feat(forwarder/sniffer): add HTTP request body rewriting, deprecate rewriteBody in favor of rewriteResponseBody

- Add RewriteRequestBody field to HTTPNodeConfig (yaml: rewriteRequestBody)
- Add RewriteRequestBody field to HTTPNodeSettings in core chain
- Add rewriteReqBody function symmetric to rewriteRespBody in sniffer_rewrite.go
- Wire up rewriteReqBody call in httpRoundTrip before body wrapping for recording
- Add new RewriteResponseBody config field, deprecate old RewriteBody
- Parse both RewriteRequestBody and RewriteResponseBody in node config parsing
- Add 10 test cases covering nil, skip, content-type filter, and chained rewrites
- Bump core dependency to v0.4.1
- Fix: clone response header map in internal/util/sniffing/sniffer_http.go

internal/util/forwarder/sniffer_rewrite.go

@@ -90,3 +90,38 @@ func drainBody(b io.ReadCloser) (body []byte, err error) {
 	return buf.Bytes(), nil
 }
 
+func rewriteReqBody(req *http.Request, rewrites ...chain.HTTPBodyRewriteSettings) error {
+	if req == nil || len(rewrites) == 0 || req.Body == nil || req.ContentLength <= 0 {
+		return nil
+	}
+
+	if encoding := req.Header.Get("Content-Encoding"); encoding != "" {
+		return nil
+	}
+
+	body, err := drainBody(req.Body)
+	if err != nil || body == nil {
+		return err
+	}
+
+	contentType, _, _ := strings.Cut(req.Header.Get("Content-Type"), ";")
+	for _, rewrite := range rewrites {
+		rewriteType := rewrite.Type
+		if rewriteType == "" {
+			rewriteType = "text/html"
+		}
+		if rewriteType != "*" && !strings.Contains(rewriteType, contentType) {
+			continue
+		}
+
+		if rewrite.Pattern != nil {
+			body = rewrite.Pattern.ReplaceAll(body, rewrite.Replacement)
+		}
+	}
+
+	req.Body = io.NopCloser(bytes.NewReader(body))
+	req.ContentLength = int64(len(body))
+
+	return nil
+}
+