diff --git a/codex-rs/app-server-protocol/src/protocol/thread_history.rs b/codex-rs/app-server-protocol/src/protocol/thread_history.rs
index 30221d944..0157101cf 100644
--- a/codex-rs/app-server-protocol/src/protocol/thread_history.rs
+++ b/codex-rs/app-server-protocol/src/protocol/thread_history.rs
@@ -3341,6 +3341,8 @@ mod tests {
                 message: String::new(),
                 replacement_history: None,
                 window_number: None,
+                first_window_id: None,
+                previous_window_id: None,
                 window_id: None,
             }),
             RolloutItem::EventMsg(EventMsg::TurnComplete(TurnCompleteEvent {
diff --git a/codex-rs/core/src/agent/control_tests.rs b/codex-rs/core/src/agent/control_tests.rs
index 66b5b5c4c..8dbcab338 100644
--- a/codex-rs/core/src/agent/control_tests.rs
+++ b/codex-rs/core/src/agent/control_tests.rs
@@ -1160,6 +1160,8 @@ async fn spawn_agent_fork_strips_parent_usage_hints_from_compacted_history() {
                 message: String::new(),
                 replacement_history: Some(replacement_history),
                 window_number: None,
+                first_window_id: None,
+                previous_window_id: None,
                 window_id: None,
             }),
             RolloutItem::TurnContext(turn_context.to_turn_context_item()),
diff --git a/codex-rs/core/src/compact.rs b/codex-rs/core/src/compact.rs
index 7a2eaf935..8a5efd594 100644
--- a/codex-rs/core/src/compact.rs
+++ b/codex-rs/core/src/compact.rs
@@ -302,7 +302,7 @@ async fn run_compact_task_inner_impl(
     let user_messages = collect_user_messages(history_items);
 
     let mut new_history = build_compacted_history(Vec::new(), &user_messages, &summary_text);
-    let (window_number, window_id) = sess.advance_auto_compact_window().await;
+    let (window_number, window_ids) = sess.advance_auto_compact_window().await;
 
     if matches!(
         initial_context_injection,
@@ -320,7 +320,9 @@ async fn run_compact_task_inner_impl(
         message: summary_text.clone(),
         replacement_history: Some(new_history.clone()),
         window_number: Some(window_number),
-        window_id: Some(window_id),
+        first_window_id: Some(window_ids.first_window_id.to_string()),
+        previous_window_id: window_ids.previous_window_id.map(|id| id.to_string()),
+        window_id: Some(window_ids.window_id.to_string()),
     };
     sess.replace_compacted_history(
         turn_context.as_ref(),
diff --git a/codex-rs/core/src/compact_remote.rs b/codex-rs/core/src/compact_remote.rs
index 26469c201..7a47881e4 100644
--- a/codex-rs/core/src/compact_remote.rs
+++ b/codex-rs/core/src/compact_remote.rs
@@ -258,7 +258,7 @@ async fn run_remote_compact_task_inner_impl(
             &responses_metadata,
         )
         .await?;
-    let (new_window_number, new_window_id) = sess.advance_auto_compact_window().await;
+    let (new_window_number, new_window_ids) = sess.advance_auto_compact_window().await;
     new_history = process_compacted_history(
         sess.as_ref(),
         turn_context.as_ref(),
@@ -275,7 +275,9 @@ async fn run_remote_compact_task_inner_impl(
         message: String::new(),
         replacement_history: Some(new_history.clone()),
         window_number: Some(new_window_number),
-        window_id: Some(new_window_id),
+        first_window_id: Some(new_window_ids.first_window_id.to_string()),
+        previous_window_id: new_window_ids.previous_window_id.map(|id| id.to_string()),
+        window_id: Some(new_window_ids.window_id.to_string()),
     };
     // Install is the semantic boundary where the compact endpoint's output becomes live
     // thread history. Keep it distinct from the later inference request so the reducer can
diff --git a/codex-rs/core/src/compact_remote_v2.rs b/codex-rs/core/src/compact_remote_v2.rs
index 6f10a474a..0b382700a 100644
--- a/codex-rs/core/src/compact_remote_v2.rs
+++ b/codex-rs/core/src/compact_remote_v2.rs
@@ -292,7 +292,7 @@ async fn run_remote_compact_task_inner_impl(
     let (compacted_history, retained_images) =
         build_v2_compacted_history(&prompt_input, compaction_output);
     analytics_details.retained_image_count = Some(retained_images);
-    let (new_window_number, new_window_id) = sess.advance_auto_compact_window().await;
+    let (new_window_number, new_window_ids) = sess.advance_auto_compact_window().await;
     let new_history = process_compacted_history(
         sess.as_ref(),
         turn_context.as_ref(),
@@ -309,7 +309,9 @@ async fn run_remote_compact_task_inner_impl(
         message: String::new(),
         replacement_history: Some(new_history.clone()),
         window_number: Some(new_window_number),
-        window_id: Some(new_window_id),
+        first_window_id: Some(new_window_ids.first_window_id.to_string()),
+        previous_window_id: new_window_ids.previous_window_id.map(|id| id.to_string()),
+        window_id: Some(new_window_ids.window_id.to_string()),
     };
     compaction_trace.record_installed(&CompactionCheckpointTracePayload {
         input_history: &trace_input_history,
diff --git a/codex-rs/core/src/context/token_budget_context.rs b/codex-rs/core/src/context/token_budget_context.rs
index b21b61735..bac1caafd 100644
--- a/codex-rs/core/src/context/token_budget_context.rs
+++ b/codex-rs/core/src/context/token_budget_context.rs
@@ -5,14 +5,24 @@ use uuid::Uuid;
 #[derive(Debug, Clone, PartialEq, Eq)]
 pub(crate) struct TokenBudgetContext {
     thread_id: ThreadId,
+    first_window_id: Uuid,
+    previous_window_id: Option<Uuid>,
     window_id: Uuid,
     tokens_left: i64,
 }
 
 impl TokenBudgetContext {
-    pub(crate) fn new(thread_id: ThreadId, window_id: Uuid, tokens_left: i64) -> Self {
+    pub(crate) fn new(
+        thread_id: ThreadId,
+        first_window_id: Uuid,
+        previous_window_id: Option<Uuid>,
+        window_id: Uuid,
+        tokens_left: i64,
+    ) -> Self {
         Self {
             thread_id,
+            first_window_id,
+            previous_window_id,
             window_id,
             tokens_left,
         }
@@ -34,10 +44,14 @@ impl ContextualUserFragment for TokenBudgetContext {
 
     fn body(&self) -> String {
         let thread_id = self.thread_id;
+        let first_window_id = self.first_window_id;
+        let previous_window_id = self
+            .previous_window_id
+            .map_or_else(|| "none".to_string(), |window_id| window_id.to_string());
         let window_id = self.window_id;
         let tokens_left = self.tokens_left;
         format!(
-            "Thread id {thread_id}.\nCurrent context window id {window_id}.\nYou have {tokens_left} tokens left in this context window."
+            "Thread id {thread_id}.\nFirst context window id {first_window_id}.\nPrevious context window id {previous_window_id}.\nCurrent context window id {window_id}.\nYou have {tokens_left} tokens left in this context window."
         )
     }
 }
diff --git a/codex-rs/core/src/session/mod.rs b/codex-rs/core/src/session/mod.rs
index 0792334b3..3cc746912 100644
--- a/codex-rs/core/src/session/mod.rs
+++ b/codex-rs/core/src/session/mod.rs
@@ -311,6 +311,7 @@ use crate::session_startup_prewarm::SessionStartupPrewarmHandle;
 use crate::shell;
 #[cfg(test)]
 use crate::skills::SkillLoadOutcome;
+use crate::state::AutoCompactWindowIds;
 use crate::state::AutoCompactWindowSnapshot;
 use crate::state::PendingRequestPermissions;
 use crate::state::SessionServices;
@@ -1364,6 +1365,8 @@ impl Session {
             previous_turn_settings,
             reference_context_item,
             window_number,
+            first_window_id,
+            previous_window_id,
             window_id,
         } = self
             .reconstruct_history_from_rollout(turn_context, rollout_items)
@@ -1382,8 +1385,16 @@ impl Session {
         {
             let mut state = self.state.lock().await;
             state.replace_history(history, reference_context_item);
-            let window_id = window_id.unwrap_or_else(|| state.auto_compact_window_id());
-            state.restore_auto_compact_window(window_number, window_id);
+            let fallback_ids = state.auto_compact_window_ids();
+            let window_id = window_id.unwrap_or(fallback_ids.window_id);
+            state.restore_auto_compact_window(
+                window_number,
+                AutoCompactWindowIds {
+                    first_window_id: first_window_id.unwrap_or(window_id),
+                    previous_window_id,
+                    window_id,
+                },
+            );
             state.set_previous_turn_settings(previous_turn_settings.clone());
         }
         let prefix_tokens = if matches!(
@@ -3011,7 +3022,7 @@ impl Session {
             collaboration_mode,
             base_instructions,
             session_source,
-            auto_compact_window_id,
+            auto_compact_window_ids,
         ) = {
             let state = self.state.lock().await;
             (
@@ -3020,7 +3031,7 @@ impl Session {
                 state.session_configuration.collaboration_mode.clone(),
                 state.session_configuration.base_instructions.clone(),
                 state.session_configuration.session_source.clone(),
-                state.auto_compact_window_id(),
+                state.auto_compact_window_ids(),
             )
         };
         if let Some(model_switch_message) =
@@ -3210,7 +3221,9 @@ impl Session {
             developer_sections.push(
                 crate::context::TokenBudgetContext::new(
                     self.thread_id(),
-                    auto_compact_window_id,
+                    auto_compact_window_ids.first_window_id,
+                    auto_compact_window_ids.previous_window_id,
+                    auto_compact_window_ids.window_id,
                     model_context_window,
                 )
                 .render(),
@@ -3309,10 +3322,9 @@ impl Session {
         format!("{thread_id}:{window_number}")
     }
 
-    pub(crate) async fn advance_auto_compact_window(&self) -> (u64, String) {
+    pub(crate) async fn advance_auto_compact_window(&self) -> (u64, AutoCompactWindowIds) {
         let mut state = self.state.lock().await;
-        let (window_number, window_id) = state.advance_auto_compact_window();
-        (window_number, window_id.to_string())
+        state.advance_auto_compact_window()
     }
 
     pub(crate) async fn request_new_context_window(&self) {
@@ -3328,7 +3340,7 @@ impl Session {
             let mut state = self.state.lock().await;
             state.start_new_context_window_if_requested()
         };
-        let (window_number, window_id) = window?;
+        let (window_number, window_ids) = window?;
         let context_items = self.build_initial_context(turn_context).await;
         let turn_context_item = turn_context.to_turn_context_item();
         let replacement_history = context_items;
@@ -3341,7 +3353,9 @@ impl Session {
                 message: String::new(),
                 replacement_history: Some(replacement_history),
                 window_number: Some(window_number),
-                window_id: Some(window_id.to_string()),
+                first_window_id: Some(window_ids.first_window_id.to_string()),
+                previous_window_id: window_ids.previous_window_id.map(|id| id.to_string()),
+                window_id: Some(window_ids.window_id.to_string()),
             }),
             RolloutItem::TurnContext(turn_context_item),
         ])
diff --git a/codex-rs/core/src/session/rollout_reconstruction.rs b/codex-rs/core/src/session/rollout_reconstruction.rs
index 22d0990e3..bf534c1e8 100644
--- a/codex-rs/core/src/session/rollout_reconstruction.rs
+++ b/codex-rs/core/src/session/rollout_reconstruction.rs
@@ -10,12 +10,16 @@ pub(super) struct RolloutReconstruction {
     pub(super) previous_turn_settings: Option<PreviousTurnSettings>,
     pub(super) reference_context_item: Option<TurnContextItem>,
     pub(super) window_number: u64,
+    pub(super) first_window_id: Option<Uuid>,
+    pub(super) previous_window_id: Option<Uuid>,
     pub(super) window_id: Option<Uuid>,
 }
 
 #[derive(Debug, Clone, Copy)]
 struct ReconstructedWindow {
     number: u64,
+    first_id: Option<Uuid>,
+    previous_id: Option<Uuid>,
     id: Option<Uuid>,
 }
 
@@ -133,6 +137,11 @@ impl Session {
                     {
                         active_segment.window = Some(ReconstructedWindow {
                             number: window_number,
+                            first_id: compacted.first_window_id.as_deref().and_then(parse_uuid_v7),
+                            previous_id: compacted
+                                .previous_window_id
+                                .as_deref()
+                                .and_then(parse_uuid_v7),
                             id: compacted.window_id.as_deref().and_then(parse_uuid_v7),
                         });
                     }
@@ -341,6 +350,8 @@ impl Session {
 
         let window = window.unwrap_or(ReconstructedWindow {
             number: fallback_window_number,
+            first_id: None,
+            previous_id: None,
             id: None,
         });
         RolloutReconstruction {
@@ -348,6 +359,8 @@ impl Session {
             previous_turn_settings,
             reference_context_item,
             window_number: window.number,
+            first_window_id: window.first_id,
+            previous_window_id: window.previous_id,
             window_id: window.id,
         }
     }
diff --git a/codex-rs/core/src/session/rollout_reconstruction_tests.rs b/codex-rs/core/src/session/rollout_reconstruction_tests.rs
index 43563d233..1823b28fd 100644
--- a/codex-rs/core/src/session/rollout_reconstruction_tests.rs
+++ b/codex-rs/core/src/session/rollout_reconstruction_tests.rs
@@ -829,6 +829,8 @@ async fn record_initial_history_resumed_rollback_drops_incomplete_user_turn_comp
             message: String::new(),
             replacement_history: Some(Vec::new()),
             window_number: None,
+            first_window_id: None,
+            previous_window_id: None,
             window_id: None,
         }),
         RolloutItem::EventMsg(EventMsg::ThreadRolledBack(
@@ -887,6 +889,8 @@ async fn record_initial_history_resumed_does_not_seed_reference_context_item_aft
             message: String::new(),
             replacement_history: Some(Vec::new()),
             window_number: None,
+            first_window_id: None,
+            previous_window_id: None,
             window_id: None,
         }),
     ];
@@ -914,6 +918,8 @@ async fn reconstruct_history_legacy_compaction_without_replacement_history_does_
             message: "legacy summary".to_string(),
             replacement_history: None,
             window_number: None,
+            first_window_id: None,
+            previous_window_id: None,
             window_id: None,
         }),
     ];
@@ -947,6 +953,8 @@ async fn reconstruct_history_legacy_compaction_without_replacement_history_clear
             message: "legacy summary".to_string(),
             replacement_history: None,
             window_number: None,
+            first_window_id: None,
+            previous_window_id: None,
             window_id: None,
         }),
         RolloutItem::EventMsg(EventMsg::TurnStarted(
@@ -1043,6 +1051,8 @@ async fn record_initial_history_resumed_turn_context_after_compaction_reestablis
             message: String::new(),
             replacement_history: Some(Vec::new()),
             window_number: None,
+            first_window_id: None,
+            previous_window_id: None,
             window_id: None,
         }),
         RolloutItem::TurnContext(previous_context_item),
@@ -1196,6 +1206,8 @@ async fn record_initial_history_resumed_aborted_turn_without_id_clears_active_tu
             message: String::new(),
             replacement_history: Some(Vec::new()),
             window_number: None,
+            first_window_id: None,
+            previous_window_id: None,
             window_id: None,
         }),
     ];
@@ -1433,6 +1445,8 @@ async fn record_initial_history_resumed_trailing_incomplete_turn_compaction_clea
             message: String::new(),
             replacement_history: Some(Vec::new()),
             window_number: None,
+            first_window_id: None,
+            previous_window_id: None,
             window_id: None,
         }),
     ];
@@ -1599,6 +1613,8 @@ async fn record_initial_history_resumed_replaced_incomplete_compacted_turn_clear
             message: String::new(),
             replacement_history: Some(Vec::new()),
             window_number: None,
+            first_window_id: None,
+            previous_window_id: None,
             window_id: None,
         }),
         // A newer TurnStarted replaces the incomplete compacted turn without a matching
diff --git a/codex-rs/core/src/session/tests.rs b/codex-rs/core/src/session/tests.rs
index bca6be6a7..6f84da3c7 100644
--- a/codex-rs/core/src/session/tests.rs
+++ b/codex-rs/core/src/session/tests.rs
@@ -1653,11 +1653,15 @@ async fn reconstruct_history_uses_replacement_history_verbatim() {
             metadata: None,
         },
     ];
+    let first_window_id = Uuid::now_v7();
+    let previous_window_id = Uuid::now_v7();
     let window_id = Uuid::now_v7();
     let rollout_items = vec![RolloutItem::Compacted(CompactedItem {
         message: String::new(),
         replacement_history: Some(replacement_history.clone()),
         window_number: Some(42),
+        first_window_id: Some(first_window_id.to_string()),
+        previous_window_id: Some(previous_window_id.to_string()),
         window_id: Some(window_id.to_string()),
     })];
 
@@ -1667,6 +1671,8 @@ async fn reconstruct_history_uses_replacement_history_verbatim() {
 
     assert_eq!(reconstructed.history, replacement_history);
     assert_eq!(42, reconstructed.window_number);
+    assert_eq!(Some(first_window_id), reconstructed.first_window_id);
+    assert_eq!(Some(previous_window_id), reconstructed.previous_window_id);
     assert_eq!(Some(window_id), reconstructed.window_id);
 }
 
@@ -3059,6 +3065,8 @@ async fn thread_rollback_restores_cleared_reference_context_item_after_compactio
         user_message("turn 1 user"),
         user_message("summary after compaction"),
     ];
+    let first_window_id = Uuid::now_v7();
+    let previous_window_id = Uuid::now_v7();
     let compacted_window_id = Uuid::now_v7();
 
     sess.persist_rollout_items(&[
@@ -3102,6 +3110,8 @@ async fn thread_rollback_restores_cleared_reference_context_item_after_compactio
             message: "summary after compaction".to_string(),
             replacement_history: Some(compacted_history.clone()),
             window_number: Some(7),
+            first_window_id: Some(first_window_id.to_string()),
+            previous_window_id: Some(previous_window_id.to_string()),
             window_id: Some(compacted_window_id.to_string()),
         }),
         RolloutItem::EventMsg(EventMsg::TurnComplete(TurnCompleteEvent {
@@ -3152,7 +3162,14 @@ async fn thread_rollback_restores_cleared_reference_context_item_after_compactio
     .await;
     {
         let mut state = sess.state.lock().await;
-        state.restore_auto_compact_window(/*window_number*/ 99, Uuid::now_v7());
+        state.restore_auto_compact_window(
+            /*window_number*/ 99,
+            AutoCompactWindowIds {
+                first_window_id: Uuid::now_v7(),
+                previous_window_id: Some(Uuid::now_v7()),
+                window_id: Uuid::now_v7(),
+            },
+        );
     }
 
     handlers::thread_rollback(&sess, "sub-1".to_string(), /*num_turns*/ 1).await;
@@ -3162,8 +3179,12 @@ async fn thread_rollback_restores_cleared_reference_context_item_after_compactio
     assert_eq!(sess.clone_history().await.raw_items(), compacted_history);
     assert!(sess.reference_context_item().await.is_none());
     assert_eq!(
-        sess.state.lock().await.auto_compact_window_id(),
-        compacted_window_id
+        sess.state.lock().await.auto_compact_window_ids(),
+        AutoCompactWindowIds {
+            first_window_id,
+            previous_window_id: Some(previous_window_id),
+            window_id: compacted_window_id,
+        }
     );
     assert!(sess.current_window_id().await.ends_with(":7"));
 }
@@ -9910,12 +9931,14 @@ async fn sample_rollout(
     let user_messages1 = collect_user_messages(&snapshot1);
     let rebuilt1 = compact::build_compacted_history(Vec::new(), &user_messages1, summary1);
     live_history.replace(rebuilt1);
-    let (window_number, window_id) = session.advance_auto_compact_window().await;
+    let (window_number, window_ids) = session.advance_auto_compact_window().await;
     rollout_items.push(RolloutItem::Compacted(CompactedItem {
         message: summary1.to_string(),
         replacement_history: None,
         window_number: Some(window_number),
-        window_id: Some(window_id),
+        first_window_id: Some(window_ids.first_window_id.to_string()),
+        previous_window_id: window_ids.previous_window_id.map(|id| id.to_string()),
+        window_id: Some(window_ids.window_id.to_string()),
     }));
 
     let user2 = ResponseItem::Message {
@@ -9955,12 +9978,14 @@ async fn sample_rollout(
     let user_messages2 = collect_user_messages(&snapshot2);
     let rebuilt2 = compact::build_compacted_history(Vec::new(), &user_messages2, summary2);
     live_history.replace(rebuilt2);
-    let (window_number, window_id) = session.advance_auto_compact_window().await;
+    let (window_number, window_ids) = session.advance_auto_compact_window().await;
     rollout_items.push(RolloutItem::Compacted(CompactedItem {
         message: summary2.to_string(),
         replacement_history: None,
         window_number: Some(window_number),
-        window_id: Some(window_id),
+        first_window_id: Some(window_ids.first_window_id.to_string()),
+        previous_window_id: window_ids.previous_window_id.map(|id| id.to_string()),
+        window_id: Some(window_ids.window_id.to_string()),
     }));
 
     let user3 = ResponseItem::Message {
diff --git a/codex-rs/core/src/state/auto_compact_window.rs b/codex-rs/core/src/state/auto_compact_window.rs
index e1fde2750..ff5d7a2a2 100644
--- a/codex-rs/core/src/state/auto_compact_window.rs
+++ b/codex-rs/core/src/state/auto_compact_window.rs
@@ -1,6 +1,13 @@
 use codex_protocol::protocol::TokenUsage;
 use uuid::Uuid;
 
+#[derive(Debug, Clone, Copy, PartialEq, Eq)]
+pub(crate) struct AutoCompactWindowIds {
+    pub(crate) first_window_id: Uuid,
+    pub(crate) previous_window_id: Option<Uuid>,
+    pub(crate) window_id: Uuid,
+}
+
 #[derive(Debug, Clone, Copy, PartialEq, Eq)]
 pub(crate) struct AutoCompactWindowSnapshot {
     pub(crate) prefill_input_tokens: Option<i64>,
@@ -15,7 +22,7 @@ enum AutoCompactWindowPrefill {
 #[derive(Debug, Clone, Copy, PartialEq, Eq)]
 pub(super) struct AutoCompactWindow {
     window_number: u64,
-    window_id: Uuid,
+    ids: AutoCompactWindowIds,
     new_context_window_requested: bool,
     /// Absolute input-token baseline for the current compaction window.
     ///
@@ -27,9 +34,14 @@ pub(super) struct AutoCompactWindow {
 
 impl AutoCompactWindow {
     pub(super) fn new() -> Self {
+        let window_id = Uuid::now_v7();
         Self {
             window_number: 0,
-            window_id: Uuid::now_v7(),
+            ids: AutoCompactWindowIds {
+                first_window_id: window_id,
+                previous_window_id: None,
+                window_id,
+            },
             new_context_window_requested: false,
             prefill_input_tokens: None,
         }
@@ -43,20 +55,21 @@ impl AutoCompactWindow {
         self.window_number
     }
 
-    pub(super) fn window_id(&self) -> Uuid {
-        self.window_id
+    pub(super) fn ids(&self) -> AutoCompactWindowIds {
+        self.ids
     }
 
-    pub(super) fn restore(&mut self, window_number: u64, window_id: Uuid) {
+    pub(super) fn restore(&mut self, window_number: u64, ids: AutoCompactWindowIds) {
         self.window_number = window_number;
-        self.window_id = window_id;
+        self.ids = ids;
     }
 
-    pub(super) fn advance(&mut self) -> (u64, Uuid) {
+    pub(super) fn advance(&mut self) -> (u64, AutoCompactWindowIds) {
         self.window_number = self.window_number.saturating_add(1);
-        self.window_id = Uuid::now_v7();
+        self.ids.previous_window_id = Some(self.ids.window_id);
+        self.ids.window_id = Uuid::now_v7();
         self.new_context_window_requested = false;
-        (self.window_number, self.window_id)
+        (self.window_number, self.ids)
     }
 
     pub(super) fn request_new_context_window(&mut self) {
@@ -118,21 +131,41 @@ mod tests {
         let mut window = AutoCompactWindow::new();
 
         assert_eq!(window.window_number(), 0);
-        assert_eq!(window.window_id().get_version_num(), 7);
+        let initial_window_id = window.ids().window_id;
+        assert_eq!(initial_window_id.get_version_num(), 7);
+        assert_eq!(
+            window.ids(),
+            AutoCompactWindowIds {
+                first_window_id: initial_window_id,
+                previous_window_id: None,
+                window_id: initial_window_id,
+            }
+        );
+        let first_window_id = initial_window_id;
         let restored_window_id = Uuid::now_v7();
-        window.restore(/*window_number*/ 3, restored_window_id);
+        let restored_previous_window_id = Uuid::now_v7();
+        window.restore(
+            /*window_number*/ 3,
+            AutoCompactWindowIds {
+                first_window_id,
+                previous_window_id: Some(restored_previous_window_id),
+                window_id: restored_window_id,
+            },
+        );
         assert_eq!(window.window_number(), 3);
-        assert_eq!(window.window_id(), restored_window_id);
+        assert_eq!(window.ids().window_id, restored_window_id);
         window.request_new_context_window();
         assert!(window.take_new_context_window_request());
         assert!(!window.take_new_context_window_request());
         window.request_new_context_window();
-        let (window_number, window_id) = window.advance();
+        let (window_number, ids) = window.advance();
         assert_eq!(window_number, 4);
         assert_eq!(window.window_number(), 4);
-        assert_eq!(window.window_id(), window_id);
-        assert_eq!(window_id.get_version_num(), 7);
-        assert_ne!(window_id, restored_window_id);
+        assert_eq!(window.ids(), ids);
+        assert_eq!(ids.first_window_id, first_window_id);
+        assert_eq!(ids.previous_window_id, Some(restored_window_id));
+        assert_eq!(ids.window_id.get_version_num(), 7);
+        assert_ne!(ids.window_id, restored_window_id);
         assert!(!window.take_new_context_window_request());
 
         assert_eq!(
diff --git a/codex-rs/core/src/state/mod.rs b/codex-rs/core/src/state/mod.rs
index c693221be..20ff78b54 100644
--- a/codex-rs/core/src/state/mod.rs
+++ b/codex-rs/core/src/state/mod.rs
@@ -5,6 +5,7 @@ mod session;
 mod turn;
 
 pub(crate) use additional_context::AdditionalContextStore;
+pub(crate) use auto_compact_window::AutoCompactWindowIds;
 pub(crate) use auto_compact_window::AutoCompactWindowSnapshot;
 pub(crate) use service::SessionServices;
 pub(crate) use session::SessionState;
diff --git a/codex-rs/core/src/state/session.rs b/codex-rs/core/src/state/session.rs
index 83cef227f..824f5f636 100644
--- a/codex-rs/core/src/state/session.rs
+++ b/codex-rs/core/src/state/session.rs
@@ -6,10 +6,10 @@ use codex_sandboxing::policy_transforms::merge_permission_profiles;
 use std::collections::HashMap;
 use std::collections::HashSet;
 use std::collections::VecDeque;
-use uuid::Uuid;
 
 use super::AdditionalContextStore;
 use super::auto_compact_window::AutoCompactWindow;
+use super::auto_compact_window::AutoCompactWindowIds;
 use super::auto_compact_window::AutoCompactWindowSnapshot;
 use crate::context_manager::ContextManager;
 use crate::session::PreviousTurnSettings;
@@ -152,15 +152,19 @@ impl SessionState {
         self.auto_compact_window.window_number()
     }
 
-    pub(crate) fn auto_compact_window_id(&self) -> Uuid {
-        self.auto_compact_window.window_id()
+    pub(crate) fn auto_compact_window_ids(&self) -> AutoCompactWindowIds {
+        self.auto_compact_window.ids()
     }
 
-    pub(crate) fn restore_auto_compact_window(&mut self, window_number: u64, window_id: Uuid) {
-        self.auto_compact_window.restore(window_number, window_id);
+    pub(crate) fn restore_auto_compact_window(
+        &mut self,
+        window_number: u64,
+        ids: AutoCompactWindowIds,
+    ) {
+        self.auto_compact_window.restore(window_number, ids);
     }
 
-    pub(crate) fn advance_auto_compact_window(&mut self) -> (u64, Uuid) {
+    pub(crate) fn advance_auto_compact_window(&mut self) -> (u64, AutoCompactWindowIds) {
         self.auto_compact_window.advance()
     }
 
@@ -168,7 +172,9 @@ impl SessionState {
         self.auto_compact_window.request_new_context_window();
     }
 
-    pub(crate) fn start_new_context_window_if_requested(&mut self) -> Option<(u64, Uuid)> {
+    pub(crate) fn start_new_context_window_if_requested(
+        &mut self,
+    ) -> Option<(u64, AutoCompactWindowIds)> {
         if !self.auto_compact_window.take_new_context_window_request() {
             return None;
         }
diff --git a/codex-rs/core/tests/suite/snapshots/all__suite__token_budget__token_budget_new_context_window_tool_full_context.snap b/codex-rs/core/tests/suite/snapshots/all__suite__token_budget__token_budget_new_context_window_tool_full_context.snap
index 12bab10ec..3b933b4ed 100644
--- a/codex-rs/core/tests/suite/snapshots/all__suite__token_budget__token_budget_new_context_window_tool_full_context.snap
+++ b/codex-rs/core/tests/suite/snapshots/all__suite__token_budget__token_budget_new_context_window_tool_full_context.snap
@@ -1,5 +1,6 @@
 ---
 source: core/tests/suite/token_budget.rs
+assertion_line: 539
 expression: snapshot
 ---
 Scenario: New context window tool installs fresh full context before the next follow-up request.
@@ -8,7 +9,7 @@ Scenario: New context window tool installs fresh full context before the next fo
 00:message/developer[3]:
     [01] <PERMISSIONS_INSTRUCTIONS>
     [02] <SKILLS_INSTRUCTIONS>
-    [03] <token_budget>\nThread id <THREAD_ID>.\nCurrent context window id <UUID>.\nYou have 121600 tokens left in this context window.\n</token_budget>
+    [03] <token_budget>\nThread id <THREAD_ID>.\nFirst context window id <FIRST_WINDOW_ID>.\nPrevious context window id <FIRST_WINDOW_ID>.\nCurrent context window id <WINDOW_ID>.\nYou have 121600 tokens left in this context window.\n</token_budget>
 01:message/user:<ENVIRONMENT_CONTEXT:cwd=<CWD>>
 02:function_call/update_plan
 03:function_call_output:Plan updated
diff --git a/codex-rs/core/tests/suite/token_budget.rs b/codex-rs/core/tests/suite/token_budget.rs
index db70d3f33..7c4dfa1be 100644
--- a/codex-rs/core/tests/suite/token_budget.rs
+++ b/codex-rs/core/tests/suite/token_budget.rs
@@ -35,6 +35,35 @@ fn token_budget_texts(request: &ResponsesRequest) -> Vec<String> {
         .collect()
 }
 
+fn token_budget_window_ids(
+    text: &str,
+    thread_id: codex_protocol::ThreadId,
+    tokens_left: i64,
+) -> (String, Option<String>, String) {
+    let captures = assert_regex_match(
+        &format!(
+            r"^<token_budget>\nThread id {thread_id}\.\nFirst context window id ([0-9a-f-]{{36}})\.\nPrevious context window id (none|[0-9a-f-]{{36}})\.\nCurrent context window id ([0-9a-f-]{{36}})\.\nYou have {tokens_left} tokens left in this context window\.\n</token_budget>$"
+        ),
+        text,
+    );
+    let first_window_id = captures
+        .get(1)
+        .expect("first window id capture")
+        .as_str()
+        .to_string();
+    let previous_window_id = captures
+        .get(2)
+        .expect("previous window id capture")
+        .as_str();
+    let previous_window_id = (previous_window_id != "none").then(|| previous_window_id.to_string());
+    let window_id = captures
+        .get(3)
+        .expect("window id capture")
+        .as_str()
+        .to_string();
+    (first_window_id, previous_window_id, window_id)
+}
+
 fn tool_names(request: &ResponsesRequest) -> Vec<String> {
     request
         .body_json()
@@ -83,12 +112,13 @@ async fn token_budget_context_is_only_emitted_with_full_context() -> Result<()>
     let thread_id = test.session_configured.thread_id;
     let initial_token_budget = token_budget_texts(&requests[0]);
     assert_eq!(initial_token_budget.len(), 1);
-    assert_regex_match(
-        &format!(
-            r"^<token_budget>\nThread id {thread_id}\.\nCurrent context window id [0-9a-f-]{{36}}\.\nYou have {EFFECTIVE_CONTEXT_WINDOW} tokens left in this context window\.\n</token_budget>$"
-        ),
+    let (first_window_id, previous_window_id, window_id) = token_budget_window_ids(
         &initial_token_budget[0],
+        thread_id,
+        EFFECTIVE_CONTEXT_WINDOW,
     );
+    assert_eq!(previous_window_id, None);
+    assert_eq!(first_window_id, window_id);
     assert_eq!(
         token_budget_texts(&requests[1]),
         initial_token_budget,
@@ -147,12 +177,7 @@ async fn token_budget_remaining_context_emits_on_first_threshold_crossing() -> R
     let thread_id = test.session_configured.thread_id;
     let full_context = token_budget_texts(&requests[0]);
     assert_eq!(full_context.len(), 1);
-    assert_regex_match(
-        &format!(
-            r"^<token_budget>\nThread id {thread_id}\.\nCurrent context window id [0-9a-f-]{{36}}\.\nYou have 9500 tokens left in this context window\.\n</token_budget>$"
-        ),
-        &full_context[0],
-    );
+    token_budget_window_ids(&full_context[0], thread_id, /*tokens_left*/ 9_500);
     let full_context = full_context[0].clone();
     let threshold_25 =
         "<token_budget>\nYou have 7000 tokens left in this context window.\n</token_budget>"
@@ -245,12 +270,7 @@ async fn get_context_remaining_returns_token_budget_remaining_fragment() -> Resu
             .to_string();
     let token_budgets = token_budget_texts(&requests[1]);
     assert_eq!(token_budgets.len(), 2);
-    assert_regex_match(
-        &format!(
-            r"^<token_budget>\nThread id {thread_id}\.\nCurrent context window id [0-9a-f-]{{36}}\.\nYou have 9500 tokens left in this context window\.\n</token_budget>$"
-        ),
-        &token_budgets[0],
-    );
+    token_budget_window_ids(&token_budgets[0], thread_id, /*tokens_left*/ 9_500);
     assert_eq!(token_budgets[1], remaining_context);
     assert_eq!(
         requests[2].function_call_output_content_and_success(call_id),
@@ -373,28 +393,30 @@ async fn token_budget_context_uses_new_window_after_compaction() -> Result<()> {
     let thread_id = test.session_configured.thread_id;
     let initial_token_budget = token_budget_texts(&requests[0]);
     assert_eq!(initial_token_budget.len(), 1);
-    let initial_window_id = assert_regex_match(
-        &format!(
-            r"^<token_budget>\nThread id {thread_id}\.\nCurrent context window id ([0-9a-f-]{{36}})\.\nYou have {EFFECTIVE_CONTEXT_WINDOW} tokens left in this context window\.\n</token_budget>$"
-        ),
-        &initial_token_budget[0],
-    )
-    .get(1)
-    .expect("window id capture")
-    .as_str()
-    .to_string();
+    let (initial_first_window_id, initial_previous_window_id, initial_window_id) =
+        token_budget_window_ids(
+            &initial_token_budget[0],
+            thread_id,
+            EFFECTIVE_CONTEXT_WINDOW,
+        );
     let post_compaction_token_budget = token_budget_texts(&requests[2]);
     assert_eq!(post_compaction_token_budget.len(), 1);
-    let post_compaction_window_id = assert_regex_match(
-        &format!(
-            r"^<token_budget>\nThread id {thread_id}\.\nCurrent context window id ([0-9a-f-]{{36}})\.\nYou have {EFFECTIVE_CONTEXT_WINDOW} tokens left in this context window\.\n</token_budget>$"
-        ),
+    let (
+        post_compaction_first_window_id,
+        post_compaction_previous_window_id,
+        post_compaction_window_id,
+    ) = token_budget_window_ids(
         &post_compaction_token_budget[0],
-    )
-    .get(1)
-    .expect("window id capture")
-    .as_str()
-    .to_string();
+        thread_id,
+        EFFECTIVE_CONTEXT_WINDOW,
+    );
+    assert_eq!(initial_previous_window_id, None);
+    assert_eq!(initial_first_window_id, initial_window_id);
+    assert_eq!(post_compaction_first_window_id, initial_first_window_id);
+    assert_eq!(
+        post_compaction_previous_window_id.as_deref(),
+        Some(initial_window_id.as_str())
+    );
     assert_ne!(post_compaction_window_id, initial_window_id);
 
     Ok(())
@@ -458,29 +480,24 @@ async fn new_context_tool_starts_new_window_before_follow_up() -> Result<()> {
     let thread_id = test.session_configured.thread_id;
     let initial_token_budget = token_budget_texts(&requests[0]);
     assert_eq!(initial_token_budget.len(), 1);
-    let initial_window_id = assert_regex_match(
-        &format!(
-            r"^<token_budget>\nThread id {thread_id}\.\nCurrent context window id ([0-9a-f-]{{36}})\.\nYou have {EFFECTIVE_CONTEXT_WINDOW} tokens left in this context window\.\n</token_budget>$"
-        ),
+    let (initial_first_window_id, _, initial_window_id) = token_budget_window_ids(
         &initial_token_budget[0],
-    )
-    .get(1)
-    .expect("window id capture")
-    .as_str()
-    .to_string();
+        thread_id,
+        EFFECTIVE_CONTEXT_WINDOW,
+    );
     let new_window_token_budget = token_budget_texts(&requests[2]);
     assert_eq!(new_window_token_budget.len(), 1);
-    let window_id = assert_regex_match(
-        &format!(
-            r"^<token_budget>\nThread id {thread_id}\.\nCurrent context window id ([0-9a-f-]{{36}})\.\nYou have {EFFECTIVE_CONTEXT_WINDOW} tokens left in this context window\.\n</token_budget>$"
-        ),
+    let (new_first_window_id, new_previous_window_id, new_window_id) = token_budget_window_ids(
         &new_window_token_budget[0],
-    )
-    .get(1)
-    .expect("window id capture")
-    .as_str()
-    .to_string();
-    assert_ne!(window_id, initial_window_id);
+        thread_id,
+        EFFECTIVE_CONTEXT_WINDOW,
+    );
+    assert_eq!(new_first_window_id, initial_first_window_id);
+    assert_eq!(
+        new_previous_window_id.as_deref(),
+        Some(initial_window_id.as_str())
+    );
+    assert_ne!(new_window_id, initial_window_id);
     assert!(
         !requests[2].body_contains_text("request new context window"),
         "new_context should drop the prior window history before continuing the turn"
@@ -496,7 +513,8 @@ async fn new_context_tool_starts_new_window_before_follow_up() -> Result<()> {
     );
     let snapshot = snapshot
         .replace(&thread_id.to_string(), "<THREAD_ID>")
-        .replace(&window_id, "<UUID>");
+        .replace(&new_first_window_id, "<FIRST_WINDOW_ID>")
+        .replace(&new_window_id, "<WINDOW_ID>");
     insta::assert_snapshot!(
         "token_budget_new_context_window_tool_full_context",
         snapshot
diff --git a/codex-rs/protocol/src/compacted_item.rs b/codex-rs/protocol/src/compacted_item.rs
index 341537389..0f437e0bb 100644
--- a/codex-rs/protocol/src/compacted_item.rs
+++ b/codex-rs/protocol/src/compacted_item.rs
@@ -23,6 +23,8 @@ impl<'de> Deserialize<'de> for CompactedItem {
             message: serialized.message,
             replacement_history: serialized.replacement_history,
             window_number,
+            first_window_id: serialized.first_window_id,
+            previous_window_id: serialized.previous_window_id,
             window_id,
         })
     }
@@ -36,6 +38,10 @@ struct SerializedCompactedItem {
     #[serde(default)]
     window_number: Option<u64>,
     #[serde(default)]
+    first_window_id: Option<String>,
+    #[serde(default)]
+    previous_window_id: Option<String>,
+    #[serde(default)]
     window_id: Option<SerializedWindowId>,
 }
 
@@ -59,6 +65,8 @@ mod tests {
             message: "summary".to_string(),
             replacement_history: None,
             window_number: Some(3),
+            first_window_id: Some("019b3f6e-0000-7000-8000-000000000001".to_string()),
+            previous_window_id: Some("019b3f6e-0000-7000-8000-000000000002".to_string()),
             window_id: Some("019b3f6e-7a10-7cc3-8b6e-1d09e2f7a001".to_string()),
         };
 
@@ -67,6 +75,8 @@ mod tests {
             json!({
                 "message": "summary",
                 "window_number": 3,
+                "first_window_id": "019b3f6e-0000-7000-8000-000000000001",
+                "previous_window_id": "019b3f6e-0000-7000-8000-000000000002",
                 "window_id": "019b3f6e-7a10-7cc3-8b6e-1d09e2f7a001",
             })
         );
@@ -86,6 +96,8 @@ mod tests {
                 message: "summary".to_string(),
                 replacement_history: None,
                 window_number: Some(3),
+                first_window_id: None,
+                previous_window_id: None,
                 window_id: None,
             }
         );
diff --git a/codex-rs/protocol/src/protocol.rs b/codex-rs/protocol/src/protocol.rs
index 1fe732c4f..081649b7a 100644
--- a/codex-rs/protocol/src/protocol.rs
+++ b/codex-rs/protocol/src/protocol.rs
@@ -2996,6 +2996,12 @@ pub struct CompactedItem {
     /// Monotonic position of this context window within the thread.
     #[serde(default, skip_serializing_if = "Option::is_none")]
     pub window_number: Option<u64>,
+    /// UUIDv7 identity of the first context window in this thread's window chain.
+    #[serde(default, skip_serializing_if = "Option::is_none")]
+    pub first_window_id: Option<String>,
+    /// UUIDv7 identity of the context window immediately before this one.
+    #[serde(default, skip_serializing_if = "Option::is_none")]
+    pub previous_window_id: Option<String>,
     /// UUIDv7 identity of this context window.
     #[serde(default, skip_serializing_if = "Option::is_none")]
     pub window_id: Option<String>,
diff --git a/codex-rs/rollout/src/metadata_tests.rs b/codex-rs/rollout/src/metadata_tests.rs
index 446743955..e6771e37c 100644
--- a/codex-rs/rollout/src/metadata_tests.rs
+++ b/codex-rs/rollout/src/metadata_tests.rs
@@ -155,6 +155,8 @@ fn builder_from_items_falls_back_to_filename() {
         message: "noop".to_string(),
         replacement_history: None,
         window_number: None,
+        first_window_id: None,
+        previous_window_id: None,
         window_id: None,
     })];
 
diff --git a/codex-rs/thread-store/src/thread_metadata_sync.rs b/codex-rs/thread-store/src/thread_metadata_sync.rs
index b45bb2d63..0336006fb 100644
--- a/codex-rs/thread-store/src/thread_metadata_sync.rs
+++ b/codex-rs/thread-store/src/thread_metadata_sync.rs
@@ -484,6 +484,8 @@ mod tests {
             message: "compacted".to_string(),
             replacement_history: None,
             window_number: None,
+            first_window_id: None,
+            previous_window_id: None,
             window_id: None,
         });