Stabilize remote full-ci turn startup waits

Honor pre-cancelled delegate spawns before starting work, wait for TurnStarted in the remote no-wait helper, and give serialized rollback integration tests matching nextest headroom.

Co-authored-by: Codex <noreply@openai.com>

codex-rs/.config/nextest.toml

@@ -58,6 +58,7 @@ slow-timeout = { period = "30s", terminate-after = 3 }
 # other while waiting for append-only history rewrites on saturated CI runners.
 filter = 'package(codex-core) & kind(test) & (test(snapshot_rollback_followup_turn_trims_context_updates) | test(snapshot_rollback_past_compaction_replays_append_only_history) | test(thread_rollback_after_generated_image_drops_entire_image_turn_history))'
 test-group = 'core_thread_rollback_integration'
+slow-timeout = { period = "30s", terminate-after = 3 }
 
 [[profile.default.overrides]]
 # These tests create restricted-token Windows child processes and private desktops.

codex-rs/core/src/codex_delegate.rs

@@ -72,6 +72,10 @@ pub(crate) async fn run_codex_thread_interactive(
     subagent_source: SubAgentSource,
     initial_history: Option<InitialHistory>,
 ) -> Result<Codex, CodexErr> {
+    if cancel_token.is_cancelled() {
+        return Err(CodexErr::TurnAborted);
+    }
+
     let (tx_sub, rx_sub) = async_channel::bounded(SUBMISSION_CHANNEL_CAPACITY);
     let (tx_ops, rx_ops) = async_channel::bounded(SUBMISSION_CHANNEL_CAPACITY);
     let CodexSpawnOk { codex, .. } = Box::pin(Codex::spawn(CodexSpawnArgs {

codex-rs/core/tests/common/test_codex.rs

@@ -722,6 +722,12 @@ impl TestCodex {
                 personality: None,
             })
             .await?;
+        wait_for_event_with_timeout(
+            &self.codex,
+            |event| matches!(event, EventMsg::TurnStarted(_)),
+            SUBMIT_TURN_COMPLETE_TIMEOUT,
+        )
+        .await;
         Ok(())
     }