chore: fix merge race (auto-compaction feature access) (#29393)

## Summary

- read the `AutoCompaction` feature flag through `TurnContext::config`
- fix both the mid-turn and pre-sampling compaction checks

## Why

#28260 was validated against an older base where `TurnContext` exposed a
direct `features` field. It was then merged after that field had moved
under `config`, leaving the merge result unable to compile with `E0609`
on `turn_context.features`.

This restores compilation for Bazel, SDK, and argument-comment-lint jobs
that build `codex-core`. Behavior is unchanged: disabling
`auto_compaction` still skips automatic compaction.

## Validation

- `just fmt`
- `CODEX_HOME=/private/tmp/codex-fix-auto-compaction-test-home just test
-p codex-core auto_compaction_feature_disabled` — 4 passed
- `just test -p codex-core` — `codex-core` compiled; 2,722 passed and 89
unrelated local-environment failures remained because the sandbox could
not write the default Codex SQLite/proxy paths and some first-party test
binaries were unavailable

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

@@ -334,7 +334,10 @@ pub(crate) async fn run_turn(
                 }
 
                 // as long as compaction works well in getting us way below the token limit, we shouldn't worry about being in an infinite loop.
-                if turn_context.features.enabled(Feature::AutoCompaction)
+                if turn_context
+                    .config
+                    .features
+                    .enabled(Feature::AutoCompaction)
                     && token_limit_reached
                     && needs_follow_up
                 {
@@ -848,7 +851,11 @@ async fn run_pre_sampling_compact(
     turn_context: &Arc<TurnContext>,
     client_session: &mut ModelClientSession,
 ) -> CodexResult<()> {
-    if !turn_context.features.enabled(Feature::AutoCompaction) {
+    if !turn_context
+        .config
+        .features
+        .enabled(Feature::AutoCompaction)
+    {
         return Ok(());
     }