[Bug] v3.4.2 (Windows): Pasted text is present in the composer but invisible / uneditable

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. (The closest, #55, is a Linux/Wayland character-duplication bug whose reporter explicitly notes paste works fine for them — this is a different problem.)
• 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

必现 · Always

问题描述 · Description

On Windows in ZCode v3.4.2, when pasting text (Ctrl+V) into the chat message composer, the paste is accepted — the composer indicates that content is present (e.g. the composer state / send button reflects new content) — but the pasted text itself is not visually rendered and cannot be edited. The text effectively becomes invisible inside the input box, so it can't be reviewed or modified before sending.

Notes:

• Typing characters by hand works and is visible as expected.
• The issue is specific to pasted content: the data is received (the app recognizes there is text) but it isn't painted or editable in the composer.
• Editor text input (outside the composer) is unaffected.
• Environment: Windows 10 (10.0.26200), x64, locale en-US, no external input method (standard US keyboard), no IME.

复现步骤 · Steps to reproduce

1. Launch ZCode v3.4.2 on Windows.
2. Copy any text to the clipboard (e.g. a few lines from a file or browser).
3. Focus the chat message composer.
4. Press Ctrl+V (or right-click → Paste).
5. Observe: the composer registers that content exists (e.g. send/char state changes), but the pasted text is not visible and cannot be edited in the input box.

期望表现 · Expected behavior

Pasted text appears in the composer just like manually typed text, fully visible and editable before sending.

实际表现 · Actual behavior

Pasted text is not visually displayed and cannot be edited in the composer, even though the app recognizes that content is present.

ZCode 版本 · ZCode version

v3.4.2

设备 / 系统 / 浏览器 · Device / OS / Browser

Windows 10 (10.0.26200), x64, Electron build. No external input method (standard US keyboard).

截图 / 录屏 / 日志 · Screenshots / Recordings / Logs

Happy to attach a screen recording on request — please let me know if it would help with triage.

Start by reproducing the paste workflow in the Windows Electron build using the chat message composer and Ctrl+V, then trace the composer’s paste and rendering behavior. Compare pasted text with manually typed text and verify that the fix makes pasted content visible and editable before sending.