feat(codec): add a provider codec factory and route built-in consumers through it

crates/adaptive/Cargo.toml

@@ -25,6 +25,7 @@ tokio = { version = "1", features = ["rt", "macros", "sync", "time"] }
 regex = "1"
 serde_json_canonicalizer = "0.3"
 sha2 = "0.11"
+strum = { version = "0.27", features = ["derive"] }
 
 redis = { version = "1.1", features = ["tokio-comp", "connection-manager"], optional = true }
 

crates/adaptive/src/acg/request_surfaces/mod.rs

@@ -18,12 +18,14 @@ use std::collections::HashSet;
 use nemo_relay::api::llm::LlmRequest;
 use nemo_relay::codec::resolve::{ProviderSurface, detect_request_surface};
 use serde_json::Value;
+use strum::AsRefStr;
 
 use crate::acg::prompt_ir::PromptIR;
 use crate::acg::translation::{HintPlan, HintTarget};
 
 #[cfg_attr(not(test), allow(dead_code))]
-#[derive(Debug, Clone, Copy, PartialEq, Eq)]
+#[derive(Debug, Clone, Copy, PartialEq, Eq, AsRefStr)]
+#[strum(serialize_all = "snake_case")]
 pub(crate) enum RequestSurface {
     AnthropicMessages,
     OpenAIChat,
@@ -49,6 +51,14 @@ impl RequestSurface {
         }
     }
 
+    pub(crate) fn provider_surface(self) -> ProviderSurface {
+        match self {
+            Self::AnthropicMessages => ProviderSurface::AnthropicMessages,
+            Self::OpenAIChat => ProviderSurface::OpenAIChat,
+            Self::OpenAIResponses => ProviderSurface::OpenAIResponses,
+        }
+    }
+
     pub(crate) fn supports_provider(self, provider: &str) -> bool {
         match provider {
             "anthropic" => matches!(self, Self::AnthropicMessages),

crates/adaptive/src/acg_component.rs

@@ -28,11 +28,8 @@ use nemo_relay::api::runtime::{
     LlmExecutionFn, LlmExecutionNextFn, LlmRequestInterceptFn, LlmStreamExecutionFn,
     LlmStreamExecutionNextFn,
 };
-use nemo_relay::codec::anthropic::AnthropicMessagesCodec;
-use nemo_relay::codec::openai_chat::OpenAIChatCodec;
-use nemo_relay::codec::openai_responses::OpenAIResponsesCodec;
 use nemo_relay::codec::request::AnnotatedLlmRequest;
-use nemo_relay::codec::traits::LlmCodec;
+use nemo_relay::codec::resolve::request_codec;
 use nemo_relay::json::Json;
 use uuid::Uuid;
 
@@ -91,21 +88,12 @@ fn decode_request_for_surface(
     request_surface: RequestSurface,
     request: &LlmRequest,
 ) -> Result<AnnotatedLlmRequest> {
-    match request_surface {
-        RequestSurface::AnthropicMessages => {
-            AnthropicMessagesCodec.decode(request).map_err(|error| {
-                AdaptiveError::Internal(format!("failed to decode anthropic request: {error}"))
-            })
-        }
-        RequestSurface::OpenAIChat => OpenAIChatCodec.decode(request).map_err(|error| {
-            AdaptiveError::Internal(format!("failed to decode openai chat request: {error}"))
-        }),
-        RequestSurface::OpenAIResponses => OpenAIResponsesCodec.decode(request).map_err(|error| {
-            AdaptiveError::Internal(format!(
-                "failed to decode openai responses request: {error}"
-            ))
-        }),
-    }
+    request_codec(request_surface.provider_surface())
+        .decode(request)
+        .map_err(|error| {
+            let surface_label: &str = request_surface.as_ref();
+            AdaptiveError::Internal(format!("failed to decode {surface_label} request: {error}"))
+        })
 }
 
 fn build_semantic_request_view(request: &LlmRequest) -> Result<SemanticRequestView> {

crates/adaptive/tests/unit/acg_component_tests.rs

@@ -1124,15 +1124,15 @@ fn acg_component_decode_request_for_surface_reports_codec_specific_errors() {
 
     assert!(matches!(
         decode_request_for_surface(RequestSurface::AnthropicMessages, &invalid_request),
-        Err(AdaptiveError::Internal(message)) if message.contains("failed to decode anthropic request")
+        Err(AdaptiveError::Internal(message)) if message.contains("failed to decode anthropic_messages request")
     ));
     assert!(matches!(
         decode_request_for_surface(RequestSurface::OpenAIChat, &invalid_request),
-        Err(AdaptiveError::Internal(message)) if message.contains("failed to decode openai chat request")
+        Err(AdaptiveError::Internal(message)) if message.contains("failed to decode open_ai_chat request")
     ));
     assert!(matches!(
         decode_request_for_surface(RequestSurface::OpenAIResponses, &invalid_request),
-        Err(AdaptiveError::Internal(message)) if message.contains("failed to decode openai responses request")
+        Err(AdaptiveError::Internal(message)) if message.contains("failed to decode open_ai_responses request")
     ));
 }
 

crates/cli/src/gateway.rs

@@ -17,9 +17,10 @@ use nemo_relay::api::llm::{
 use nemo_relay::api::runtime::{
     LlmExecutionNextFn, LlmJsonStream, LlmStreamExecutionNextFn, TASK_SCOPE_STACK,
 };
-use nemo_relay::codec::anthropic::{AnthropicMessagesCodec, AnthropicMessagesStreamingCodec};
-use nemo_relay::codec::openai_chat::{OpenAIChatCodec, OpenAIChatStreamingCodec};
-use nemo_relay::codec::openai_responses::{OpenAIResponsesCodec, OpenAIResponsesStreamingCodec};
+use nemo_relay::codec::resolve::{
+    ProviderSurface, response_codec as build_response_codec,
+    streaming_codec as build_streaming_codec,
+};
 use nemo_relay::codec::streaming::StreamingCodec;
 use nemo_relay::codec::traits::LlmResponseCodec;
 use nemo_relay::error::FlowError;
@@ -248,20 +249,12 @@ struct RouteCodecs {
 }
 
 fn codecs_for_route(route: ProviderRoute) -> RouteCodecs {
-    match route {
-        ProviderRoute::AnthropicMessages => RouteCodecs {
-            streaming: Some(Box::new(AnthropicMessagesStreamingCodec::new())),
-            response: Some(Arc::new(AnthropicMessagesCodec) as Arc<dyn LlmResponseCodec>),
-        },
-        ProviderRoute::OpenAiResponses => RouteCodecs {
-            streaming: Some(Box::new(OpenAIResponsesStreamingCodec::new())),
-            response: Some(Arc::new(OpenAIResponsesCodec) as Arc<dyn LlmResponseCodec>),
+    match route.provider_surface() {
+        Some(surface) => RouteCodecs {
+            streaming: Some(build_streaming_codec(surface)),
+            response: Some(build_response_codec(surface)),
         },
-        ProviderRoute::OpenAiChatCompletions => RouteCodecs {
-            streaming: Some(Box::new(OpenAIChatStreamingCodec::new())),
-            response: Some(Arc::new(OpenAIChatCodec) as Arc<dyn LlmResponseCodec>),
-        },
-        ProviderRoute::AnthropicCountTokens | ProviderRoute::OpenAiModels => RouteCodecs {
+        None => RouteCodecs {
             streaming: None,
             response: None,
         },
@@ -955,6 +948,15 @@ impl ProviderRoute {
         }
     }
 
+    const fn provider_surface(self) -> Option<ProviderSurface> {
+        match self {
+            Self::OpenAiResponses => Some(ProviderSurface::OpenAIResponses),
+            Self::OpenAiChatCompletions => Some(ProviderSurface::OpenAIChat),
+            Self::AnthropicMessages => Some(ProviderSurface::AnthropicMessages),
+            Self::AnthropicCountTokens | Self::OpenAiModels => None,
+        }
+    }
+
     // Returns the provider route name recorded on managed LLM events. These names split OpenAI API
     // variants because their request/response schemas differ even when they share a base URL, and
     // they double as codec hints for ambiguous provider request shapes.

crates/core/src/codec/anthropic.rs

@@ -56,6 +56,10 @@ pub(crate) const PROVIDER_SURFACE: ProviderSurfaceDescriptor = ProviderSurfaceDe
     },
     decode_request: |request| AnthropicMessagesCodec.decode(request),
     decode_response: |raw| AnthropicMessagesCodec.decode_response(raw),
+    codec_name: "anthropic_messages",
+    request_codec: || std::sync::Arc::new(AnthropicMessagesCodec),
+    response_codec: || std::sync::Arc::new(AnthropicMessagesCodec),
+    streaming_codec: || Box::new(AnthropicMessagesStreamingCodec::new()),
 };
 
 // ---------------------------------------------------------------------------

crates/core/src/codec/openai_chat.rs

@@ -33,6 +33,10 @@ pub(crate) const PROVIDER_SURFACE: ProviderSurfaceDescriptor = ProviderSurfaceDe
     detect_response: |obj| obj.get("choices").is_some_and(Json::is_array),
     decode_request: |request| OpenAIChatCodec.decode(request),
     decode_response: |raw| OpenAIChatCodec.decode_response(raw),
+    codec_name: "openai_chat",
+    request_codec: || std::sync::Arc::new(OpenAIChatCodec),
+    response_codec: || std::sync::Arc::new(OpenAIChatCodec),
+    streaming_codec: || Box::new(OpenAIChatStreamingCodec::new()),
 };
 
 // ---------------------------------------------------------------------------

crates/core/src/codec/openai_responses.rs

@@ -48,6 +48,10 @@ pub(crate) const PROVIDER_SURFACE: ProviderSurfaceDescriptor = ProviderSurfaceDe
     },
     decode_request: |request| OpenAIResponsesCodec.decode(request),
     decode_response: |raw| OpenAIResponsesCodec.decode_response(raw),
+    codec_name: "openai_responses",
+    request_codec: || std::sync::Arc::new(OpenAIResponsesCodec),
+    response_codec: || std::sync::Arc::new(OpenAIResponsesCodec),
+    streaming_codec: || Box::new(OpenAIResponsesStreamingCodec::new()),
 };
 
 // ---------------------------------------------------------------------------

crates/core/src/codec/resolve.rs

@@ -1,16 +1,19 @@
 // SPDX-FileCopyrightText: Copyright (c) 2026, NVIDIA CORPORATION & AFFILIATES. All rights reserved.
 // SPDX-License-Identifier: Apache-2.0
 
-//! Provider-surface detection and best-effort normalization: the preferred path
-//! for turning raw provider JSON into normalized types when no codec annotation
-//! is present.
+//! Provider-surface detection, best-effort normalization, and construction of
+//! the matching built-in codecs from a raw payload, surface, or codec name.
+
+use std::sync::Arc;
 
 use crate::api::llm::LlmRequest;
 use crate::error::Result;
 use crate::json::Json;
 
 use super::request::AnnotatedLlmRequest;
 use super::response::AnnotatedLlmResponse;
+use super::streaming::StreamingCodec;
+use super::traits::{LlmCodec, LlmResponseCodec};
 use super::{anthropic, openai_chat, openai_responses};
 
 /// A built-in provider request/response surface.
@@ -48,6 +51,10 @@ pub(crate) struct ProviderSurfaceDescriptor {
     pub(crate) detect_response: ResponseSurfaceDetector,
     pub(crate) decode_request: fn(&LlmRequest) -> Result<AnnotatedLlmRequest>,
     pub(crate) decode_response: fn(&Json) -> Result<AnnotatedLlmResponse>,
+    pub(crate) codec_name: &'static str,
+    pub(crate) request_codec: fn() -> Arc<dyn LlmCodec>,
+    pub(crate) response_codec: fn() -> Arc<dyn LlmResponseCodec>,
+    pub(crate) streaming_codec: fn() -> Box<dyn StreamingCodec>,
 }
 
 /// Built-in provider surfaces in request-detection priority order.
@@ -140,6 +147,64 @@ pub fn normalize_response(raw: &Json) -> Option<AnnotatedLlmResponse> {
     (descriptor.decode_response)(raw).ok()
 }
 
+fn descriptor_for(surface: ProviderSurface) -> &'static ProviderSurfaceDescriptor {
+    match surface {
+        ProviderSurface::OpenAIChat => &openai_chat::PROVIDER_SURFACE,
+        ProviderSurface::OpenAIResponses => &openai_responses::PROVIDER_SURFACE,
+        ProviderSurface::AnthropicMessages => &anthropic::PROVIDER_SURFACE,
+    }
+}
+
+impl ProviderSurface {
+    /// The canonical codec name for this surface (e.g. `"openai_chat"`), the
+    /// inverse of [`Self::from_codec_name`].
+    #[must_use]
+    pub fn codec_name(self) -> &'static str {
+        descriptor_for(self).codec_name
+    }
+
+    /// Resolves a canonical codec name to its surface, or `None` when `name` is
+    /// not a built-in provider codec.
+    #[must_use]
+    pub fn from_codec_name(name: &str) -> Option<Self> {
+        BUILTIN_PROVIDER_SURFACES
+            .iter()
+            .find(|descriptor| descriptor.codec_name == name)
+            .map(|descriptor| descriptor.surface)
+    }
+}
+
+/// The canonical codec names of every built-in provider surface, for config
+/// validation and "supported codec" messages.
+#[must_use]
+pub fn supported_codec_names() -> Vec<&'static str> {
+    BUILTIN_PROVIDER_SURFACES
+        .iter()
+        .map(|descriptor| descriptor.codec_name)
+        .collect()
+}
+
+/// Constructs the built-in bidirectional request codec ([`LlmCodec`]) for a surface.
+#[must_use]
+pub fn request_codec(surface: ProviderSurface) -> Arc<dyn LlmCodec> {
+    (descriptor_for(surface).request_codec)()
+}
+
+/// Constructs the built-in decode-only response codec ([`LlmResponseCodec`]) for a surface.
+#[must_use]
+pub fn response_codec(surface: ProviderSurface) -> Arc<dyn LlmResponseCodec> {
+    (descriptor_for(surface).response_codec)()
+}
+
+/// Constructs a fresh, single-use streaming codec ([`StreamingCodec`]) for a surface.
+///
+/// A [`StreamingCodec`] finalizer consumes its accumulator, so callers must
+/// construct one instance per managed streaming call.
+#[must_use]
+pub fn streaming_codec(surface: ProviderSurface) -> Box<dyn StreamingCodec> {
+    (descriptor_for(surface).streaming_codec)()
+}
+
 #[cfg(test)]
 #[path = "../../tests/unit/codec/resolve_tests.rs"]
 mod tests;

crates/core/src/plugins/nemo_guardrails/component.rs

@@ -11,6 +11,7 @@ use std::sync::Arc;
 use serde::{Deserialize, Serialize};
 use serde_json::{Map, Value as Json};
 
+use crate::codec::resolve::supported_codec_names;
 use crate::plugin::{
     ConfigDiagnostic, ConfigPolicy, DiagnosticLevel, Plugin, PluginComponentSpec, PluginError,
     PluginRegistrationContext, Result as PluginResult, UnsupportedBehavior, deregister_plugin,
@@ -901,10 +902,7 @@ fn validate_codec_requirements(
         return;
     };
 
-    if !matches!(
-        codec,
-        "openai_chat" | "openai_responses" | "anthropic_messages"
-    ) {
+    if !supported_codec_names().contains(&codec) {
         push_policy_diag(
             diagnostics,
             policy.unsupported_value,