W19: plugin_loader hardening — ABI try/catch, path validation, atomic IDs, CLI exit codes (W19.1-W19.5)

Fixes: F-18.3-1 through F-18.3-5 (all CLOSED, findings registry at zero)

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

agents/designer-zhu/profile.md

@@ -27,6 +27,9 @@ performance_log:
   - date: 2026-05-27
     event: "W18.2: 协作赵码完成 CLI 命令分发修复 — 定义 /context 无 session 错误文案 No active session，定义 /status 连接状态三态交互语义（已连接/插件已加载模型未配置/未连接），编译 0 error + ctest 4/4 pass"
     rating: A
+  - date: 2026-05-27
+    event: "W19.4: 定义 CLI 退出码语义 — 0=正常退出, 1=用户中断(SIGINT/Ctrl+C), 2=致命错误, 3=配置错误；定义信号中断退出再见消息「再见!」文案；协作赵码在 main.cpp 统一实现并验证"
+    rating: A
 current_groups:
   - grp-cli-ux
 ---