!(credential.value().secret().expose(), "caller-token");
+    }
+
+    #[tokio::test]
+    async fn empty_caller_token_is_rejected() {
+        let error = AzureAuthService::default()
+            .get_azure_ad_token(&caller_inputs(""), &|_| None)
+            .await
+            .unwrap_err();
+
+        assert!(matches!(error, Error::EmptyAzureToken));
+    }
 }

litellm-rust/crates/auth/src/credential.rs

@@ -9,21 +9,6 @@ use crate::Error;
 
 use super::{ResolvedCredential, SecretValue, TokenProviderHandle};
 
-pub fn credential_index(requested: &str, names: &[String]) -> Option<usize> {
-    names.iter().position(|name| name == requested)
-}
-
-pub fn credential_default_fields<'a>(
-    supplied: &[String],
-    credential_fields: &'a [String],
-) -> Vec<&'a str> {
-    credential_fields
-        .iter()
-        .filter(|name| !supplied.contains(name))
-        .map(String::as_str)
-        .collect()
-}
-
 #[derive(Clone, Debug, PartialEq, Eq)]
 pub enum CredentialFileRef {
     Path(PathBuf),

litellm-rust/crates/auth/src/lib.rs

@@ -47,7 +47,6 @@ impl<T> Sourced<T> {
 pub use credential::{
     CredentialFileRef, CredentialLookup, CredentialLookupFuture, CredentialPlan,
     CredentialPlanResolution, CredentialRef, CredentialResolver, CredentialResolverHandle,
-    credential_default_fields, credential_index,
 };
 pub use error::Error;
 pub use http::{CredentialPlacement, RequestAuth};

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

@@ -0,0 +1,17 @@
+- 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)
+  - The driver in `litellm-host-python`, the routes and core see one `CallbackAdapter`; they never learn which Python objects consume a call
+  - `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` decides once who owns the `Logging` instance and returns it as `CallSetup.bridge_owned`; `PythonLogger` carries it and nothing on the instance records it
+  - A logger the caller passed as `litellm_logging_obj` is caller-owned and observed in full, because the caller reads it after the call; the proxy is the live case
+  - A logger `function_setup` built for this call is bridge-owned, so each fan-out phase is skipped when `callbacks_needed` finds no registry, dynamic callback, `logger_fn` or debug switch for it; cost, timing and response metadata still run
+- 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
+  - Re-alias every `passthrough_fields` body key to the caller's object before `pre_call`; a keyword wins over the request attribute even when it is an explicit `None`
+  - 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-callbacks`, `litellm-host-python` and the bridge; the only facts that cross from the route are the prepared keyword view and `RequestContext.passthrough_fields`
+- 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
+  - 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/Cargo.toml

@@ -0,0 +1,16 @@
+[package]
+name = "litellm-callbacks-legacy"
+version = "0.1.0"
+edition.workspace = true
+license.workspace = true
+repository.workspace = true
+autotests = false
+
+[dependencies]
+litellm-callbacks.workspace = true
+litellm-host-python.workspace = true
+pyo3.workspace = true
+
+[dev-dependencies]
+rstest.workspace = true
+serde_json.workspace = true