refactor(core): replace Rust compatibility APIs with Python

AGENTS.md

@@ -144,9 +144,10 @@ Everything flows through a fixed-shape chain enforced at construction time:
 request-side component* → LLMBackend → response-side component* → TranslationEngine
 ```
 
-The chain executor is `Switchyard` (`switchyard/lib/switchyard.py`). `LLMBackend` remains the
-shared role class re-exported from `switchyard/lib/roles.py`; request-side and response-side
-processors are plain async components with `process(...)` methods.
+The chain executor is `Switchyard` (`switchyard/lib/switchyard.py`). `LLMBackend` is the shared
+Python role class re-exported from `switchyard/lib/roles.py`; native implementations register with
+it, and request-side and response-side processors are plain async components with `process(...)`
+methods.
 Direct Rust bindings for migrated concrete processors/backends are exposed from
 `switchyard_rust.components` and implemented under `crates/switchyard-py/src/component_bindings/`.
 
@@ -163,7 +164,7 @@ Direct Rust bindings for migrated concrete processors/backends are exposed from
 switchyard/
 ├── __init__.py                     # Public API — all exports live here
 ├── lib/                            # Core library
-│   ├── roles.py                    # Rust-owned LLMBackend re-export and translation aliases
+│   ├── roles.py                    # Python LLMBackend re-export and translation aliases
 │   ├── switchyard.py               # Switchyard — chain executor
 │   ├── proxy_context.py            # ProxyContext — per-request state carrier
 │   ├── profiles/                   # Profile configs/runtimes for pre-built routing behavior
@@ -372,7 +373,7 @@ uvicorn.run(build_switchyard_app(switchyard), port=4000)
 
 ### Ask first
 - Modifying `pyproject.toml` dependencies.
-- Changes to the chain shape or Rust-owned role classes in `switchyard/lib/roles.py`.
+- Changes to the chain shape or public role classes in `switchyard/lib/roles.py`.
 - Adding new HTTP endpoints.
 - Removing or renaming any public API currently in `switchyard/__init__.__all__`.
 

Cargo.toml

@@ -7,7 +7,6 @@ members = [
     "crates/libsy",
     "crates/libsy-llm-client",
     "crates/switchyard-components",
-    "crates/switchyard-core",
     "crates/switchyard-py",
     "crates/protocol",
     "crates/switchyard-server",
@@ -32,7 +31,7 @@ rand = "0.8"
 reqwest = { version = "0.12", default-features = false, features = ["json", "rustls-tls-webpki-roots", "stream"] }
 serde = { version = "1", features = ["derive"] }
 serde_json = "1"
-switchyard-core = { path = "crates/switchyard-core", version = "0.1.0" }
+switchyard-components = { path = "crates/switchyard-components", version = "0.1.0" }
 switchyard-libsy = { path = "crates/libsy", version = "0.1.0" }
 switchyard-llm-client = { path = "crates/libsy-llm-client", version = "0.1.0" }
 switchyard-protocol = { path = "crates/protocol", version = "0.1.0" }

crates/switchyard-components/Cargo.toml

@@ -14,17 +14,18 @@ rust-version.workspace = true
 [dependencies]
 async-stream.workspace = true
 async-trait.workspace = true
+futures-core = "0.3"
 futures-util.workspace = true
 parking_lot.workspace = true
 rand.workspace = true
 reqwest.workspace = true
 serde.workspace = true
 serde_json.workspace = true
-switchyard-core.workspace = true
 switchyard-libsy.workspace = true
 switchyard-protocol.workspace = true
 switchyard-translation.workspace = true
 tokio.workspace = true
+thiserror.workspace = true
 tracing.workspace = true
 
 [dev-dependencies]

crates/switchyard-components/src/backends/anthropic.rs

@@ -8,15 +8,15 @@ use std::env;
 use std::fmt;
 use std::sync::Arc;
 
-use async_stream::try_stream;
-use async_trait::async_trait;
-use futures_util::StreamExt;
-use serde_json::{json, Map, Value};
-use switchyard_core::{
+use crate::{
     merge_target_extra_body, BackendFormat, BoxResponseStream, ChatRequest, ChatRequestType,
     ChatResponse, LlmBackend, LlmTarget, LlmTargetId, ProxyContext, Result, StreamEvent,
     SwitchyardError,
 };
+use async_stream::try_stream;
+use async_trait::async_trait;
+use futures_util::StreamExt;
+use serde_json::{json, Map, Value};
 use switchyard_translation::{
     normalize_anthropic_tool_use_ids, TranslationEngine, TranslationPolicy, WireFormat,
 };
@@ -546,9 +546,9 @@ fn anthropic_sse_stream(response: reqwest::Response) -> BoxResponseStream {
 
 #[cfg(test)]
 mod tests {
+    use crate::{EndpointConfig, LlmTargetId, ModelId};
     use parking_lot::Mutex;
     use serde_json::json;
-    use switchyard_core::{EndpointConfig, LlmTargetId, ModelId};
 
     use super::*;
 

crates/switchyard-components/src/backends/common.rs

@@ -6,8 +6,8 @@
 use std::sync::{Arc, OnceLock};
 use std::time::Duration;
 
+use crate::{ChatRequestType, Result, SwitchyardError};
 use serde_json::{Map, Value};
-use switchyard_core::{ChatRequestType, Result, SwitchyardError};
 use switchyard_translation::{TranslationEngine, WireFormat};
 
 pub(crate) enum ParsedSseFrame {

crates/switchyard-components/src/backends/multi.rs

@@ -12,11 +12,11 @@ use std::collections::HashSet;
 use std::fmt;
 use std::sync::Arc;
 
-use async_trait::async_trait;
-use switchyard_core::{
+use crate::{
     ChatRequest, ChatRequestType, ChatResponse, LlmBackend, LlmTarget, LlmTargetId, ProxyContext,
     Result, SwitchyardError,
 };
+use async_trait::async_trait;
 
 use super::{BackendSelection, BackendSelectionReason};
 

crates/switchyard-components/src/backends/openai.rs

@@ -8,15 +8,15 @@ use std::env;
 use std::fmt;
 use std::sync::Arc;
 
-use async_stream::try_stream;
-use async_trait::async_trait;
-use futures_util::StreamExt;
-use serde_json::{Map, Value};
-use switchyard_core::{
+use crate::{
     merge_target_extra_body, BackendFormat, BoxResponseStream, ChatRequest, ChatRequestType,
     ChatResponse, EndpointConfig, LlmBackend, LlmTarget, LlmTargetId, ModelId, ProxyContext,
     Result, StreamEvent, SwitchyardError,
 };
+use async_stream::try_stream;
+use async_trait::async_trait;
+use futures_util::StreamExt;
+use serde_json::{Map, Value};
 use switchyard_translation::{TranslationEngine, TranslationPolicy, WireFormat};
 
 use super::common::{
@@ -580,9 +580,9 @@ fn openai_sse_stream(response: reqwest::Response) -> BoxResponseStream {
 
 #[cfg(test)]
 mod tests {
+    use crate::{EndpointConfig, LlmTargetId, ModelId};
     use parking_lot::Mutex;
     use serde_json::json;
-    use switchyard_core::{EndpointConfig, LlmTargetId, ModelId};
 
     use super::*;
 

crates/switchyard-components/src/backends/selection.rs

@@ -3,8 +3,8 @@
 
 //! Backend execution metadata for observability components.
 
+use crate::{LlmTargetId, ModelId};
 use serde::{Deserialize, Serialize};
-use switchyard_core::{LlmTargetId, ModelId};
 
 /// How a backend resolved the final upstream target/model for a request.
 #[derive(Clone, Copy, Debug, Eq, Hash, PartialEq, Serialize, Deserialize)]

crates/switchyard-components/src/backends/stats.rs

@@ -7,10 +7,8 @@ use std::fmt;
 use std::sync::Arc;
 use std::time::Instant;
 
+use crate::{ChatRequest, ChatRequestType, ChatResponse, LlmBackend, ProxyContext, Result};
 use async_trait::async_trait;
-use switchyard_core::{
-    ChatRequest, ChatRequestType, ChatResponse, LlmBackend, ProxyContext, Result,
-};
 
 use crate::stats::{
     selected_stats_model, selected_stats_tier, StatsAccumulator, StatsBackendLatency,

crates/switchyard-core/src/backend.rs → crates/switchyard-components/src/contracts/backend.rs

@@ -1,14 +1,14 @@
 // SPDX-FileCopyrightText: Copyright (c) 2026 NVIDIA CORPORATION & AFFILIATES. All rights reserved.
 // SPDX-License-Identifier: Apache-2.0
 
-//! LLM target configuration shared by routing and factory code.
+//! LLM target configuration shared by compatibility routing and factory code.
 
 use std::collections::BTreeMap;
 
 use serde::{Deserialize, Serialize};
 use serde_json::Value;
 
-use crate::ids::{LlmTargetId, ModelId};
+use super::ids::{LlmTargetId, ModelId};
 
 /// Wire format expected by an LLM target.
 #[derive(Clone, Copy, Debug, Default, Eq, Hash, PartialEq, Serialize, Deserialize)]

crates/switchyard-core/src/context.rs → crates/switchyard-components/src/contracts/context.rs

@@ -1,14 +1,14 @@
 // SPDX-FileCopyrightText: Copyright (c) 2026 NVIDIA CORPORATION & AFFILIATES. All rights reserved.
 // SPDX-License-Identifier: Apache-2.0
 
-//! Per-request context and typed extension storage for chain components.
+//! Per-request context and typed extension storage for compatibility components.
 
 use std::any::{Any, TypeId};
 use std::collections::{HashMap, HashSet};
 use std::fmt;
 
-use crate::ids::{LlmTargetId, RequestId};
-use crate::types::ChatRequestType;
+use super::ids::{LlmTargetId, RequestId};
+use super::types::ChatRequestType;
 
 /// Mutable state shared across processors and the backend for one request.
 #[derive(Default)]

crates/switchyard-core/src/error.rs → crates/switchyard-components/src/contracts/error.rs

@@ -1,12 +1,12 @@
 // SPDX-FileCopyrightText: Copyright (c) 2026 NVIDIA CORPORATION & AFFILIATES. All rights reserved.
 // SPDX-License-Identifier: Apache-2.0
 
-//! Error types used by the Rust core contracts.
+//! Errors shared by compatibility backends and Python bindings.
 
 use thiserror::Error;
 
-use crate::ids::{InvalidId, ModelId};
-use crate::types::ChatRequestType;
+use super::ids::{InvalidId, ModelId};
+use super::types::ChatRequestType;
 
 /// Result alias for core Switchyard operations.
 pub type Result<T> = std::result::Result<T, SwitchyardError>;

crates/switchyard-core/src/ids.rs → crates/switchyard-components/src/contracts/ids.rs

@@ -1,7 +1,7 @@
 // SPDX-FileCopyrightText: Copyright (c) 2026 NVIDIA CORPORATION & AFFILIATES. All rights reserved.
 // SPDX-License-Identifier: Apache-2.0
 
-//! Non-empty string identifiers used across core routing and component wiring.
+//! Non-empty string identifiers used by compatibility component wiring.
 
 use std::fmt;
 use std::str::FromStr;
@@ -106,10 +106,6 @@ macro_rules! string_id {
     };
 }
 
-string_id!(BackendId);
-string_id!(ComponentId);
-string_id!(EndpointId);
 string_id!(LlmTargetId);
 string_id!(ModelId);
-string_id!(ProfileId);
 string_id!(RequestId);

crates/switchyard-components/src/contracts/mod.rs

@@ -0,0 +1,18 @@
+// SPDX-FileCopyrightText: Copyright (c) 2026 NVIDIA CORPORATION & AFFILIATES. All rights reserved.
+// SPDX-License-Identifier: Apache-2.0
+
+//! Contracts retained by the compatibility component and Python layers.
+
+mod backend;
+mod context;
+mod error;
+mod ids;
+mod roles;
+mod types;
+
+pub use backend::*;
+pub use context::*;
+pub use error::*;
+pub use ids::*;
+pub use roles::*;
+pub use types::*;

crates/switchyard-core/src/roles.rs → crates/switchyard-components/src/contracts/roles.rs

@@ -1,13 +1,13 @@
 // SPDX-FileCopyrightText: Copyright (c) 2026 NVIDIA CORPORATION & AFFILIATES. All rights reserved.
 // SPDX-License-Identifier: Apache-2.0
 
-//! Backend trait shared by Rust-owned LLM callers.
+//! Backend trait shared by compatibility LLM callers.
 
 use async_trait::async_trait;
 
-use crate::context::ProxyContext;
-use crate::error::Result;
-use crate::types::{ChatRequest, ChatRequestType, ChatResponse};
+use super::context::ProxyContext;
+use super::error::Result;
+use super::types::{ChatRequest, ChatRequestType, ChatResponse};
 
 /// Backend abstraction responsible for making the LLM call.
 #[async_trait]