[Bug] Text blocks render with a top-to-bottom fade — later lines nearly unreadable (light theme)

提交前确认 · Pre-submission checklist

• 我已搜索过现有 issue，确认这不是重复 / I searched existing issues and confirmed this isn't a duplicate.
• 我已阅读 CONTRIBUTING.md / I've read CONTRIBUTING.md.

问题类别 · Category

UI / 界面体验 · UI / UX

涉及的 Agent 框架 · Agent framework

ZCode Agent（自研）

严重程度 · Severity

影响体验 · Major (功能可用但体验受损 / works but degraded)

复现频率 · Reproducibility

偶现 · Sometimes

问题描述 · Description

A plain text block whose lines are longer than the block width renders with a progressive opacity fade from top to bottom. By the 3rd–5th line the text is essentially invisible, even though the block is fully in view and no content is actually truncated. Observed on a receipt-style plain text block in the chat transcript; expected to affect any text block with long single lines (a horizontal scrollbar appears under the block).

复现步骤 · Steps to reproduce

1. Have the assistant output a multi-line plain text block with several long single lines (e.g. a receipt or summary where each line exceeds the block width).
2. View the block normally — no hover, collapse, or scrolling required.
3. Look at the lines from top to bottom.

期望表现 · Expected behavior

All lines render at uniform, readable contrast. A fade/mask should only ever indicate content that is actually truncated or requires scrolling.

实际表现 · Actual behavior

Each successive line renders fainter than the one above it, fading to near-zero contrast, while a horizontal scrollbar sits below the block. The content is complete but unreadable on screen.

ZCode 版本 · ZCode version

3.10.1 (3.10.1.6272)

设备 / 系统 / 浏览器 · Device / OS / Browser

Windows 11 x64 (build 26200) · ZCode desktop app · light theme

截图 / 录屏 / 日志 · Screenshots / Recordings / Logs

Screenshot of the affected text block (light theme):

The issue names no source files, tests, or code entry points. First reproduce the fade in ZCode 3.10.1.6272 on Windows 11 with the light theme using a multi-line plain-text block with long lines; done means all lines have uniform readable contrast and any fade appears only for genuinely truncated or scrollable content.