diff --git a/codex-rs/code-mode-protocol/src/description.rs b/codex-rs/code-mode-protocol/src/description.rs
index dde8ac2980..860074e769 100644
--- a/codex-rs/code-mode-protocol/src/description.rs
+++ b/codex-rs/code-mode-protocol/src/description.rs
@@ -5,6 +5,7 @@ use serde_json::Value as JsonValue;
 use std::collections::BTreeMap;
 
 use crate::PUBLIC_TOOL_NAME;
+use crate::json_schema_types::render_json_schema_to_typescript;
 
 const MAX_JS_SAFE_INTEGER: u64 = (1_u64 << 53) - 1;
 const DEFERRED_NESTED_TOOLS_GUIDANCE: &str = r#"Some deferred nested tools may be omitted from this description. They are still available on the global `tools` object and listed in `ALL_TOOLS`.
@@ -332,8 +333,7 @@ pub fn build_exec_tool_description(
             }
         }
 
-        let nested_tool_reference = nested_tool_sections.join("\n\n");
-        sections.push(nested_tool_reference);
+        sections.push(nested_tool_sections.join("\n\n"));
     }
 
     sections.join("\n\n")
@@ -400,7 +400,7 @@ pub fn render_code_mode_sample(
 ) -> String {
     let declaration = format!(
         "declare const tools: {{ {} }};",
-        render_code_mode_tool_declaration(tool_name, input_name, input_type, output_type)
+        render_code_mode_tool_declaration(tool_name, input_name, &input_type, &output_type)
     );
     format!("{description}\n\nexec tool declaration:\n```ts\n{declaration}\n```")
 }
@@ -446,8 +446,8 @@ fn render_code_mode_sample_for_definition(definition: &ToolDefinition) -> String
 fn render_code_mode_tool_declaration(
     tool_name: &str,
     input_name: &str,
-    input_type: String,
-    output_type: String,
+    input_type: &str,
+    output_type: &str,
 ) -> String {
     let tool_name = normalize_code_mode_identifier(tool_name);
     format!("{tool_name}({input_name}: {input_type}): Promise<{output_type}>;")
@@ -461,10 +461,6 @@ fn render_tool_heading(global_name: &str, raw_name: &str) -> String {
     }
 }
 
-pub fn render_json_schema_to_typescript(schema: &JsonValue) -> String {
-    render_json_schema_to_typescript_inner(schema)
-}
-
 fn mcp_structured_content_schema(output_schema: Option<&JsonValue>) -> Option<&JsonValue> {
     let output_schema = output_schema?;
     let properties = output_schema
@@ -506,226 +502,6 @@ fn mcp_structured_content_schema(output_schema: Option<&JsonValue>) -> Option<&J
     )
 }
 
-fn render_json_schema_to_typescript_inner(schema: &JsonValue) -> String {
-    match schema {
-        JsonValue::Bool(true) => "unknown".to_string(),
-        JsonValue::Bool(false) => "never".to_string(),
-        JsonValue::Object(map) => {
-            if let Some(value) = map.get("const") {
-                return render_json_schema_literal(value);
-            }
-
-            if let Some(values) = map.get("enum").and_then(JsonValue::as_array) {
-                let rendered = values
-                    .iter()
-                    .map(render_json_schema_literal)
-                    .collect::<Vec<_>>();
-                if !rendered.is_empty() {
-                    return rendered.join(" | ");
-                }
-            }
-
-            for key in ["anyOf", "oneOf"] {
-                if let Some(variants) = map.get(key).and_then(JsonValue::as_array) {
-                    let rendered = variants
-                        .iter()
-                        .map(render_json_schema_to_typescript_inner)
-                        .collect::<Vec<_>>();
-                    if !rendered.is_empty() {
-                        return rendered.join(" | ");
-                    }
-                }
-            }
-
-            if let Some(variants) = map.get("allOf").and_then(JsonValue::as_array) {
-                let rendered = variants
-                    .iter()
-                    .map(render_json_schema_to_typescript_inner)
-                    .collect::<Vec<_>>();
-                if !rendered.is_empty() {
-                    return rendered.join(" & ");
-                }
-            }
-
-            if let Some(schema_type) = map.get("type") {
-                if let Some(types) = schema_type.as_array() {
-                    let rendered = types
-                        .iter()
-                        .filter_map(JsonValue::as_str)
-                        .map(|schema_type| render_json_schema_type_keyword(map, schema_type))
-                        .collect::<Vec<_>>();
-                    if !rendered.is_empty() {
-                        return rendered.join(" | ");
-                    }
-                }
-
-                if let Some(schema_type) = schema_type.as_str() {
-                    return render_json_schema_type_keyword(map, schema_type);
-                }
-            }
-
-            if map.contains_key("properties")
-                || map.contains_key("additionalProperties")
-                || map.contains_key("required")
-            {
-                return render_json_schema_object(map);
-            }
-
-            if map.contains_key("items") || map.contains_key("prefixItems") {
-                return render_json_schema_array(map);
-            }
-
-            "unknown".to_string()
-        }
-        _ => "unknown".to_string(),
-    }
-}
-
-fn render_json_schema_type_keyword(
-    map: &serde_json::Map<String, JsonValue>,
-    schema_type: &str,
-) -> String {
-    match schema_type {
-        "string" => "string".to_string(),
-        "number" | "integer" => "number".to_string(),
-        "boolean" => "boolean".to_string(),
-        "null" => "null".to_string(),
-        "array" => render_json_schema_array(map),
-        "object" => render_json_schema_object(map),
-        _ => "unknown".to_string(),
-    }
-}
-
-fn render_json_schema_array(map: &serde_json::Map<String, JsonValue>) -> String {
-    if let Some(items) = map.get("items") {
-        let item_type = render_json_schema_to_typescript_inner(items);
-        return format!("Array<{item_type}>");
-    }
-
-    if let Some(items) = map.get("prefixItems").and_then(JsonValue::as_array) {
-        let item_types = items
-            .iter()
-            .map(render_json_schema_to_typescript_inner)
-            .collect::<Vec<_>>();
-        if !item_types.is_empty() {
-            return format!("[{}]", item_types.join(", "));
-        }
-    }
-
-    "unknown[]".to_string()
-}
-
-fn append_additional_properties_line(
-    lines: &mut Vec<String>,
-    map: &serde_json::Map<String, JsonValue>,
-    properties: &serde_json::Map<String, JsonValue>,
-    line_prefix: &str,
-) {
-    if let Some(additional_properties) = map.get("additionalProperties") {
-        let property_type = match additional_properties {
-            JsonValue::Bool(true) => Some("unknown".to_string()),
-            JsonValue::Bool(false) => None,
-            value => Some(render_json_schema_to_typescript_inner(value)),
-        };
-
-        if let Some(property_type) = property_type {
-            lines.push(format!("{line_prefix}[key: string]: {property_type};"));
-        }
-    } else if properties.is_empty() {
-        lines.push(format!("{line_prefix}[key: string]: unknown;"));
-    }
-}
-
-fn has_property_description(value: &JsonValue) -> bool {
-    value
-        .get("description")
-        .and_then(JsonValue::as_str)
-        .is_some_and(|description| !description.is_empty())
-}
-
-fn render_json_schema_object_property(name: &str, value: &JsonValue, required: &[&str]) -> String {
-    let optional = if required.iter().any(|required_name| required_name == &name) {
-        ""
-    } else {
-        "?"
-    };
-    let property_name = render_json_schema_property_name(name);
-    let property_type = render_json_schema_to_typescript_inner(value);
-    format!("{property_name}{optional}: {property_type};")
-}
-
-fn render_json_schema_object(map: &serde_json::Map<String, JsonValue>) -> String {
-    let required = map
-        .get("required")
-        .and_then(JsonValue::as_array)
-        .map(|items| {
-            items
-                .iter()
-                .filter_map(JsonValue::as_str)
-                .collect::<Vec<_>>()
-        })
-        .unwrap_or_default();
-    let properties = map
-        .get("properties")
-        .and_then(JsonValue::as_object)
-        .cloned()
-        .unwrap_or_default();
-
-    let mut sorted_properties = properties.iter().collect::<Vec<_>>();
-    sorted_properties.sort_unstable_by_key(|(name_a, _)| *name_a);
-    if sorted_properties
-        .iter()
-        .any(|(_, value)| has_property_description(value))
-    {
-        let mut lines = vec!["{".to_string()];
-        for (name, value) in sorted_properties {
-            if let Some(description) = value.get("description").and_then(JsonValue::as_str) {
-                for description_line in description
-                    .lines()
-                    .map(str::trim)
-                    .filter(|line| !line.is_empty())
-                {
-                    lines.push(format!("  // {description_line}"));
-                }
-            }
-
-            lines.push(format!(
-                "  {}",
-                render_json_schema_object_property(name, value, &required)
-            ));
-        }
-
-        append_additional_properties_line(&mut lines, map, &properties, "  ");
-        lines.push("}".to_string());
-        return lines.join("\n");
-    }
-
-    let mut lines = sorted_properties
-        .into_iter()
-        .map(|(name, value)| render_json_schema_object_property(name, value, &required))
-        .collect::<Vec<_>>();
-
-    append_additional_properties_line(&mut lines, map, &properties, "");
-
-    if lines.is_empty() {
-        return "{}".to_string();
-    }
-
-    format!("{{ {} }}", lines.join(" "))
-}
-
-fn render_json_schema_property_name(name: &str) -> String {
-    if normalize_code_mode_identifier(name) == name {
-        name.to_string()
-    } else {
-        serde_json::to_string(name).unwrap_or_else(|_| format!("\"{}\"", name.replace('"', "\\\"")))
-    }
-}
-
-fn render_json_schema_literal(value: &JsonValue) -> String {
-    serde_json::to_string(value).unwrap_or_else(|_| "unknown".to_string())
-}
-
 #[cfg(test)]
 mod tests {
     use super::CodeModeToolKind;
@@ -875,6 +651,48 @@ mod tests {
         ));
     }
 
+    #[test]
+    fn code_mode_types_structured_content_result_refs() {
+        let definition = ToolDefinition {
+            name: "mcp__sample__search".to_string(),
+            tool_name: ToolName::namespaced("mcp__sample__", "search"),
+            description: "Search".to_string(),
+            kind: CodeModeToolKind::Function,
+            input_schema: Some(json!({
+                "type": "object",
+                "properties": {},
+                "additionalProperties": false
+            })),
+            output_schema: Some(mcp_call_tool_result_schema(json!({
+                "type": "object",
+                "properties": {
+                    "results": {
+                        "type": "array",
+                        "items": { "$ref": "#/definitions/Result~1item~0v1" }
+                    }
+                },
+                "required": ["results"],
+                "additionalProperties": false,
+                "definitions": {
+                    "Result/item~v1": {
+                        "type": "object",
+                        "properties": {
+                            "id": { "type": "string" },
+                            "score": { "type": "number" }
+                        },
+                        "required": ["id", "score"],
+                        "additionalProperties": false
+                    }
+                }
+            }))),
+        };
+
+        let description = augment_tool_definition(definition).description;
+        assert!(description.contains(
+            "mcp__sample__search(args: {}): Promise<CallToolResult<{ results: Array<{ id: string; score: number; }>; }>>;"
+        ));
+    }
+
     #[test]
     fn code_mode_only_description_includes_nested_tools() {
         let description = build_exec_tool_description(
diff --git a/codex-rs/code-mode-protocol/src/json_schema_types.rs b/codex-rs/code-mode-protocol/src/json_schema_types.rs
new file mode 100644
index 0000000000..0c519528a4
--- /dev/null
+++ b/codex-rs/code-mode-protocol/src/json_schema_types.rs
@@ -0,0 +1,538 @@
+use serde_json::Value as JsonValue;
+use std::collections::BTreeMap;
+
+use crate::description::normalize_code_mode_identifier;
+
+// Expose one nested recursive shape, then fall back to `unknown` on the next
+// occurrence so generated tool declarations remain finite.
+const MAX_LOCAL_REF_EXPANSIONS_PER_PATH: usize = 2;
+// Bound repeated refs and DAG fan-out separately from cycle depth so one
+// compact schema cannot expand into an arbitrarily large model-visible item.
+const MAX_TOTAL_LOCAL_REF_EXPANSIONS: usize = 32;
+// Bound individual schema rendering before assembling the final declaration.
+const MAX_RENDERED_SCHEMA_BYTES: usize = 16_000;
+// Charge intermediate render strings as they are built so repeated local refs
+// cannot allocate unbounded expanded copies before the final schema cap runs.
+const MAX_RENDER_WORK_BYTES: usize = MAX_RENDERED_SCHEMA_BYTES * 4;
+
+pub fn render_json_schema_to_typescript(schema: &JsonValue) -> String {
+    let rendered = JsonSchemaTypeRenderer::new(schema).render(schema);
+    if rendered.len() > MAX_RENDERED_SCHEMA_BYTES {
+        "unknown".to_string()
+    } else {
+        rendered
+    }
+}
+
+struct JsonSchemaTypeRenderer<'a> {
+    root: &'a JsonValue,
+    nested_schema_resource_depth: usize,
+    active_local_ref_expansions: BTreeMap<String, usize>,
+    remaining_local_ref_expansions: usize,
+    remaining_render_work_bytes: usize,
+    render_work_budget_exhausted: bool,
+}
+
+impl<'a> JsonSchemaTypeRenderer<'a> {
+    fn new(root: &'a JsonValue) -> Self {
+        Self {
+            root,
+            nested_schema_resource_depth: 0,
+            active_local_ref_expansions: BTreeMap::new(),
+            remaining_local_ref_expansions: MAX_TOTAL_LOCAL_REF_EXPANSIONS,
+            remaining_render_work_bytes: MAX_RENDER_WORK_BYTES,
+            render_work_budget_exhausted: false,
+        }
+    }
+
+    fn render(&mut self, schema: &JsonValue) -> String {
+        if self.render_work_budget_exhausted {
+            return "unknown".to_string();
+        }
+
+        // A nested `$id` starts a new schema resource. Fragment-only refs below
+        // it are scoped to that resource, not to the outer document root.
+        let enters_nested_schema_resource = !std::ptr::eq(schema, self.root)
+            && schema
+                .as_object()
+                .is_some_and(|map| map.contains_key("$id"));
+        if enters_nested_schema_resource {
+            self.nested_schema_resource_depth += 1;
+        }
+
+        let rendered = match schema {
+            JsonValue::Bool(true) => "unknown".to_string(),
+            JsonValue::Bool(false) => "never".to_string(),
+            JsonValue::Object(map) => self.render_map(map),
+            _ => "unknown".to_string(),
+        };
+        if enters_nested_schema_resource {
+            self.nested_schema_resource_depth -= 1;
+        }
+        self.finish_render(rendered)
+    }
+
+    fn render_map(&mut self, map: &serde_json::Map<String, JsonValue>) -> String {
+        if self.render_work_budget_exhausted {
+            return "unknown".to_string();
+        }
+
+        if map.contains_key("$ref") {
+            return self.render_ref(map);
+        }
+
+        if let Some(value) = map.get("const") {
+            return self.render_literal(value);
+        }
+
+        if let Some(values) = map.get("enum").and_then(JsonValue::as_array) {
+            let mut rendered = Vec::new();
+            for value in values {
+                let literal = self.render_literal(value);
+                if self.render_work_budget_exhausted {
+                    return "unknown".to_string();
+                }
+                if !self.consume_render_work(literal.len()) {
+                    return "unknown".to_string();
+                }
+                rendered.push(literal);
+            }
+            if !rendered.is_empty() {
+                return rendered.join(" | ");
+            }
+        }
+
+        for key in ["anyOf", "oneOf"] {
+            if let Some(variants) = map.get(key).and_then(JsonValue::as_array) {
+                let mut rendered = Vec::new();
+                for variant in variants {
+                    if self.render_work_budget_exhausted {
+                        return "unknown".to_string();
+                    }
+                    rendered.push(self.render(variant));
+                }
+                if !rendered.is_empty() {
+                    return rendered.join(" | ");
+                }
+            }
+        }
+
+        if let Some(variants) = map.get("allOf").and_then(JsonValue::as_array) {
+            let mut rendered = Vec::new();
+            for variant in variants {
+                if self.render_work_budget_exhausted {
+                    return "unknown".to_string();
+                }
+                rendered.push(parenthesize_union_for_intersection(self.render(variant)));
+            }
+            if !rendered.is_empty() {
+                return rendered.join(" & ");
+            }
+        }
+
+        if let Some(schema_type) = map.get("type") {
+            if let Some(types) = schema_type.as_array() {
+                let mut rendered = Vec::new();
+                for schema_type in types.iter().filter_map(JsonValue::as_str) {
+                    if self.render_work_budget_exhausted {
+                        return "unknown".to_string();
+                    }
+                    rendered.push(self.render_type_keyword(map, schema_type));
+                }
+                if !rendered.is_empty() {
+                    return rendered.join(" | ");
+                }
+            }
+
+            if let Some(schema_type) = schema_type.as_str() {
+                return self.render_type_keyword(map, schema_type);
+            }
+        }
+
+        if map.contains_key("properties")
+            || map.contains_key("additionalProperties")
+            || map.contains_key("required")
+        {
+            return self.render_object(map);
+        }
+
+        if map.contains_key("items") || map.contains_key("prefixItems") {
+            return self.render_array(map);
+        }
+
+        "unknown".to_string()
+    }
+
+    fn render_ref(&mut self, map: &serde_json::Map<String, JsonValue>) -> String {
+        let referenced_type = if self.nested_schema_resource_depth > 0 {
+            None
+        } else {
+            map.get("$ref")
+                .and_then(JsonValue::as_str)
+                .and_then(local_json_pointer)
+                .and_then(|pointer| {
+                    let active_expansions = self
+                        .active_local_ref_expansions
+                        .get(&pointer)
+                        .copied()
+                        .unwrap_or_default();
+                    if active_expansions >= MAX_LOCAL_REF_EXPANSIONS_PER_PATH {
+                        return Some("unknown".to_string());
+                    }
+                    if self.remaining_local_ref_expansions == 0 {
+                        return Some("unknown".to_string());
+                    }
+
+                    let root = self.root;
+                    let target = if pointer.is_empty() {
+                        Some(root)
+                    } else {
+                        root.pointer(&pointer)
+                    }?;
+                    self.remaining_local_ref_expansions -= 1;
+                    self.active_local_ref_expansions
+                        .insert(pointer.clone(), active_expansions + 1);
+
+                    let rendered = self.render(target);
+                    if active_expansions == 0 {
+                        self.active_local_ref_expansions.remove(&pointer);
+                    } else {
+                        self.active_local_ref_expansions
+                            .insert(pointer, active_expansions);
+                    }
+                    Some(rendered)
+                })
+        }
+        .unwrap_or_else(|| "unknown".to_string());
+        if self.render_work_budget_exhausted {
+            return "unknown".to_string();
+        }
+
+        let siblings = map
+            .iter()
+            .filter(|(key, _)| !matches!(key.as_str(), "$ref" | "$defs" | "definitions"))
+            .map(|(key, value)| (key.clone(), value.clone()))
+            .collect();
+        if !has_renderable_schema_keywords(&siblings) {
+            return referenced_type;
+        }
+
+        let sibling_type = self.render_map(&siblings);
+        match (referenced_type.as_str(), sibling_type.as_str()) {
+            ("unknown", _) => sibling_type,
+            (_, "unknown") => referenced_type,
+            _ => format!("({referenced_type}) & ({sibling_type})"),
+        }
+    }
+
+    fn render_type_keyword(
+        &mut self,
+        map: &serde_json::Map<String, JsonValue>,
+        schema_type: &str,
+    ) -> String {
+        match schema_type {
+            "string" => "string".to_string(),
+            "number" | "integer" => "number".to_string(),
+            "boolean" => "boolean".to_string(),
+            "null" => "null".to_string(),
+            "array" => self.render_array(map),
+            "object" => self.render_object(map),
+            _ => "unknown".to_string(),
+        }
+    }
+
+    fn render_array(&mut self, map: &serde_json::Map<String, JsonValue>) -> String {
+        if let Some(items) = map.get("items") {
+            let item_type = self.render(items);
+            if self.render_work_budget_exhausted {
+                return "unknown".to_string();
+            }
+            return format!("Array<{item_type}>");
+        }
+
+        if let Some(items) = map.get("prefixItems").and_then(JsonValue::as_array) {
+            let mut item_types = Vec::new();
+            for item in items {
+                if self.render_work_budget_exhausted {
+                    return "unknown".to_string();
+                }
+                item_types.push(self.render(item));
+            }
+            if !item_types.is_empty() {
+                return format!("[{}]", item_types.join(", "));
+            }
+        }
+
+        "unknown[]".to_string()
+    }
+
+    fn append_additional_properties_line(
+        &mut self,
+        lines: &mut Vec<String>,
+        map: &serde_json::Map<String, JsonValue>,
+        properties: &serde_json::Map<String, JsonValue>,
+        line_prefix: &str,
+    ) -> bool {
+        if let Some(additional_properties) = map.get("additionalProperties") {
+            let property_type = match additional_properties {
+                JsonValue::Bool(true) => Some("unknown".to_string()),
+                JsonValue::Bool(false) => None,
+                value => Some(self.render(value)),
+            };
+
+            if let Some(property_type) = property_type {
+                return self.push_render_line(
+                    lines,
+                    format!("{line_prefix}[key: string]: {property_type};"),
+                );
+            }
+        } else if properties.is_empty() {
+            return self.push_render_line(lines, format!("{line_prefix}[key: string]: unknown;"));
+        }
+        true
+    }
+
+    fn render_object_property(
+        &mut self,
+        name: &str,
+        value: &JsonValue,
+        required: &[&str],
+    ) -> String {
+        if name.len() > self.remaining_render_work_bytes {
+            self.render_work_budget_exhausted = true;
+            return "unknown".to_string();
+        }
+        let optional = if required.iter().any(|required_name| required_name == &name) {
+            ""
+        } else {
+            "?"
+        };
+        let property_name = render_json_schema_property_name(name);
+        let property_type = self.render(value);
+        if self.render_work_budget_exhausted {
+            return "unknown".to_string();
+        }
+        format!("{property_name}{optional}: {property_type};")
+    }
+
+    fn render_object(&mut self, map: &serde_json::Map<String, JsonValue>) -> String {
+        let required = map
+            .get("required")
+            .and_then(JsonValue::as_array)
+            .map(|items| {
+                items
+                    .iter()
+                    .filter_map(JsonValue::as_str)
+                    .collect::<Vec<_>>()
+            })
+            .unwrap_or_default();
+        let empty_properties = serde_json::Map::new();
+        let properties = map
+            .get("properties")
+            .and_then(JsonValue::as_object)
+            .unwrap_or(&empty_properties);
+
+        let mut sorted_properties = properties.iter().collect::<Vec<_>>();
+        sorted_properties.sort_unstable_by_key(|(name_a, _)| *name_a);
+        if sorted_properties
+            .iter()
+            .any(|(_, value)| has_property_description(value))
+        {
+            let mut lines = Vec::new();
+            if !self.push_render_line(&mut lines, "{".to_string()) {
+                return "unknown".to_string();
+            }
+            for (name, value) in sorted_properties {
+                if let Some(description) = value.get("description").and_then(JsonValue::as_str) {
+                    for description_line in description
+                        .lines()
+                        .map(str::trim)
+                        .filter(|line| !line.is_empty())
+                    {
+                        if description_line.len().saturating_add(5)
+                            > self.remaining_render_work_bytes
+                            || !self
+                                .push_render_line(&mut lines, format!("  // {description_line}"))
+                        {
+                            return "unknown".to_string();
+                        }
+                    }
+                }
+
+                let property = self.render_object_property(name, value, &required);
+                if self.render_work_budget_exhausted
+                    || !self.push_render_line(&mut lines, format!("  {property}"))
+                {
+                    return "unknown".to_string();
+                }
+            }
+
+            if !self.append_additional_properties_line(&mut lines, map, properties, "  ")
+                || !self.push_render_line(&mut lines, "}".to_string())
+            {
+                return "unknown".to_string();
+            }
+            return lines.join("\n");
+        }
+
+        let mut lines = Vec::new();
+        for (name, value) in sorted_properties {
+            let property = self.render_object_property(name, value, &required);
+            if self.render_work_budget_exhausted || !self.push_render_line(&mut lines, property) {
+                return "unknown".to_string();
+            }
+        }
+
+        if !self.append_additional_properties_line(&mut lines, map, properties, "") {
+            return "unknown".to_string();
+        }
+
+        if lines.is_empty() {
+            return "{}".to_string();
+        }
+
+        format!("{{ {} }}", lines.join(" "))
+    }
+
+    fn finish_render(&mut self, rendered: String) -> String {
+        if self.consume_render_work(rendered.len()) {
+            rendered
+        } else {
+            "unknown".to_string()
+        }
+    }
+
+    fn render_literal(&mut self, value: &JsonValue) -> String {
+        if json_literal_serialization_upper_bound(value) > self.remaining_render_work_bytes {
+            self.render_work_budget_exhausted = true;
+            "unknown".to_string()
+        } else {
+            render_json_schema_literal(value)
+        }
+    }
+
+    fn consume_render_work(&mut self, rendered_bytes: usize) -> bool {
+        if rendered_bytes > self.remaining_render_work_bytes {
+            self.render_work_budget_exhausted = true;
+            false
+        } else {
+            self.remaining_render_work_bytes -= rendered_bytes;
+            true
+        }
+    }
+
+    fn push_render_line(&mut self, lines: &mut Vec<String>, line: String) -> bool {
+        if !self.consume_render_work(line.len()) {
+            return false;
+        }
+        lines.push(line);
+        true
+    }
+}
+
+fn parenthesize_union_for_intersection(rendered: String) -> String {
+    if rendered.contains(" | ") {
+        format!("({rendered})")
+    } else {
+        rendered
+    }
+}
+
+fn local_json_pointer(reference: &str) -> Option<String> {
+    let fragment = reference.strip_prefix('#')?;
+    let pointer = percent_decode_uri_fragment(fragment)?;
+    if pointer.is_empty() || pointer.starts_with('/') {
+        Some(pointer)
+    } else {
+        None
+    }
+}
+
+fn percent_decode_uri_fragment(fragment: &str) -> Option<String> {
+    let bytes = fragment.as_bytes();
+    let mut decoded = Vec::with_capacity(bytes.len());
+    let mut index = 0;
+    while index < bytes.len() {
+        if bytes[index] == b'%' {
+            let high = decode_hex_digit(*bytes.get(index + 1)?)?;
+            let low = decode_hex_digit(*bytes.get(index + 2)?)?;
+            decoded.push((high << 4) | low);
+            index += 3;
+        } else {
+            decoded.push(bytes[index]);
+            index += 1;
+        }
+    }
+    String::from_utf8(decoded).ok()
+}
+
+fn decode_hex_digit(digit: u8) -> Option<u8> {
+    match digit {
+        b'0'..=b'9' => Some(digit - b'0'),
+        b'a'..=b'f' => Some(digit - b'a' + 10),
+        b'A'..=b'F' => Some(digit - b'A' + 10),
+        _ => None,
+    }
+}
+
+fn has_renderable_schema_keywords(map: &serde_json::Map<String, JsonValue>) -> bool {
+    [
+        "const",
+        "enum",
+        "anyOf",
+        "oneOf",
+        "allOf",
+        "type",
+        "properties",
+        "additionalProperties",
+        "required",
+        "items",
+        "prefixItems",
+    ]
+    .iter()
+    .any(|key| map.contains_key(*key))
+}
+
+fn has_property_description(value: &JsonValue) -> bool {
+    value
+        .get("description")
+        .and_then(JsonValue::as_str)
+        .is_some_and(|description| !description.is_empty())
+}
+
+fn render_json_schema_property_name(name: &str) -> String {
+    if normalize_code_mode_identifier(name) == name {
+        name.to_string()
+    } else {
+        serde_json::to_string(name).unwrap_or_else(|_| format!("\"{}\"", name.replace('"', "\\\"")))
+    }
+}
+
+fn render_json_schema_literal(value: &JsonValue) -> String {
+    serde_json::to_string(value).unwrap_or_else(|_| "unknown".to_string())
+}
+
+fn json_literal_serialization_upper_bound(value: &JsonValue) -> usize {
+    match value {
+        JsonValue::Null => 4,
+        JsonValue::Bool(false) => 5,
+        JsonValue::Bool(true) => 4,
+        JsonValue::Number(number) => number.to_string().len(),
+        // JSON escaping can expand one UTF-8 byte to at most one six-byte
+        // Unicode escape, so this bounds allocation before serialization.
+        JsonValue::String(string) => string.len().saturating_mul(6).saturating_add(2),
+        JsonValue::Array(values) => values.iter().fold(2, |size, value| {
+            size.saturating_add(1)
+                .saturating_add(json_literal_serialization_upper_bound(value))
+        }),
+        JsonValue::Object(map) => map.iter().fold(2, |size, (key, value)| {
+            size.saturating_add(4)
+                .saturating_add(key.len().saturating_mul(6))
+                .saturating_add(json_literal_serialization_upper_bound(value))
+        }),
+    }
+}
+
+#[cfg(test)]
+#[path = "json_schema_types_tests.rs"]
+mod tests;
diff --git a/codex-rs/code-mode-protocol/src/json_schema_types_tests.rs b/codex-rs/code-mode-protocol/src/json_schema_types_tests.rs
new file mode 100644
index 0000000000..449865f60e
--- /dev/null
+++ b/codex-rs/code-mode-protocol/src/json_schema_types_tests.rs
@@ -0,0 +1,200 @@
+use super::*;
+use pretty_assertions::assert_eq;
+use serde_json::json;
+
+#[test]
+fn renders_recursive_local_refs_with_escaped_pointer_segments() {
+    let schema = json!({
+        "type": "object",
+        "properties": {
+            "clauses": {
+                "type": "array",
+                "items": { "$ref": "#/$defs/Boolean~1Clause~0v1" }
+            }
+        },
+        "$defs": {
+            "Boolean/Clause~v1": {
+                "type": "object",
+                "properties": {
+                    "query": { "$ref": "#/$defs/Query" }
+                }
+            },
+            "Query": {
+                "oneOf": [
+                    { "type": "string" },
+                    {
+                        "type": "object",
+                        "properties": {
+                            "clauses": {
+                                "type": "array",
+                                "items": { "$ref": "#/$defs/Boolean~1Clause~0v1" }
+                            }
+                        }
+                    }
+                ]
+            }
+        }
+    });
+
+    let rendered = render_json_schema_to_typescript(&schema);
+    assert!(rendered.contains("clauses?: Array<{ query?: string | { clauses?: Array<{"));
+    assert!(rendered.contains("query?: string | { clauses?: Array<unknown>; };"));
+}
+
+#[test]
+fn renders_ref_siblings_uri_fragments_and_all_of_precedence() {
+    assert_eq!(
+        render_json_schema_to_typescript(&json!({
+            "$ref": "#/$defs/Label",
+            "enum": ["A"],
+            "$defs": { "Label": { "type": "string" } }
+        })),
+        r#"(string) & ("A")"#
+    );
+    assert_eq!(
+        render_json_schema_to_typescript(&json!({
+            "$ref": "#/$defs/Foo%20Bar",
+            "$defs": { "Foo Bar": { "type": "string" } }
+        })),
+        "string"
+    );
+    assert_eq!(
+        render_json_schema_to_typescript(&json!({
+            "allOf": [
+                { "$ref": "#/$defs/Choice" },
+                { "type": "object", "properties": { "value": { "type": "string" } } }
+            ],
+            "$defs": {
+                "Choice": { "oneOf": [{ "type": "string" }, { "type": "number" }] }
+            }
+        })),
+        "(string | number) & { value?: string; }"
+    );
+}
+
+#[test]
+fn leaves_local_refs_under_nested_schema_resources_unresolved() {
+    let schema = json!({
+        "$defs": {
+            "Choice": { "type": "string" }
+        },
+        "type": "object",
+        "properties": {
+            "nested": {
+                "$id": "urn:nested",
+                "$defs": {
+                    "Choice": { "type": "number" }
+                },
+                "type": "object",
+                "properties": {
+                    "value": { "$ref": "#/$defs/Choice" }
+                }
+            }
+        }
+    });
+
+    assert_eq!(
+        render_json_schema_to_typescript(&schema),
+        "{ nested?: { value?: unknown; }; }"
+    );
+}
+
+#[test]
+fn bounds_expansions_without_charging_dangling_refs() {
+    let mut properties = (0..MAX_TOTAL_LOCAL_REF_EXPANSIONS)
+        .map(|index| {
+            (
+                format!("a_missing_{index}"),
+                json!({ "$ref": format!("#/$defs/Missing{index}") }),
+            )
+        })
+        .collect::<serde_json::Map<_, _>>();
+    properties.insert("z_valid".to_string(), json!({ "$ref": "#/$defs/Valid" }));
+    let schema = json!({
+        "type": "object",
+        "properties": properties,
+        "$defs": { "Valid": { "type": "string" } }
+    });
+
+    let rendered = render_json_schema_to_typescript(&schema);
+    assert!(rendered.contains("z_valid?: string;"));
+
+    let properties = (0..MAX_TOTAL_LOCAL_REF_EXPANSIONS + 2)
+        .map(|index| {
+            (
+                format!("property_{index}"),
+                json!({ "$ref": "#/$defs/Item" }),
+            )
+        })
+        .collect::<serde_json::Map<_, _>>();
+    let rendered = render_json_schema_to_typescript(&json!({
+        "type": "object",
+        "properties": properties,
+        "$defs": { "Item": { "type": "string" } }
+    }));
+    assert_eq!(
+        rendered.matches("string").count(),
+        MAX_TOTAL_LOCAL_REF_EXPANSIONS
+    );
+    assert_eq!(rendered.matches("unknown").count(), 2);
+}
+
+#[test]
+fn repeated_large_ref_expansions_exhaust_render_work_budget() {
+    let properties = (0..MAX_TOTAL_LOCAL_REF_EXPANSIONS)
+        .map(|index| {
+            (
+                format!("property_{index}"),
+                json!({ "$ref": "#/$defs/Item" }),
+            )
+        })
+        .collect::<serde_json::Map<_, _>>();
+    let schema = json!({
+        "type": "object",
+        "properties": properties,
+        "$defs": {
+            "Item": {
+                "type": "object",
+                "properties": {
+                    "value": {
+                        "type": "string",
+                        "description": "x".repeat(MAX_RENDERED_SCHEMA_BYTES / 2)
+                    }
+                }
+            }
+        }
+    });
+
+    let mut renderer = JsonSchemaTypeRenderer::new(&schema);
+    assert_eq!(renderer.render(&schema), "unknown");
+    assert!(renderer.render_work_budget_exhausted);
+}
+
+#[test]
+fn oversized_ref_literal_exhausts_render_work_budget() {
+    let schema = json!({
+        "$ref": "#/$defs/Value",
+        "$defs": {
+            "Value": {
+                "const": "x".repeat(MAX_RENDER_WORK_BYTES)
+            }
+        }
+    });
+
+    let mut renderer = JsonSchemaTypeRenderer::new(&schema);
+    assert_eq!(renderer.render(&schema), "unknown");
+    assert!(renderer.render_work_budget_exhausted);
+}
+
+#[test]
+fn rendered_schema_has_a_hard_size_cap() {
+    let description = "x".repeat(MAX_RENDERED_SCHEMA_BYTES);
+    let schema = json!({
+        "type": "object",
+        "properties": {
+            "value": { "type": "string", "description": description }
+        }
+    });
+
+    assert_eq!(render_json_schema_to_typescript(&schema), "unknown");
+}
diff --git a/codex-rs/code-mode-protocol/src/lib.rs b/codex-rs/code-mode-protocol/src/lib.rs
index 6af942a4e8..93eed078a4 100644
--- a/codex-rs/code-mode-protocol/src/lib.rs
+++ b/codex-rs/code-mode-protocol/src/lib.rs
@@ -1,6 +1,7 @@
 mod description;
 pub mod grpc;
 pub mod host;
+mod json_schema_types;
 mod response;
 mod runtime;
 mod session;
@@ -19,7 +20,7 @@ pub use description::is_code_mode_nested_tool;
 pub use description::normalize_code_mode_identifier;
 pub use description::parse_exec_source;
 pub use description::render_code_mode_sample;
-pub use description::render_json_schema_to_typescript;
+pub use json_schema_types::render_json_schema_to_typescript;
 pub use response::DEFAULT_IMAGE_DETAIL;
 pub use response::FunctionCallOutputContentItem;
 pub use response::ImageDetail;
diff --git a/codex-rs/core/tests/suite/code_mode.rs b/codex-rs/core/tests/suite/code_mode.rs
index e23331d5b0..f9429a1464 100644
--- a/codex-rs/core/tests/suite/code_mode.rs
+++ b/codex-rs/core/tests/suite/code_mode.rs
@@ -5417,6 +5417,89 @@ text(JSON.stringify({
     Ok(())
 }
 
+#[tokio::test(flavor = "multi_thread", worker_threads = 2)]
+async fn code_mode_renders_local_refs_in_outbound_exec_description() -> Result<()> {
+    skip_if_no_network!(Ok(()));
+
+    let server = responses::start_mock_server().await;
+    let response = responses::mount_sse_once(
+        &server,
+        sse(vec![
+            ev_assistant_message("msg-1", "done"),
+            ev_completed("resp-1"),
+        ]),
+    )
+    .await;
+    let mut builder = test_codex().with_config(|config| {
+        config
+            .features
+            .enable(Feature::CodeModeOnly)
+            .expect("code mode only should be enabled");
+    });
+    let base_test = builder.build_with_auto_env(&server).await?;
+    let new_thread = base_test
+        .thread_manager
+        .start_thread(StartThreadOptions {
+            dynamic_tools: vec![DynamicToolSpec::Function(DynamicToolFunctionSpec {
+                name: "boolean_search".to_string(),
+                description: "Search with nested Boolean clauses.".to_string(),
+                input_schema: serde_json::json!({
+                    "type": "object",
+                    "properties": {
+                        "clauses": {
+                            "type": "array",
+                            "items": { "$ref": "#/$defs/Clause" }
+                        }
+                    },
+                    "$defs": {
+                        "Clause": {
+                            "type": "object",
+                            "properties": {
+                                "query": {
+                                    "oneOf": [
+                                        { "type": "string" },
+                                        {
+                                            "type": "object",
+                                            "properties": {
+                                                "clauses": {
+                                                    "type": "array",
+                                                    "items": { "$ref": "#/$defs/Clause" }
+                                                }
+                                            }
+                                        }
+                                    ]
+                                }
+                            }
+                        }
+                    }
+                }),
+                defer_loading: false,
+            })],
+            ..StartThreadOptions::new(base_test.config.clone())
+        })
+        .await?;
+    let mut test = base_test;
+    test.codex = new_thread.thread;
+    test.session_configured = new_thread.session_configured;
+
+    test.submit_turn("inspect the tool schema").await?;
+
+    let body = response.single_request().body_json();
+    let exec_description = body["tools"]
+        .as_array()
+        .expect("request should contain tools")
+        .iter()
+        .find_map(|tool| {
+            (tool["name"].as_str() == Some("exec"))
+                .then(|| tool["description"].as_str())
+                .flatten()
+        })
+        .expect("Code Mode exec should remain available");
+    assert!(exec_description.contains("query?: string | { clauses?: Array<"));
+
+    Ok(())
+}
+
 #[tokio::test(flavor = "multi_thread", worker_threads = 2)]
 async fn code_mode_can_call_hidden_dynamic_tools() -> Result<()> {
     skip_if_no_network!(Ok(()));