diff --git a/deepseek-recipe/src/protocol/openai/responses/request/mod.rs b/deepseek-recipe/src/protocol/openai/responses/request/mod.rs
index 7ae9cff..a28bd08 100644
--- a/deepseek-recipe/src/protocol/openai/responses/request/mod.rs
+++ b/deepseek-recipe/src/protocol/openai/responses/request/mod.rs
@@ -35,8 +35,9 @@
 //! output is placed right after that output. For V4, a namespace tool is named
 //! `{namespace}__{name}`, or `{namespace}{name}` when the namespace ends with
 //! or the name starts with an underscore, and `apply_patch` uses the V4
-//! description. The caller supplies model inference, tool execution, and HTTP
-//! transport.
+//! description. Flattened namespace names also avoid top-level names found in
+//! historical calls, including calls to tools no longer declared in the request.
+//! The caller supplies model inference, tool execution, and HTTP transport.
 //!
 //! [`WebSearchBehavior::Reject`]: crate::request::WebSearchBehavior::Reject
 //! [`ModelVersion::DeepseekV41Flash`]:
diff --git a/deepseek-recipe/src/protocol/openai/responses/request/tools.rs b/deepseek-recipe/src/protocol/openai/responses/request/tools.rs
index 9e0919b..63b92b2 100644
--- a/deepseek-recipe/src/protocol/openai/responses/request/tools.rs
+++ b/deepseek-recipe/src/protocol/openai/responses/request/tools.rs
@@ -83,6 +83,21 @@ impl ResponsesToolSet {
             model_version,
             response_options: ResponseOptions::default(),
         };
+        if let Some(ResponsesInput::Items(items)) = input {
+            converted
+                .top_level_names
+                .extend(items.iter().filter_map(|item| match item {
+                    ResponsesInputItem::Typed(ResponsesTypedInputItem::FunctionCall(call))
+                        if call.namespace.is_none() =>
+                    {
+                        Some(call.name.clone())
+                    }
+                    ResponsesInputItem::Typed(ResponsesTypedInputItem::CustomToolCall(call)) => {
+                        Some(call.name.clone())
+                    }
+                    _ => None,
+                }));
+        }
         for (item_index, tools) in groups {
             let start = converted.client_tools.len();
             for (index, tool) in tools.into_iter().enumerate() {
diff --git a/deepseek-recipe/tests/responses_history.rs b/deepseek-recipe/tests/responses_history.rs
new file mode 100644
index 0000000..760231d
--- /dev/null
+++ b/deepseek-recipe/tests/responses_history.rs
@@ -0,0 +1,139 @@
+use std::collections::HashMap;
+
+use deepseek_recipe::openai::ResponsesRequest;
+use deepseek_recipe::request::{ConversionOptions, ProtocolRequest};
+use deepseek_recipe_core::messages::InputMessage;
+use serde_json::{Value, json};
+
+fn convert_history(
+    model: &str,
+    bare_name: &str,
+    reversed: bool,
+    declared: bool,
+) -> (HashMap<String, String>, Vec<String>) {
+    let mut calls = vec![
+        json!({"type": "function_call", "call_id": "namespaced", "namespace": "ns", "name": "run", "arguments": "{}"}),
+        json!({"type": "function_call", "call_id": "bare", "name": bare_name, "arguments": "{}"}),
+    ];
+    if reversed {
+        calls.reverse();
+    }
+    calls.extend([
+        json!({"type": "function_call_output", "call_id": "namespaced", "output": "namespace result"}),
+        json!({"type": "function_call_output", "call_id": "bare", "output": "top-level result"}),
+        json!({"role": "user", "content": "continue"}),
+    ]);
+    let tools: Vec<Value> = if declared {
+        vec![
+            json!({"type": "namespace", "name": "ns", "tools": [{"type": "function", "name": "run"}]}),
+        ]
+    } else {
+        Vec::new()
+    };
+    let request: ResponsesRequest = serde_json::from_value(json!({
+        "model": model,
+        "reasoning": {"effort": "none"},
+        "input": calls,
+        "tools": tools,
+    }))
+    .unwrap();
+    let converted = request.convert(ConversionOptions::default()).unwrap();
+    let mut names = HashMap::new();
+    for message in &converted.conversation.messages {
+        if let InputMessage::Assistant {
+            tool_calls: Some(calls),
+            ..
+        } = message
+        {
+            for call in calls {
+                names.insert(call.id.clone(), call.name.clone());
+            }
+        }
+    }
+    if declared {
+        let mapped = converted
+            .response_options
+            .namespace_tool_map
+            .as_ref()
+            .unwrap();
+        assert_eq!(
+            mapped.get(&names["namespaced"]),
+            Some(&("ns".to_owned(), "run".to_owned()))
+        );
+    }
+    let declarations = converted
+        .conversation
+        .tools
+        .iter()
+        .map(|tool| tool.name.clone())
+        .collect();
+    (names, declarations)
+}
+
+#[test]
+fn a_historical_custom_call_reserves_its_original_name() {
+    let request: ResponsesRequest = serde_json::from_value(json!({
+        "model": "DeepSeek-V4-Pro",
+        "reasoning": {"effort": "none"},
+        "tools": [{"type": "namespace", "name": "apply_", "tools": [{"type": "function", "name": "patch"}]}],
+        "input": [
+            {"type": "custom_tool_call", "call_id": "old_patch", "name": "apply_patch", "input": "old patch"},
+            {"type": "custom_tool_call_output", "call_id": "old_patch", "output": "done"},
+            {"role": "user", "content": "continue"}
+        ]
+    })).unwrap();
+    let converted = request.convert(ConversionOptions::default()).unwrap();
+    assert_ne!(converted.conversation.tools[0].name, "apply_patch");
+    let historical = converted
+        .conversation
+        .messages
+        .iter()
+        .find_map(|message| {
+            if let InputMessage::Assistant {
+                tool_calls: Some(calls),
+                ..
+            } = message
+            {
+                calls.first()
+            } else {
+                None
+            }
+        })
+        .unwrap();
+    assert_eq!(historical.name, "apply_patch");
+}
+
+#[test]
+fn undeclared_historical_namespace_does_not_alias_a_bare_tool() {
+    for (model, bare) in [
+        ("DeepSeek-V4-Pro", "ns__run"),
+        ("DeepSeek-V4.1-Flash", "ns::run"),
+    ] {
+        for reversed in [false, true] {
+            let (names, _) = convert_history(model, bare, reversed, false);
+            assert_eq!(names["bare"], bare);
+            assert_ne!(
+                names["namespaced"], names["bare"],
+                "{model}, reversed={reversed}"
+            );
+        }
+    }
+}
+
+#[test]
+fn current_namespace_reserves_historical_bare_names_before_flattening() {
+    for (model, bare) in [
+        ("DeepSeek-V4-Pro", "ns__run"),
+        ("DeepSeek-V4.1-Flash", "ns::run"),
+    ] {
+        for reversed in [false, true] {
+            let (names, declarations) = convert_history(model, bare, reversed, true);
+            assert_eq!(names["bare"], bare);
+            assert_ne!(
+                names["namespaced"], names["bare"],
+                "{model}, reversed={reversed}"
+            );
+            assert_eq!(declarations, vec![names["namespaced"].clone()]);
+        }
+    }
+}