diff --git a/CHANGELOG.md b/CHANGELOG.md
index 19f8d77..c382531 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -3,6 +3,18 @@ All notable changes to this project will be documented in this file.
 
 ## [Unreleased]
 
+## [0.24.4] - 2025-10-20
+
+### Fixed
+- Implemented a manual OpenAPI schema for `AppCode`, restoring `utoipa`
+  compatibility and documenting the SCREAMING_SNAKE_CASE contract in generated
+  specs.
+- Emitted owned label values when incrementing `error_total` telemetry metrics
+  so the updated `metrics` crate no longer requires `'static` lifetimes.
+- Relaxed gRPC metadata serialization to avoid `'static` lifetime requirements
+  introduced by recent compiler changes, preserving zero-copy formatting where
+  possible.
+
 ## [0.24.3] - 2025-10-19
 
 ### Fixed
diff --git a/Cargo.lock b/Cargo.lock
index 9e4de6f..96b7deb 100644
--- a/Cargo.lock
+++ b/Cargo.lock
@@ -1826,7 +1826,7 @@ dependencies = [
 
 [[package]]
 name = "masterror"
-version = "0.24.3"
+version = "0.24.4"
 dependencies = [
  "actix-web",
  "anyhow",
diff --git a/Cargo.toml b/Cargo.toml
index 7965c7c..534ef7c 100644
--- a/Cargo.toml
+++ b/Cargo.toml
@@ -1,6 +1,6 @@
 [package]
 name = "masterror"
-version = "0.24.3"
+version = "0.24.4"
 rust-version = "1.90"
 edition = "2024"
 license = "MIT OR Apache-2.0"
diff --git a/README.md b/README.md
index c9279af..b73e739 100644
--- a/README.md
+++ b/README.md
@@ -74,9 +74,9 @@ The build script keeps the full feature snippet below in sync with
 
 ~~~toml
 [dependencies]
-masterror = { version = "0.24.3", default-features = false }
+masterror = { version = "0.24.4", default-features = false }
 # or with features:
-# masterror = { version = "0.24.3", features = [
+# masterror = { version = "0.24.4", features = [
 #   "std", "axum", "actix", "openapi",
 #   "serde_json", "tracing", "metrics", "backtrace",
 #   "sqlx", "sqlx-migrate", "reqwest", "redis",
diff --git a/src/app_error/core.rs b/src/app_error/core.rs
index cc743c0..b329d72 100644
--- a/src/app_error/core.rs
+++ b/src/app_error/core.rs
@@ -311,10 +311,12 @@ impl Error {
 
             #[cfg(feature = "metrics")]
             {
+                let code_label = self.code.as_str().to_owned();
+                let category_label = kind_label(self.kind).to_owned();
                 metrics::counter!(
                     "error_total",
-                    "code" => self.code.as_str(),
-                    "category" => kind_label(self.kind)
+                    "code" => code_label,
+                    "category" => category_label
                 )
                 .increment(1);
             }
diff --git a/src/code/app_code.rs b/src/code/app_code.rs
index b6236c5..280d545 100644
--- a/src/code/app_code.rs
+++ b/src/code/app_code.rs
@@ -7,7 +7,10 @@ use core::{
 
 use serde::{Deserialize, Deserializer, Serialize, Serializer};
 #[cfg(feature = "openapi")]
-use utoipa::ToSchema;
+use utoipa::{
+    PartialSchema, ToSchema,
+    openapi::schema::{ObjectBuilder, Type}
+};
 
 use crate::kind::AppErrorKind;
 
@@ -40,7 +43,6 @@ impl CoreError for ParseAppCodeError {}
 /// - Do not encode private/internal details in codes.
 /// - Validate custom codes using [`AppCode::try_new`] before exposing them
 ///   publicly.
-#[cfg_attr(feature = "openapi", derive(ToSchema))]
 #[non_exhaustive]
 #[derive(Debug, Clone, PartialEq, Eq, Hash)]
 pub struct AppCode {
@@ -295,6 +297,23 @@ impl<'de> Deserialize<'de> for AppCode {
     }
 }
 
+#[cfg(feature = "openapi")]
+impl PartialSchema for AppCode {
+    fn schema() -> utoipa::openapi::RefOr<utoipa::openapi::schema::Schema> {
+        ObjectBuilder::new()
+            .schema_type(Type::String)
+            .description(Some(
+                "Stable machine-readable error code in SCREAMING_SNAKE_CASE.".to_owned()
+            ))
+            .pattern(Some("^[A-Z0-9_]+$".to_owned()))
+            .build()
+            .into()
+    }
+}
+
+#[cfg(feature = "openapi")]
+impl ToSchema for AppCode {}
+
 fn validate_code(value: &str) -> Result<(), ParseAppCodeError> {
     if !is_valid_literal(value) {
         return Err(ParseAppCodeError);
diff --git a/src/convert/tonic.rs b/src/convert/tonic.rs
index 7193e1c..c9cb656 100644
--- a/src/convert/tonic.rs
+++ b/src/convert/tonic.rs
@@ -147,7 +147,8 @@ enum MetadataAscii<'a> {
 impl AsRef<str> for MetadataAscii<'_> {
     fn as_ref(&self) -> &str {
         match self {
-            Self::Static(text) | Self::Buffer(text) => text,
+            Self::Static(text) => text,
+            Self::Buffer(text) => text,
             Self::Owned(text) => text.as_str()
         }
     }
@@ -175,7 +176,14 @@ fn metadata_value_to_ascii<'a>(
     match value {
         FieldValue::Str(value) => {
             let text = value.as_ref();
-            is_ascii_metadata_value(text).then_some(MetadataAscii::Static(text))
+            if !is_ascii_metadata_value(text) {
+                return None;
+            }
+
+            match value {
+                Cow::Borrowed(borrowed) => Some(MetadataAscii::Static(borrowed)),
+                Cow::Owned(owned) => Some(MetadataAscii::Owned(owned.clone()))
+            }
         }
         FieldValue::I64(value) => Some(MetadataAscii::Buffer(formatter.integers.format(*value))),
         FieldValue::U64(value) => Some(MetadataAscii::Buffer(formatter.integers.format(*value))),