Simplify queued user message admission (#38092)

## What changed

- Resolve user message admission when Core accepts the input as a new turn or a steer, without waiting for rollout persistence.
- Remove persistence- and hook-specific admission errors and task bookkeeping.
- Delete queued messages after Core accepts them for turn processing, including messages subsequently stopped by a prompt hook.

## Testing

- Update concurrent admission and queue service tests for acceptance-based admission.

GitOrigin-RevId: 7dcc311cfecd3d710733b420f2add546edb86153

codex-rs/core/src/state/turn.rs

@@ -19,7 +19,6 @@ use rmcp::model::RequestId;
 use tokio::sync::oneshot;
 
 use crate::agent::control::AgentExecutionGuard;
-use crate::codex_thread::TryStartTurnIfIdleRejectionReason;
 use crate::mcp_tool_call::McpToolApprovalMetadata;
 use crate::session::TurnInputQueue;
 use crate::session::turn_context::TurnContext;
@@ -76,8 +75,6 @@ pub(crate) struct RunningTask {
     pub(crate) done: Arc<Notify>,
     pub(crate) kind: TaskKind,
     pub(crate) task: Arc<dyn AnySessionTask>,
-    pub(crate) input_persisted:
-        Option<oneshot::Sender<Result<(), TryStartTurnIfIdleRejectionReason>>>,
     pub(crate) cancellation_token: CancellationToken,
     pub(crate) handle: AbortOnDropHandle<()>,
     pub(crate) turn_context: Arc<TurnContext>,