feat(runtime): track upstream response headers in logging and usage reporting

- Added APIs to store, retrieve, and clone upstream response headers in context for detailed logging.
- Updated `RecordAPIResponseMetadata`, `RecordAPIWebsocketHandshake`, and related methods to capture response headers.
- Extended `UsageReporter` to include response headers in published usage records.
- Enhanced payload tests to validate response headers' integrity and persistence.
- Refactored `usage.Record` to support optional `ResponseHeaders` field.

internal/logging/requestmeta.go

@@ -2,16 +2,24 @@ package logging
 
 import (
 	"context"
+	"net/http"
+	"sync"
 	"sync/atomic"
 )
 
 type endpointKey struct{}
 type responseStatusKey struct{}
+type responseHeadersKey struct{}
 
 type responseStatusHolder struct {
 	status atomic.Int32
 }
 
+type responseHeadersHolder struct {
+	mu      sync.RWMutex
+	headers http.Header
+}
+
 func WithEndpoint(ctx context.Context, endpoint string) context.Context {
 	if ctx == nil {
 		ctx = context.Background()
@@ -39,6 +47,16 @@ func WithResponseStatusHolder(ctx context.Context) context.Context {
 	return context.WithValue(ctx, responseStatusKey{}, &responseStatusHolder{})
 }
 
+func WithResponseHeadersHolder(ctx context.Context) context.Context {
+	if ctx == nil {
+		ctx = context.Background()
+	}
+	if holder, ok := ctx.Value(responseHeadersKey{}).(*responseHeadersHolder); ok && holder != nil {
+		return ctx
+	}
+	return context.WithValue(ctx, responseHeadersKey{}, &responseHeadersHolder{})
+}
+
 func SetResponseStatus(ctx context.Context, status int) {
 	if ctx == nil || status <= 0 {
 		return
@@ -50,6 +68,19 @@ func SetResponseStatus(ctx context.Context, status int) {
 	holder.status.Store(int32(status))
 }
 
+func SetResponseHeaders(ctx context.Context, headers http.Header) {
+	if ctx == nil {
+		return
+	}
+	holder, ok := ctx.Value(responseHeadersKey{}).(*responseHeadersHolder)
+	if !ok || holder == nil {
+		return
+	}
+	holder.mu.Lock()
+	defer holder.mu.Unlock()
+	holder.headers = cloneHTTPHeader(headers)
+}
+
 func GetResponseStatus(ctx context.Context) int {
 	if ctx == nil {
 		return 0
@@ -60,3 +91,27 @@ func GetResponseStatus(ctx context.Context) int {
 	}
 	return int(holder.status.Load())
 }
+
+func GetResponseHeaders(ctx context.Context) http.Header {
+	if ctx == nil {
+		return nil
+	}
+	holder, ok := ctx.Value(responseHeadersKey{}).(*responseHeadersHolder)
+	if !ok || holder == nil {
+		return nil
+	}
+	holder.mu.RLock()
+	defer holder.mu.RUnlock()
+	return cloneHTTPHeader(holder.headers)
+}
+
+func cloneHTTPHeader(src http.Header) http.Header {
+	if len(src) == 0 {
+		return nil
+	}
+	dst := make(http.Header, len(src))
+	for key, values := range src {
+		dst[key] = append([]string(nil), values...)
+	}
+	return dst
+}