[codex] Use TurnInput for session task input (#24151)

## Why

The idea here is to erase the difference between initial and followup
inputs to a turn. Followup inputs are already represented as TurnInput.

Eventual goal is not to have explicit on task input at all and pull
everything from input Q.

## What Changed

- Changes `SessionTask::run` and the erased `AnySessionTask::run` path
to accept `Vec<TurnInput>`.
- Wraps user-submitted spawn input as `TurnInput::UserInput` at the
session task start boundary.
- Updates `run_turn` to record initial `TurnInput` using the same hook
and recording path used for pending input.
- Keeps review-specific conversion local to `ReviewTask`, where the
sub-Codex one-shot API still expects `Vec<UserInput>`.
- Moves the synthetic compact prompt into `CompactTask` and starts
compact tasks with empty task input.

## Validation

- `cargo check -p codex-core`
- `just test -p codex-core -E
'test(task_finish_emits_turn_item_lifecycle_for_leftover_pending_user_input)
| test(queued_response_items_for_next_turn_move_into_next_active_turn) |
test(steered_input_reopens_mailbox_delivery_for_current_turn)'`

codex-rs/core/src/tasks/compact.rs

@@ -2,6 +2,7 @@ use std::sync::Arc;
 
 use super::SessionTask;
 use super::SessionTaskContext;
+use crate::session::TurnInput;
 use crate::session::turn_context::TurnContext;
 use crate::state::TaskKind;
 use codex_protocol::user_input::UserInput;
@@ -23,7 +24,7 @@ impl SessionTask for CompactTask {
         self: Arc<Self>,
         session: Arc<SessionTaskContext>,
         ctx: Arc<TurnContext>,
-        input: Vec<UserInput>,
+        _input: Vec<TurnInput>,
         _cancellation_token: CancellationToken,
     ) -> Option<String> {
         let session = session.clone_session();
@@ -47,6 +48,11 @@ impl SessionTask for CompactTask {
                 /*inc*/ 1,
                 &[("type", "local")],
             );
+            let input = vec![UserInput::Text {
+                text: ctx.compact_prompt().to_string(),
+                // Compaction prompt is synthesized; no UI element ranges to preserve.
+                text_elements: Vec::new(),
+            }];
             crate::compact::run_compact_task(session.clone(), ctx, input).await
         };
         None

codex-rs/core/src/tasks/mod.rs

@@ -214,7 +214,7 @@ pub(crate) trait SessionTask: Send + Sync + 'static {
         self: Arc<Self>,
         session: Arc<SessionTaskContext>,
         ctx: Arc<TurnContext>,
-        input: Vec<UserInput>,
+        input: Vec<TurnInput>,
         cancellation_token: CancellationToken,
     ) -> impl std::future::Future<Output = Option<String>> + Send;
 
@@ -245,7 +245,7 @@ pub(crate) trait AnySessionTask: Send + Sync + 'static {
         self: Arc<Self>,
         session: Arc<SessionTaskContext>,
         ctx: Arc<TurnContext>,
-        input: Vec<UserInput>,
+        input: Vec<TurnInput>,
         cancellation_token: CancellationToken,
     ) -> BoxFuture<'static, Option<String>>;
 
@@ -276,7 +276,7 @@ where
         self: Arc<Self>,
         session: Arc<SessionTaskContext>,
         ctx: Arc<TurnContext>,
-        input: Vec<UserInput>,
+        input: Vec<TurnInput>,
         cancellation_token: CancellationToken,
     ) -> BoxFuture<'static, Option<String>> {
         Box::pin(SessionTask::run(
@@ -380,6 +380,11 @@ impl Session {
         ));
         let ctx = Arc::clone(&turn_context);
         let task_for_run = Arc::clone(&task);
+        let task_input = if input.is_empty() {
+            Vec::new()
+        } else {
+            vec![TurnInput::UserInput(input)]
+        };
         let task_cancellation_token = cancellation_token.child_token();
         // Task-owned turn spans keep a core-owned span open for the
         // full task lifecycle after the submission dispatch span ends.
@@ -405,7 +410,7 @@ impl Session {
                     .run(
                         Arc::clone(&session_ctx),
                         ctx,
-                        input,
+                        task_input,
                         task_cancellation_token.child_token(),
                     )
                     .await;

codex-rs/core/src/tasks/regular.rs

@@ -2,13 +2,13 @@ use std::sync::Arc;
 
 use tokio_util::sync::CancellationToken;
 
+use crate::session::TurnInput;
 use crate::session::turn::run_turn;
 use crate::session::turn_context::TurnContext;
 use crate::session_startup_prewarm::SessionStartupPrewarmResolution;
 use crate::state::TaskKind;
 use codex_protocol::protocol::EventMsg;
 use codex_protocol::protocol::TurnStartedEvent;
-use codex_protocol::user_input::UserInput;
 use tracing::Instrument;
 use tracing::trace_span;
 
@@ -41,7 +41,7 @@ impl SessionTask for RegularTask {
         self: Arc<Self>,
         session: Arc<SessionTaskContext>,
         ctx: Arc<TurnContext>,
-        input: Vec<UserInput>,
+        input: Vec<TurnInput>,
         cancellation_token: CancellationToken,
     ) -> Option<String> {
         let sess = session.clone_session();

codex-rs/core/src/tasks/review.rs

@@ -20,6 +20,7 @@ use crate::codex_delegate::run_codex_thread_one_shot;
 use crate::config::Constrained;
 use crate::review_format::format_review_findings_block;
 use crate::review_format::render_review_output_text;
+use crate::session::TurnInput;
 use crate::session::session::Session;
 use crate::session::turn_context::TurnContext;
 use crate::state::TaskKind;
@@ -59,7 +60,7 @@ impl SessionTask for ReviewTask {
         self: Arc<Self>,
         session: Arc<SessionTaskContext>,
         ctx: Arc<TurnContext>,
-        input: Vec<UserInput>,
+        input: Vec<TurnInput>,
         cancellation_token: CancellationToken,
     ) -> Option<String> {
         session.session.services.session_telemetry.counter(
@@ -68,11 +69,19 @@ impl SessionTask for ReviewTask {
             &[],
         );
 
+        let mut user_input = Vec::new();
+        for item in input {
+            match item {
+                TurnInput::UserInput(mut content) => user_input.append(&mut content),
+                TurnInput::ResponseInputItem(_) => {}
+            }
+        }
+
         // Start sub-codex conversation and get the receiver for events.
         let output = match start_review_conversation(
             session.clone(),
             ctx.clone(),
-            input,
+            user_input,
             cancellation_token.clone(),
         )
         .await

codex-rs/core/src/tasks/user_shell.rs

@@ -7,7 +7,6 @@ use codex_network_proxy::PROXY_ACTIVE_ENV_KEY;
 use codex_network_proxy::PROXY_ENV_KEYS;
 #[cfg(target_os = "macos")]
 use codex_network_proxy::PROXY_GIT_SSH_COMMAND_ENV_KEY;
-use codex_protocol::user_input::UserInput;
 use tokio_util::sync::CancellationToken;
 use tracing::error;
 use uuid::Uuid;
@@ -17,6 +16,7 @@ use crate::exec::StdoutStream;
 use crate::exec::execute_exec_request;
 use crate::exec_env::create_env;
 use crate::sandboxing::ExecRequest;
+use crate::session::TurnInput;
 use crate::session::turn_context::TurnContext;
 use crate::state::TaskKind;
 use crate::tools::format_exec_output_str;
@@ -77,7 +77,7 @@ impl SessionTask for UserShellCommandTask {
         self: Arc<Self>,
         session: Arc<SessionTaskContext>,
         turn_context: Arc<TurnContext>,
-        _input: Vec<UserInput>,
+        _input: Vec<TurnInput>,
         cancellation_token: CancellationToken,
     ) -> Option<String> {
         execute_user_shell_command(