feat(tui): native Arabic and RTL (bidi) support for prompts and messages

[muhamedbeshir]

Issue for this PR

Closes #38524
Closes #40004
Closes #39525
Closes #32984

Type of change

• Bug fix
• New feature
• Refactor / code improvement
• Documentation

What does this PR do?

All four linked issues have the same root cause: nothing in the TUI render path applies the Unicode Bidirectional Algorithm. Arabic/Persian/Urdu/Hebrew words come out in logical (left-to-right) order, mixed English identifiers scramble the sentence order, RTL paragraphs stay left-aligned, wrapping reorders lines, and the prompt caret moves on an LTR assumption.

OpenTUI (@opentui/core@0.4.5) does wrapping, layout and cell painting in a native Zig library with no bidi support and no JS fallback, and the published package ships bundled JS, so this can't be fixed by patching OpenTUI. This PR subclasses its public renderables and overrides only the paint and caret entry points:

• packages/tui/src/util/bidi.ts wraps bidi-js and adds what the renderer needs: paragraph direction from the first strong character (UAX full-auto / permissions / etc #9 P2/P3), LRI/PDI isolates around LTR islands (URLs, paths, dotted/dashed identifiers, numbers, code spans), grapheme- and width-aware wrapping, and logical<->visual boundary maps for the caret.
• packages/tui/src/component/bidi-textarea.ts is a TextareaRenderable subclass for the prompt. Painting, caret placement and left/right/up/down motion are visual; the edit buffer stays logical, so typing, paste, undo, values and extmarks are untouched and copy returns the original text.
• packages/tui/src/component/bidi-markdown.ts uses the markdown renderNode hook for assistant paragraphs/headings and captures tree-sitter chunks for styling. Fenced code, tables and diffs keep the stock renderer, so code is always LTR.
• packages/tui/src/component/bidi-text.ts is a TextRenderable subclass for user message echoes.
• Wiring: <textarea> -> <bidi_textarea> in packages/tui/src/component/prompt/index.tsx; renderNode + user echo in packages/tui/src/routes/session/index.tsx.

Why it works: the bidi algorithm only runs for paragraphs that contain strong RTL characters; English-only content takes the stock paint path unchanged. Isolates live in a layout-only stream and are never written to any buffer, so selection/copy stays logical. Wrapped logical text is synced into the native buffer so measurement and selection keep working.

How did you verify your code works?

On Windows 11, from a build of this branch:

bun test --cwd packages/tui ./test/util/bidi.test.ts
bun test --cwd packages/tui ./test/component/bidi-render.test.tsx
bun test --cwd packages/tui ./test/bidi-e2e.test.tsx
bun run --cwd packages/tui typecheck

• unit tests cover direction detection, ordering, isolates, wrapping and cursor round-trips;
• component tests render through the real OpenTUI test renderer and assert the actual painted cell frame: RTL order, right alignment, fenced code LTR, English-only output identical to the stock renderer, caret geometry, selection copy returning logical text;
• the e2e test boots the app with a mocked SDK, types Arabic into the real prompt with real key presses, and streams a real assistant message.

I also built the native binary (bun run --cwd packages/opencode script/build.ts --single) and used it interactively. The full tui suite is 226 tests with 1 pre-existing Windows-only failure unrelated to this change (abbreviates paths within home boundaries uses path.join, so it returns backslashes on Windows).

Screenshots / recordings

Text-only change, so here are two of the exact cell-order frames the component tests assert (a real terminal renders these right-to-left correctly because the cells are already in visual order).

Arabic on its own, right-aligned:

                                 ملاعلاب ابحرم

Mixed Arabic + English, with the English run kept intact:

                     ةمزحلا تيبثتل npm install مدختسا

Checklist

• I have tested my changes locally
• I have not included unrelated changes in this PR

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