[BUG] ModifyResponsePlugin always parses and re-serializes response body as JSON even for header-only configurations

• severity: Medium
• files: shenyu-plugin/shenyu-plugin-modify-response/.../ModifyResponsePlugin.java:148-171
• description: In writeWith, modifyBody(bytes) is unconditionally called regardless of whether any body modification rules are configured. JsonPath.parse(jsonValue) is always called and context.jsonString() always re-serializes. For non-JSON responses (XML, HTML, binary), JsonPath.parse throws → ShenyuException.
• impact: (a) Non-JSON responses crash the plugin even when only header modifications are configured. (b) Re-serialization can change whitespace/key ordering for valid JSON.
• suggested_fix: Short-circuit modifyBody when all body-key lists are empty/null; add a content-type guard.
• confidence: Medium
• related_existing: none

---

Identified during the 2026-08-02 deep re-scan; full list in docs/scan2-2026-08-02/06-medium-tiers.md.