TUI: single-tilde runs (\~x~\) vanish from rendered assistant text

Bug

When an assistant text part contains content wrapped in single tildes (e.g. 3~5 or 30~60%), the TUI markdown renderer swallows the ~ (and sometimes content between delimiters). Data is intact in the session store; this is purely a rendering-layer issue.

Example from a real session (assistant text part, verified via opencode.db):

• Stored text: 按 3~5 倍放大，应用在选择器中赢得 30~60%
• Rendered as: 按 35 倍放大，应用在选择器中赢得 3060%

The same part contained 19 occurrences of ~ (+15%~30%, ~1,100/天, 7 功能 ~26,000 次/天 ...); all were swallowed on display. Verified the raw bytes: 33 7E 35 and 33 30 7E 36 30 25 — the 0x7E is present in storage, absent from screen.

Repro

1. opencode (v1.18.23, Windows 10, Windows Terminal)
2. Ask the model to output text like 按 3~5 倍放大，赢得 30~60% (any ~x~ fragment works)
3. Observe rendered output shows 35 and 3060%

Live reproduction (v1.18.23, this session)

Assistant message sent (contains 10 tildes total: 6 single + 2 double runs):

- 单波浪号测试: 3~5 倍、30~60%、~1,100/天、a~b~c、~/Downloads/foo
- 双波浪号测试: ~~这段应该被删除线处理~~

What actually renders in the TUI (copy-pasted from screen, 0 tildes remain):

- 单波浪号测试: 35 倍、3060%、1,100/天、abc、/Downloads/foo
- 双波浪号测试: 这段应该被删除线处理

Notes:

• Every ~ is swallowed. Single tildes are paired across the whole line into del spans: 3~5 倍、30~60% pairs as one span, ~1,100/天、a~ as another, and the trailing ~ of a~b~c pairs all the way with the tilde in ~/Downloads/foo (strikethrough-styling c、 in between).
• For readers the text silently changes meaning: 3~5 倍 reads as 35 倍, 30~60% as 3060%.

Expected

Single tildes pass through as literal text. Only ~~text~~ should trigger strikethrough (per GFM spec, ~x~ is not strikethrough; marked's del rule /^(~~?)…/ is overly permissive here).

Related

• #26138 (Desktop, closed as not planned) — a comment there confirms the same issue exists in TUI mode; this issue provides a concrete TUI repro and shows content loss, not just strikethrough styling.
• #35835 fixed tilde/backtick adjacency but does not cover the plain ~x~ swallowing case.
• Same class of issue elsewhere: microsoft/vscode#323198, anthropics/claude-code#19251, open-webui/open-webui#16743.

Environment

• opencode v1.18.23 (opencode-windows-x64)
• Windows 10, Windows Terminal