Delegate review to codex instance (#5572)

In this PR, I am exploring migrating task kind to an invocation of
Codex. The main reason would be getting rid off multiple
`ConversationHistory` state and streamlining our context/history
management.

This approach depends on opening a channel between the sub-codex and
codex. This channel is responsible for forwarding `interactive`
(`approvals`) and `non-interactive` events. The `task` is responsible
for handling those events.

This opens the door for implementing `codex as a tool`, replacing
`compact` and `review`, and potentially subagents.

One consideration is this code is very similar to `app-server` specially
in the approval part. If in the future we wanted an interactive
`sub-codex` we should consider using `codex-mcp`

codex-rs/core/src/client.rs

@@ -13,6 +13,7 @@ use codex_protocol::ConversationId;
 use codex_protocol::config_types::ReasoningEffort as ReasoningEffortConfig;
 use codex_protocol::config_types::ReasoningSummary as ReasoningSummaryConfig;
 use codex_protocol::models::ResponseItem;
+use codex_protocol::protocol::SessionSource;
 use eventsource_stream::Eventsource;
 use futures::prelude::*;
 use regex_lite::Regex;
@@ -56,7 +57,6 @@ use crate::openai_model_info::get_model_info;
 use crate::protocol::RateLimitSnapshot;
 use crate::protocol::RateLimitWindow;
 use crate::protocol::TokenUsage;
-use crate::state::TaskKind;
 use crate::token_data::PlanType;
 use crate::tools::spec::create_tools_json_for_responses_api;
 use crate::util::backoff;
@@ -87,8 +87,10 @@ pub struct ModelClient {
     conversation_id: ConversationId,
     effort: Option<ReasoningEffortConfig>,
     summary: ReasoningSummaryConfig,
+    session_source: SessionSource,
 }
 
+#[allow(clippy::too_many_arguments)]
 impl ModelClient {
     pub fn new(
         config: Arc<Config>,
@@ -98,6 +100,7 @@ impl ModelClient {
         effort: Option<ReasoningEffortConfig>,
         summary: ReasoningSummaryConfig,
         conversation_id: ConversationId,
+        session_source: SessionSource,
     ) -> Self {
         let client = create_client();
 
@@ -110,6 +113,7 @@ impl ModelClient {
             conversation_id,
             effort,
             summary,
+            session_source,
         }
     }
 
@@ -127,13 +131,6 @@ impl ModelClient {
         })
     }
 
-    /// Dispatches to either the Responses or Chat implementation depending on
-    /// the provider config.  Public callers always invoke `stream()` – the
-    /// specialised helpers are private to avoid accidental misuse.
-    pub async fn stream(&self, prompt: &Prompt) -> Result<ResponseStream> {
-        self.stream_with_task_kind(prompt, TaskKind::Regular).await
-    }
-
     pub fn config(&self) -> Arc<Config> {
         Arc::clone(&self.config)
     }
@@ -142,13 +139,9 @@ impl ModelClient {
         &self.provider
     }
 
-    pub(crate) async fn stream_with_task_kind(
-        &self,
-        prompt: &Prompt,
-        task_kind: TaskKind,
-    ) -> Result<ResponseStream> {
+    pub async fn stream(&self, prompt: &Prompt) -> Result<ResponseStream> {
         match self.provider.wire_api {
-            WireApi::Responses => self.stream_responses(prompt, task_kind).await,
+            WireApi::Responses => self.stream_responses(prompt).await,
             WireApi::Chat => {
                 // Create the raw streaming connection first.
                 let response_stream = stream_chat_completions(
@@ -157,6 +150,7 @@ impl ModelClient {
                     &self.client,
                     &self.provider,
                     &self.otel_event_manager,
+                    &self.session_source,
                 )
                 .await?;
 
@@ -189,11 +183,7 @@ impl ModelClient {
     }
 
     /// Implementation for the OpenAI *Responses* experimental API.
-    async fn stream_responses(
-        &self,
-        prompt: &Prompt,
-        task_kind: TaskKind,
-    ) -> Result<ResponseStream> {
+    async fn stream_responses(&self, prompt: &Prompt) -> Result<ResponseStream> {
         if let Some(path) = &*CODEX_RS_SSE_FIXTURE {
             // short circuit for tests
             warn!(path, "Streaming from fixture");
@@ -268,7 +258,7 @@ impl ModelClient {
         let max_attempts = self.provider.request_max_retries();
         for attempt in 0..=max_attempts {
             match self
-                .attempt_stream_responses(attempt, &payload_json, &auth_manager, task_kind)
+                .attempt_stream_responses(attempt, &payload_json, &auth_manager)
                 .await
             {
                 Ok(stream) => {
@@ -296,7 +286,6 @@ impl ModelClient {
         attempt: u64,
         payload_json: &Value,
         auth_manager: &Option<Arc<AuthManager>>,
-        task_kind: TaskKind,
     ) -> std::result::Result<ResponseStream, StreamAttemptError> {
         // Always fetch the latest auth in case a prior attempt refreshed the token.
         let auth = auth_manager.as_ref().and_then(|m| m.auth());
@@ -314,12 +303,19 @@ impl ModelClient {
             .await
             .map_err(StreamAttemptError::Fatal)?;
 
+        // Include session source for backend telemetry and routing.
+        let task_type = match serde_json::to_value(&self.session_source) {
+            Ok(serde_json::Value::String(s)) => s,
+            Ok(other) => other.to_string(),
+            Err(_) => "unknown".to_string(),
+        };
+        req_builder = req_builder.header("Codex-Task-Type", task_type);
+
         req_builder = req_builder
             // Send session_id for compatibility.
             .header("conversation_id", self.conversation_id.to_string())
             .header("session_id", self.conversation_id.to_string())
             .header(reqwest::header::ACCEPT, "text/event-stream")
-            .header("Codex-Task-Type", task_kind.header_value())
             .json(payload_json);
 
         if let Some(auth) = auth.as_ref()
@@ -462,6 +458,10 @@ impl ModelClient {
         self.otel_event_manager.clone()
     }
 
+    pub fn get_session_source(&self) -> SessionSource {
+        self.session_source.clone()
+    }
+
     /// Returns the currently configured model slug.
     pub fn get_model(&self) -> String {
         self.config.model.clone()