diff --git a/codex-rs/app-server/src/external_agent_migration/session_importer.rs b/codex-rs/app-server/src/external_agent_migration/session_importer.rs
index 4a05a1d078..dabce8a39f 100644
--- a/codex-rs/app-server/src/external_agent_migration/session_importer.rs
+++ b/codex-rs/app-server/src/external_agent_migration/session_importer.rs
@@ -490,7 +490,7 @@ impl ExternalAgentSessionImporter {
             history_mode: ThreadHistoryMode::Legacy,
             history_base: None,
             subagent_history_start_ordinal: None,
-            initial_window_id: uuid::Uuid::now_v7().to_string(),
+            initial_window_id: codex_protocol::ContextWindowId::new_uuid_v7().to_string(),
             metadata: ThreadPersistenceMetadata {
                 cwd: Some(cwd.clone()),
                 model_provider: model_provider.clone(),
diff --git a/codex-rs/app-server/tests/suite/conversation_summary.rs b/codex-rs/app-server/tests/suite/conversation_summary.rs
index aaeed4ec19..cf5bd8ea3a 100644
--- a/codex-rs/app-server/tests/suite/conversation_summary.rs
+++ b/codex-rs/app-server/tests/suite/conversation_summary.rs
@@ -140,7 +140,7 @@ async fn get_conversation_summary_by_thread_id_reads_pathless_store_thread() ->
             history_mode: Default::default(),
             history_base: None,
             subagent_history_start_ordinal: None,
-            initial_window_id: Uuid::now_v7().to_string(),
+            initial_window_id: codex_protocol::ContextWindowId::new_uuid_v7().to_string(),
             runtime_workspace_roots: None,
             metadata: ThreadPersistenceMetadata {
                 cwd: None,
diff --git a/codex-rs/app-server/tests/suite/v2/remote_thread_store.rs b/codex-rs/app-server/tests/suite/v2/remote_thread_store.rs
index 0850c13700..b59ac6e0c0 100644
--- a/codex-rs/app-server/tests/suite/v2/remote_thread_store.rs
+++ b/codex-rs/app-server/tests/suite/v2/remote_thread_store.rs
@@ -13,6 +13,7 @@
 //! is a stop-gap that prevents additional local persistence writes from slipping
 //! in unnoticed.
 
+use codex_protocol::ContextWindowId;
 use std::collections::BTreeSet;
 use std::path::Path;
 use std::sync::Arc;
@@ -300,7 +301,7 @@ async fn thread_list_repeated_cursor_returns_internal_error() -> Result<()> {
             history_mode: Default::default(),
             history_base: None,
             subagent_history_start_ordinal: None,
-            initial_window_id: Uuid::now_v7().to_string(),
+            initial_window_id: ContextWindowId::new_uuid_v7().to_string(),
             runtime_workspace_roots: None,
             metadata: ThreadPersistenceMetadata {
                 cwd: Some(codex_home.path().to_path_buf()),
@@ -548,7 +549,7 @@ async fn thread_delete_with_non_local_thread_store_does_not_create_local_persist
             history_mode: Default::default(),
             history_base: None,
             subagent_history_start_ordinal: None,
-            initial_window_id: Uuid::now_v7().to_string(),
+            initial_window_id: ContextWindowId::new_uuid_v7().to_string(),
             runtime_workspace_roots: None,
             metadata: ThreadPersistenceMetadata {
                 cwd: Some(codex_home.path().to_path_buf()),
diff --git a/codex-rs/app-server/tests/suite/v2/thread_read.rs b/codex-rs/app-server/tests/suite/v2/thread_read.rs
index 4daf547939..ff22262fe8 100644
--- a/codex-rs/app-server/tests/suite/v2/thread_read.rs
+++ b/codex-rs/app-server/tests/suite/v2/thread_read.rs
@@ -63,6 +63,7 @@ use codex_core::ARCHIVED_SESSIONS_SUBDIR;
 use codex_core::config::ConfigBuilder;
 use codex_exec_server::EnvironmentManager;
 use codex_feedback::CodexFeedback;
+use codex_protocol::ContextWindowId;
 use codex_protocol::items::AgentMessageContent;
 use codex_protocol::items::AgentMessageItem;
 use codex_protocol::items::TurnItem as CoreTurnItem;
@@ -653,7 +654,7 @@ async fn thread_search_occurrences_reads_paginated_projection() -> Result<()> {
             history_mode: codex_protocol::protocol::ThreadHistoryMode::Paginated,
             history_base: None,
             subagent_history_start_ordinal: None,
-            initial_window_id: Uuid::now_v7().to_string(),
+            initial_window_id: ContextWindowId::new_uuid_v7().to_string(),
             runtime_workspace_roots: None,
             metadata: ThreadPersistenceMetadata {
                 cwd: Some(codex_home.path().to_path_buf()),
@@ -1864,7 +1865,7 @@ async fn paginated_history_lists_and_legacy_reads_use_projected_turns_and_items(
             history_mode: codex_protocol::protocol::ThreadHistoryMode::Paginated,
             history_base: None,
             subagent_history_start_ordinal: None,
-            initial_window_id: Uuid::now_v7().to_string(),
+            initial_window_id: ContextWindowId::new_uuid_v7().to_string(),
             runtime_workspace_roots: None,
             metadata: ThreadPersistenceMetadata {
                 cwd: Some(codex_home.path().to_path_buf()),
@@ -2833,7 +2834,7 @@ async fn seed_pathless_store_thread(
             history_mode: Default::default(),
             history_base: None,
             subagent_history_start_ordinal: None,
-            initial_window_id: Uuid::now_v7().to_string(),
+            initial_window_id: ContextWindowId::new_uuid_v7().to_string(),
             runtime_workspace_roots: None,
             metadata: ThreadPersistenceMetadata {
                 cwd: None,
diff --git a/codex-rs/app-server/tests/suite/v2/thread_timeline.rs b/codex-rs/app-server/tests/suite/v2/thread_timeline.rs
index f336be27d1..68ebe2be11 100644
--- a/codex-rs/app-server/tests/suite/v2/thread_timeline.rs
+++ b/codex-rs/app-server/tests/suite/v2/thread_timeline.rs
@@ -37,7 +37,6 @@ use codex_thread_store::ThreadStore;
 use codex_utils_absolute_path::test_support::PathExt;
 use pretty_assertions::assert_eq;
 use tempfile::TempDir;
-use uuid::Uuid;
 
 #[tokio::test]
 async fn timeline_pages_mix_items_and_resolve_the_opening_realtime_session() -> Result<()> {
@@ -77,7 +76,7 @@ async fn timeline_pages_mix_items_and_resolve_the_opening_realtime_session() ->
             history_mode: ThreadHistoryMode::Paginated,
             history_base: None,
             subagent_history_start_ordinal: None,
-            initial_window_id: Uuid::now_v7().to_string(),
+            initial_window_id: codex_protocol::ContextWindowId::new_uuid_v7().to_string(),
             runtime_workspace_roots: None,
             metadata: ThreadPersistenceMetadata {
                 cwd: Some(codex_home.path().to_path_buf()),
diff --git a/codex-rs/app-server/tests/suite/v2/thread_unarchive.rs b/codex-rs/app-server/tests/suite/v2/thread_unarchive.rs
index 2a18e911fd..fff83e6fe5 100644
--- a/codex-rs/app-server/tests/suite/v2/thread_unarchive.rs
+++ b/codex-rs/app-server/tests/suite/v2/thread_unarchive.rs
@@ -265,7 +265,7 @@ async fn thread_unarchive_preserves_pathless_store_metadata() -> Result<()> {
             history_mode: Default::default(),
             history_base: None,
             subagent_history_start_ordinal: None,
-            initial_window_id: Uuid::now_v7().to_string(),
+            initial_window_id: codex_protocol::ContextWindowId::new_uuid_v7().to_string(),
             runtime_workspace_roots: None,
             metadata: ThreadPersistenceMetadata {
                 cwd: None,
diff --git a/codex-rs/core/src/compact_remote_v2_attempt.rs b/codex-rs/core/src/compact_remote_v2_attempt.rs
index 72f00f2e30..e10fb74092 100644
--- a/codex-rs/core/src/compact_remote_v2_attempt.rs
+++ b/codex-rs/core/src/compact_remote_v2_attempt.rs
@@ -64,7 +64,7 @@ pub(crate) struct BackgroundCompactionCandidate {
 pub(crate) struct BackgroundCompactionInput {
     prefix: CompactionPrefix,
     turn_state: Option<String>,
-    window: (String, u64, uuid::Uuid),
+    window: (String, u64, codex_protocol::ContextWindowId),
     base_instructions: BaseInstructions,
     input: Vec<ResponseItem>,
     metadata: Vec<Option<CodexHarnessMetadata>>,
@@ -283,7 +283,7 @@ pub(crate) async fn capture_background_input(
     base_instructions: BaseInstructions,
     turn_state: Option<String>,
     auth_owner_generation: Option<u64>,
-    window: (String, u64, uuid::Uuid),
+    window: (String, u64, codex_protocol::ContextWindowId),
 ) -> BackgroundCompactionInput {
     let base_instructions = if step_context.settings.model_info.use_responses_lite
         && snapshot
diff --git a/codex-rs/core/src/context/token_budget_context.rs b/codex-rs/core/src/context/token_budget_context.rs
index 454d40a606..7aa415526d 100644
--- a/codex-rs/core/src/context/token_budget_context.rs
+++ b/codex-rs/core/src/context/token_budget_context.rs
@@ -6,6 +6,7 @@ use crate::context::world_state::WorldStateUpdate;
 use codex_context_fragments::AnnotatedContent;
 use codex_context_fragments::message_from_parts;
 use codex_protocol::AgentPath;
+use codex_protocol::ContextWindowId;
 use codex_protocol::models::ContentItem;
 use codex_protocol::models::ContentItemKind;
 use codex_protocol::models::ResponseItem;
@@ -14,22 +15,21 @@ use codex_protocol::protocol::CONTEXT_WINDOW_CLOSE_TAG;
 use codex_protocol::protocol::CONTEXT_WINDOW_GUIDANCE_CLOSE_TAG;
 use codex_protocol::protocol::CONTEXT_WINDOW_GUIDANCE_OPEN_TAG;
 use codex_protocol::protocol::CONTEXT_WINDOW_OPEN_TAG;
-use uuid::Uuid;
 
 #[derive(Debug, Clone, PartialEq, Eq)]
 pub(crate) struct TokenBudgetContext {
     agent_path: AgentPath,
-    first_window_id: Uuid,
-    previous_window_id: Option<Uuid>,
-    window_id: Uuid,
+    first_window_id: ContextWindowId,
+    previous_window_id: Option<ContextWindowId>,
+    window_id: ContextWindowId,
 }
 
 impl TokenBudgetContext {
     pub(crate) fn new(
         agent_path: AgentPath,
-        first_window_id: Uuid,
-        previous_window_id: Option<Uuid>,
-        window_id: Uuid,
+        first_window_id: ContextWindowId,
+        previous_window_id: Option<ContextWindowId>,
+        window_id: ContextWindowId,
     ) -> Self {
         Self {
             agent_path,
@@ -73,14 +73,14 @@ impl ContextualUserFragment for TokenBudgetContext {
     }
 
     fn body(&self) -> ContentItem {
-        let first_window_id = self.first_window_id;
-        let window_id = self.window_id;
+        let first_window_id = &self.first_window_id;
+        let window_id = &self.window_id;
         let mut lines = vec![
             format!("Agent name: {}", self.agent_path),
             format!("First context window id: {first_window_id}"),
             format!("Current context window id: {window_id}"),
         ];
-        if let Some(previous_window_id) = self.previous_window_id {
+        if let Some(previous_window_id) = &self.previous_window_id {
             lines.push(format!("Previous context window id: {previous_window_id}"));
         }
         input_text(format!("\n{}\n", lines.join("\n")))
diff --git a/codex-rs/core/src/responses_metadata.rs b/codex-rs/core/src/responses_metadata.rs
index 27bd6e4e0c..8f886779c0 100644
--- a/codex-rs/core/src/responses_metadata.rs
+++ b/codex-rs/core/src/responses_metadata.rs
@@ -8,6 +8,7 @@ use codex_analytics::CompactionReason;
 use codex_analytics::CompactionStrategy;
 use codex_analytics::CompactionTrigger;
 use codex_git_utils::SanitizedGitUrl;
+use codex_protocol::ContextWindowId;
 use codex_protocol::ThreadId;
 use codex_protocol::mcp::McpAttribution;
 use codex_protocol::protocol::SessionSource;
@@ -19,7 +20,6 @@ use http::HeaderMap as ApiHeaderMap;
 use http::HeaderValue;
 use serde::Serialize;
 use serde_json::Value;
-use uuid::Uuid;
 
 use crate::client::X_CODEX_INSTALLATION_ID_HEADER;
 use crate::client::X_CODEX_PARENT_THREAD_ID_HEADER;
@@ -248,7 +248,7 @@ pub struct CodexResponsesMetadata {
     pub(crate) routing_hint: Option<HeaderValue>,
     pub(crate) window_id: String,
     pub(crate) window_number: Option<u64>,
-    pub(crate) context_window_id: Option<Uuid>,
+    pub(crate) context_window_id: Option<ContextWindowId>,
     pub(crate) history_initialization: Option<HistoryInitialization>,
     pub(crate) request_kind: Option<CodexResponsesRequestKind>,
     pub(crate) forked_from_thread_id: Option<ThreadId>,
@@ -439,7 +439,7 @@ impl CodexResponsesMetadata {
             window_id: has_request_identity.then_some(self.window_id.as_str()),
             window_number: has_request_identity.then_some(self.window_number).flatten(),
             context_window_id: has_request_identity
-                .then_some(self.context_window_id)
+                .then_some(self.context_window_id.as_ref())
                 .flatten(),
             request_kind: request_kind_value,
             history_initialization: self.history_initialization,
@@ -572,7 +572,7 @@ struct CodexTurnMetadataPayload<'a> {
     #[serde(default, skip_serializing_if = "Option::is_none")]
     window_number: Option<u64>,
     #[serde(default, skip_serializing_if = "Option::is_none")]
-    context_window_id: Option<Uuid>,
+    context_window_id: Option<&'a ContextWindowId>,
     #[serde(default, skip_serializing_if = "Option::is_none")]
     request_kind: Option<&'static str>,
     #[serde(default, skip_serializing_if = "Option::is_none")]
diff --git a/codex-rs/core/src/session/compaction_replay_tests.rs b/codex-rs/core/src/session/compaction_replay_tests.rs
new file mode 100644
index 0000000000..8a0e6c5902
--- /dev/null
+++ b/codex-rs/core/src/session/compaction_replay_tests.rs
@@ -0,0 +1,90 @@
+//! Checks reconstructed history against live compaction and persisted replacement items.
+#![cfg(test)]
+
+use super::*;
+use pretty_assertions::assert_eq;
+
+#[tokio::test]
+async fn reconstruct_history_matches_live_compactions() {
+    let (session, turn_context) = make_session_and_context().await;
+    let (rollout_items, expected) = sample_rollout(&session, &turn_context).await;
+
+    let reconstruction_turn = session.new_default_turn().await;
+    let reconstructed = session
+        .reconstruct_history_from_rollout(reconstruction_turn.as_ref(), &rollout_items)
+        .await;
+
+    assert_eq!(expected, raw_envelopes(&reconstructed.history));
+    assert_eq!(2, reconstructed.window_number);
+    assert_eq!(
+        reconstructed
+            .window_id
+            .map(|window_id| Uuid::parse_str(&window_id.to_string())
+                .unwrap()
+                .get_version_num()),
+        Some(7)
+    );
+}
+
+#[tokio::test]
+async fn reconstruct_history_uses_replacement_history_verbatim() {
+    let (session, turn_context) = make_session_and_context().await;
+    let summary_item = ResponseItem::Message {
+        status: None,
+        encrypted_content: None,
+        id: None,
+        role: "user".to_string(),
+        content: vec![ContentItem::InputText {
+            text: "summary".to_string(),
+        }],
+        phase: None,
+        internal_chat_message_metadata_passthrough: Some(InternalChatMessageMetadataPassthrough {
+            turn_id: Some("compact-turn".to_string()),
+            ..Default::default()
+        }),
+    };
+    let replacement_history = vec![
+        ResponseItemEnvelope {
+            item: summary_item.clone(),
+            metadata: Some(CodexHarnessMetadata::default()),
+        },
+        ResponseItemEnvelope::new(ResponseItem::Message {
+            status: None,
+            encrypted_content: None,
+            id: None,
+            role: "developer".to_string(),
+            content: vec![ContentItem::InputText {
+                text: "stale developer instructions".to_string(),
+            }],
+            phase: None,
+            internal_chat_message_metadata_passthrough: None,
+        }),
+    ];
+    let first_window_id = ContextWindowId::new_uuid_v7();
+    let previous_window_id = ContextWindowId::new_uuid_v7();
+    let window_id = ContextWindowId::new_uuid_v7();
+    let rollout_items = vec![RolloutItem::Compacted(Box::new(CompactedItem {
+        message: String::new(),
+        replacement_history: Some(replacement_history.clone()),
+        retained_context: None,
+        guardian_history: None,
+        mcp_resource_origins: None,
+        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()),
+        compaction_response_id: None,
+        latest_token_usage_record: None,
+        resume_metadata: None,
+    }))];
+
+    let reconstructed = session
+        .reconstruct_history_from_rollout(&turn_context, &rollout_items)
+        .await;
+
+    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);
+}
diff --git a/codex-rs/core/src/session/file_audio_tests.rs b/codex-rs/core/src/session/file_audio_tests.rs
index a3cff4108b..0e12b5b340 100644
--- a/codex-rs/core/src/session/file_audio_tests.rs
+++ b/codex-rs/core/src/session/file_audio_tests.rs
@@ -6,12 +6,13 @@ use crate::context_manager::ContextManager;
 use codex_protocol::models::BaseInstructions;
 use codex_protocol::models::ResponseInputItem;
 use codex_protocol::user_input::UserInput;
+use codex_protocol_test_support::uuid_v7_item_id_generator_for_test;
 use codex_utils_output_truncation::TruncationPolicy;
 use pretty_assertions::assert_eq;
 
 #[test]
 fn history_sums_measured_and_unknown_file_audio() {
-    let mut history = ContextManager::new();
+    let mut history = ContextManager::new(uuid_v7_item_id_generator_for_test());
     let item = ResponseInputItem::from(
         ["short", "unknown"]
             .map(|file_id| UserInput::Audio {
diff --git a/codex-rs/core/src/session/guardian_checkpoint.rs b/codex-rs/core/src/session/guardian_checkpoint.rs
index 4ccfef86ab..6df9b2669e 100644
--- a/codex-rs/core/src/session/guardian_checkpoint.rs
+++ b/codex-rs/core/src/session/guardian_checkpoint.rs
@@ -20,7 +20,10 @@ impl Session {
             mcp_resource_origins: self.services.mcp_runtime.resource_origin_checkpoint(),
             window_number: Some(state.auto_compact_window_number()),
             first_window_id: Some(window_ids.first_window_id.to_string()),
-            previous_window_id: window_ids.previous_window_id.map(|id| id.to_string()),
+            previous_window_id: window_ids
+                .previous_window_id
+                .as_ref()
+                .map(ToString::to_string),
             window_id: Some(window_ids.window_id.to_string()),
             compaction_response_id: None,
             latest_token_usage_record: state.latest_token_usage_record.clone(),
diff --git a/codex-rs/core/src/session/mod.rs b/codex-rs/core/src/session/mod.rs
index 08e68e45c2..e2b43fec18 100644
--- a/codex-rs/core/src/session/mod.rs
+++ b/codex-rs/core/src/session/mod.rs
@@ -367,6 +367,7 @@ use codex_mcp::effective_mcp_servers;
 use codex_otel::SessionTelemetry;
 use codex_otel::THREAD_STARTED_METRIC;
 use codex_otel::TelemetryAuthMode;
+use codex_protocol::ContextWindowId;
 use codex_protocol::ResponseItemId;
 use codex_protocol::approvals::ExecApprovalKind;
 use codex_protocol::config_types::CollaborationMode;
@@ -2017,11 +2018,11 @@ impl Session {
                 state.history.set_world_state_baseline(world_state);
             }
             let fallback_ids = state.auto_compact_window_ids();
-            let window_id = window_id.unwrap_or(fallback_ids.window_id);
+            let window_id = window_id.unwrap_or_else(|| fallback_ids.window_id.clone());
             state.restore_auto_compact_window(
                 window_number,
                 AutoCompactWindowIds {
-                    first_window_id: first_window_id.unwrap_or(window_id),
+                    first_window_id: first_window_id.unwrap_or_else(|| window_id.clone()),
                     previous_window_id,
                     window_id,
                 },
@@ -4952,7 +4953,7 @@ impl Session {
             let state = self.state.lock().await;
             (
                 state.session_configuration.session_source.clone(),
-                state.auto_compact_window_ids(),
+                state.auto_compact_window_ids().clone(),
             )
         };
         let separate_guardian_developer_message =
@@ -5254,15 +5255,18 @@ impl Session {
         self.current_window().await.0
     }
 
-    pub(crate) async fn current_window(&self) -> (String, u64, Uuid) {
+    pub(crate) async fn current_window(&self) -> (String, u64, ContextWindowId) {
         let state = self.state.lock().await;
         self.current_window_from_state(&state)
     }
 
-    pub(crate) fn current_window_from_state(&self, state: &SessionState) -> (String, u64, Uuid) {
+    pub(crate) fn current_window_from_state(
+        &self,
+        state: &SessionState,
+    ) -> (String, u64, ContextWindowId) {
         let thread_id = self.thread_id;
         let window_number = state.auto_compact_window_number();
-        let context_window_id = state.auto_compact_window_ids().window_id;
+        let context_window_id = state.auto_compact_window_ids().window_id.clone();
         (
             format!("{thread_id}:{window_number}"),
             window_number,
diff --git a/codex-rs/core/src/session/rollout_reconstruction.rs b/codex-rs/core/src/session/rollout_reconstruction.rs
index 56d931e03c..134e64991d 100644
--- a/codex-rs/core/src/session/rollout_reconstruction.rs
+++ b/codex-rs/core/src/session/rollout_reconstruction.rs
@@ -3,11 +3,11 @@ use crate::context::world_state::WorldStateSnapshot;
 use crate::context_manager::is_user_turn_boundary;
 use codex_history::ResponseItemEnvelope;
 use codex_history::TurnAttribution;
+use codex_protocol::ContextWindowId;
 use codex_protocol::protocol::SessionContextWindow;
 use codex_protocol::protocol::ThreadHistoryMode;
 use codex_utils_output_truncation::TruncationPolicy;
 use std::collections::BTreeSet;
-use uuid::Uuid;
 
 // Return value of `Session::reconstruct_history_from_rollout`, bundling the rebuilt history with
 // the resume/fork hydration metadata derived from the same replay.
@@ -23,17 +23,17 @@ pub(crate) struct RolloutReconstruction {
     pub(super) turn_attribution: Option<TurnAttribution>,
     pub(super) world_state_baseline: Option<WorldStateSnapshot>,
     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>,
+    pub(super) first_window_id: Option<ContextWindowId>,
+    pub(super) previous_window_id: Option<ContextWindowId>,
+    pub(super) window_id: Option<ContextWindowId>,
 }
 
-#[derive(Debug, Clone, Copy)]
+#[derive(Debug, Clone)]
 struct ReconstructedWindow {
     number: u64,
-    first_id: Option<Uuid>,
-    previous_id: Option<Uuid>,
-    id: Option<Uuid>,
+    first_id: Option<ContextWindowId>,
+    previous_id: Option<ContextWindowId>,
+    id: Option<ContextWindowId>,
 }
 
 #[derive(Debug, Default)]
@@ -653,31 +653,31 @@ impl ContextManager {
     }
 }
 
-fn parse_uuid_v7(value: &str) -> Option<Uuid> {
-    Uuid::parse_str(value)
-        .ok()
-        .filter(|uuid| uuid.get_version_num() == 7)
-}
-
 fn reconstructed_window_from_compaction(compacted: &CompactedItem) -> Option<ReconstructedWindow> {
     Some(ReconstructedWindow {
         number: compacted.window_number?,
-        first_id: compacted.first_window_id.as_deref().and_then(parse_uuid_v7),
+        first_id: compacted
+            .first_window_id
+            .as_deref()
+            .and_then(ContextWindowId::parse),
         previous_id: compacted
             .previous_window_id
             .as_deref()
-            .and_then(parse_uuid_v7),
-        id: compacted.window_id.as_deref().and_then(parse_uuid_v7),
+            .and_then(ContextWindowId::parse),
+        id: compacted
+            .window_id
+            .as_deref()
+            .and_then(ContextWindowId::parse),
     })
 }
 
 fn reconstructed_window_from_session_context_window(
     context_window: &SessionContextWindow,
 ) -> Option<ReconstructedWindow> {
-    let id = parse_uuid_v7(&context_window.window_id)?;
+    let id = ContextWindowId::parse(&context_window.window_id)?;
     Some(ReconstructedWindow {
         number: 0,
-        first_id: Some(id),
+        first_id: Some(id.clone()),
         previous_id: None,
         id: Some(id),
     })
diff --git a/codex-rs/core/src/session/rollout_reconstruction_tests.rs b/codex-rs/core/src/session/rollout_reconstruction_tests.rs
index 280691b867..3e20cf7301 100644
--- a/codex-rs/core/src/session/rollout_reconstruction_tests.rs
+++ b/codex-rs/core/src/session/rollout_reconstruction_tests.rs
@@ -10,6 +10,7 @@ use codex_history::InitialHistory;
 use codex_history::ResponseItemEnvelope;
 use codex_history::ResumedHistory;
 use codex_protocol::AgentPath;
+use codex_protocol::ContextWindowId;
 use codex_protocol::ThreadId;
 use codex_protocol::models::ContentItem;
 use codex_protocol::models::ResponseItem;
@@ -30,7 +31,6 @@ use serde_json::json;
 use std::collections::BTreeMap;
 use std::path::PathBuf;
 use test_case::test_case;
-use uuid::Uuid;
 
 #[tokio::test]
 async fn recorded_questions_share_queued_input_order_across_resume() {
@@ -1444,7 +1444,7 @@ async fn record_initial_history_resumed_does_not_seed_reference_context_item_aft
 async fn reconstruct_history_restores_initial_window_from_session_meta() {
     let (session, turn_context) = make_session_and_context().await;
     let thread_id = ThreadId::default();
-    let initial_window_id = Uuid::now_v7();
+    let initial_window_id = ContextWindowId::new_uuid_v7();
     let rollout_items = vec![RolloutItem::SessionMeta(Box::new(SessionMetaLine {
         meta: SessionMeta {
             session_id: thread_id.into(),
@@ -1462,7 +1462,10 @@ async fn reconstruct_history_restores_initial_window_from_session_meta() {
         .await;
 
     assert_eq!(reconstructed.window_number, 0);
-    assert_eq!(reconstructed.first_window_id, Some(initial_window_id));
+    assert_eq!(
+        reconstructed.first_window_id.as_ref(),
+        Some(&initial_window_id)
+    );
     assert_eq!(reconstructed.previous_window_id, None);
     assert_eq!(reconstructed.window_id, Some(initial_window_id));
 }
@@ -1471,10 +1474,10 @@ async fn reconstruct_history_restores_initial_window_from_session_meta() {
 async fn reconstruct_history_prefers_compacted_window_over_session_meta() {
     let (session, turn_context) = make_session_and_context().await;
     let thread_id = ThreadId::default();
-    let initial_window_id = Uuid::now_v7();
-    let compacted_first_window_id = Uuid::now_v7();
-    let compacted_previous_window_id = Uuid::now_v7();
-    let compacted_window_id = Uuid::now_v7();
+    let initial_window_id = ContextWindowId::new_uuid_v7();
+    let compacted_first_window_id = ContextWindowId::new_uuid_v7();
+    let compacted_previous_window_id = ContextWindowId::new_uuid_v7();
+    let compacted_window_id = ContextWindowId::new_uuid_v7();
     let rollout_items = vec![
         RolloutItem::SessionMeta(Box::new(SessionMetaLine {
             meta: SessionMeta {
@@ -1593,7 +1596,11 @@ async fn bounded_replay_matches_full_replay_after_empty_turn_compactions(
             user_message("original task").into(),
         )],
     ));
-    let window_ids = [Uuid::now_v7(), Uuid::now_v7(), Uuid::now_v7()];
+    let window_ids = [
+        ContextWindowId::new_uuid_v7(),
+        ContextWindowId::new_uuid_v7(),
+        ContextWindowId::new_uuid_v7(),
+    ];
     let current = matches!(compaction_format, CompactionFormat::Current);
     let mut latest_compaction_index = 0;
     for window_number in 1..=2 {
@@ -1961,7 +1968,7 @@ async fn completed_turn_suffix_after_compaction_overrides_resume_metadata(
 async fn reconstruct_history_preserves_legacy_compaction_count_with_session_meta_window() {
     let (session, turn_context) = make_session_and_context().await;
     let thread_id = ThreadId::default();
-    let initial_window_id = Uuid::now_v7();
+    let initial_window_id = ContextWindowId::new_uuid_v7();
     let rollout_items = vec![
         RolloutItem::SessionMeta(Box::new(SessionMetaLine {
             meta: SessionMeta {
diff --git a/codex-rs/core/src/session/session.rs b/codex-rs/core/src/session/session.rs
index e94527c80a..7677e92296 100644
--- a/codex-rs/core/src/session/session.rs
+++ b/codex-rs/core/src/session/session.rs
@@ -33,6 +33,7 @@ use codex_http_client::RouteAwareClientPool;
 use codex_login::auth::AgentIdentityAuthPolicy;
 use codex_model_provider::SharedModelProvider;
 use codex_prompts::render_model_instructions;
+use codex_protocol::ContextWindowId;
 use codex_protocol::ItemIdGenerator;
 use codex_protocol::SessionId;
 use codex_protocol::capabilities::SelectedCapabilityRoot;
@@ -815,7 +816,7 @@ impl Session {
         &self,
         turn_context: &TurnContext,
         compaction_metadata: CompactionTurnMetadata,
-        (window_id, window_number, context_window_id): (String, u64, uuid::Uuid),
+        (window_id, window_number, context_window_id): (String, u64, ContextWindowId),
     ) -> CodexResponsesMetadata {
         let responses_metadata = turn_context.turn_metadata_state.to_responses_metadata(
             self.installation_id.clone(),
@@ -835,7 +836,7 @@ impl Session {
         turn_context: &TurnContext,
         responses_metadata: CodexResponsesMetadata,
         window_number: u64,
-        context_window_id: uuid::Uuid,
+        context_window_id: ContextWindowId,
     ) -> CodexResponsesMetadata {
         CodexResponsesMetadata {
             history_initialization: Some(self.history_initialization),
@@ -1631,7 +1632,7 @@ impl Session {
             session_configuration.thread_name = thread_name.clone();
             let mut state = SessionState::new_with_auto_compact_window_ids(
                 session_configuration.clone(),
-                initial_auto_compact_window_ids,
+                initial_auto_compact_window_ids.clone(),
                 ContextManager::for_session(
                     session_configuration.root_capabilities_restricted,
                     &config.features,
diff --git a/codex-rs/core/src/session/tests.rs b/codex-rs/core/src/session/tests.rs
index 9edd5643ec..aaf6e5f8e9 100644
--- a/codex-rs/core/src/session/tests.rs
+++ b/codex-rs/core/src/session/tests.rs
@@ -1,4 +1,8 @@
 use crate::agent::LocalAgentControl;
+use codex_protocol::ContextWindowId;
+#[path = "compaction_replay_tests.rs"]
+mod compaction_replay_tests;
+
 #[path = "notification_tests.rs"]
 mod notification_tests;
 
@@ -2465,89 +2469,6 @@ fn collect_explicit_app_ids_from_skill_items_skips_plain_mentions_with_skill_con
     assert_eq!(connector_ids, HashSet::<String>::new());
 }
 
-#[tokio::test]
-async fn reconstruct_history_matches_live_compactions() {
-    let (session, turn_context) = make_session_and_context().await;
-    let (rollout_items, expected) = sample_rollout(&session, &turn_context).await;
-
-    let reconstruction_turn = session.new_default_turn().await;
-    let reconstructed = session
-        .reconstruct_history_from_rollout(reconstruction_turn.as_ref(), &rollout_items)
-        .await;
-
-    assert_eq!(expected, raw_envelopes(&reconstructed.history));
-    assert_eq!(2, reconstructed.window_number);
-    assert_eq!(
-        reconstructed
-            .window_id
-            .map(|window_id| window_id.get_version_num()),
-        Some(7)
-    );
-}
-
-#[tokio::test]
-async fn reconstruct_history_uses_replacement_history_verbatim() {
-    let (session, turn_context) = make_session_and_context().await;
-    let summary_item = ResponseItem::Message {
-        status: None,
-        encrypted_content: None,
-        id: None,
-        role: "user".to_string(),
-        content: vec![ContentItem::InputText {
-            text: "summary".to_string(),
-        }],
-        phase: None,
-        internal_chat_message_metadata_passthrough: Some(InternalChatMessageMetadataPassthrough {
-            turn_id: Some("compact-turn".to_string()),
-            ..Default::default()
-        }),
-    };
-    let replacement_history = vec![
-        ResponseItemEnvelope {
-            item: summary_item.clone(),
-            metadata: Some(CodexHarnessMetadata::default()),
-        },
-        ResponseItemEnvelope::new(ResponseItem::Message {
-            status: None,
-            encrypted_content: None,
-            id: None,
-            role: "developer".to_string(),
-            content: vec![ContentItem::InputText {
-                text: "stale developer instructions".to_string(),
-            }],
-            phase: None,
-            internal_chat_message_metadata_passthrough: 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(Box::new(CompactedItem {
-        message: String::new(),
-        replacement_history: Some(replacement_history.clone()),
-        retained_context: None,
-        guardian_history: None,
-        mcp_resource_origins: None,
-        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()),
-        compaction_response_id: None,
-        latest_token_usage_record: None,
-        resume_metadata: None,
-    }))];
-
-    let reconstructed = session
-        .reconstruct_history_from_rollout(&turn_context, &rollout_items)
-        .await;
-
-    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);
-}
-
 #[tokio::test]
 async fn record_initial_history_reconstructs_resumed_transcript() {
     let (session, turn_context) = make_session_and_context().await;
@@ -5075,7 +4996,7 @@ async fn open_thread_persistence(session: &mut Session) -> PathBuf {
             history_mode: Default::default(),
             subagent_history_start_ordinal: None,
             history_base: None,
-            initial_window_id: Uuid::now_v7().to_string(),
+            initial_window_id: ContextWindowId::new_uuid_v7().to_string(),
             runtime_workspace_roots: None,
             metadata: ThreadPersistenceMetadata {
                 cwd: Some(config.cwd.to_path_buf()),
@@ -8867,7 +8788,7 @@ async fn shutdown_complete_does_not_append_to_thread_store_after_shutdown() {
             history_mode: Default::default(),
             subagent_history_start_ordinal: None,
             history_base: None,
-            initial_window_id: Uuid::now_v7().to_string(),
+            initial_window_id: ContextWindowId::new_uuid_v7().to_string(),
             runtime_workspace_roots: None,
             metadata: ThreadPersistenceMetadata {
                 cwd: Some(config.cwd.to_path_buf()),
@@ -9006,7 +8927,7 @@ async fn submission_loop_channel_close_runs_full_thread_teardown() -> anyhow::Re
             history_mode: Default::default(),
             subagent_history_start_ordinal: None,
             history_base: None,
-            initial_window_id: Uuid::now_v7().to_string(),
+            initial_window_id: ContextWindowId::new_uuid_v7().to_string(),
             runtime_workspace_roots: None,
             metadata: ThreadPersistenceMetadata {
                 cwd: Some(config.cwd.to_path_buf()),
@@ -12008,7 +11929,7 @@ async fn attach_in_memory_thread_store(
             history_mode: Default::default(),
             subagent_history_start_ordinal: None,
             history_base: None,
-            initial_window_id: Uuid::now_v7().to_string(),
+            initial_window_id: ContextWindowId::new_uuid_v7().to_string(),
             runtime_workspace_roots: None,
             metadata: ThreadPersistenceMetadata {
                 cwd: Some(config.cwd.to_path_buf()),
diff --git a/codex-rs/core/src/session/time_reminder.rs b/codex-rs/core/src/session/time_reminder.rs
index 92c60389fe..02f1cecb74 100644
--- a/codex-rs/core/src/session/time_reminder.rs
+++ b/codex-rs/core/src/session/time_reminder.rs
@@ -41,7 +41,7 @@ pub(super) fn apply_persistent_defaults(config: &mut Config) {
 pub(crate) struct CurrentTimeReminderState {
     last_delivery_time: Option<DateTime<Utc>>,
     last_window_id: Option<String>,
-    last_clock_failure: Option<(String, uuid::Uuid)>,
+    last_clock_failure: Option<(String, codex_protocol::ContextWindowId)>,
     pending_user_or_tool_output_boundary: bool,
 }
 
@@ -134,7 +134,7 @@ impl Session {
             let mut state = self.state.lock().await;
             let failure = (
                 turn_context.sub_id.clone(),
-                state.auto_compact_window_ids().window_id,
+                state.auto_compact_window_ids().window_id.clone(),
             );
             // A compacted window may no longer contain the earlier notice.
             if state.current_time_reminder.last_clock_failure.as_ref() == Some(&failure) {
diff --git a/codex-rs/core/src/session/world_state.rs b/codex-rs/core/src/session/world_state.rs
index 49fef5f3ac..f4c8ee6249 100644
--- a/codex-rs/core/src/session/world_state.rs
+++ b/codex-rs/core/src/session/world_state.rs
@@ -195,7 +195,7 @@ impl Session {
                 .resolved_context_window()
                 .is_some();
         if token_budget_enabled {
-            let window_ids = self.state.lock().await.auto_compact_window_ids();
+            let window_ids = self.state.lock().await.auto_compact_window_ids().clone();
             world_state.add_section(TokenBudgetContext::new(
                 turn_context
                     .session_source
diff --git a/codex-rs/core/src/state/auto_compact_window.rs b/codex-rs/core/src/state/auto_compact_window.rs
index 2571749ed6..600df8c0cd 100644
--- a/codex-rs/core/src/state/auto_compact_window.rs
+++ b/codex-rs/core/src/state/auto_compact_window.rs
@@ -1,18 +1,18 @@
+use codex_protocol::ContextWindowId;
 use codex_protocol::protocol::TokenUsage;
-use uuid::Uuid;
 
-#[derive(Debug, Clone, Copy, PartialEq, Eq)]
+#[derive(Debug, Clone, PartialEq, Eq)]
 pub(crate) struct AutoCompactWindowIds {
-    pub(crate) first_window_id: Uuid,
-    pub(crate) previous_window_id: Option<Uuid>,
-    pub(crate) window_id: Uuid,
+    pub(crate) first_window_id: ContextWindowId,
+    pub(crate) previous_window_id: Option<ContextWindowId>,
+    pub(crate) window_id: ContextWindowId,
 }
 
 impl AutoCompactWindowIds {
     pub(crate) fn new_initial() -> Self {
-        let window_id = Uuid::now_v7();
+        let window_id = ContextWindowId::new_uuid_v7();
         Self {
-            first_window_id: window_id,
+            first_window_id: window_id.clone(),
             previous_window_id: None,
             window_id,
         }
@@ -30,7 +30,7 @@ enum AutoCompactWindowPrefill {
     Estimated(i64),
 }
 
-#[derive(Debug, Clone, Copy, PartialEq, Eq)]
+#[derive(Debug, Clone, PartialEq, Eq)]
 pub(super) struct AutoCompactWindow {
     window_number: u64,
     ids: AutoCompactWindowIds,
@@ -65,8 +65,8 @@ impl AutoCompactWindow {
         self.window_number
     }
 
-    pub(super) fn ids(&self) -> AutoCompactWindowIds {
-        self.ids
+    pub(super) fn ids(&self) -> &AutoCompactWindowIds {
+        &self.ids
     }
 
     pub(super) fn restore(&mut self, window_number: u64, ids: AutoCompactWindowIds) {
@@ -76,12 +76,14 @@ impl AutoCompactWindow {
 
     pub(super) fn advance(&mut self) -> (u64, AutoCompactWindowIds) {
         self.window_number = self.window_number.saturating_add(1);
-        self.ids.previous_window_id = Some(self.ids.window_id);
-        self.ids.window_id = Uuid::now_v7();
+        self.ids.previous_window_id = Some(std::mem::replace(
+            &mut self.ids.window_id,
+            ContextWindowId::new_uuid_v7(),
+        ));
         self.new_context_window_requested = false;
         self.token_budget_reminder_delivered = false;
         self.auto_compact_fallback_delivered = false;
-        (self.window_number, self.ids)
+        (self.window_number, self.ids.clone())
     }
 
     pub(super) fn claim_token_budget_reminder(&mut self) -> bool {
@@ -151,25 +153,30 @@ mod tests {
         let mut window = AutoCompactWindow::new_with_ids(AutoCompactWindowIds::new_initial());
 
         assert_eq!(window.window_number(), 0);
-        let initial_window_id = window.ids().window_id;
-        assert_eq!(initial_window_id.get_version_num(), 7);
+        let initial_window_id = window.ids().window_id.clone();
+        assert_eq!(
+            uuid::Uuid::parse_str(&initial_window_id.to_string())
+                .unwrap()
+                .get_version_num(),
+            7
+        );
         assert_eq!(
             window.ids(),
-            AutoCompactWindowIds {
-                first_window_id: initial_window_id,
+            &AutoCompactWindowIds {
+                first_window_id: initial_window_id.clone(),
                 previous_window_id: None,
-                window_id: initial_window_id,
+                window_id: initial_window_id.clone(),
             }
         );
         let first_window_id = initial_window_id;
-        let restored_window_id = Uuid::now_v7();
-        let restored_previous_window_id = Uuid::now_v7();
+        let restored_window_id = ContextWindowId::new_uuid_v7();
+        let restored_previous_window_id = ContextWindowId::new_uuid_v7();
         window.restore(
             /*window_number*/ 3,
             AutoCompactWindowIds {
-                first_window_id,
+                first_window_id: first_window_id.clone(),
                 previous_window_id: Some(restored_previous_window_id),
-                window_id: restored_window_id,
+                window_id: restored_window_id.clone(),
             },
         );
         assert_eq!(window.window_number(), 3);
@@ -185,10 +192,15 @@ mod tests {
         let (window_number, ids) = window.advance();
         assert_eq!(window_number, 4);
         assert_eq!(window.window_number(), 4);
-        assert_eq!(window.ids(), ids);
+        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_eq!(ids.previous_window_id, Some(restored_window_id.clone()));
+        assert_eq!(
+            uuid::Uuid::parse_str(&ids.window_id.to_string())
+                .unwrap()
+                .get_version_num(),
+            7
+        );
         assert_ne!(ids.window_id, restored_window_id);
         assert!(!window.take_new_context_window_request());
         assert!(window.claim_token_budget_reminder());
diff --git a/codex-rs/core/src/state/session.rs b/codex-rs/core/src/state/session.rs
index 972cf5092b..a9853cf486 100644
--- a/codex-rs/core/src/state/session.rs
+++ b/codex-rs/core/src/state/session.rs
@@ -337,7 +337,7 @@ impl SessionState {
         self.auto_compact_window.window_number()
     }
 
-    pub(crate) fn auto_compact_window_ids(&self) -> AutoCompactWindowIds {
+    pub(crate) fn auto_compact_window_ids(&self) -> &AutoCompactWindowIds {
         self.auto_compact_window.ids()
     }
 
diff --git a/codex-rs/protocol/src/context_window_id.rs b/codex-rs/protocol/src/context_window_id.rs
new file mode 100644
index 0000000000..38e77f4a94
--- /dev/null
+++ b/codex-rs/protocol/src/context_window_id.rs
@@ -0,0 +1,30 @@
+//! Context window identity used for compaction, rollout restoration, and request metadata.
+
+use serde::Serialize;
+use std::fmt;
+use uuid::Uuid;
+
+#[derive(derive_more::Debug, Clone, PartialEq, Eq, Serialize)]
+#[debug("{_0}")]
+#[serde(transparent)]
+pub struct ContextWindowId(String);
+
+impl ContextWindowId {
+    pub fn new_uuid_v7() -> Self {
+        Self(Uuid::now_v7().to_string())
+    }
+
+    /// Reads a persisted window ID, ignoring IDs outside the supported format.
+    pub fn parse(value: &str) -> Option<Self> {
+        Uuid::parse_str(value)
+            .ok()
+            .filter(|uuid| uuid.get_version_num() == 7)
+            .map(|uuid| Self(uuid.to_string()))
+    }
+}
+
+impl fmt::Display for ContextWindowId {
+    fn fmt(&self, formatter: &mut fmt::Formatter<'_>) -> fmt::Result {
+        self.0.fmt(formatter)
+    }
+}
diff --git a/codex-rs/protocol/src/lib.rs b/codex-rs/protocol/src/lib.rs
index e399d52d5c..8c7442499d 100644
--- a/codex-rs/protocol/src/lib.rs
+++ b/codex-rs/protocol/src/lib.rs
@@ -1,6 +1,7 @@
 pub mod account;
 mod agent_path;
 pub mod auth;
+mod context_window_id;
 mod item_id_generator;
 mod response_item_id;
 mod response_usage;
@@ -9,6 +10,7 @@ mod session_id;
 mod thread_id;
 mod tool_name;
 pub use agent_path::AgentPath;
+pub use context_window_id::ContextWindowId;
 pub use item_id_generator::ItemIdGenerator;
 #[cfg(test)]
 use item_id_generator::uuid_v7_item_id_generator_for_test;
diff --git a/codex-rs/rollout/src/recorder_tests.rs b/codex-rs/rollout/src/recorder_tests.rs
index eac55e6fbb..b1d3e7b04f 100644
--- a/codex-rs/rollout/src/recorder_tests.rs
+++ b/codex-rs/rollout/src/recorder_tests.rs
@@ -698,7 +698,7 @@ async fn recorder_materializes_on_flush_with_pending_items() -> std::io::Result<
     let config = test_config(home.path());
     let session_id = SessionId::default();
     let thread_id = ThreadId::new();
-    let initial_window_id = Uuid::now_v7().to_string();
+    let initial_window_id = codex_protocol::ContextWindowId::new_uuid_v7().to_string();
     let recorder = RolloutRecorder::new(
         &config,
         RolloutRecorderParams::new(
diff --git a/codex-rs/thread-store/src/in_memory.rs b/codex-rs/thread-store/src/in_memory.rs
index 137d0dda0c..049e89cafc 100644
--- a/codex-rs/thread-store/src/in_memory.rs
+++ b/codex-rs/thread-store/src/in_memory.rs
@@ -64,6 +64,7 @@ mod tests {
     use crate::StoredTurnItemsView;
     use crate::ThreadPersistenceMetadata;
     use crate::ThreadSortKey;
+    use codex_protocol::ContextWindowId;
     use codex_protocol::models::BaseInstructions;
     use codex_protocol::protocol::SessionSource;
 
@@ -184,7 +185,7 @@ mod tests {
                     history_mode: ThreadHistoryMode::Legacy,
                     history_base: None,
                     subagent_history_start_ordinal: None,
-                    initial_window_id: uuid::Uuid::now_v7().to_string(),
+                    initial_window_id: ContextWindowId::new_uuid_v7().to_string(),
                     runtime_workspace_roots: None,
                     metadata: ThreadPersistenceMetadata {
                         cwd: None,
@@ -461,7 +462,7 @@ mod tests {
             history_mode,
             history_base: None,
             subagent_history_start_ordinal: None,
-            initial_window_id: uuid::Uuid::now_v7().to_string(),
+            initial_window_id: ContextWindowId::new_uuid_v7().to_string(),
             runtime_workspace_roots: None,
             metadata: thread_metadata(),
         }
diff --git a/codex-rs/thread-store/src/local/mod.rs b/codex-rs/thread-store/src/local/mod.rs
index 23f533d9f7..f2e7c3ea6e 100644
--- a/codex-rs/thread-store/src/local/mod.rs
+++ b/codex-rs/thread-store/src/local/mod.rs
@@ -2393,7 +2393,7 @@ mod tests {
             history_mode: ThreadHistoryMode::Legacy,
             history_base: None,
             subagent_history_start_ordinal: None,
-            initial_window_id: uuid::Uuid::now_v7().to_string(),
+            initial_window_id: codex_protocol::ContextWindowId::new_uuid_v7().to_string(),
             runtime_workspace_roots: None,
             metadata: thread_metadata(),
         }
diff --git a/codex-rs/thread-store/src/local/pending_thread_metadata_tests.rs b/codex-rs/thread-store/src/local/pending_thread_metadata_tests.rs
index a81eb389a7..d6973cf3c5 100644
--- a/codex-rs/thread-store/src/local/pending_thread_metadata_tests.rs
+++ b/codex-rs/thread-store/src/local/pending_thread_metadata_tests.rs
@@ -600,7 +600,7 @@ fn create_thread_params(thread_id: ThreadId) -> CreateThreadParams {
         history_mode: ThreadHistoryMode::Legacy,
         history_base: None,
         subagent_history_start_ordinal: None,
-        initial_window_id: uuid::Uuid::now_v7().to_string(),
+        initial_window_id: codex_protocol::ContextWindowId::new_uuid_v7().to_string(),
         runtime_workspace_roots: None,
         metadata: ThreadPersistenceMetadata {
             cwd: Some(std::env::current_dir().expect("cwd")),
diff --git a/codex-rs/thread-store/src/thread_metadata_sync.rs b/codex-rs/thread-store/src/thread_metadata_sync.rs
index 6f1a7d1791..f5c3191ba1 100644
--- a/codex-rs/thread-store/src/thread_metadata_sync.rs
+++ b/codex-rs/thread-store/src/thread_metadata_sync.rs
@@ -504,7 +504,7 @@ mod tests {
             history_mode: ThreadHistoryMode::Legacy,
             history_base: None,
             subagent_history_start_ordinal: None,
-            initial_window_id: uuid::Uuid::now_v7().to_string(),
+            initial_window_id: codex_protocol::ContextWindowId::new_uuid_v7().to_string(),
             runtime_workspace_roots: None,
             metadata: ThreadPersistenceMetadata {
                 cwd: None,