fix(tui): termux-gate composer rendering tweaks for Ink TUI

Salvaged from #28942 (adybag14-cyber). Only the Ink TUI half is taken
here — the bundled "termux compatibility note" added to skills_tool.py
in the original PR did not address the actual user-reported bug
(skill_matches_platform() filtering Linux skills out on Termux) and
also regressed the EXCLUDED_SKILL_DIRS set used to prune nested
.venv/site-packages skills.

Changes:
- ui-tui/src/lib/prompt.ts: single-cell ASCII '>' marker in Termux mode
  to avoid ambiguous-width glyph artifacts while typing.
- ui-tui/src/components/appLayout.tsx: suppress profile prefix on
  narrow Termux panes (>=90 cols still shows it).
- ui-tui/src/lib/inputMetrics.ts + components/messageLine.tsx +
  lib/virtualHeights.ts: termux-aware transcript body width — drop
  the desktop 20-col floor on narrow mobile layouts, align virtual
  heights with actual rendered width.
- ui-tui/src/components/textInput.tsx: disable fast-echo bypass by
  default in Termux to avoid ghosting at soft-wrap boundaries.
  HERMES_TUI_TERMUX_FAST_ECHO=1 opts back in.

Tests: ui-tui/src/__tests__/{prompt,termuxComposerLayout,textInputFastEcho}.test.ts
(12 PR-added tests pass; 3 pre-existing wrapAnsi-bundling failures on
main are unrelated.)

The real skill-listing fix on Termux ('android' platform matching
Linux skills) ships as a follow-up commit on this branch.

ui-tui/src/__tests__/prompt.test.ts

@@ -16,4 +16,16 @@ describe('composerPromptText', () => {
     expect(composerPromptText('❯', 'custom')).toBe('❯')
     expect(composerPromptText('❯')).toBe('❯')
   })
+
+  it('uses a Termux-safe ASCII prompt marker in normal mode', () => {
+    expect(composerPromptText('❯', 'coder', false, true, 50)).toBe('>')
+  })
+
+  it('keeps profile prefix suppressed on narrow Termux widths', () => {
+    expect(composerPromptText('❯', 'upstr', false, true, 72)).toBe('>')
+  })
+
+  it('allows profile prefix on very wide Termux panes', () => {
+    expect(composerPromptText('❯', 'upstr', false, true, 120)).toBe('upstr >')
+  })
 })

ui-tui/src/__tests__/termuxComposerLayout.test.ts

@@ -0,0 +1,40 @@
+import { describe, expect, it } from 'vitest'
+
+import { stableComposerColumns, transcriptBodyWidth } from '../lib/inputMetrics.js'
+import { composerPromptText } from '../lib/prompt.js'
+
+describe('Termux composer prompt + width guards', () => {
+  it('uses a single-cell ASCII prompt marker in Termux mode', () => {
+    expect(composerPromptText('❯', 'coder', false, true, 50)).toBe('>')
+  })
+
+  it('suppresses profile prefixes on narrow Termux panes', () => {
+    expect(composerPromptText('❯', 'upstr', false, true, 72)).toBe('>')
+  })
+
+  it('keeps profile context on very wide Termux panes', () => {
+    expect(composerPromptText('❯', 'upstr', false, true, 120)).toBe('upstr >')
+  })
+
+  it('reserves fewer columns for gutter on narrow Termux widths', () => {
+    // 32 columns after prompt: desktop reserves 2 for transcript scrollbar,
+    // Termux keeps those 2 columns for the active composer.
+    expect(stableComposerColumns(40, 8, false)).toBe(28)
+    expect(stableComposerColumns(40, 8, true)).toBe(30)
+
+    // With ample room, Termux still reserves the gutter for alignment.
+    expect(stableComposerColumns(60, 8, true)).toBe(48)
+  })
+
+  it('never over-allocates transcript body width on narrow panes', () => {
+    // Old behavior hard-minned to 20 columns and overflowed narrow layouts.
+    expect(transcriptBodyWidth(24, 'assistant', '>', true)).toBe(19)
+    expect(transcriptBodyWidth(24, 'user', 'upstr >', true)).toBe(14)
+    expect(transcriptBodyWidth(10, 'user', '>', true)).toBeGreaterThanOrEqual(1)
+  })
+
+  it('keeps legacy desktop floor outside Termux mode', () => {
+    expect(transcriptBodyWidth(24, 'assistant', '>')).toBe(20)
+    expect(transcriptBodyWidth(24, 'user', 'upstr >')).toBe(20)
+  })
+})

ui-tui/src/__tests__/textInputFastEcho.test.ts

@@ -178,7 +178,22 @@ describe('supportsFastEchoTerminal', () => {
     expect(supportsFastEchoTerminal({ TERM_PROGRAM: 'Apple_Terminal' } as NodeJS.ProcessEnv)).toBe(false)
   })
 
-  it('keeps fast-echo enabled in VS Code and unknown terminals', () => {
+  it('disables fast-echo by default in Termux mode', () => {
+    expect(
+      supportsFastEchoTerminal({ TERMUX_VERSION: '0.118.0', PREFIX: '/data/data/com.termux/files/usr' } as NodeJS.ProcessEnv)
+    ).toBe(false)
+  })
+
+  it('allows explicit Termux fast-echo opt-in via env override', () => {
+    expect(
+      supportsFastEchoTerminal({
+        HERMES_TUI_TERMUX_FAST_ECHO: '1',
+        TERMUX_VERSION: '0.118.0'
+      } as NodeJS.ProcessEnv)
+    ).toBe(true)
+  })
+
+  it('keeps fast-echo enabled in VS Code and unknown non-Termux terminals', () => {
     expect(supportsFastEchoTerminal({ TERM_PROGRAM: 'vscode' } as NodeJS.ProcessEnv)).toBe(true)
     expect(supportsFastEchoTerminal({ TERM: 'xterm-256color' } as NodeJS.ProcessEnv)).toBe(true)
   })

ui-tui/src/components/appLayout.tsx

@@ -6,7 +6,7 @@ import { useGateway } from '../app/gatewayContext.js'
 import type { AppLayoutProps } from '../app/interfaces.js'
 import { $isBlocked, $overlayState, patchOverlayState } from '../app/overlayStore.js'
 import { $uiState } from '../app/uiStore.js'
-import { INLINE_MODE, SHOW_FPS } from '../config/env.js'
+import { INLINE_MODE, SHOW_FPS, TERMUX_TUI_MODE } from '../config/env.js'
 import { PLACEHOLDER } from '../content/placeholders.js'
 import {
   COMPOSER_PROMPT_GAP_WIDTH,
@@ -169,10 +169,10 @@ const ComposerPane = memo(function ComposerPane({
   const ui = useStore($uiState)
   const isBlocked = useStore($isBlocked)
   const sh = (composer.inputBuf[0] ?? composer.input).startsWith('!')
-  const promptText = composerPromptText(ui.theme.brand.prompt, ui.info?.profile_name, sh)
+  const promptText = composerPromptText(ui.theme.brand.prompt, ui.info?.profile_name, sh, TERMUX_TUI_MODE, composer.cols)
   const promptWidth = composerPromptWidth(promptText)
   const promptBlank = ' '.repeat(promptWidth)
-  const inputColumns = stableComposerColumns(composer.cols, promptWidth)
+  const inputColumns = stableComposerColumns(composer.cols, promptWidth, TERMUX_TUI_MODE)
   const inputHeight = inputVisualHeight(composer.input, inputColumns)
   const inputMouseRef = useRef<null | TextInputMouseApi>(null)
 

ui-tui/src/components/messageLine.tsx

@@ -1,6 +1,7 @@
 import { Ansi, Box, NoSelect, Text } from '@hermes/ink'
 import { memo, useState } from 'react'
 
+import { TERMUX_TUI_MODE } from '../config/env.js'
 import { LONG_MSG } from '../config/limits.js'
 import { sectionMode } from '../domain/details.js'
 import { userDisplay } from '../domain/messages.js'
@@ -139,7 +140,7 @@ export const MessageLine = memo(function MessageLine({
     }
 
     if (msg.role === 'assistant') {
-      const bodyWidth = transcriptBodyWidth(cols, msg.role, t.brand.prompt)
+      const bodyWidth = transcriptBodyWidth(cols, msg.role, t.brand.prompt, TERMUX_TUI_MODE)
 
       return isStreaming ? (
         // Incremental markdown: split at the last stable block boundary so
@@ -201,7 +202,7 @@ export const MessageLine = memo(function MessageLine({
           </Text>
         </NoSelect>
 
-        <Box width={transcriptBodyWidth(cols, msg.role, t.brand.prompt)}>{content}</Box>
+        <Box width={transcriptBodyWidth(cols, msg.role, t.brand.prompt, TERMUX_TUI_MODE)}>{content}</Box>
       </Box>
     </Box>
   )

ui-tui/src/components/textInput.tsx

@@ -13,6 +13,7 @@ import {
   isVoiceToggleKey,
   type ParsedVoiceRecordKey
 } from '../lib/platform.js'
+import { isTermuxTuiMode } from '../lib/termux.js'
 
 type InkExt = typeof Ink & {
   stringWidth: (s: string) => number
@@ -298,7 +299,23 @@ export function canFastBackspaceShape(current: string, cursor: number, columns?:
 export function supportsFastEchoTerminal(env: NodeJS.ProcessEnv = process.env): boolean {
   // Terminal.app still shows paint/cursor artifacts under the fast-echo
   // bypass path. Fall back to the normal Ink render path there.
-  return (env.TERM_PROGRAM ?? '').trim() !== 'Apple_Terminal'
+  if ((env.TERM_PROGRAM ?? '').trim() === 'Apple_Terminal') {
+    return false
+  }
+
+  // Termux terminals are especially sensitive to bypass-path cursor drift and
+  // stale paints at soft-wrap boundaries on tall/narrow viewports. Keep this
+  // off by default in Termux mode; allow explicit opt-in for local debugging.
+  if (isTermuxTuiMode(env)) {
+    const override = String(env.HERMES_TUI_TERMUX_FAST_ECHO ?? '').trim().toLowerCase()
+    if (override) {
+      return /^(?:1|true|yes|on)$/i.test(override)
+    }
+
+    return false
+  }
+
+  return true
 }
 
 function renderWithCursor(value: string, cursor: number) {

ui-tui/src/lib/inputMetrics.ts

@@ -177,14 +177,25 @@ export function transcriptGutterWidth(role: Role, userPrompt: string) {
   return role === 'user' ? composerPromptWidth(userPrompt) : 3
 }
 
-export function transcriptBodyWidth(totalCols: number, role: Role, userPrompt: string) {
-  return Math.max(20, totalCols - transcriptGutterWidth(role, userPrompt) - 2)
+export function transcriptBodyWidth(totalCols: number, role: Role, userPrompt: string, termuxMode = false) {
+  const available = Math.max(1, totalCols - transcriptGutterWidth(role, userPrompt) - 2)
+
+  if (termuxMode) {
+    // On narrow / unusual aspect-ratio mobile panes, forcing a wide minimum
+    // width causes right-edge clipping and chopped words.
+    return available
+  }
+
+  return Math.max(20, available)
 }
 
-export function stableComposerColumns(totalCols: number, promptWidth: number) {
+export function stableComposerColumns(totalCols: number, promptWidth: number, termuxMode = false) {
   // Physical render/wrap width. Always reserve outer composer padding and
   // prompt prefix. Only reserve the transcript scrollbar gutter when the
   // terminal is wide enough; on narrow panes, preserving input columns beats
   // keeping gutters visually aligned.
-  return Math.max(1, totalCols - promptWidth - 2 - (totalCols - promptWidth >= 24 ? 2 : 0))
+  const afterPrompt = totalCols - promptWidth
+  const reserveScrollbar = afterPrompt >= (termuxMode ? 36 : 24) ? 2 : 0
+
+  return Math.max(1, totalCols - promptWidth - 2 - reserveScrollbar)
 }

ui-tui/src/lib/prompt.ts

@@ -1,8 +1,32 @@
-export function composerPromptText(prompt: string, profileName?: null | string, shellMode = false): string {
+const TERMUX_SAFE_PROMPT = '>'
+
+export function composerPromptText(
+  prompt: string,
+  profileName?: null | string,
+  shellMode = false,
+  termuxMode = false,
+  totalCols?: number
+): string {
   if (shellMode) {
     return '$'
   }
 
+  if (termuxMode) {
+    // Termux fonts/terminal backends can render decorative prompt glyphs with
+    // ambiguous width; keep the live composer marker strictly single-cell ASCII
+    // so we never leave stale arrow artifacts while typing.
+    const basePrompt = TERMUX_SAFE_PROMPT
+
+    // On very wide panes we can still include profile context. On narrow/mobile
+    // panes this burns precious columns and increases wrap/clipping risk.
+    const wideEnoughForProfile = typeof totalCols === 'number' ? totalCols >= 90 : false
+    if (wideEnoughForProfile && profileName && !['default', 'custom'].includes(profileName)) {
+      return `${profileName} ${basePrompt}`
+    }
+
+    return basePrompt
+  }
+
   if (profileName && !['default', 'custom'].includes(profileName)) {
     return `${profileName} ${prompt}`
   }

ui-tui/src/lib/virtualHeights.ts

@@ -1,5 +1,6 @@
 import type { Msg } from '../types.js'
 
+import { TERMUX_TUI_MODE } from '../config/env.js'
 import { transcriptBodyWidth } from './inputMetrics.js'
 
 const hashText = (text: string) => {
@@ -96,7 +97,7 @@ export const estimatedMsgHeight = (
     return Math.max(2, msg.todos.length + 2)
   }
 
-  const bodyWidth = transcriptBodyWidth(cols, msg.role, userPrompt)
+  const bodyWidth = transcriptBodyWidth(cols, msg.role, userPrompt, TERMUX_TUI_MODE)
   const text = msg.text
   let h = wrappedLines(text || ' ', bodyWidth)