feat(app): use opentui markdown component behind experimental flag

[remorses]

Swaps <code filetype="markdown"> with the native opentui <markdown> component in TextPart, gated behind OPENCODE_EXPERIMENTAL_MARKDOWN (also enabled by OPENCODE_EXPERIMENTAL).

ReasoningPart is left unchanged for now.

Fix #7671
Fix #3845

Still experimental, sometimes result does not look great, for example multiline quotes. Will land more improvements in opentui

CI seems to failing at Playwright e2e "file-tree can expand folders and open a file" which is unrelated

[github-actions]

Thanks for your contribution!

This PR doesn't have a linked issue. All PRs must reference an existing issue.

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2. Add Fixes #<number> or Closes #<number> to this PR description

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[github-actions]

The following comment was made by an LLM, it may be inaccurate:

No duplicate PRs found

[Copilot]

Pull request overview

This PR introduces experimental support for the native opentui <markdown> component to fix markdown table formatting issues. The change replaces <code filetype="markdown"> with <markdown> in the TextPart component, controlled by the OPENCODE_EXPERIMENTAL_MARKDOWN flag (also enabled via OPENCODE_EXPERIMENTAL).

Changes:

• Added new experimental flag OPENCODE_EXPERIMENTAL_MARKDOWN to enable the native markdown component
• Updated TextPart component to conditionally use either the new <markdown> component or the existing <code> component based on the flag
• ReasoningPart remains unchanged and continues using the <code> component

Reviewed changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated 1 comment.

File	Description
packages/opencode/src/flag/flag.ts	Adds the OPENCODE_EXPERIMENTAL_MARKDOWN flag following the existing experimental flag pattern
packages/opencode/src/cli/cmd/tui/routes/session/index.tsx	Imports Flag module and wraps TextPart's markdown rendering in a Switch/Match to conditionally use the new markdown component

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[R44VC0RP]

Can you add a video of usage?

Maybe something similar to seeing how it handles a case similar to this tweet:

https://x.com/willmcgugan/status/2016227602218848748?s=46

[msgongora]

Can you add a video of usage?

I don't think a video is needed, it's pretty much documented here anomalyco/opentui/pull/433, but also #3845

[msgongora]

@remorses, take a look at what I shared through Discord about the conceal feature.