docs: point consumers to adapter seam / 文件明確導向 adapter seam

HANDOFF.md

@@ -33,6 +33,17 @@ In `openclawtest`, the Telegram + OpenClaw PoC has already proven:
 
 This is not yet a clean cross-agent installable package. It is a successful PoC being pushed toward a cleaner reusable path.
 
+## Preferred integration seam now
+
+When extending the project, prefer the repo-side OpenClaw adapter path over directly expanding runtime patch logic.
+
+Current preferred seam:
+
+- `src/adapters/openclaw-plugin-skeleton.ts`
+- `src/adapters/openclaw-interactive-handler.ts`
+- `src/adapters/openclaw-message-tool.ts`
+- `src/adapters/openclaw-state-file.ts`
+
 ## Where to start reading
 
 Read these files first: