diff --git a/codex-rs/app-server/tests/suite/v2/history_notes_extension.rs b/codex-rs/app-server/tests/suite/v2/history_notes_extension.rs
index 93196d78f8..add607e5df 100644
--- a/codex-rs/app-server/tests/suite/v2/history_notes_extension.rs
+++ b/codex-rs/app-server/tests/suite/v2/history_notes_extension.rs
@@ -170,6 +170,31 @@ async fn app_server_uses_configured_notes_backend_for_context_window_hints(
                 "app-server should expose {namespace}.{tool_name} to the model"
             );
         }
+        // Reserved tools must retain their parameter constraints in the model request.
+        for (namespace, tool_name, property, expected) in [
+            (
+                "history",
+                "list_items",
+                "limit",
+                json!({"type": "integer", "minimum": 1, "maximum": 20}),
+            ),
+            (
+                "notes",
+                "search_contents",
+                "query",
+                json!({"type": "string", "maxLength": 1000}),
+            ),
+        ] {
+            let tool = request
+                .tool_by_name(namespace, tool_name)
+                .expect("history/notes tool should be exposed");
+            let mut schema = tool["parameters"]["properties"][property].clone();
+            schema
+                .as_object_mut()
+                .expect("parameter schema")
+                .remove("description");
+            assert_eq!(schema, expected, "{namespace}.{tool_name}.{property}");
+        }
     }
     assert!(request.tool_by_name("notes", "thread_hint").is_none());
 
diff --git a/codex-rs/tools/src/json_schema.rs b/codex-rs/tools/src/json_schema.rs
index 7c9edd08e1..0d8a67b183 100644
--- a/codex-rs/tools/src/json_schema.rs
+++ b/codex-rs/tools/src/json_schema.rs
@@ -50,6 +50,13 @@ pub struct JsonSchema {
     pub encrypted: Option<bool>,
     #[serde(rename = "enum", skip_serializing_if = "Option::is_none")]
     pub enum_values: Option<Vec<JsonValue>>,
+    // Preserve bounds in reserved tool declarations, including exact integer values.
+    #[serde(skip_serializing_if = "Option::is_none")]
+    pub minimum: Option<serde_json::Number>,
+    #[serde(skip_serializing_if = "Option::is_none")]
+    pub maximum: Option<serde_json::Number>,
+    #[serde(rename = "maxLength", skip_serializing_if = "Option::is_none")]
+    pub max_length: Option<u64>,
     #[serde(skip_serializing_if = "Option::is_none")]
     pub items: Option<Box<JsonSchema>>,
     #[serde(skip_serializing_if = "Option::is_none")]
@@ -521,7 +528,10 @@ fn sanitize_json_schema(value: &mut JsonValue) {
                     schema_types.push(JsonSchemaPrimitiveType::Object);
                 } else if map.contains_key("items") || map.contains_key("prefixItems") {
                     schema_types.push(JsonSchemaPrimitiveType::Array);
-                } else if map.contains_key("enum") || map.contains_key("format") {
+                } else if map.contains_key("enum")
+                    || map.contains_key("format")
+                    || map.contains_key("maxLength")
+                {
                     schema_types.push(JsonSchemaPrimitiveType::String);
                 } else if map.contains_key("minimum")
                     || map.contains_key("maximum")
diff --git a/codex-rs/tools/src/json_schema_tests.rs b/codex-rs/tools/src/json_schema_tests.rs
index c7377f31d9..01192f4266 100644
--- a/codex-rs/tools/src/json_schema_tests.rs
+++ b/codex-rs/tools/src/json_schema_tests.rs
@@ -38,6 +38,34 @@ fn json_schema_serializes_encrypted_marker() {
     );
 }
 
+#[test]
+fn parse_tool_input_schema_preserves_numeric_and_string_bounds() {
+    let input = serde_json::json!({
+        "type": "object",
+        "properties": {
+            "count": {
+                "type": "integer",
+                "minimum": 0,
+                "maximum": 9_007_199_254_740_993_u64
+            },
+            "score": {"type": "number", "minimum": -1.5, "maximum": 3.25},
+            "query": {"type": "string", "maxLength": 1000}
+        },
+        "additionalProperties": false
+    });
+
+    for parse in [
+        parse_tool_input_schema,
+        parse_tool_input_schema_without_compaction,
+    ] {
+        let schema = parse(&input).expect("parse schema");
+        assert_eq!(
+            serde_json::to_value(schema).expect("serialize schema"),
+            input
+        );
+    }
+}
+
 #[test]
 fn parse_tool_input_schema_infers_object_shape_and_defaults_properties() {
     // Example schema shape:
@@ -224,7 +252,10 @@ fn parse_tool_input_schema_infers_number_from_numeric_keywords() {
     }))
     .expect("parse schema");
 
-    assert_eq!(schema, JsonSchema::number(/*description*/ None));
+    assert_eq!(
+        serde_json::to_value(schema).expect("serialize schema"),
+        serde_json::json!({"type": "number", "minimum": 1})
+    );
 }
 
 #[test]
@@ -246,11 +277,12 @@ fn parse_tool_input_schema_infers_number_from_multiple_of() {
 }
 
 #[test]
-fn parse_tool_input_schema_infers_string_from_enum_const_and_format_keywords() {
+fn parse_tool_input_schema_infers_string_from_keywords() {
     // Example schema shapes:
     // { "enum": ["fast", "safe"] }
     // { "const": "file" }
     // { "format": "date-time" }
+    // { "maxLength": 1000 }
     //
     // Expected normalization behavior:
     // - `enum` and `const` normalize into explicit string-enum schemas.
@@ -267,6 +299,10 @@ fn parse_tool_input_schema_infers_string_from_enum_const_and_format_keywords() {
         "format": "date-time"
     }))
     .expect("parse format schema");
+    let max_length_schema = parse_tool_input_schema(&serde_json::json!({
+        "maxLength": 1000
+    }))
+    .expect("parse maxLength schema");
 
     assert_eq!(
         enum_schema,
@@ -280,6 +316,10 @@ fn parse_tool_input_schema_infers_string_from_enum_const_and_format_keywords() {
         JsonSchema::string_enum(vec![serde_json::json!("file")], /*description*/ None)
     );
     assert_eq!(format_schema, JsonSchema::string(/*description*/ None));
+    assert_eq!(
+        serde_json::to_value(max_length_schema).expect("serialize schema"),
+        serde_json::json!({"type": "string", "maxLength": 1000})
+    );
 }
 
 #[test]