diff --git a/mobile/src/terminal/document/document-terminal-shape.ts b/mobile/src/terminal/document/document-terminal-shape.ts
index b5807efdf7f..60067acfd4f 100644
--- a/mobile/src/terminal/document/document-terminal-shape.ts
+++ b/mobile/src/terminal/document/document-terminal-shape.ts
@@ -33,6 +33,8 @@ export type TerminalInitialOscLink = {
  * every reader here is a truthiness test rather than a comparison.
  */
 export type TerminalDocumentCell = {
+  getChars?: () => string
+  getWidth?: () => number
   isBgDefault: () => boolean
   extended?: { urlId?: number }
   isInverse: () => number
diff --git a/mobile/src/terminal/document/selection-range.test.ts b/mobile/src/terminal/document/selection-range.test.ts
new file mode 100644
index 00000000000..2ea75091bb6
--- /dev/null
+++ b/mobile/src/terminal/document/selection-range.test.ts
@@ -0,0 +1,175 @@
+// @vitest-environment happy-dom
+import { Unicode11Addon } from '@xterm/addon-unicode11'
+import { Terminal } from '@xterm/xterm'
+import { afterEach, describe, expect, it, vi } from 'vitest'
+import { createTerminalDocumentScope, type TerminalDocumentScope } from './document-scope'
+import { seedWordSelection } from './selection-range'
+import { armLongPress, dispatcherShouldBlockSurface } from './tap-dispatch'
+import { handleDragMove, stopEdgeScroll } from './selection-overlay'
+import { terminalDocumentDouble } from './document-terminal-double.test-support'
+
+const terminals: Terminal[] = []
+
+afterEach(() => {
+  terminals.splice(0).forEach((term) => term.dispose())
+  vi.unstubAllGlobals()
+  vi.useRealTimers()
+})
+
+async function fixture(text: string) {
+  const term = new Terminal({ cols: 60, rows: 3, allowProposedApi: true })
+  terminals.push(term)
+  term.loadAddon(new Unicode11Addon())
+  term.unicode.activeVersion = '11'
+  await new Promise<void>((resolve) => term.write(text, resolve))
+  const scope = createTerminalDocumentScope()
+  // oxlint-disable-next-line typescript/consistent-type-assertions -- SAFETY: the real xterm exposes the narrower document terminal API.
+  scope.term = term as unknown as TerminalDocumentScope['term']
+  const select = vi.spyOn(term, 'select').mockImplementation(() => {})
+  const selected = () => {
+    const [col, row, length] = select.mock.calls.at(-1)!
+    return term.buffer.active.getLine(row)?.translateToString(false, col, col + length)
+  }
+  return { term, scope, select, selected }
+}
+
+describe('word selection uses the rendered xterm cell range', () => {
+  it.each([
+    ['합성 행 0001', 0, '합성', 0, 4],
+    ['합성 행 0001', 1, '합성', 0, 4],
+    ['합성 행 0001', 2, '합성', 0, 4],
+    ['합성 행 0001', 3, '합성', 0, 4],
+    ['합성 행 0001', 5, '행', 5, 2],
+    ['합성 행 0001', 6, '행', 5, 2],
+    ['합성 행 0001', 10, '0001', 8, 4],
+    ['🙂 hello', 0, '🙂', 0, 2],
+    ['🙂 hello', 1, '🙂', 0, 2],
+    ['🙂 hello', 3, 'hello', 3, 5],
+    ['cafe\u0301 done', 3, 'cafe\u0301', 0, 4],
+    ['cafe\u0301 done', 5, 'done', 5, 4],
+    ['𐐀x done', 0, '𐐀x', 0, 2],
+    ['🧑‍💻 done', 0, '🧑‍💻', 0, 4],
+    ['🧑‍💻 done', 3, '🧑‍💻', 0, 4],
+    ['🇰🇷 done', 0, '🇰🇷', 0, 2],
+    ['가 나', 2, ' ', 2, 1],
+    ['before /tmp/file.ts after', 10, '/tmp/file.ts', 7, 12],
+    ['', 6, ' ', 6, 1]
+  ] as const)('selects %s at cell %i', async (text, col, expected, start, length) => {
+    const f = await fixture(text)
+    seedWordSelection(f.scope, col, 0)
+    expect(f.select).toHaveBeenLastCalledWith(start, 0, length)
+    expect(f.selected()).toBe(expected)
+    expect(f.scope.sel).toEqual({
+      anchor: { col: start, row: 0 },
+      focus: { col: start + length - 1, row: 0 },
+      activeHandle: null
+    })
+  })
+
+  it('keeps cell mapping when a legacy WebView has no grapheme segmenter', async () => {
+    const f = await fixture('합성 🙂 cafe\u0301')
+    vi.stubGlobal('Intl', Object.assign(Object.create(Intl), { Segmenter: undefined }))
+    seedWordSelection(f.scope, 3, 0)
+    expect(f.select).toHaveBeenLastCalledWith(0, 0, 4)
+    expect(f.selected()).toBe('합성')
+    seedWordSelection(f.scope, 6, 0)
+    expect(f.select).toHaveBeenLastCalledWith(5, 0, 2)
+    expect(f.selected()).toBe('🙂')
+  })
+
+  it('keeps ASCII behavior for a terminal seam without cell readers', async () => {
+    const f = await fixture('hello world')
+    const line = f.term.buffer.active.getLine(0)!
+    const getLine = vi.spyOn(f.term.buffer.active, 'getLine').mockReturnValue(line)
+    vi.spyOn(line, 'getCell').mockReturnValue(undefined)
+    seedWordSelection(f.scope, 8, 0)
+    expect(f.select).toHaveBeenLastCalledWith(6, 0, 5)
+    expect(getLine).toHaveBeenCalledWith(0)
+  })
+
+  it('keeps an absolute scrollback row and tolerates an evicted line', async () => {
+    const f = await fixture('한글\r\nsecond\r\nthird\r\nfourth')
+    expect(f.term.buffer.active.viewportY).toBeGreaterThan(0)
+    seedWordSelection(f.scope, 2, 0)
+    expect(f.select).toHaveBeenLastCalledWith(0, 0, 4)
+    expect(f.selected()).toBe('한글')
+    seedWordSelection(f.scope, 2, 99)
+    expect(f.select).toHaveBeenLastCalledWith(2, 99, 1)
+  })
+})
+
+describe('Unicode selection boundaries across every rendered column', () => {
+  it.each([
+    ['한글', 4],
+    ['cafe\u0301', 4],
+    ['𐐀x', 2],
+    ['👍🏽', 4],
+    ['👨‍👩‍👧‍👦', 8],
+    ['🏳️‍🌈', 3],
+    ['🇰🇷', 2],
+    ['❤️', 1]
+  ] as const)('keeps %s whole at each of its %i cells after wide text', async (text, width) => {
+    const f = await fixture(`가 ${text} next`)
+    for (let col = 3; col < 3 + width; col++) {
+      seedWordSelection(f.scope, col, 0)
+      expect(f.select).toHaveBeenLastCalledWith(3, 0, width)
+      expect(f.selected()).toBe(text)
+    }
+    seedWordSelection(f.scope, 3 + width + 1, 0)
+    expect(f.selected()).toBe('next')
+  })
+
+  it('keeps the last wide word on the row and the next wrapped row independent', async () => {
+    const f = await fixture(' '.repeat(56) + '한글next')
+    for (const col of [56, 57, 58, 59]) {
+      seedWordSelection(f.scope, col, 0)
+      expect(f.select).toHaveBeenLastCalledWith(56, 0, 4)
+      expect(f.selected()).toBe('한글')
+    }
+    seedWordSelection(f.scope, 0, 1)
+    expect(f.select).toHaveBeenLastCalledWith(0, 1, 4)
+    expect(f.selected()).toBe('next')
+  })
+})
+
+it('keeps the Unicode seed while the long-press finger owns a forward or backward drag', async () => {
+  const f = await fixture('가 한글 next')
+  const surface = document.createElement('div')
+  f.scope.term = {
+    ...terminalDocumentDouble().terminal,
+    cols: f.term.cols,
+    rows: f.term.rows,
+    buffer: f.scope.term!.buffer,
+    select: f.select,
+    _core: { _renderService: { dimensions: { css: { cell: { width: 8, height: 15 } } } } }
+  }
+  Object.assign(f.scope, {
+    surface,
+    selectionOverlay: document.createElement('div'),
+    handleStart: document.createElement('div'),
+    handleEnd: document.createElement('div'),
+    selMenu: document.createElement('div'),
+    viewportRect: () => ({ left: 0, top: 50, width: 480, height: 200 }),
+    currentScale: 1,
+    userScale: 1
+  })
+  f.scope.touchDispatch.mode = 'surface'
+  f.scope.touchDispatch.touchId = 7
+  f.scope.tapCandidate = { x: 36, y: 57, t: Date.now(), identifier: 7 }
+  vi.useFakeTimers()
+  armLongPress(f.scope, new Touch({ identifier: 7, target: surface, clientX: 36, clientY: 57 }))
+  vi.advanceTimersByTime(500)
+  expect(f.selected()).toBe('한글')
+  expect(f.scope.sel?.anchor).toEqual({ col: 3, row: 0 })
+  expect(f.scope.sel?.focus).toEqual({ col: 6, row: 0 })
+  expect(f.scope.touchDispatch).toMatchObject({ mode: 'select-drag', touchId: 7 })
+  expect(dispatcherShouldBlockSurface(f.scope)).toBe(true)
+  expect(f.scope.tapCandidate).toBeNull()
+
+  handleDragMove(f.scope, 'end', 11 * 8 + 4, 57)
+  expect(f.selected()).toBe('한글 next')
+  handleDragMove(f.scope, 'end', 4, 57)
+  expect(f.select).toHaveBeenLastCalledWith(0, 0, 4)
+  expect(f.selected()).toBe('가 한')
+  stopEdgeScroll(f.scope)
+})
diff --git a/mobile/src/terminal/document/selection-range.ts b/mobile/src/terminal/document/selection-range.ts
index bde95116758..b38d4cadf85 100644
--- a/mobile/src/terminal/document/selection-range.ts
+++ b/mobile/src/terminal/document/selection-range.ts
@@ -1,9 +1,62 @@
 import { getLineText } from './cell-geometry'
 import type { TerminalDocumentScope, TerminalDocumentSelection } from './document-scope'
+import type { TerminalDocumentLine } from './document-terminal-shape'
 
 /** What counts as one word for select-all and for word seeding. */
 const WORD_RE = /[\p{L}\p{N}_./:@~+=?&#%-]/u
 
+type SelectionUnit = { text: string; start: number; end: number }
+
+function selectionUnits(line: TerminalDocumentLine, cols: number): SelectionUnit[] | null {
+  const cells: SelectionUnit[] = []
+  for (let col = 0; col < Math.min(cols, line.length);) {
+    const cell = line.getCell?.(col)
+    if (!cell?.getChars || !cell.getWidth) {
+      return null
+    }
+    const width = cell.getWidth()
+    if (width <= 0) {
+      col++
+      continue
+    }
+    cells.push({ text: cell.getChars() || ' ', start: col, end: col + width - 1 })
+    col += width
+  }
+  if (typeof Intl.Segmenter !== 'function') {
+    return cells
+  }
+  // A grapheme can occupy several xterm cells; UTF-16 length is never its cell width.
+  const columns = cells.flatMap((cell) => Array.from({ length: cell.text.length }, () => cell))
+  const text = cells.map((cell) => cell.text).join('')
+  return Array.from(
+    new Intl.Segmenter(undefined, { granularity: 'grapheme' }).segment(text),
+    (part) => ({
+      text: part.segment,
+      start: columns[part.index].start,
+      end: columns[part.index + part.segment.length - 1].end
+    })
+  )
+}
+
+function wordCellRange(line: TerminalDocumentLine | undefined, col: number, cols: number) {
+  const units = line && selectionUnits(line, cols)
+  const index = units?.findIndex((unit) => unit.start <= col && col <= unit.end) ?? -1
+  if (!units || index < 0) {
+    return null
+  }
+  let start = index
+  let end = index
+  if (WORD_RE.test(units[index].text)) {
+    while (start > 0 && WORD_RE.test(units[start - 1].text)) {
+      start--
+    }
+    while (end + 1 < units.length && WORD_RE.test(units[end + 1].text)) {
+      end++
+    }
+  }
+  return { start: units[start].start, end: units[end].end }
+}
+
 /** The ordered ends of the selection, whichever way the user dragged it. */
 export type TerminalSelectionRange = {
   start: TerminalDocumentSelection['anchor']
@@ -11,6 +64,17 @@ export type TerminalSelectionRange = {
 }
 
 export function seedWordSelection(scope: TerminalDocumentScope, col: number, absRow: number) {
+  const cells = wordCellRange(scope.term?.buffer.active.getLine(absRow), col, scope.term?.cols ?? 0)
+  if (cells) {
+    scope.sel = {
+      anchor: { col: cells.start, row: absRow },
+      focus: { col: cells.end, row: absRow },
+      activeHandle: null
+    }
+    applyXtermSelection(scope)
+    return
+  }
+  // Small host/test seams can expose text only; keep their existing ASCII behavior.
   const line = getLineText(scope, absRow)
   if (!line) {
     scope.sel = {