[test-build] Handler.call_action wraps peer errors twice

[huanghuoguoguo]

Background

While building the SDK test-build coverage branch, a runtime IO test found that Handler.call_action() wraps peer error responses in a second ActionCallError.

Reproducer

When a peer response has code != 0 and message == 'peer failed', call_action() first raises:

ActionCallError('peer failed')

but the broad except Exception immediately catches it and raises another error:

ActionCallError('ActionCallError: peer failed')

Expected

The caller should receive the peer error message without an extra exception-class prefix, or the method should preserve the original ActionCallError.

Risk

• Callers cannot reliably match peer error messages.
• Error strings become noisy and inconsistent with timeout / transport errors.
• API users may need brittle string parsing.

Test Signal

Locked in test-build as an xfail(strict=True) contract test:

tests/runtime/io/test_handler.py::test_call_action_error_response_should_preserve_peer_message

No source fix is included in the test-build branch.

[huanghuoguoguo]

已在 #65（commit 9723b59）修复。

修复方式：Handler.call_action 捕获到已有 ActionCallError 时直接 raise，不再进入通用异常分支二次包装，因此 peer 返回的错误消息会被原样保留。

回归用例：tests/runtime/io/test_handler.py::test_call_action_error_response_should_preserve_peer_message。

测试：

• 对应 strict xfail 已取消，回归用例现在正常执行并通过。
• SDK：uv run pytest -> 269 passed, 10 warnings。
• LangBot master E2E：将本地 SDK editable 安装到 master worktree，WebUI 上传安装 qa/plugin-smoke，验证插件安装、Tool/Page 注册、Smoke Page iframe 渲染，以及 page-api /ping 返回 qa-plugin-smoke-page。