refactor(remote-config)!: DI via RemoteConfigParsedData trait + ParserRegistry (#1945)

# What does this PR do?

The `datadog-remote-config` crate previously owned the full deserialization pipeline for every product via a closed `RemoteConfigData` enum. Adding a new product required editing the RC crate itself, importing product types, and adding enum variants — creating compile-time coupling to `datadog-live-debugger` and `datadog-ffe` via Cargo optional features.

This PR flips the dependency: RC defines a typed `RemoteConfigContent` trait (with a `PRODUCT` const and a `parse` method), an opaque `RemoteConfigParsedData` trait-object boundary, and a `ParserRegistry` to compose products. Product crates implement `RemoteConfigContent` on their own types; a blanket `impl<T: RemoteConfigContent> RemoteConfigParsedData for T` lets the registry hold them as `Box<dyn RemoteConfigParsedData>` without knowing the concrete type.

## Follow-up changes on this branch

- **Sidecar LiveDebugger parser registration.** Pre-refactor, `datadog-sidecar` enabled the `live-debugger` Cargo feature on `datadog-remote-config`, which made the closed-enum parser handle LiveDebugger payloads. After the DI refactor that feature is gone, so `RemoteConfigManager::new()` now explicitly registers the `LiveDebuggingData` parser on top of `default_registry()` to preserve pre-refactor sidecar behavior. Added a regression test (`test_live_debugger_config_parsed`) that drives a `SERVICE_CONFIGURATION` payload through the SHM round trip and asserts the downcast to `LiveDebuggingData` succeeds.
- **`set_extra_services` on the fetchers.** Runtime-discovered extra services live on `ConfigClientState` (the per-client mutable state), not on `Target`. New API: `ConfigClientState::set_extra_services(Vec<String>)`, `SingleFetcher::set_extra_services`, `SingleChangesFetcher::set_extra_services`. `fetch_once` reads from `opaque_state` and forwards via `ClientTracer.extra_services` exactly as before. Replace-semantics: each set fully overrides the previous list. This was kept off `Target` because `Target` is `Hash + Eq + Clone` (used as a map key in `MultiTargetFetcher`) — putting growing dynamic state on it would force costly map rekeying or break the `Hash`/`Eq` contract.

## Adding a new RC product going forward

1. **In `datadog-remote-config`** (still required): add a variant to `RemoteConfigProduct` and its `Display`/`try_parse` arms in `path.rs`. The product taxonomy is still a closed enum.
2. **In the product crate**: implement `RemoteConfigContent` on the product's config type:

   ```rust
   impl RemoteConfigContent for MyProductConfig {
       const PRODUCT: RemoteConfigProduct = RemoteConfigProduct::MyProduct;
       fn parse(data: &[u8]) -> anyhow::Result<Self> { /* … */ }
   }
   ```
3. **At construction time**: chain `.with::<MyProductConfig>()` onto a `ParserRegistry` (typically `default_registry()`).

Only the parsing is fully extensible after this PR; the product enumeration is still closed. Making `RemoteConfigProduct` open (e.g. `Cow<'static, str>` or a sealed trait) would close that gap and is a reasonable follow-up.

## Motivation

Drives `datadog-remote-config`'s coupling to product crates from compile-time (Cargo features + closed enum) to runtime (registry injection), so consumers compose the products they care about without forcing the RC crate to know about every product.

## Note
Check [this](#1958) other PR with a different approach

Co-authored-by: igor.unanua <igor.unanua@datadoghq.com>

Author: iunanua

Cargo.lock

@@ -11,6 +11,7 @@ publish = false
 bench = false
 
 [dependencies]
+datadog-remote-config = { path = "../datadog-remote-config", default-features = false, optional = true }
 faststr = { version = "0.2.23", default-features = false, features = ["serde"] }
 serde = { version = "1.0", default-features = false, features = ["derive", "rc"] }
 serde_json = { version = "1.0", default-features = false, features = ["std", "raw_value"] }
@@ -30,6 +31,8 @@ prost = { version = "0.14.1", optional = true }
 pyo3 = { version = "0.28", optional = true, default-features = false, features = ["macros"] }
 
 [features]
+default = ["remote-config"]
 exposure-events = ["dep:lru"]
 evaluation-metrics = ["dep:libdd-trace-protobuf", "dep:prost"]
 pyo3 = ["dep:pyo3"]
+remote-config = ["dep:datadog-remote-config"]

datadog-ffe/Cargo.toml

@@ -3,6 +3,8 @@
 
 mod flag_type;
 
+#[cfg(feature = "remote-config")]
+mod remote_config;
 pub mod rules_based;
 #[cfg(any(feature = "exposure-events", feature = "evaluation-metrics"))]
 pub mod telemetry;

datadog-ffe/src/lib.rs

@@ -0,0 +1,13 @@
+// Copyright 2025-Present Datadog, Inc. https://www.datadoghq.com/
+// SPDX-License-Identifier: Apache-2.0
+
+use crate::rules_based::UniversalFlagConfig;
+use datadog_remote_config::{ParseError, RemoteConfigContent, RemoteConfigProduct};
+
+impl RemoteConfigContent for UniversalFlagConfig {
+    const PRODUCT: RemoteConfigProduct = RemoteConfigProduct::FfeFlags;
+
+    fn parse(data: &[u8]) -> Result<Self, ParseError> {
+        Ok(UniversalFlagConfig::from_json(data.to_vec())?)
+    }
+}

datadog-ffe/src/remote_config.rs

@@ -7,6 +7,7 @@ publish = false
 
 [dependencies]
 anyhow = "1.0"
+datadog-remote-config = { path = "../datadog-remote-config", default-features = false }
 libdd-common = { path = "../libdd-common" }
 libdd-data-pipeline = { path = "../libdd-data-pipeline" }
 http-body-util = "0.1"

datadog-live-debugger/Cargo.toml

@@ -13,6 +13,7 @@ mod probe_defs;
 
 pub mod debugger_defs;
 mod redacted_names;
+mod remote_config;
 pub mod sender;
 
 pub use expr_eval::*;

datadog-live-debugger/src/lib.rs

@@ -0,0 +1,14 @@
+// Copyright 2021-Present Datadog, Inc. https://www.datadoghq.com/
+// SPDX-License-Identifier: Apache-2.0
+
+use crate::probe_defs::LiveDebuggingData;
+use datadog_remote_config::{ParseError, RemoteConfigContent, RemoteConfigProduct};
+
+impl RemoteConfigContent for LiveDebuggingData {
+    const PRODUCT: RemoteConfigProduct = RemoteConfigProduct::LiveDebugger;
+
+    fn parse(data: &[u8]) -> Result<Self, ParseError> {
+        crate::parse_json::parse(&String::from_utf8_lossy(data))
+            .map_err(|e| ParseError::Custom(e.into()))
+    }
+}

datadog-live-debugger/src/remote_config.rs

@@ -21,17 +21,14 @@ client = [
     "time",
     "tracing"
 ]
-live-debugger = ["datadog-live-debugger"]
+
 regex-lite = ["libdd-common/regex-lite"]
-ffe = ["datadog-ffe"]
 test = ["hyper/server", "hyper-util"]
 
 [dependencies]
 anyhow = { version = "1.0" }
 libdd-common = { path = "../libdd-common"}
 libdd-trace-protobuf = { path = "../libdd-trace-protobuf", optional = true }
-datadog-live-debugger = { path = "../datadog-live-debugger", optional = true }
-datadog-ffe = { path = "../datadog-ffe", optional = true }
 hyper = { workspace = true, optional = true, default-features = false }
 http-body-util = {version = "0.1", optional = true }
 http = { version = "1.1", optional = true }
@@ -47,6 +44,7 @@ tracing = { version = "0.1", default-features = false, optional = true }
 serde = "1.0"
 serde_json = { version = "1.0", features = ["raw_value"] }
 serde_with = "3"
+thiserror = "2"
 
 # Test feature
 hyper-util = { workspace = true, features = ["service"], optional = true }

datadog-remote-config/Cargo.toml

@@ -5,7 +5,7 @@ use datadog_remote_config::fetch::{ConfigInvariants, ConfigOptions, SingleChange
 use datadog_remote_config::file_change_tracker::{Change, FilePath};
 use datadog_remote_config::file_storage::ParsedFileStorage;
 use datadog_remote_config::RemoteConfigProduct::ApmTracing;
-use datadog_remote_config::{RemoteConfigData, Target};
+use datadog_remote_config::{RemoteConfigParsed, Target};
 use libdd_common::tag::Tag;
 use libdd_common::Endpoint;
 use std::time::Duration;
@@ -86,12 +86,15 @@ async fn main() {
     }
 }
 
-fn print_file_contents(contents: &anyhow::Result<RemoteConfigData>) {
+fn print_file_contents(contents: &anyhow::Result<Option<RemoteConfigParsed>>) {
     // Note: these contents may be large. Do not actually print it fully in a non-dev env.
     match contents {
-        Ok(data) => {
+        Ok(Some(data)) => {
             println!("File contents: {data:?}");
         }
+        Ok(None) => {
+            println!("Unregistered product, no parsed data");
+        }
         Err(e) => {
             println!("Failed parsing file: {e:?}");
         }

datadog-remote-config/examples/remote_config_fetch.rs

@@ -4,7 +4,7 @@
 use serde::{Deserialize, Serialize};
 use std::collections::HashMap;
 
-#[derive(Debug, Deserialize)]
+#[derive(Debug, Clone, Deserialize)]
 #[cfg_attr(feature = "test", derive(Default, Serialize))]
 pub struct DynamicConfigTarget {
     #[serde(default)]
@@ -13,7 +13,7 @@ pub struct DynamicConfigTarget {
     pub env: Option<String>,
 }
 
-#[derive(Debug, Deserialize)]
+#[derive(Debug, Clone, Deserialize)]
 #[cfg_attr(feature = "test", derive(Serialize))]
 pub struct DynamicConfigFile {
     pub action: String,
@@ -76,7 +76,7 @@ pub struct TracingSamplingRule {
     pub sample_rate: f64,
 }
 
-#[derive(Debug, Deserialize)]
+#[derive(Debug, Clone, Deserialize)]
 #[cfg_attr(feature = "test", derive(Default, Serialize))]
 pub struct DynamicConfig {
     pub(crate) tracing_header_tags: Option<Vec<TracingHeaderTag>>,