fix(tui): preserve prompt separator width (#19340)

* fix(tui): preserve prompt separator width

* fix(tui): align transcript height estimates with prompt width

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

@@ -1,7 +1,13 @@
+import { renderSync } from '@hermes/ink'
+import React from 'react'
+import { PassThrough } from 'stream'
 import { describe, expect, it } from 'vitest'
 
+import { MessageLine } from '../components/messageLine.js'
 import { toTranscriptMessages } from '../domain/messages.js'
 import { upsert } from '../lib/messages.js'
+import { stripAnsi } from '../lib/text.js'
+import { DEFAULT_THEME } from '../theme.js'
 
 describe('toTranscriptMessages', () => {
   it('preserves assistant tool-call rows so resume does not drop prior turns', () => {
@@ -21,6 +27,50 @@ describe('toTranscriptMessages', () => {
   })
 })
 
+describe('MessageLine', () => {
+  it('preserves a separator after compound user prompt glyphs in transcript rows', () => {
+    const stdout = new PassThrough()
+    const stdin = new PassThrough()
+    const stderr = new PassThrough()
+    let output = ''
+
+    Object.assign(stdout, { columns: 80, isTTY: false, rows: 24 })
+    Object.assign(stdin, { isTTY: false })
+    Object.assign(stderr, { isTTY: false })
+    stdout.on('data', chunk => {
+      output += chunk.toString()
+    })
+
+    const t = {
+      ...DEFAULT_THEME,
+      brand: { ...DEFAULT_THEME.brand, prompt: 'Ψ >' }
+    }
+
+    const instance = renderSync(
+      React.createElement(MessageLine, {
+        cols: 80,
+        msg: { role: 'user', text: 'Okay' },
+        t
+      }),
+      {
+        patchConsole: false,
+        stderr: stderr as NodeJS.WriteStream,
+        stdin: stdin as NodeJS.ReadStream,
+        stdout: stdout as NodeJS.WriteStream
+      }
+    )
+
+    instance.unmount()
+    instance.cleanup()
+
+    const renderedLine = stripAnsi(output)
+      .split('\n')
+      .find(line => line.includes('Okay'))
+
+    expect(renderedLine).toContain('Ψ > Okay')
+  })
+})
+
 describe('upsert', () => {
   it('appends when last role differs', () => {
     expect(upsert([{ role: 'user', text: 'hi' }], 'assistant', 'hello')).toHaveLength(2)