Markdown rendering broken since opentui upgrade from 0.1.79 to 0.1.88+

[ars-ppi]

Description

Bug

Markdown in assistant responses is not rendered — headings (###), bold (**text**), code blocks, and inline code all appear as raw text.

Environment

• Tested on macOS Tahoe 26.4 (Terminal + iTerm2) and WSL2/Windows
• OpenCode versions tested: v1.3.0, v1.3.13, v1.3.17
• TERM=xterm-256color

What works

• OpenCode v1.2.0 (opentui 0.1.79) — markdown renders correctly

What doesn't work

• OpenCode v1.3.0+ (opentui 0.1.88+) — markdown is raw text
• Setting OPENCODE_EXPERIMENTAL_MARKDOWN=false does not fix it — the fallback <code filetype="markdown"> path is also broken with opentui 0.1.88+

Root cause analysis

The opentui upgrade from 0.1.79 → 0.1.88 (introduced in v1.3.0 via #18079) appears to have regressed both rendering paths:

• The new <markdown> component (default since v1.3.0)
• The old <code filetype="markdown"> fallback

Both worked with opentui 0.1.79 in v1.2.0.

Version comparison

OpenCode	opentui	Markdown flag default	Renders?
v1.2.0	0.1.79	opt-in (false)	✅ Yes
v1.3.0	0.1.88	opt-out (true)	❌ No
v1.3.13	0.1.95	opt-out (true)	❌ No
v1.3.17	0.1.96	opt-out (true)	❌ No

Relevant code

• packages/opencode/src/flag/flag.ts:70 — OPENCODE_EXPERIMENTAL_MARKDOWN changed from truthy() (opt-in) to !falsy() (opt-out)
• packages/opencode/src/cli/cmd/tui/routes/session/index.tsx — Both <markdown> and <code filetype="markdown"> paths affected
• Commit that upgraded opentui: 040f551 (Upgrade opentui to 0.1.88 #18079)

Plugins

None

OpenCode version

1.3.13 - 1.3.17

Steps to reproduce

1. Start OpenCode v1.3.0 or later
2. Ask any question that produces a markdown-formatted response
3. Headings, bold, code blocks render as raw plaintext

Screenshot and/or share link

No response

Operating System

Windows 11
MacOS
Linux Ubuntu 24.04

Terminal

Git Bash
Zsh
WSL2 Ubuntu