[codex] Compact when comp_hash changes

codex-rs/analytics/src/facts.rs

@@ -364,6 +364,7 @@ pub enum CompactionReason {
     UserRequested,
     ContextLimit,
     ModelDownshift,
+    CompHashChanged,
 }
 
 #[derive(Clone, Copy, Debug, Serialize)]

codex-rs/core/src/compact_tests.rs

@@ -483,6 +483,7 @@ async fn process_compacted_history_reinjects_model_switch_message() {
     }];
     let previous_turn_settings = PreviousTurnSettings {
         model: "previous-regular-model".to_string(),
+        comp_hash: None,
         realtime_active: None,
     };
 

codex-rs/core/src/context/environment_context_tests.rs

@@ -178,6 +178,7 @@ fn turn_context_item_filesystem_uses_workspace_roots_instead_of_cwd() {
         network: None,
         file_system_sandbox_policy: None,
         model: "gpt-5".to_string(),
+        comp_hash: None,
         personality: None,
         collaboration_mode: None,
         multi_agent_version: None,

codex-rs/core/src/context_manager/history_tests.rs

@@ -130,6 +130,7 @@ fn reference_context_item() -> TurnContextItem {
         network: None,
         file_system_sandbox_policy: None,
         model: "gpt-test".to_string(),
+        comp_hash: None,
         personality: None,
         collaboration_mode: None,
         multi_agent_version: None,

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

@@ -276,10 +276,12 @@ impl SteerInputError {
 /// Conceptually this is the same role that `previous_model` used to fill, but
 /// it can carry other prior-turn settings that matter when constructing
 /// sensible state-change diffs or full-context reinjection, such as model
-/// switches or detecting a prior `realtime_active -> false` transition.
+/// switches, compaction compatibility, or detecting a prior
+/// `realtime_active -> false` transition.
 #[derive(Clone, Debug, PartialEq, Eq)]
 pub(crate) struct PreviousTurnSettings {
     pub(crate) model: String,
+    pub(crate) comp_hash: Option<String>,
     pub(crate) realtime_active: Option<bool>,
 }
 

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

@@ -114,6 +114,7 @@ pub(super) async fn spawn_review_thread(
         config: per_turn_config,
         auth_manager: auth_manager_for_context,
         model_info: model_info.clone(),
+        comp_hash: model_info.comp_hash.clone(),
         tool_mode,
         session_telemetry: session_telemetry_for_context,
         provider: provider_for_context,

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

@@ -184,6 +184,7 @@ impl Session {
                     ) {
                         active_segment.previous_turn_settings = Some(PreviousTurnSettings {
                             model: ctx.model.clone(),
+                            comp_hash: ctx.comp_hash.clone(),
                             realtime_active: ctx.realtime_active,
                         });
                         if matches!(

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

@@ -70,6 +70,7 @@ async fn record_initial_history_resumed_bare_turn_context_does_not_hydrate_previ
         network: None,
         file_system_sandbox_policy: None,
         model: previous_model.to_string(),
+        comp_hash: None,
         personality: turn_context.personality,
         collaboration_mode: Some(turn_context.collaboration_mode.clone()),
         multi_agent_version: None,
@@ -109,6 +110,7 @@ async fn record_initial_history_resumed_hydrates_previous_turn_settings_from_lif
         network: None,
         file_system_sandbox_policy: None,
         model: previous_model.to_string(),
+        comp_hash: Some("comp-hash-a".to_string()),
         personality: turn_context.personality,
         collaboration_mode: Some(turn_context.collaboration_mode.clone()),
         multi_agent_version: None,
@@ -166,6 +168,7 @@ async fn record_initial_history_resumed_hydrates_previous_turn_settings_from_lif
         session.previous_turn_settings().await,
         Some(PreviousTurnSettings {
             model: previous_model.to_string(),
+            comp_hash: Some("comp-hash-a".to_string()),
             realtime_active: Some(turn_context.realtime_active),
         })
     );
@@ -271,6 +274,7 @@ async fn reconstruct_history_rollback_keeps_history_and_metadata_in_sync_for_com
         reconstructed.previous_turn_settings,
         Some(PreviousTurnSettings {
             model: turn_context.model_info.slug.clone(),
+            comp_hash: None,
             realtime_active: Some(turn_context.realtime_active),
         })
     );
@@ -364,6 +368,7 @@ async fn reconstruct_history_rollback_keeps_history_and_metadata_in_sync_for_inc
         reconstructed.previous_turn_settings,
         Some(PreviousTurnSettings {
             model: turn_context.model_info.slug.clone(),
+            comp_hash: None,
             realtime_active: Some(turn_context.realtime_active),
         })
     );
@@ -489,6 +494,7 @@ async fn reconstruct_history_rollback_skips_non_user_turns_for_history_and_metad
         reconstructed.previous_turn_settings,
         Some(PreviousTurnSettings {
             model: turn_context.model_info.slug.clone(),
+            comp_hash: None,
             realtime_active: Some(turn_context.realtime_active),
         })
     );
@@ -589,6 +595,7 @@ async fn reconstruct_history_rollback_counts_inter_agent_assistant_turns() {
         reconstructed.previous_turn_settings,
         Some(PreviousTurnSettings {
             model: turn_context.model_info.slug.clone(),
+            comp_hash: None,
             realtime_active: Some(turn_context.realtime_active),
         })
     );
@@ -810,6 +817,7 @@ async fn record_initial_history_resumed_rollback_drops_incomplete_user_turn_comp
         session.previous_turn_settings().await,
         Some(PreviousTurnSettings {
             model: turn_context.model_info.slug.clone(),
+            comp_hash: None,
             realtime_active: Some(turn_context.realtime_active),
         })
     );
@@ -963,6 +971,7 @@ async fn record_initial_history_resumed_turn_context_after_compaction_reestablis
         network: None,
         file_system_sandbox_policy: None,
         model: previous_model.to_string(),
+        comp_hash: None,
         personality: turn_context.personality,
         collaboration_mode: Some(turn_context.collaboration_mode.clone()),
         multi_agent_version: None,
@@ -1024,6 +1033,7 @@ async fn record_initial_history_resumed_turn_context_after_compaction_reestablis
         session.previous_turn_settings().await,
         Some(PreviousTurnSettings {
             model: previous_model.to_string(),
+            comp_hash: None,
             realtime_active: Some(turn_context.realtime_active),
         })
     );
@@ -1043,6 +1053,7 @@ async fn record_initial_history_resumed_turn_context_after_compaction_reestablis
             network: None,
             file_system_sandbox_policy: None,
             model: previous_model.to_string(),
+            comp_hash: None,
             personality: turn_context.personality,
             collaboration_mode: Some(turn_context.collaboration_mode.clone()),
             multi_agent_version: None,
@@ -1072,6 +1083,7 @@ async fn record_initial_history_resumed_aborted_turn_without_id_clears_active_tu
         network: None,
         file_system_sandbox_policy: None,
         model: previous_model.to_string(),
+        comp_hash: None,
         personality: turn_context.personality,
         collaboration_mode: Some(turn_context.collaboration_mode.clone()),
         multi_agent_version: None,
@@ -1161,6 +1173,7 @@ async fn record_initial_history_resumed_aborted_turn_without_id_clears_active_tu
         session.previous_turn_settings().await,
         Some(PreviousTurnSettings {
             model: previous_model.to_string(),
+            comp_hash: None,
             realtime_active: Some(turn_context.realtime_active),
         })
     );
@@ -1192,6 +1205,7 @@ async fn record_initial_history_resumed_unmatched_abort_preserves_active_turn_fo
         network: None,
         file_system_sandbox_policy: None,
         model: current_model.to_string(),
+        comp_hash: None,
         personality: turn_context.personality,
         collaboration_mode: Some(turn_context.collaboration_mode.clone()),
         multi_agent_version: None,
@@ -1281,6 +1295,7 @@ async fn record_initial_history_resumed_unmatched_abort_preserves_active_turn_fo
         session.previous_turn_settings().await,
         Some(PreviousTurnSettings {
             model: current_model.to_string(),
+            comp_hash: None,
             realtime_active: Some(turn_context.realtime_active),
         })
     );
@@ -1310,6 +1325,7 @@ async fn record_initial_history_resumed_trailing_incomplete_turn_compaction_clea
         network: None,
         file_system_sandbox_policy: None,
         model: previous_model.to_string(),
+        comp_hash: None,
         personality: turn_context.personality,
         collaboration_mode: Some(turn_context.collaboration_mode.clone()),
         multi_agent_version: None,
@@ -1391,6 +1407,7 @@ async fn record_initial_history_resumed_trailing_incomplete_turn_compaction_clea
         session.previous_turn_settings().await,
         Some(PreviousTurnSettings {
             model: previous_model.to_string(),
+            comp_hash: None,
             realtime_active: Some(turn_context.realtime_active),
         })
     );
@@ -1441,6 +1458,7 @@ async fn record_initial_history_resumed_trailing_incomplete_turn_preserves_turn_
         session.previous_turn_settings().await,
         Some(PreviousTurnSettings {
             model: turn_context.model_info.slug.clone(),
+            comp_hash: None,
             realtime_active: Some(turn_context.realtime_active),
         })
     );
@@ -1470,6 +1488,7 @@ async fn record_initial_history_resumed_replaced_incomplete_compacted_turn_clear
         network: None,
         file_system_sandbox_policy: None,
         model: previous_model.to_string(),
+        comp_hash: None,
         personality: turn_context.personality,
         collaboration_mode: Some(turn_context.collaboration_mode.clone()),
         multi_agent_version: None,
@@ -1563,6 +1582,7 @@ async fn record_initial_history_resumed_replaced_incomplete_compacted_turn_clear
         session.previous_turn_settings().await,
         Some(PreviousTurnSettings {
             model: previous_model.to_string(),
+            comp_hash: None,
             realtime_active: Some(turn_context.realtime_active),
         })
     );

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

@@ -2669,6 +2669,7 @@ async fn record_initial_history_forked_hydrates_previous_turn_settings() {
         network: None,
         file_system_sandbox_policy: None,
         model: previous_model.to_string(),
+        comp_hash: None,
         personality: turn_context.personality,
         collaboration_mode: Some(turn_context.collaboration_mode.clone()),
         multi_agent_version: None,
@@ -2721,6 +2722,7 @@ async fn record_initial_history_forked_hydrates_previous_turn_settings() {
         session.previous_turn_settings().await,
         Some(PreviousTurnSettings {
             model: previous_model.to_string(),
+            comp_hash: None,
             realtime_active: Some(turn_context.realtime_active),
         })
     );
@@ -2763,6 +2765,7 @@ async fn thread_rollback_drops_last_turn_from_history() {
     sess.persist_rollout_items(&rollout_items).await;
     sess.set_previous_turn_settings(Some(PreviousTurnSettings {
         model: "stale-model".to_string(),
+        comp_hash: None,
         realtime_active: Some(tc.realtime_active),
     }))
     .await;
@@ -2945,6 +2948,7 @@ async fn thread_rollback_recomputes_previous_turn_settings_and_reference_context
     .await;
     sess.set_previous_turn_settings(Some(PreviousTurnSettings {
         model: "stale-model".to_string(),
+        comp_hash: None,
         realtime_active: None,
     }))
     .await;
@@ -2961,6 +2965,7 @@ async fn thread_rollback_recomputes_previous_turn_settings_and_reference_context
         sess.previous_turn_settings().await,
         Some(PreviousTurnSettings {
             model: tc.model_info.slug.clone(),
+            comp_hash: None,
             realtime_active: Some(tc.realtime_active),
         })
     );
@@ -3061,6 +3066,7 @@ async fn thread_rollback_restores_cleared_reference_context_item_after_compactio
         RolloutItem::TurnContext(TurnContextItem {
             turn_id: Some(rolled_back_turn_id.clone()),
             model: "rolled-back-model".to_string(),
+            comp_hash: None,
             ..first_context_item.clone()
         }),
         RolloutItem::ResponseItem(user_message("turn 2 user")),
@@ -7457,6 +7463,7 @@ async fn build_settings_update_items_uses_previous_turn_settings_for_realtime_en
     previous_context_item.realtime_active = None;
     let previous_turn_settings = PreviousTurnSettings {
         model: previous_context.model_info.slug.clone(),
+        comp_hash: None,
         realtime_active: Some(true),
     };
     let mut current_context = previous_context
@@ -8050,6 +8057,7 @@ async fn build_initial_context_uses_previous_turn_settings_for_realtime_end() {
     let (session, turn_context) = make_session_and_context().await;
     let previous_turn_settings = PreviousTurnSettings {
         model: turn_context.model_info.slug.clone(),
+        comp_hash: None,
         realtime_active: Some(true),
     };
 
@@ -8072,6 +8080,7 @@ async fn build_initial_context_restates_realtime_start_when_reference_context_is
     turn_context.realtime_active = true;
     let previous_turn_settings = PreviousTurnSettings {
         model: turn_context.model_info.slug.clone(),
+        comp_hash: None,
         realtime_active: Some(true),
     };
 
@@ -8105,6 +8114,18 @@ fn file_system_policy_with_unreadable_glob(turn_context: &TurnContext) -> FileSy
     policy
 }
 
+#[tokio::test]
+async fn turn_context_item_uses_turn_context_comp_hash_snapshot() {
+    let (_session, mut turn_context) = make_session_and_context().await;
+    turn_context.comp_hash = Some("turn-context-hash".to_string());
+    turn_context.model_info.comp_hash = Some("model-info-hash".to_string());
+
+    assert_eq!(
+        turn_context.to_turn_context_item().comp_hash.as_deref(),
+        Some("turn-context-hash")
+    );
+}
+
 #[tokio::test]
 async fn turn_context_item_omits_legacy_equivalent_file_system_sandbox_policy() {
     let (_session, turn_context) = make_session_and_context().await;
@@ -8296,6 +8317,7 @@ async fn build_initial_context_prepends_model_switch_message() {
     let (session, turn_context) = make_session_and_context().await;
     let previous_turn_settings = PreviousTurnSettings {
         model: "previous-regular-model".to_string(),
+        comp_hash: None,
         realtime_active: None,
     };
 
@@ -8348,6 +8370,7 @@ async fn record_context_updates_and_set_reference_context_item_persists_full_rei
     session
         .set_previous_turn_settings(Some(PreviousTurnSettings {
             model: previous_context.model_info.slug.clone(),
+            comp_hash: None,
             realtime_active: Some(previous_context.realtime_active),
         }))
         .await;

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

@@ -172,6 +172,7 @@ pub(crate) async fn run_turn(
         .await;
     sess.set_previous_turn_settings(Some(PreviousTurnSettings {
         model: turn_context.model_info.slug.clone(),
+        comp_hash: turn_context.comp_hash.clone(),
         realtime_active: Some(turn_context.realtime_active),
     }))
     .await;
@@ -798,8 +799,16 @@ async fn run_pre_sampling_compact(
     Ok(())
 }
 
-/// Runs pre-sampling compaction against the previous model when switching to a smaller
-/// context-window model.
+/// Returns true only when both turns declare compaction compatibility hashes and they differ.
+/// A missing hash does not provide enough information to trigger compaction.
+fn comp_hash_changed(previous: Option<&str>, current: Option<&str>) -> bool {
+    previous
+        .zip(current)
+        .is_some_and(|(previous, current)| previous != current)
+}
+
+/// Runs pre-sampling compaction against the previous model when its compaction compatibility
+/// hash changed or when switching to a smaller context-window model.
 ///
 /// Returns `Err(_)` only when compaction was attempted and failed.
 async fn maybe_run_previous_model_inline_compact(
@@ -810,12 +819,29 @@ async fn maybe_run_previous_model_inline_compact(
     let Some(previous_turn_settings) = sess.previous_turn_settings().await else {
         return Ok(());
     };
+    let should_compact_for_comp_hash_change = comp_hash_changed(
+        previous_turn_settings.comp_hash.as_deref(),
+        turn_context.comp_hash.as_deref(),
+    );
     let previous_model_turn_context = Arc::new(
         turn_context
             .with_model(previous_turn_settings.model, &sess.services.models_manager)
             .await,
     );
 
+    if should_compact_for_comp_hash_change {
+        run_auto_compact(
+            sess,
+            &previous_model_turn_context,
+            client_session,
+            InitialContextInjection::DoNotInject,
+            CompactionReason::CompHashChanged,
+            CompactionPhase::PreTurn,
+        )
+        .await?;
+        return Ok(());
+    }
+
     let Some(old_context_window) = previous_model_turn_context.model_context_window() else {
         return Ok(());
     };