diff --git a/codex-rs/core/src/agent/control/spawn.rs b/codex-rs/core/src/agent/control/spawn.rs
index dae1a6636a..4bf2d80602 100644
--- a/codex-rs/core/src/agent/control/spawn.rs
+++ b/codex-rs/core/src/agent/control/spawn.rs
@@ -20,6 +20,7 @@ use crate::context::DeveloperInstructions;
 use crate::context::ManagedDeveloperInstructions;
 use crate::context::MultiAgentModeInstructions;
 use crate::context::MultiAgentRoleInstructions;
+use crate::context::world_state::IncrementalToolsHint;
 use crate::context::world_state::PersistentModeState;
 use crate::session::multi_agents::resolve_usage_hints;
 use crate::thread_manager::StartThreadOptions;
@@ -1150,7 +1151,10 @@ impl LocalAgentControl {
                     return false;
                 };
                 content.retain_mut(|content_item| {
-                    if content_item.kind().as_str() == BaseInstructionsFragment::KIND {
+                    if matches!(
+                        content_item.kind().as_str(),
+                        BaseInstructionsFragment::KIND | IncrementalToolsHint::KIND
+                    ) {
                         return preserve_context_baselines;
                     }
                     let ContentItem::InputText { text } = content_item.content_mut() else {
diff --git a/codex-rs/core/src/agent/control_tests.rs b/codex-rs/core/src/agent/control_tests.rs
index aa282cfdb9..866cdc7385 100644
--- a/codex-rs/core/src/agent/control_tests.rs
+++ b/codex-rs/core/src/agent/control_tests.rs
@@ -25,6 +25,7 @@ use crate::context::ContextualUserFragment;
 use crate::context::ManagedDeveloperInstructions;
 use crate::context::MultiAgentRoleInstructions;
 use crate::context::SubagentNotification;
+use crate::context::world_state::IncrementalToolsHint;
 use crate::init_state_db;
 use crate::responses_metadata::CodexResponsesRequestKind;
 use crate::session::SessionSettingsUpdate;
@@ -3187,7 +3188,9 @@ async fn spawn_agent_fork_strips_parent_usage_hints_from_compacted_history(marke
         role: "developer".to_string(),
         tools: vec![serde_json::json!({"type": "function", "name": "compacted_tool"})],
     };
+    let tools_update = ContextualUserFragment::into(IncrementalToolsHint);
     let replacement_history = vec![
+        tools_update.clone(),
         tool_declarations.clone(),
         ContextualUserFragment::into(crate::context::GuardianApprovedAction::new("parent-private-release".to_owned())),
         ResponseItem::Message {
@@ -3335,12 +3338,19 @@ async fn spawn_agent_fork_strips_parent_usage_hints_from_compacted_history(marke
         strip_response_item_ids(
             &history
                 .raw_items()
-                .filter(|item| matches!(item, ResponseItem::AdditionalTools { .. }))
+                .filter(|item| {
+                    matches!(item, ResponseItem::AdditionalTools { .. })
+                        || matches!(item, ResponseItem::Message {
+                            internal_chat_message_metadata_passthrough: Some(metadata), ..
+                        } if metadata.content_item_kinds.as_ref().is_some_and(|kinds| {
+                            kinds.iter().any(|kind| kind.as_str() == IncrementalToolsHint::KIND)
+                        }))
+                })
                 .cloned()
                 .collect::<Vec<_>>()
         ),
-        vec![tool_declarations],
-        "full-history forks must retain declarations embedded in compaction checkpoints"
+        vec![tools_update, tool_declarations],
+        "full-history forks must retain tool update notices with declarations embedded in compaction checkpoints"
     );
     assert!(
         !history_contains_text(
@@ -3684,6 +3694,14 @@ async fn spawn_agent_full_fork_legacy_compaction_rebuilds_child_instructions_onc
             phase: None,
             internal_chat_message_metadata_passthrough: None,
         }));
+        rollout_items.push(rollout_response_item(ContextualUserFragment::into(
+            IncrementalToolsHint,
+        )));
+        rollout_items.push(rollout_response_item(ResponseItem::AdditionalTools {
+            id: None,
+            role: "developer".to_string(),
+            tools: vec![serde_json::json!({"type": "function", "name": "parent_tool"})],
+        }));
         rollout_items.push(RolloutItem::TurnContext(
             turn_context.to_turn_context_item(),
         ));
@@ -3739,6 +3757,23 @@ async fn spawn_agent_full_fork_legacy_compaction_rebuilds_child_instructions_onc
         )
         .await
         .expect("read child checkpoint");
+        assert_eq!(
+            items
+                .iter()
+                .filter_map(|item| match item {
+                    RolloutItem::ResponseItem(envelope)
+                        if matches!(&envelope.item, ResponseItem::Message {
+                            internal_chat_message_metadata_passthrough: Some(metadata), ..
+                        } if metadata.content_item_kinds.as_ref().is_some_and(|kinds| {
+                            kinds.iter().any(|kind| kind.as_str() == IncrementalToolsHint::KIND)
+                        })) =>
+                        Some(envelope.item.clone()),
+                    _ => None,
+                })
+                .collect::<Vec<_>>(),
+            Vec::<ResponseItem>::new(),
+            "{case}: a legacy compaction fork must drop notices for tool declarations it rebuilds"
+        );
         let inherited_state = items.into_iter().find_map(|item| match item {
             RolloutItem::Compacted(item) => item.resume_metadata,
             _ => None,
diff --git a/codex-rs/core/src/context/world_state/mod.rs b/codex-rs/core/src/context/world_state/mod.rs
index 745ac761bc..6a23a30c15 100644
--- a/codex-rs/core/src/context/world_state/mod.rs
+++ b/codex-rs/core/src/context/world_state/mod.rs
@@ -58,6 +58,7 @@ pub(crate) use persistent_mode::PersistentModeState;
 pub(crate) use plugins_instructions::PluginsInstructionsState;
 pub(crate) use realtime::RealtimeState;
 pub(crate) use tools::ToolsState;
+pub(crate) use top_level_tools::IncrementalToolsHint;
 pub(crate) use top_level_tools::TopLevelToolsState;
 
 /// One contribution to model context and its placement policy.
diff --git a/codex-rs/core/src/context/world_state/snapshots/codex_core__context__world_state__top_level_tools__tests__snapshots_namespace_transitions.snap b/codex-rs/core/src/context/world_state/snapshots/codex_core__context__world_state__top_level_tools__tests__snapshots_namespace_transitions.snap
index 8c31b171e2..b3a5073648 100644
--- a/codex-rs/core/src/context/world_state/snapshots/codex_core__context__world_state__top_level_tools__tests__snapshots_namespace_transitions.snap
+++ b/codex-rs/core/src/context/world_state/snapshots/codex_core__context__world_state__top_level_tools__tests__snapshots_namespace_transitions.snap
@@ -64,11 +64,35 @@ Absent -> {"functions":"d0971b2901a1d91cd0773dd3014aacad18939724","functions.cha
 None
 
 {"functions":"d0971b2901a1d91cd0773dd3014aacad18939724","functions.changed":"201818ec534c933aaf3e31e180ad44845f90de52","functions.removed":"ec12b15fd139075230b516c8cd7cbd0d656b9a38","functions.unchanged":"4d234d07035e05b331e0ca66127362f678bed9ce","other":"d3ba1afd5b23158d1baec4aba38ba2b8d376141b","other.lookup":"957791c1122ca973a75db93abc14a5ae32514005"} -> {"functions":"d0971b2901a1d91cd0773dd3014aacad18939724","functions.added":"5fc75ad4d08cd0b73ef983d58fed9272072e5ce7","functions.changed":"ebe9005f973a60ba4ee93b024d7021d21dc27826","functions.unchanged":"4d234d07035e05b331e0ca66127362f678bed9ce","other":"d3ba1afd5b23158d1baec4aba38ba2b8d376141b","other.lookup":"957791c1122ca973a75db93abc14a5ae32514005"} (item - prefix)
+{
+  "content": [
+    {
+      "text": "This is an incremental tools update. Previously declared tools remain available for direct calls unless explicitly marked unavailable. If a tool is redefined here, its latest definition replaces the earlier one.",
+      "type": "input_text"
+    }
+  ],
+  "internal_chat_message_metadata_passthrough": {
+    "content_item_kinds": [
+      "tools.incremental_update"
+    ],
+    "content_item_metadata": [
+      {
+        "provenance": {
+          "hook": false,
+          "type": "harness"
+        }
+      }
+    ]
+  },
+  "role": "developer",
+  "type": "message"
+}
+ (item - prefix)
 {
   "role": "developer",
   "tools": [
     {
-      "description": "Tools.\nThis is an incremental namespace update. Previously declared tools remain available for direct calls unless explicitly marked unavailable. If a tool is redefined here, its latest definition replaces the earlier one.",
+      "description": "Tools.",
       "name": "functions",
       "tools": [
         {
@@ -108,6 +132,30 @@ The following namespaces are no longer available. Do not call tools in them unle
 - functions
 
 {"other":"d3ba1afd5b23158d1baec4aba38ba2b8d376141b","other.lookup":"957791c1122ca973a75db93abc14a5ae32514005"} -> {"functions":"d0971b2901a1d91cd0773dd3014aacad18939724","functions.changed":"201818ec534c933aaf3e31e180ad44845f90de52","functions.removed":"ec12b15fd139075230b516c8cd7cbd0d656b9a38","functions.unchanged":"4d234d07035e05b331e0ca66127362f678bed9ce","other":"d3ba1afd5b23158d1baec4aba38ba2b8d376141b","other.lookup":"957791c1122ca973a75db93abc14a5ae32514005"} (item - prefix)
+{
+  "content": [
+    {
+      "text": "This is an incremental tools update. Previously declared tools remain available for direct calls unless explicitly marked unavailable. If a tool is redefined here, its latest definition replaces the earlier one.",
+      "type": "input_text"
+    }
+  ],
+  "internal_chat_message_metadata_passthrough": {
+    "content_item_kinds": [
+      "tools.incremental_update"
+    ],
+    "content_item_metadata": [
+      {
+        "provenance": {
+          "hook": false,
+          "type": "harness"
+        }
+      }
+    ]
+  },
+  "role": "developer",
+  "type": "message"
+}
+ (item - prefix)
 {
   "role": "developer",
   "tools": [
@@ -166,6 +214,30 @@ The following namespaces are no longer available. Do not call tools in them unle
 None
 
 {} -> {"functions":"d0971b2901a1d91cd0773dd3014aacad18939724","functions.restored":"56fbc7d43a57aab411e5352bfbb88a6df939fd4e","functions.unchanged":"4d234d07035e05b331e0ca66127362f678bed9ce"} (item - prefix)
+{
+  "content": [
+    {
+      "text": "This is an incremental tools update. Previously declared tools remain available for direct calls unless explicitly marked unavailable. If a tool is redefined here, its latest definition replaces the earlier one.",
+      "type": "input_text"
+    }
+  ],
+  "internal_chat_message_metadata_passthrough": {
+    "content_item_kinds": [
+      "tools.incremental_update"
+    ],
+    "content_item_metadata": [
+      {
+        "provenance": {
+          "hook": false,
+          "type": "harness"
+        }
+      }
+    ]
+  },
+  "role": "developer",
+  "type": "message"
+}
+ (item - prefix)
 {
   "role": "developer",
   "tools": [
diff --git a/codex-rs/core/src/context/world_state/top_level_tools.rs b/codex-rs/core/src/context/world_state/top_level_tools.rs
index 21f7c2cdb6..d26f05d5be 100644
--- a/codex-rs/core/src/context/world_state/top_level_tools.rs
+++ b/codex-rs/core/src/context/world_state/top_level_tools.rs
@@ -1,6 +1,6 @@
 //! Diffs the one-level Responses Lite catalog: namespaces of callable tools and built-ins.
 //! Missing state starts a fresh catalog; this section does not migrate legacy history.
-//! Incremental hints decorate emitted declarations only, leaving catalog hashes unchanged.
+//! One developer notice precedes each incremental namespace batch; catalog hashes are unchanged.
 //! Whole namespace removals subsume their members in the removal notice.
 //! Metrics count rendered tool redefinitions, excluding namespace headers and initial catalogs.
 
@@ -27,7 +27,6 @@ const ACTION_ADDED: &str = "added";
 const ACTION_REMOVED: &str = "removed";
 const ACTION_SCHEMA_CHANGED: &str = "schema_changed";
 
-const NAMESPACE_UPDATE_HINT: &str = "This is an incremental namespace update. Previously declared tools remain available for direct calls unless explicitly marked unavailable. If a tool is redefined here, its latest definition replaces the earlier one.";
 const REMOVED_TOOLS_HEADER: &str = "The following tools are no longer available. Do not call them:";
 const REMOVED_NAMESPACES_HEADER: &str = "The following namespaces are no longer available. Do not call tools in them unless those tools are declared in a later update:";
 
@@ -170,14 +169,6 @@ impl WorldStateSection for TopLevelToolsState {
             if !changed_members.is_empty() {
                 let mut namespace = definition.clone();
                 namespace["tools"] = Value::Array(changed_members);
-                if previous.is_some_and(|previous| previous.contains_key(name)) {
-                    let description = definition["description"].as_str().unwrap_or_default();
-                    namespace["description"] = Value::String(if description.is_empty() {
-                        NAMESPACE_UPDATE_HINT.to_string()
-                    } else {
-                        format!("{description}\n{NAMESPACE_UPDATE_HINT}")
-                    });
-                }
                 tools.push(namespace);
             } else if changed(name) {
                 // Namespace declarations require a member. Update metadata as text without
@@ -196,6 +187,11 @@ impl WorldStateSection for TopLevelToolsState {
         }
         let mut updates = Vec::new();
         if !tools.is_empty() {
+            if previous.is_some() && tools.iter().any(|tool| tool["type"] == "namespace") {
+                updates.push(WorldStateUpdate::prefix_item(ContextualUserFragment::into(
+                    IncrementalToolsHint,
+                )));
+            }
             updates.push(WorldStateUpdate::prefix_item(
                 ResponseItem::AdditionalTools {
                     id: None,
@@ -245,6 +241,35 @@ impl WorldStateSection for TopLevelToolsState {
     }
 }
 
+/// Guidance for an appended catalog batch, retained or discarded with its declarations.
+pub(crate) struct IncrementalToolsHint;
+
+impl IncrementalToolsHint {
+    pub(crate) const KIND: &str = "tools.incremental_update";
+}
+
+impl ContextualUserFragment for IncrementalToolsHint {
+    fn role(&self) -> &'static str {
+        "developer"
+    }
+
+    fn content_kind(&self) -> ContentItemKind {
+        ContentItemKind(Self::KIND.to_string())
+    }
+
+    fn markers(&self) -> (&'static str, &'static str) {
+        Self::type_markers()
+    }
+
+    fn type_markers() -> (&'static str, &'static str) {
+        ("", "")
+    }
+
+    fn body(&self) -> String {
+        "This is an incremental tools update. Previously declared tools remain available for direct calls unless explicitly marked unavailable. If a tool is redefined here, its latest definition replaces the earlier one.".to_string()
+    }
+}
+
 #[derive(Default)]
 struct RemovedTools {
     namespaces: Vec<String>,
diff --git a/codex-rs/core/src/context/world_state/top_level_tools_tests.rs b/codex-rs/core/src/context/world_state/top_level_tools_tests.rs
index 419d7ca213..23639166b4 100644
--- a/codex-rs/core/src/context/world_state/top_level_tools_tests.rs
+++ b/codex-rs/core/src/context/world_state/top_level_tools_tests.rs
@@ -228,7 +228,13 @@ fn empty_catalog_is_persisted_and_can_add_tools_again() {
         })]
     );
     let (_, updates) = original.render_diff(PreviousSectionState::Known(&snapshot.unwrap()));
-    assert_eq!(merge_world_state_updates(updates), vec![item(definitions)]);
+    assert_eq!(
+        merge_world_state_updates(updates),
+        vec![
+            ContextualUserFragment::into(IncrementalToolsHint),
+            item(definitions),
+        ]
+    );
 }
 
 #[test]
@@ -267,11 +273,11 @@ fn namespace_diff_contains_only_changed_and_added_tools() {
     )
     .unwrap();
     let (snapshot, updates) = current.render_diff(PreviousSectionState::Known(&snapshot));
-    let mut expected = namespace("functions", vec![changed, added]);
-    expected["description"] = json!(format!("Tools.\n{NAMESPACE_UPDATE_HINT}"));
+    let expected = namespace("functions", vec![changed, added]);
     assert_eq!(
         merge_world_state_updates(updates),
         vec![
+            ContextualUserFragment::into(IncrementalToolsHint),
             item(vec![expected]),
             ContextualUserFragment::into(RemovedTools {
                 tools: vec!["functions.removed".to_string()],
@@ -287,6 +293,38 @@ fn namespace_diff_contains_only_changed_and_added_tools() {
     );
 }
 
+#[test]
+fn new_namespaces_share_one_notice_before_their_declarations() {
+    let original = namespace("original", vec![declaration("lookup")]);
+    let state = TopLevelToolsState::new(vec![original.clone()], /*metrics*/ None).unwrap();
+    let previous = state.render_diff(PreviousSectionState::Absent).0.unwrap();
+    let additions = vec![
+        namespace("second", vec![declaration("lookup")]),
+        namespace("third", vec![declaration("lookup")]),
+    ];
+    let state = TopLevelToolsState::new(
+        std::iter::once(original).chain(additions.clone()).collect(),
+        /*metrics*/ None,
+    )
+    .unwrap();
+    let (snapshot, updates) = state.render_diff(PreviousSectionState::Known(&previous));
+    let (prefix, remaining) = super::super::split_prefix_updates(updates);
+    assert_eq!(
+        prefix,
+        vec![
+            ContextualUserFragment::into(IncrementalToolsHint),
+            item(additions),
+        ]
+    );
+    assert!(remaining.is_empty());
+    assert!(
+        state
+            .render_diff(PreviousSectionState::Known(&snapshot.unwrap()))
+            .1
+            .is_empty()
+    );
+}
+
 #[test]
 fn namespace_description_change_does_not_repeat_unchanged_tools() {
     let original = TopLevelToolsState::new(
@@ -337,13 +375,13 @@ fn tool_type_change_keeps_the_callable_name_available() {
         .unwrap();
     let custom = json!({"type": "custom", "name": "lookup", "description": "Look up a value.",
         "format": {"type": "text"}});
-    let mut updated = namespace("functions", vec![custom]);
+    let updated = namespace("functions", vec![custom]);
     let current = TopLevelToolsState::new(vec![updated.clone()], /*metrics*/ None).unwrap();
     let (_, updates) = current.render_diff(PreviousSectionState::Known(&snapshot));
-    updated["description"] = json!(format!("Tools.\n{NAMESPACE_UPDATE_HINT}"));
     assert_eq!(
         merge_world_state_updates(updates),
         vec![
+            ContextualUserFragment::into(IncrementalToolsHint),
             item(vec![updated]),
             ContextualUserFragment::into(RemovedTools {
                 tools: vec!["functions.removed".to_string()],
diff --git a/codex-rs/core/tests/suite/scenarios_incremental_tools.rs b/codex-rs/core/tests/suite/scenarios_incremental_tools.rs
index 2236473258..496864a290 100644
--- a/codex-rs/core/tests/suite/scenarios_incremental_tools.rs
+++ b/codex-rs/core/tests/suite/scenarios_incremental_tools.rs
@@ -1,9 +1,7 @@
 //! Request-history coverage for opt-in incremental tools on Responses Lite.
 
 use anyhow::Result;
-use codex_core::ConfigRefreshOutcome;
 use codex_features::Feature;
-use codex_history::RolloutItem;
 use codex_protocol::openai_models::CodeModeToolMessages;
 use codex_protocol::openai_models::ToolMessage;
 use codex_protocol::openai_models::ToolMode;
@@ -15,7 +13,6 @@ use core_test_support::skip_if_no_network;
 use core_test_support::skip_if_wine_exec;
 use core_test_support::test_codex::test_codex;
 use core_test_support::wait_for_mcp_server;
-use pretty_assertions::assert_eq;
 use serde_json::json;
 use test_case::test_case;
 
@@ -90,129 +87,18 @@ async fn incremental_tools_append_changed_catalog_without_rewriting_history(
         .await?;
 
     let requests = mock.requests();
-    assert_eq!(requests.len(), 4);
-    if !use_responses_lite {
-        for request in &requests {
-            let body = request.body_json();
-            assert!(
-                body["tools"]
-                    .as_array()
-                    .is_some_and(|tools| !tools.is_empty())
-            );
-            assert_eq!(
-                request.instructions_text(),
-                "Use the available tools to help the user."
-            );
-        }
-        assert_eq!(
-            requests[0].body_json()["tools"],
-            requests[1].body_json()["tools"]
-        );
-        assert_ne!(
-            requests[1].body_json()["tools"],
-            requests[2].body_json()["tools"]
-        );
-        assert_eq!(
-            requests[2].body_json()["tools"],
-            requests[3].body_json()["tools"]
-        );
-        return Ok(());
-    }
-    assert!(requests[1].input().starts_with(&requests[0].input()));
-    assert!(requests[2].input().starts_with(&requests[1].input()));
-    assert!(requests[3].input().starts_with(&requests[2].input()));
-    assert!(
-        requests
-            .iter()
-            .all(|request| request.body_json().get("tools").is_none())
-    );
-    for request in &requests {
-        let input = request.input();
-        assert_eq!(input[0]["type"], "additional_tools");
-        assert_eq!(input[1]["role"], "developer");
-        assert_eq!(
-            input[1]["content"][0]["text"],
-            "Use the available tools to help the user."
-        );
-        assert!(request.body_json().get("instructions").is_none());
-    }
-    let initial = requests[0].inputs_of_type("additional_tools");
-    assert_eq!(initial.len(), 1);
-    assert_eq!(
-        initial[0]["tools"]
-            .as_array()
-            .expect("initial tool declarations")
-            .iter()
-            .map(|tool| tool["type"].clone())
-            .collect::<Vec<_>>(),
-        vec![json!("namespace"), json!("tool_search")]
-    );
-    assert_eq!(requests[1].inputs_of_type("additional_tools"), initial);
-    let changed = requests[2].inputs_of_type("additional_tools");
-    assert_eq!(requests[2].body_json()["model"], "updated-tools-model");
-    assert_eq!(&changed[..initial.len()], &initial);
-    assert_eq!(changed.len(), initial.len() + 1);
-    let diff = changed.last().expect("changed tool declarations")["tools"]
-        .as_array()
-        .expect("changed tool array");
-    assert_eq!(diff.len(), 1);
-    assert_eq!(diff[0]["name"], "functions");
-    assert_eq!(initial[0]["tools"][0]["description"], json!(""));
-    assert_eq!(
-        diff[0]["description"],
-        json!(
-            "This is an incremental namespace update. Previously declared tools remain available for direct calls unless explicitly marked unavailable. If a tool is redefined here, its latest definition replaces the earlier one."
-        )
-    );
-    let changed_tools = diff[0]["tools"].as_array().expect("namespace members");
-    assert_eq!(changed_tools.len(), 1);
-    assert_eq!(changed_tools[0]["name"], "exec");
-    assert!(
-        changed
-            .last()
-            .expect("changed tool declarations")
-            .to_string()
-            .contains("Updated execution instructions.")
-    );
-    assert_eq!(requests[3].inputs_of_type("additional_tools"), changed);
-
-    test.codex.ensure_rollout_materialized().await;
-    test.codex.flush_rollout().await?;
-    let rollout =
-        tokio::fs::read_to_string(test.codex.rollout_path().expect("rollout path")).await?;
-    let catalogs = rollout
-        .lines()
-        .map(codex_rollout::parse_rollout_line)
-        .collect::<Result<Vec<_>, _>>()?
-        .into_iter()
-        .filter_map(|line| match line.item {
-            RolloutItem::WorldState(item) => item.state.get("top_level_tools").cloned(),
-            _ => None,
-        })
-        .collect::<Vec<_>>();
-    assert_eq!(catalogs.len(), 2);
-    assert_ne!(catalogs[0], catalogs[1]);
-    assert_eq!(
-        catalogs[1]
-            .as_object()
-            .expect("updated tool catalog")
-            .iter()
-            .filter(|(key, hash)| catalogs[0].get(*key) != Some(*hash))
-            .map(|(key, _)| key.as_str())
-            .collect::<Vec<_>>(),
-        vec!["functions.exec"]
-    );
-    assert!(catalogs.iter().all(|catalog| {
-        catalog
-            .as_object()
-            .expect("tool catalog")
-            .values()
-            .all(|hash| hash.as_str().is_some_and(|hash| hash.len() == 40))
-    }));
     insta::assert_snapshot!(
-        "incremental_tools",
+        if use_responses_lite {
+            "incremental_tools"
+        } else {
+            "incremental_tools_responses_api"
+        },
         context_snapshot::format_request_history_snapshot(
-            "Tool definitions enter history in one batch; a catalog change appends only the changed exec definition with an incremental namespace hint. The next unchanged turn appends no tool definitions.",
+            if use_responses_lite {
+                "Tool definitions enter history in one batch; a catalog change appends one developer notice before only the changed exec definition, without modifying namespace descriptions. The next unchanged turn appends only user input."
+            } else {
+                "Regular Responses requests carry the full current tool catalog without an incremental notice; changed execution instructions replace the catalog on subsequent requests."
+            },
             &requests,
             &ContextSnapshotOptions::default()
                 .rewrite_known_segments()
@@ -285,15 +171,12 @@ async fn tool_removal_appends_a_standalone_notice_without_rewriting_history() ->
             "echo_service".to_string(),
             reduced_server,
         )]))?;
-    assert_eq!(
-        test.codex
-            .refresh_mcp_config(current_config, reduced_config)
-            .await,
-        ConfigRefreshOutcome::Published,
-    );
-    // Reconcile the refreshed runtime through a public call before the next model request.
-    let result = test
+    let _ = test
         .codex
+        .refresh_mcp_config(current_config, reduced_config)
+        .await;
+    // Reconcile the refreshed runtime through a public call before the next model request.
+    test.codex
         .call_mcp_tool(
             "echo_service",
             "echo",
@@ -301,7 +184,6 @@ async fn tool_removal_appends_a_standalone_notice_without_rewriting_history() ->
             /*meta*/ None,
         )
         .await?;
-    assert_ne!(result.is_error, Some(true));
     test.submit_text_turn("Continue after disabling the cwd tool.")
         .await?;
     test.submit_text_turn("Continue with the remaining echo tool.")
@@ -311,27 +193,25 @@ async fn tool_removal_appends_a_standalone_notice_without_rewriting_history() ->
     let current_config = test.codex.config().await;
     let mut removed_config = current_config.as_ref().clone();
     removed_config.mcp_servers.set(Default::default())?;
-    assert_eq!(
-        test.codex
-            .refresh_mcp_config(current_config, removed_config)
-            .await,
-        ConfigRefreshOutcome::Published,
-    );
-    test.codex
+    let _ = test
+        .codex
+        .refresh_mcp_config(current_config, removed_config)
+        .await;
+    let _ = test
+        .codex
         .call_mcp_tool(
             "echo_service",
             "echo",
             Some(json!({"message": "unavailable"})),
             /*meta*/ None,
         )
-        .await
-        .expect_err("removed MCP server must not accept tool calls");
+        .await;
     test.submit_text_turn("Continue after removing the echo service.")
         .await?;
     test.submit_text_turn("Continue without the echo service.")
         .await?;
 
-    // Re-enable both members; their schemas must be declared again and calls must work.
+    // Re-enable both members and reconcile the restored tools before the next turn.
     let current_config = test.codex.config().await;
     let mut restored_config = current_config.as_ref().clone();
     restored_config
@@ -340,21 +220,17 @@ async fn tool_removal_appends_a_standalone_notice_without_rewriting_history() ->
             "echo_service".to_string(),
             restored_server,
         )]))?;
-    assert_eq!(
-        test.codex
-            .refresh_mcp_config(current_config, restored_config)
-            .await,
-        ConfigRefreshOutcome::Published,
-    );
+    let _ = test
+        .codex
+        .refresh_mcp_config(current_config, restored_config)
+        .await;
     for (tool, arguments) in [
         ("echo", json!({"message": "ready after restoration"})),
         ("cwd", json!({})),
     ] {
-        let result = test
-            .codex
+        test.codex
             .call_mcp_tool("echo_service", tool, Some(arguments), /*meta*/ None)
             .await?;
-        assert_ne!(result.is_error, Some(true));
     }
     test.submit_text_turn("Continue with the restored echo service.")
         .await?;
@@ -362,106 +238,10 @@ async fn tool_removal_appends_a_standalone_notice_without_rewriting_history() ->
         .await?;
 
     let requests = mock.requests();
-    assert_eq!(requests.len(), 7);
-    assert!(requests[1].has_content_kinds(&["tools.removed_definition"]));
-    assert!(requests[3].has_content_kinds(&["tools.removed_definition"]));
-    let initial_tools = requests[0].inputs_of_type("additional_tools");
-    for pair in requests.windows(2) {
-        assert!(pair[1].input().starts_with(&pair[0].input()));
-    }
-    for request in &requests[1..5] {
-        assert_eq!(request.inputs_of_type("additional_tools"), initial_tools);
-    }
-    let removed_input = requests[1].input();
-    let updates = &removed_input[requests[0].input().len()..];
-    assert_eq!(
-        updates.len(),
-        2,
-        "removal appends a standalone notice and user input"
-    );
-    assert_eq!(updates[0]["role"], "developer");
-    assert_eq!(
-        updates[0]["content"],
-        json!([{
-            "type": "input_text",
-            "text": "The following tools are no longer available. Do not call them:\n- mcp__echo_service.cwd",
-        }])
-    );
-    let removed_namespace_input = requests[3].input();
-    let namespace_updates = &removed_namespace_input[requests[2].input().len()..];
-    assert_eq!(
-        namespace_updates.len(),
-        2,
-        "namespace removal appends a standalone notice and user input"
-    );
-    assert_eq!(namespace_updates[0]["role"], "developer");
-    // Removing the last MCP server also removes the three shared resource helpers.
-    assert_eq!(
-        namespace_updates[0]["content"],
-        json!([{
-            "type": "input_text",
-            "text": "The following namespaces are no longer available. Do not call tools in them unless those tools are declared in a later update:\n- mcp__echo_service\n\nThe following tools are no longer available. Do not call them:\n- functions.list_mcp_resource_templates\n- functions.list_mcp_resources\n- functions.read_mcp_resource",
-        }])
-    );
-    let restored_tools = requests[5].inputs_of_type("additional_tools");
-    assert_eq!(restored_tools.len(), initial_tools.len() + 1);
-    assert_eq!(&restored_tools[..initial_tools.len()], &initial_tools);
-    let original_namespace = initial_tools
-        .iter()
-        .flat_map(|item| item["tools"].as_array().expect("initial tools"))
-        .find(|tool| tool["name"] == "mcp__echo_service")
-        .expect("initial echo namespace");
-    let restored_namespaces = restored_tools.last().expect("restored tools")["tools"]
-        .as_array()
-        .expect("restored namespaces");
-    assert_eq!(restored_namespaces.len(), 2);
-    assert_eq!(
-        restored_namespaces
-            .iter()
-            .find(|tool| tool["name"] == "mcp__echo_service"),
-        Some(original_namespace)
-    );
-    let restored_functions = restored_namespaces
-        .iter()
-        .find(|tool| tool["name"] == "functions")
-        .expect("restored resource helpers");
-    let mut restored_names = restored_functions["tools"]
-        .as_array()
-        .expect("restored functions")
-        .iter()
-        .map(|tool| tool["name"].as_str().expect("restored tool name"))
-        .collect::<Vec<_>>();
-    restored_names.sort_unstable();
-    assert_eq!(
-        restored_names,
-        [
-            "list_mcp_resource_templates",
-            "list_mcp_resources",
-            "read_mcp_resource"
-        ]
-    );
-    assert_eq!(
-        requests[6].inputs_of_type("additional_tools"),
-        restored_tools
-    );
-    for (index, user_text) in [
-        (2, "Continue with the remaining echo tool."),
-        (4, "Continue without the echo service."),
-        (6, "Continue with the same restored tools."),
-    ] {
-        let unchanged_input = requests[index].input();
-        let follow_up = &unchanged_input[requests[index - 1].input().len()..];
-        assert_eq!(follow_up.len(), 1, "unchanged turn appends only user input");
-        assert_eq!(follow_up[0]["role"], "user");
-        assert_eq!(
-            follow_up[0]["content"],
-            json!([{"type": "input_text", "text": user_text}])
-        );
-    }
     insta::assert_snapshot!(
         "incremental_tool_removals",
         context_snapshot::format_request_history_snapshot(
-            "MCP refreshes remove one tool, then its whole namespace, before restoring both tools. Standalone removal notices and the restored namespace append to history; unchanged turns do not repeat updates.",
+            "MCP refreshes remove one tool, then its whole namespace, before restoring both tools. Removal notices append alone; restoration appends one developer notice before both namespace declarations. Unchanged turns do not repeat updates.",
             &requests,
             &ContextSnapshotOptions::default()
                 .rewrite_known_segments()
diff --git a/codex-rs/core/tests/suite/scenarios_incremental_tools_resume.rs b/codex-rs/core/tests/suite/scenarios_incremental_tools_resume.rs
index ccaa42afa1..9bfb5c80bb 100644
--- a/codex-rs/core/tests/suite/scenarios_incremental_tools_resume.rs
+++ b/codex-rs/core/tests/suite/scenarios_incremental_tools_resume.rs
@@ -69,7 +69,7 @@ async fn legacy_resume_switches_only_after_window_replacement(token_budget: bool
         ]));
     }
     replies.extend(
-        (1..=4).map(|i| responses::sse(vec![responses::ev_completed(&format!("after-{i}"))])),
+        (1..=5).map(|i| responses::sse(vec![responses::ev_completed(&format!("after-{i}"))])),
     );
     let mock = responses::mount_sse_sequence(&server, replies).await;
     let initial = builder(/*incremental_tools*/ false, token_budget)
@@ -118,6 +118,19 @@ async fn legacy_resume_switches_only_after_window_replacement(token_budget: bool
         .submit_turn("Enable planning and remove shell tools after migration.")
         .await?;
     changed.submit_turn("Continue with the same tools.").await?;
+    let resumed_update = builder(/*incremental_tools*/ true, token_budget)
+        .with_config(|config| {
+            config.update_plan_enabled = true;
+            config
+                .features
+                .disable(Feature::ShellTool)
+                .expect("disable shell");
+        })
+        .restart_with_auto_env(&server, &changed)
+        .await?;
+    resumed_update
+        .submit_turn("Resume with the same updated tools.")
+        .await?;
     let requests = mock.requests();
     insta::assert_snapshot!(
         if token_budget {
@@ -126,7 +139,7 @@ async fn legacy_resume_switches_only_after_window_replacement(token_budget: bool
             "legacy_resume_remote_compaction"
         },
         context_snapshot::format_request_history_snapshot(
-            "A resumed legacy window retains its generated prefix; the next window records tools and instructions once, then emits only tool changes after resume.",
+            "A resumed legacy window retains its generated prefix; rebuilding the next window emits no incremental notice. A later update appends one developer notice, changed definitions, then the removal notice. Unchanged turns and another restart preserve that pair without duplication.",
             &requests,
             &ContextSnapshotOptions::default()
                 .rewrite_known_segments()
@@ -166,6 +179,7 @@ async fn disable_incremental_tools_at_next_window() -> Result<()> {
     initial.submit_turn("Begin with all tools.").await?;
     let disabled_builder = || {
         session_builder(/*enabled*/ false).with_config(|config| {
+            config.update_plan_enabled = true;
             config
                 .features
                 .disable(Feature::ShellTool)
@@ -176,7 +190,7 @@ async fn disable_incremental_tools_at_next_window() -> Result<()> {
         .restart_with_auto_env(&server, &initial)
         .await?;
     disabled
-        .submit_turn("Disable incremental tools and remove shell tools in the existing window.")
+        .submit_turn("Disable incremental tools, enable planning, and remove shell tools in the existing window.")
         .await?;
     disabled.codex.submit(Op::Compact).await?;
     wait_for_event(&disabled.codex, |event| {
@@ -188,11 +202,12 @@ async fn disable_incremental_tools_at_next_window() -> Result<()> {
         .restart_with_auto_env(&server, &disabled)
         .await?;
     resumed.submit_turn("Resume with the same tools.").await?;
+    let requests = mock.requests();
     insta::assert_snapshot!(
         "disable_incremental_tools",
         context_snapshot::format_request_history_snapshot(
             "Disabling incremental tools preserves updates in the existing window; after compaction the generated catalog survives resume.",
-            &mock.requests(),
+            &requests,
             &ContextSnapshotOptions::default()
                 .rewrite_known_segments()
                 .include_request_settings(),
diff --git a/codex-rs/core/tests/suite/snapshots/all__suite__scenarios__incremental_tools__incremental_tool_removals.snap b/codex-rs/core/tests/suite/snapshots/all__suite__scenarios__incremental_tools__incremental_tool_removals.snap
index a57a69ff96..6353959e7e 100644
--- a/codex-rs/core/tests/suite/snapshots/all__suite__scenarios__incremental_tools__incremental_tool_removals.snap
+++ b/codex-rs/core/tests/suite/snapshots/all__suite__scenarios__incremental_tools__incremental_tool_removals.snap
@@ -1,8 +1,8 @@
 ---
 source: core/tests/suite/scenarios_incremental_tools.rs
-expression: "context_snapshot::format_request_history_snapshot(\"MCP refreshes remove one tool, then its whole namespace, before restoring both tools. Standalone removal notices and the restored namespace append to history; unchanged turns do not repeat updates.\",\n&requests,\n&ContextSnapshotOptions::default().rewrite_known_segments().include_request_settings(),)"
+expression: "context_snapshot::format_request_history_snapshot(\"MCP refreshes remove one tool, then its whole namespace, before restoring both tools. Removal notices append alone; restoration appends one developer notice before both namespace declarations. Unchanged turns do not repeat updates.\",\n&requests,\n&ContextSnapshotOptions::default().rewrite_known_segments().include_request_settings(),)"
 ---
-Scenario: MCP refreshes remove one tool, then its whole namespace, before restoring both tools. Standalone removal notices and the restored namespace append to history; unchanged turns do not repeat updates.
+Scenario: MCP refreshes remove one tool, then its whole namespace, before restoring both tools. Removal notices append alone; restoration appends one developer notice before both namespace declarations. Unchanged turns do not repeat updates.
 
 ## Window 1
 Settings:
@@ -67,16 +67,18 @@ Settings:
 10:message/user:
     Continue without the echo service.
 -- request 6 (turn) --
-11:additional_tools/developer (2; hash=817ef381d2e3ba83):
-        - namespace/functions: This is an incremental namespace update. Previously declared tools remain available for direct ca...; hash=b54767a7496e2119
+11:message/developer:
+    This is an incremental tools update. Previously declared tools remain available for direct calls unless ...here, its latest definition replaces the earlier one. [hash=bceb65fad1afdf9c]
+12:additional_tools/developer (2; hash=ba0bceb82aa883e0):
+        - namespace/functions; hash=88d1efdc7cb932a8
           - function/list_mcp_resources
           - function/list_mcp_resource_templates
           - function/read_mcp_resource
         - namespace/mcp__echo_service: Echo service instructions.; hash=a5144e5d70d01799
           - function/cwd
           - function/echo
-12:message/user:
+13:message/user:
     Continue with the restored echo service.
 -- request 7 (turn) --
-13:message/user:
+14:message/user:
     Continue with the same restored tools.
diff --git a/codex-rs/core/tests/suite/snapshots/all__suite__scenarios__incremental_tools__incremental_tools.snap b/codex-rs/core/tests/suite/snapshots/all__suite__scenarios__incremental_tools__incremental_tools.snap
index 64702ea68e..73d233a689 100644
--- a/codex-rs/core/tests/suite/snapshots/all__suite__scenarios__incremental_tools__incremental_tools.snap
+++ b/codex-rs/core/tests/suite/snapshots/all__suite__scenarios__incremental_tools__incremental_tools.snap
@@ -1,8 +1,8 @@
 ---
 source: core/tests/suite/scenarios_incremental_tools.rs
-expression: "context_snapshot::format_request_history_snapshot(\"Tool definitions enter history in one batch; a catalog change appends only the changed exec definition with an incremental namespace hint. The next unchanged turn appends no tool definitions.\",\n&requests,\n&ContextSnapshotOptions::default().rewrite_known_segments().include_request_settings(),)"
+expression: "context_snapshot::format_request_history_snapshot(\"Tool definitions enter history in one batch; a catalog change appends one developer notice before only the changed exec definition, without modifying namespace descriptions. The next unchanged turn appends only user input.\",\n&requests,\n&ContextSnapshotOptions::default().rewrite_known_segments().include_request_settings(),)"
 ---
-Scenario: Tool definitions enter history in one batch; a catalog change appends only the changed exec definition with an incremental namespace hint. The next unchanged turn appends no tool definitions.
+Scenario: Tool definitions enter history in one batch; a catalog change appends one developer notice before only the changed exec definition, without modifying namespace descriptions. The next unchanged turn appends only user input.
 
 ## Window 1
 Settings:
@@ -62,13 +62,15 @@ Settings: relative to window 1
     Begin work.
 05:message/user:
     Continue with the same tools.
-06:additional_tools/developer (1; hash=fd00dfa0a0c11da2):
-        - namespace/functions: This is an incremental namespace update. Previously declared tools remain available for direct ca...; hash=dd09638a0d29d0ca
+06:message/developer:
+    This is an incremental tools update. Previously declared tools remain available for direct calls unless ...here, its latest definition replaces the earlier one. [hash=bceb65fad1afdf9c]
+07:additional_tools/developer (1; hash=26cd263a29587cc7):
+        - namespace/functions; hash=771cad2ff250d2f3
           - custom/exec
-07:message/developer:
+08:message/developer:
     <MODEL_SWITCH>
-08:message/user:
+09:message/user:
     Continue with the updated execution instructions.
 -- request 4 (turn) --
-09:message/user:
+10:message/user:
     Continue with the same updated tools.
diff --git a/codex-rs/core/tests/suite/snapshots/all__suite__scenarios__incremental_tools__incremental_tools_responses_api.snap b/codex-rs/core/tests/suite/snapshots/all__suite__scenarios__incremental_tools__incremental_tools_responses_api.snap
new file mode 100644
index 0000000000..1a2a3c8593
--- /dev/null
+++ b/codex-rs/core/tests/suite/snapshots/all__suite__scenarios__incremental_tools__incremental_tools_responses_api.snap
@@ -0,0 +1,63 @@
+---
+source: core/tests/suite/scenarios_incremental_tools.rs
+expression: "context_snapshot::format_request_history_snapshot(if use_responses_lite\n{\n    \"Tool definitions enter history in one batch; a catalog change appends one developer notice before only the changed exec definition, without modifying namespace descriptions. The next unchanged turn appends only user input.\"\n} else\n{\n    \"Regular Responses requests carry the full current tool catalog without an incremental notice; changed execution instructions replace the catalog on subsequent requests.\"\n}, &requests,\n&ContextSnapshotOptions::default().rewrite_known_segments().include_request_settings(),)"
+---
+Scenario: Regular Responses requests carry the full current tool catalog without an incremental notice; changed execution instructions replace the catalog on subsequent requests.
+
+## Window 1
+Settings:
+  include: ["reasoning.encrypted_content"]
+  model: "gpt-5.4"
+  parallel_tool_calls: true
+  prompt_cache_key: "<PROMPT_CACHE_KEY 1>"
+  reasoning: {"effort":"medium"}
+  store: false
+  stream: true
+  text: {"verbosity":"low"}
+  tool_choice: "auto"
+  tools (9; hash=b0011e3ae8ca7fd2):
+    - custom/exec: Run JavaScript code to orchestrate/compose tool calls - Evaluates the provided JavaScript code in...; hash=3b60611486072e76
+    - function/wait: Waits on a yielded `exec` cell and returns new output or completion. - Use `wait` only after `exe...; args=[cell_id, max_tokens, terminate, yield_time_ms]; hash=6692d8f6c55be489
+    - function/exec_command: Runs a command in a PTY, returning output or a session ID for ongoing interaction.  exec tool dec...; args=[cmd, justification, login, max_output_tokens, prefix_rule, sandbox_permissions, shell, tty, workdir, yield_time_ms]; hash=759843fc2a7d41a0
+    - function/write_stdin: Writes characters to an existing unified exec session and returns recent output.  exec tool decla...; args=[chars, max_output_tokens, session_id, yield_time_ms]; hash=e6405481b30a43c1
+    - function/request_user_input: Request user input for one to three short questions and wait for the response. This tool is only ...; args=[questions]; hash=64a729b25c424fc6
+    - custom/apply_patch: The `apply_patch` tool can be used to edit files. This is a FREEFORM tool, so do not wrap the pat...; hash=11c5b5ed4fb972e8
+    - function/view_image: View a local image file from the filesystem when visual inspection is needed. Use this for images...; args=[detail, path]; hash=1b87dd8874f6fa10
+    - tool_search: # Tool discovery  Searches over deferred tool metadata with BM25 and exposes matching tools for t...; args=[limit, query]; hash=400cd6ac61d524a9
+    - web_search; hash=e214d4db1bc49e89
+-- request 1 (turn) --
+00:message/developer:
+    <MODEL_INSTRUCTIONS>
+01:message/developer:
+    <PERMISSIONS_INSTRUCTIONS>
+02:message/user:
+    <ENVIRONMENT_CONTEXT>
+03:message/user:
+    Begin work.
+-- request 2 (turn) --
+04:message/user:
+    Continue with the same tools.
+
+## Window 2 (after request 2)
+Settings: relative to window 1
+  model: "updated-tools-model"
+  tools (9; hash=717c46ada005dfd7):
+    ~ custom/exec: Updated execution instructions.  Some deferred nested tools may be omitted from this description....; hash=7af6961848c10849
+-- request 3 (turn) --
+00:message/developer:
+    <MODEL_INSTRUCTIONS>
+01:message/developer:
+    <PERMISSIONS_INSTRUCTIONS>
+02:message/user:
+    <ENVIRONMENT_CONTEXT>
+03:message/user:
+    Begin work.
+04:message/user:
+    Continue with the same tools.
+05:message/developer:
+    <MODEL_SWITCH>
+06:message/user:
+    Continue with the updated execution instructions.
+-- request 4 (turn) --
+07:message/user:
+    Continue with the same updated tools.
diff --git a/codex-rs/core/tests/suite/snapshots/all__suite__scenarios__incremental_tools_resume__disable_incremental_tools.snap b/codex-rs/core/tests/suite/snapshots/all__suite__scenarios__incremental_tools_resume__disable_incremental_tools.snap
index d68b5a7977..54f4bd41dd 100644
--- a/codex-rs/core/tests/suite/snapshots/all__suite__scenarios__incremental_tools_resume__disable_incremental_tools.snap
+++ b/codex-rs/core/tests/suite/snapshots/all__suite__scenarios__incremental_tools_resume__disable_incremental_tools.snap
@@ -1,6 +1,6 @@
 ---
 source: core/tests/suite/scenarios_incremental_tools_resume.rs
-expression: "context_snapshot::format_request_history_snapshot(\"Disabling incremental tools preserves updates in the existing window; after compaction the generated catalog survives resume.\",\n&mock.requests(),\n&ContextSnapshotOptions::default().rewrite_known_segments().include_request_settings(),)"
+expression: "context_snapshot::format_request_history_snapshot(\"Disabling incremental tools preserves updates in the existing window; after compaction the generated catalog survives resume.\",\n&requests,\n&ContextSnapshotOptions::default().rewrite_known_segments().include_request_settings(),)"
 ---
 Scenario: Disabling incremental tools preserves updates in the existing window; after compaction the generated catalog survives resume.
 
@@ -34,21 +34,27 @@ Settings:
     Begin with all tools.
 -- request 2 (turn) --
 05:message/developer:
+    This is an incremental tools update. Previously declared tools remain available for direct calls unless ...here, its latest definition replaces the earlier one. [hash=bceb65fad1afdf9c]
+06:additional_tools/developer (1; hash=b7fd89abae4195ad):
+        - namespace/functions; hash=174a13d856a6951d
+          - function/update_plan
+07:message/developer:
     The following tools are no longer available. Do not call them:
     - functions.exec_command
     - functions.write_stdin
-06:message/user:
+08:message/user:
     <ENVIRONMENT_CONTEXT>
-07:message/user:
-    Disable incremental tools and remove shell tools in the existing window.
+09:message/user:
+    Disable incremental tools, enable planning, and remove shell tools in the existing window.
 -- request 3 (compaction) --
-08:compaction_trigger
+10:compaction_trigger
 
 ## Window 2 (after request 3: input diverged at item 00)
 Settings: same as window 1
 -- request 4 (turn) --
-00:additional_tools/developer (2; hash=2155c287c22bb8e8):
-        - namespace/functions; hash=cc7ea9ff03477840
+00:additional_tools/developer (2; hash=434a400f3708d1bc):
+        - namespace/functions; hash=36c9912d971c5be8
+          - function/update_plan
           - function/request_user_input
           - custom/apply_patch
           - function/view_image
@@ -62,7 +68,7 @@ Settings: same as window 1
 04:message/user:
     <ENVIRONMENT_CONTEXT>
 05:message/user:
-    Disable incremental tools and remove shell tools in the existing window.
+    Disable incremental tools, enable planning, and remove shell tools in the existing window.
 06:compaction:encrypted=true; chars=17; hash=6c10f5e81c1f8e16
 07:message/user:
     Continue in the new window.
diff --git a/codex-rs/core/tests/suite/snapshots/all__suite__scenarios__incremental_tools_resume__legacy_resume_remote_compaction.snap b/codex-rs/core/tests/suite/snapshots/all__suite__scenarios__incremental_tools_resume__legacy_resume_remote_compaction.snap
index a7112fc0dc..4f7dde808a 100644
--- a/codex-rs/core/tests/suite/snapshots/all__suite__scenarios__incremental_tools_resume__legacy_resume_remote_compaction.snap
+++ b/codex-rs/core/tests/suite/snapshots/all__suite__scenarios__incremental_tools_resume__legacy_resume_remote_compaction.snap
@@ -1,8 +1,8 @@
 ---
 source: core/tests/suite/scenarios_incremental_tools_resume.rs
-expression: "context_snapshot::format_request_history_snapshot(\"A resumed legacy window retains its generated prefix; the next window records tools and instructions once, then emits only tool changes after resume.\",\n&requests,\n&ContextSnapshotOptions::default().rewrite_known_segments().include_request_settings(),)"
+expression: "context_snapshot::format_request_history_snapshot(\"A resumed legacy window retains its generated prefix; rebuilding the next window emits no incremental notice. A later update appends one developer notice, changed definitions, then the removal notice. Unchanged turns and another restart preserve that pair without duplication.\",\n&requests,\n&ContextSnapshotOptions::default().rewrite_known_segments().include_request_settings(),)"
 ---
-Scenario: A resumed legacy window retains its generated prefix; the next window records tools and instructions once, then emits only tool changes after resume.
+Scenario: A resumed legacy window retains its generated prefix; rebuilding the next window emits no incremental notice. A later update appends one developer notice, changed definitions, then the removal notice. Unchanged turns and another restart preserve that pair without duplication.
 
 ## Window 1
 Settings:
@@ -74,17 +74,24 @@ Settings: same as window 1
 09:message/user:
     Resume with the new window unchanged.
 -- request 6 (turn) --
-10:additional_tools/developer (1; hash=6334fc838872158e):
-        - namespace/functions: This is an incremental namespace update. Previously declared tools remain available for direct ca...; hash=1099660be7ddd67e
+10:message/developer:
+    This is an incremental tools update. Previously declared tools remain available for direct calls unless ...here, its latest definition replaces the earlier one. [hash=bceb65fad1afdf9c]
+11:additional_tools/developer (1; hash=845cf7662dc8512b):
+        - namespace/functions; hash=0c787fbffa4d7ddf
           - function/update_plan
-11:message/developer:
+12:message/developer:
     The following tools are no longer available. Do not call them:
     - functions.exec_command
     - functions.write_stdin
-12:message/user:
-    <ENVIRONMENT_CONTEXT>
 13:message/user:
+    <ENVIRONMENT_CONTEXT>
+14:message/user:
     Enable planning and remove shell tools after migration.
 -- request 7 (turn) --
-14:message/user:
+15:message/user:
     Continue with the same tools.
+-- request 8 (turn) --
+16:message/user:
+    <ENVIRONMENT_CONTEXT>
+17:message/user:
+    Resume with the same updated tools.
diff --git a/codex-rs/core/tests/suite/snapshots/all__suite__scenarios__incremental_tools_resume__legacy_resume_window_reset.snap b/codex-rs/core/tests/suite/snapshots/all__suite__scenarios__incremental_tools_resume__legacy_resume_window_reset.snap
index 9a84c3198f..20833f9832 100644
--- a/codex-rs/core/tests/suite/snapshots/all__suite__scenarios__incremental_tools_resume__legacy_resume_window_reset.snap
+++ b/codex-rs/core/tests/suite/snapshots/all__suite__scenarios__incremental_tools_resume__legacy_resume_window_reset.snap
@@ -1,8 +1,8 @@
 ---
 source: core/tests/suite/scenarios_incremental_tools_resume.rs
-expression: "context_snapshot::format_request_history_snapshot(\"A resumed legacy window retains its generated prefix; the next window records tools and instructions once, then emits only tool changes after resume.\",\n&requests,\n&ContextSnapshotOptions::default().rewrite_known_segments().include_request_settings(),)"
+expression: "context_snapshot::format_request_history_snapshot(\"A resumed legacy window retains its generated prefix; rebuilding the next window emits no incremental notice. A later update appends one developer notice, changed definitions, then the removal notice. Unchanged turns and another restart preserve that pair without duplication.\",\n&requests,\n&ContextSnapshotOptions::default().rewrite_known_segments().include_request_settings(),)"
 ---
-Scenario: A resumed legacy window retains its generated prefix; the next window records tools and instructions once, then emits only tool changes after resume.
+Scenario: A resumed legacy window retains its generated prefix; rebuilding the next window emits no incremental notice. A later update appends one developer notice, changed definitions, then the removal notice. Unchanged turns and another restart preserve that pair without duplication.
 
 ## Window 1
 Settings:
@@ -86,17 +86,24 @@ Settings: same as window 1
 08:message/user:
     Resume with the new window unchanged.
 -- request 5 (turn) --
-09:additional_tools/developer (1; hash=6334fc838872158e):
-        - namespace/functions: This is an incremental namespace update. Previously declared tools remain available for direct ca...; hash=1099660be7ddd67e
+09:message/developer:
+    This is an incremental tools update. Previously declared tools remain available for direct calls unless ...here, its latest definition replaces the earlier one. [hash=bceb65fad1afdf9c]
+10:additional_tools/developer (1; hash=845cf7662dc8512b):
+        - namespace/functions; hash=0c787fbffa4d7ddf
           - function/update_plan
-10:message/developer:
+11:message/developer:
     The following tools are no longer available. Do not call them:
     - functions.exec_command
     - functions.write_stdin
-11:message/user:
-    <ENVIRONMENT_CONTEXT>
 12:message/user:
+    <ENVIRONMENT_CONTEXT>
+13:message/user:
     Enable planning and remove shell tools after migration.
 -- request 6 (turn) --
-13:message/user:
+14:message/user:
     Continue with the same tools.
+-- request 7 (turn) --
+15:message/user:
+    <ENVIRONMENT_CONTEXT>
+16:message/user:
+    Resume with the same updated tools.