init claude-code

ink/selection.ts

@@ -0,0 +1,917 @@
+/**
+ * Text selection state for fullscreen mode.
+ *
+ * Tracks a linear selection in screen-buffer coordinates (0-indexed col/row).
+ * Selection is line-based: cells from (startCol, startRow) through
+ * (endCol, endRow) inclusive, wrapping across line boundaries. This matches
+ * terminal-native selection behavior (not rectangular/block).
+ *
+ * The selection is stored as ANCHOR (where the drag started) + FOCUS (where
+ * the cursor is now). The rendered highlight normalizes to start ≤ end.
+ */
+
+import { clamp } from './layout/geometry.js'
+import type { Screen, StylePool } from './screen.js'
+import { CellWidth, cellAt, cellAtIndex, setCellStyleId } from './screen.js'
+
+type Point = { col: number; row: number }
+
+export type SelectionState = {
+  /** Where the mouse-down occurred. Null when no selection. */
+  anchor: Point | null
+  /** Current drag position (updated on mouse-move while dragging). */
+  focus: Point | null
+  /** True between mouse-down and mouse-up. */
+  isDragging: boolean
+  /** For word/line mode: the initial word/line bounds from the first
+   *  multi-click. Drag extends from this span to the word/line at the
+   *  current mouse position so the original word/line stays selected
+   *  even when dragging backward past it. Null ⇔ char mode. The kind
+   *  tells extendSelection whether to snap to word or line boundaries. */
+  anchorSpan: { lo: Point; hi: Point; kind: 'word' | 'line' } | null
+  /** Text from rows that scrolled out ABOVE the viewport during
+   *  drag-to-scroll. The screen buffer only holds the current viewport,
+   *  so without this accumulator, dragging down past the bottom edge
+   *  loses the top of the selection once the anchor clamps. Prepended
+   *  to the on-screen text by getSelectedText. Reset on start/clear. */
+  scrolledOffAbove: string[]
+  /** Symmetric: rows scrolled out BELOW when dragging up. Appended. */
+  scrolledOffBelow: string[]
+  /** Soft-wrap bits parallel to scrolledOffAbove — true means the row
+   *  is a continuation of the one before it (the `\n` was inserted by
+   *  word-wrap, not in the source). Captured alongside the text at
+   *  scroll time since the screen's softWrap bitmap shifts with content.
+   *  getSelectedText uses these to join wrapped rows back into logical
+   *  lines. */
+  scrolledOffAboveSW: boolean[]
+  /** Parallel to scrolledOffBelow. */
+  scrolledOffBelowSW: boolean[]
+  /** Pre-clamp anchor row. Set when shiftSelection clamps anchor so a
+   *  reverse scroll can restore the true position and pop accumulators.
+   *  Without this, PgDn (clamps anchor) → PgUp leaves anchor at the wrong
+   *  row AND scrolledOffAbove stale — highlight ≠ copy. Undefined when
+   *  anchor is in-bounds (no clamp debt). Cleared on start/clear. */
+  virtualAnchorRow?: number
+  /** Same for focus. */
+  virtualFocusRow?: number
+  /** True if the mouse-down that started this selection had the alt
+   *  modifier set (SGR button bit 0x08). On macOS xterm.js this is a
+   *  signal that VS Code's macOptionClickForcesSelection is OFF — if it
+   *  were on, xterm.js would have consumed the event for native selection
+   *  and we'd never receive it. Used by the footer to show the right hint. */
+  lastPressHadAlt: boolean
+}
+
+export function createSelectionState(): SelectionState {
+  return {
+    anchor: null,
+    focus: null,
+    isDragging: false,
+    anchorSpan: null,
+    scrolledOffAbove: [],
+    scrolledOffBelow: [],
+    scrolledOffAboveSW: [],
+    scrolledOffBelowSW: [],
+    lastPressHadAlt: false,
+  }
+}
+
+export function startSelection(
+  s: SelectionState,
+  col: number,
+  row: number,
+): void {
+  s.anchor = { col, row }
+  // Focus is not set until the first drag motion. A click-release with no
+  // drag leaves focus null → hasSelection/selectionBounds return false/null
+  // via the `!s.focus` check, so a bare click never highlights a cell.
+  s.focus = null
+  s.isDragging = true
+  s.anchorSpan = null
+  s.scrolledOffAbove = []
+  s.scrolledOffBelow = []
+  s.scrolledOffAboveSW = []
+  s.scrolledOffBelowSW = []
+  s.virtualAnchorRow = undefined
+  s.virtualFocusRow = undefined
+  s.lastPressHadAlt = false
+}
+
+export function updateSelection(
+  s: SelectionState,
+  col: number,
+  row: number,
+): void {
+  if (!s.isDragging) return
+  // First motion at the same cell as anchor is a no-op. Terminals in mode
+  // 1002 can fire a drag event at the anchor cell (sub-pixel tremor, or a
+  // motion-release pair). Setting focus here would turn a bare click into
+  // a 1-cell selection and clobber the clipboard via useCopyOnSelect. Once
+  // focus is set (real drag), we track normally including back to anchor.
+  if (!s.focus && s.anchor && s.anchor.col === col && s.anchor.row === row)
+    return
+  s.focus = { col, row }
+}
+
+export function finishSelection(s: SelectionState): void {
+  s.isDragging = false
+  // Keep anchor/focus so highlight stays visible and text can be copied.
+  // Clear via clearSelection() on Esc or after copy.
+}
+
+export function clearSelection(s: SelectionState): void {
+  s.anchor = null
+  s.focus = null
+  s.isDragging = false
+  s.anchorSpan = null
+  s.scrolledOffAbove = []
+  s.scrolledOffBelow = []
+  s.scrolledOffAboveSW = []
+  s.scrolledOffBelowSW = []
+  s.virtualAnchorRow = undefined
+  s.virtualFocusRow = undefined
+  s.lastPressHadAlt = false
+}
+
+// Unicode-aware word character matcher: letters (any script), digits,
+// and the punctuation set iTerm2 treats as word-part by default.
+// Matching iTerm2's default means double-clicking a path like
+// `/usr/bin/bash` or `~/.claude/config.json` selects the whole thing,
+// which is the muscle memory most macOS terminal users have.
+// iTerm2 default "characters considered part of a word": /-+\~_.
+const WORD_CHAR = /[\p{L}\p{N}_/.\-+~\\]/u
+
+/**
+ * Character class for double-click word-expansion. Cells with the same
+ * class as the clicked cell are included in the selection; a class change
+ * is a boundary. Matches typical terminal-emulator behavior (iTerm2 etc.):
+ * double-click on `foo` selects `foo`, on `->` selects `->`, on spaces
+ * selects the whitespace run.
+ */
+function charClass(c: string): 0 | 1 | 2 {
+  if (c === ' ' || c === '') return 0
+  if (WORD_CHAR.test(c)) return 1
+  return 2
+}
+
+/**
+ * Find the bounds of the same-class character run at (col, row). Returns
+ * null if the click is out of bounds or lands on a noSelect cell. Used by
+ * selectWordAt (initial double-click) and extendWordSelection (drag).
+ */
+function wordBoundsAt(
+  screen: Screen,
+  col: number,
+  row: number,
+): { lo: number; hi: number } | null {
+  if (row < 0 || row >= screen.height) return null
+  const width = screen.width
+  const noSelect = screen.noSelect
+  const rowOff = row * width
+
+  // If the click landed on the spacer tail of a wide char, step back to
+  // the head so the class check sees the actual grapheme.
+  let c = col
+  if (c > 0) {
+    const cell = cellAt(screen, c, row)
+    if (cell && cell.width === CellWidth.SpacerTail) c -= 1
+  }
+  if (c < 0 || c >= width || noSelect[rowOff + c] === 1) return null
+
+  const startCell = cellAt(screen, c, row)
+  if (!startCell) return null
+  const cls = charClass(startCell.char)
+
+  // Expand left: include cells of the same class, stop at noSelect or
+  // class change. SpacerTail cells are stepped over (the wide-char head
+  // at the preceding column determines the class).
+  let lo = c
+  while (lo > 0) {
+    const prev = lo - 1
+    if (noSelect[rowOff + prev] === 1) break
+    const pc = cellAt(screen, prev, row)
+    if (!pc) break
+    if (pc.width === CellWidth.SpacerTail) {
+      // Step over the spacer to the wide-char head
+      if (prev === 0 || noSelect[rowOff + prev - 1] === 1) break
+      const head = cellAt(screen, prev - 1, row)
+      if (!head || charClass(head.char) !== cls) break
+      lo = prev - 1
+      continue
+    }
+    if (charClass(pc.char) !== cls) break
+    lo = prev
+  }
+
+  // Expand right: same logic, skipping spacer tails.
+  let hi = c
+  while (hi < width - 1) {
+    const next = hi + 1
+    if (noSelect[rowOff + next] === 1) break
+    const nc = cellAt(screen, next, row)
+    if (!nc) break
+    if (nc.width === CellWidth.SpacerTail) {
+      // Include the spacer tail in the selection range (it belongs to
+      // the wide char at hi) and continue past it.
+      hi = next
+      continue
+    }
+    if (charClass(nc.char) !== cls) break
+    hi = next
+  }
+
+  return { lo, hi }
+}
+
+/** -1 if a < b, 1 if a > b, 0 if equal (reading order: row then col). */
+function comparePoints(a: Point, b: Point): number {
+  if (a.row !== b.row) return a.row < b.row ? -1 : 1
+  if (a.col !== b.col) return a.col < b.col ? -1 : 1
+  return 0
+}
+
+/**
+ * Select the word at (col, row) by scanning the screen buffer for the
+ * bounds of the same-class character run. Mutates the selection in place.
+ * No-op if the click is out of bounds or lands on a noSelect cell.
+ * Sets isDragging=true and anchorSpan so a subsequent drag extends the
+ * selection word-by-word (native macOS behavior).
+ */
+export function selectWordAt(
+  s: SelectionState,
+  screen: Screen,
+  col: number,
+  row: number,
+): void {
+  const b = wordBoundsAt(screen, col, row)
+  if (!b) return
+  const lo = { col: b.lo, row }
+  const hi = { col: b.hi, row }
+  s.anchor = lo
+  s.focus = hi
+  s.isDragging = true
+  s.anchorSpan = { lo, hi, kind: 'word' }
+}
+
+// Printable ASCII minus terminal URL delimiters. Restricting to single-
+// codeunit ASCII keeps cell-count === string-index, so the column-span
+// check below is exact (no wide-char/grapheme drift).
+const URL_BOUNDARY = new Set([...'<>"\'` '])
+function isUrlChar(c: string): boolean {
+  if (c.length !== 1) return false
+  const code = c.charCodeAt(0)
+  return code >= 0x21 && code <= 0x7e && !URL_BOUNDARY.has(c)
+}
+
+/**
+ * Scan the screen buffer for a plain-text URL at (col, row). Mirrors the
+ * terminal's native Cmd+Click URL detection, which fullscreen mode's mouse
+ * tracking intercepts. Called from getHyperlinkAt as a fallback when the
+ * cell has no OSC 8 hyperlink.
+ */
+export function findPlainTextUrlAt(
+  screen: Screen,
+  col: number,
+  row: number,
+): string | undefined {
+  if (row < 0 || row >= screen.height) return undefined
+  const width = screen.width
+  const noSelect = screen.noSelect
+  const rowOff = row * width
+
+  let c = col
+  if (c > 0) {
+    const cell = cellAt(screen, c, row)
+    if (cell && cell.width === CellWidth.SpacerTail) c -= 1
+  }
+  if (c < 0 || c >= width || noSelect[rowOff + c] === 1) return undefined
+
+  const startCell = cellAt(screen, c, row)
+  if (!startCell || !isUrlChar(startCell.char)) return undefined
+
+  // Expand left/right to the bounds of the URL-char run. URLs are ASCII
+  // (CellWidth.Narrow, 1 codeunit), so hitting a non-ASCII/wide/spacer
+  // cell is a boundary — no need to step over spacers like wordBoundsAt.
+  let lo = c
+  while (lo > 0) {
+    const prev = lo - 1
+    if (noSelect[rowOff + prev] === 1) break
+    const pc = cellAt(screen, prev, row)
+    if (!pc || pc.width !== CellWidth.Narrow || !isUrlChar(pc.char)) break
+    lo = prev
+  }
+  let hi = c
+  while (hi < width - 1) {
+    const next = hi + 1
+    if (noSelect[rowOff + next] === 1) break
+    const nc = cellAt(screen, next, row)
+    if (!nc || nc.width !== CellWidth.Narrow || !isUrlChar(nc.char)) break
+    hi = next
+  }
+
+  let token = ''
+  for (let i = lo; i <= hi; i++) token += cellAt(screen, i, row)!.char
+
+  // 1 cell = 1 char across [lo, hi] (ASCII-only run), so string index =
+  // column offset. Find the last scheme anchor at or before the click —
+  // a run like `https://a.com,https://b.com` has two, and clicking the
+  // second should return the second URL, not the greedy match of both.
+  const clickIdx = c - lo
+  const schemeRe = /(?:https?|file):\/\//g
+  let urlStart = -1
+  let urlEnd = token.length
+  for (let m; (m = schemeRe.exec(token)); ) {
+    if (m.index > clickIdx) {
+      urlEnd = m.index
+      break
+    }
+    urlStart = m.index
+  }
+  if (urlStart < 0) return undefined
+  let url = token.slice(urlStart, urlEnd)
+
+  // Strip trailing sentence punctuation. For closers () ] }, only strip
+  // if unbalanced — `/wiki/Foo_(bar)` keeps `)`, `/arr[0]` keeps `]`.
+  const OPENER: Record<string, string> = { ')': '(', ']': '[', '}': '{' }
+  while (url.length > 0) {
+    const last = url.at(-1)!
+    if ('.,;:!?'.includes(last)) {
+      url = url.slice(0, -1)
+      continue
+    }
+    const opener = OPENER[last]
+    if (!opener) break
+    let opens = 0
+    let closes = 0
+    for (let i = 0; i < url.length; i++) {
+      const ch = url.charAt(i)
+      if (ch === opener) opens++
+      else if (ch === last) closes++
+    }
+    if (closes > opens) url = url.slice(0, -1)
+    else break
+  }
+
+  // urlStart already guarantees click >= URL start; check right edge.
+  if (clickIdx >= urlStart + url.length) return undefined
+
+  return url
+}
+
+/**
+ * Select the entire row. Sets isDragging=true and anchorSpan so a
+ * subsequent drag extends the selection line-by-line. The anchor/focus
+ * span from col 0 to width-1; getSelectedText handles noSelect skipping
+ * and trailing-whitespace trimming so the copied text is just the visible
+ * line content.
+ */
+export function selectLineAt(
+  s: SelectionState,
+  screen: Screen,
+  row: number,
+): void {
+  if (row < 0 || row >= screen.height) return
+  const lo = { col: 0, row }
+  const hi = { col: screen.width - 1, row }
+  s.anchor = lo
+  s.focus = hi
+  s.isDragging = true
+  s.anchorSpan = { lo, hi, kind: 'line' }
+}
+
+/**
+ * Extend a word/line-mode selection to the word/line at (col, row). The
+ * anchor span (the original multi-clicked word/line) stays selected; the
+ * selection grows from that span to the word/line at the current mouse
+ * position. Word mode falls back to the raw cell when the mouse is over a
+ * noSelect cell or out of bounds, so dragging into gutters still extends.
+ */
+export function extendSelection(
+  s: SelectionState,
+  screen: Screen,
+  col: number,
+  row: number,
+): void {
+  if (!s.isDragging || !s.anchorSpan) return
+  const span = s.anchorSpan
+  let mLo: Point
+  let mHi: Point
+  if (span.kind === 'word') {
+    const b = wordBoundsAt(screen, col, row)
+    mLo = { col: b ? b.lo : col, row }
+    mHi = { col: b ? b.hi : col, row }
+  } else {
+    const r = clamp(row, 0, screen.height - 1)
+    mLo = { col: 0, row: r }
+    mHi = { col: screen.width - 1, row: r }
+  }
+  if (comparePoints(mHi, span.lo) < 0) {
+    // Mouse target ends before anchor span: extend backward.
+    s.anchor = span.hi
+    s.focus = mLo
+  } else if (comparePoints(mLo, span.hi) > 0) {
+    // Mouse target starts after anchor span: extend forward.
+    s.anchor = span.lo
+    s.focus = mHi
+  } else {
+    // Mouse overlaps the anchor span: just select the anchor span.
+    s.anchor = span.lo
+    s.focus = span.hi
+  }
+}
+
+/** Semantic keyboard focus moves. See moveSelectionFocus in ink.tsx for
+ *  how screen bounds + row-wrap are applied. */
+export type FocusMove =
+  | 'left'
+  | 'right'
+  | 'up'
+  | 'down'
+  | 'lineStart'
+  | 'lineEnd'
+
+/**
+ * Set focus to (col, row) for keyboard selection extension (shift+arrow).
+ * Anchor stays fixed; selection grows or shrinks depending on where focus
+ * moves relative to anchor. Drops to char mode (clears anchorSpan) —
+ * native macOS does this too: shift+arrow after a double-click word-select
+ * extends char-by-char from the word edge, not word-by-word. Scrolled-off
+ * accumulators are preserved: keyboard-extending a drag-scrolled selection
+ * keeps the off-screen rows. Caller supplies coords already clamped/wrapped.
+ */
+export function moveFocus(s: SelectionState, col: number, row: number): void {
+  if (!s.focus) return
+  s.anchorSpan = null
+  s.focus = { col, row }
+  // Explicit user repositioning — any stale virtual focus (from a prior
+  // shiftSelection clamp) no longer reflects intent. Anchor stays put so
+  // virtualAnchorRow is still valid for its own round-trip.
+  s.virtualFocusRow = undefined
+}
+
+/**
+ * Shift anchor AND focus by dRow, clamped to [minRow, maxRow]. Used for
+ * keyboard scroll (PgUp/PgDn/ctrl+u/d/b/f): the whole selection must track
+ * the content, unlike drag-to-scroll where focus stays at the mouse. Any
+ * point that hits a clamp bound gets its col reset to the full-width edge —
+ * its original content scrolled off-screen and was captured by
+ * captureScrolledRows, so the col constraint was already consumed. Keeping
+ * it would truncate the NEW content now at that screen row. Clamp col is 0
+ * for dRow<0 (scrolling down, top leaves, 'above' semantics) or width-1 for
+ * dRow>0 (scrolling up, bottom leaves, 'below' semantics).
+ *
+ * If both ends overshoot the SAME viewport edge (select text → Home/End/g/G
+ * jumps far enough that both are out of view), clear — otherwise both clamp
+ * to the same corner cell and a ghost 1-cell highlight lingers, and
+ * getSelectedText returns one unrelated char from that corner. Symmetric
+ * with shiftSelectionForFollow's top-edge check, but bidirectional: keyboard
+ * scroll can jump either way.
+ */
+export function shiftSelection(
+  s: SelectionState,
+  dRow: number,
+  minRow: number,
+  maxRow: number,
+  width: number,
+): void {
+  if (!s.anchor || !s.focus) return
+  // Virtual rows track pre-clamp positions so reverse scrolls restore
+  // correctly. Without this, clamp(5→0) + shift(+10) = 10, not the true 5,
+  // and scrolledOffAbove stays stale (highlight ≠ copy).
+  const vAnchor = (s.virtualAnchorRow ?? s.anchor.row) + dRow
+  const vFocus = (s.virtualFocusRow ?? s.focus.row) + dRow
+  if (
+    (vAnchor < minRow && vFocus < minRow) ||
+    (vAnchor > maxRow && vFocus > maxRow)
+  ) {
+    clearSelection(s)
+    return
+  }
+  // Debt = how far the nearer endpoint overshoots each edge. When debt
+  // shrinks (reverse scroll), those rows are back on-screen — pop from
+  // the accumulator so getSelectedText doesn't double-count them.
+  const oldMin = Math.min(
+    s.virtualAnchorRow ?? s.anchor.row,
+    s.virtualFocusRow ?? s.focus.row,
+  )
+  const oldMax = Math.max(
+    s.virtualAnchorRow ?? s.anchor.row,
+    s.virtualFocusRow ?? s.focus.row,
+  )
+  const oldAboveDebt = Math.max(0, minRow - oldMin)
+  const oldBelowDebt = Math.max(0, oldMax - maxRow)
+  const newAboveDebt = Math.max(0, minRow - Math.min(vAnchor, vFocus))
+  const newBelowDebt = Math.max(0, Math.max(vAnchor, vFocus) - maxRow)
+  if (newAboveDebt < oldAboveDebt) {
+    // scrolledOffAbove pushes newest at the end (closest to on-screen).
+    const drop = oldAboveDebt - newAboveDebt
+    s.scrolledOffAbove.length -= drop
+    s.scrolledOffAboveSW.length = s.scrolledOffAbove.length
+  }
+  if (newBelowDebt < oldBelowDebt) {
+    // scrolledOffBelow unshifts newest at the front (closest to on-screen).
+    const drop = oldBelowDebt - newBelowDebt
+    s.scrolledOffBelow.splice(0, drop)
+    s.scrolledOffBelowSW.splice(0, drop)
+  }
+  // Invariant: accumulator length ≤ debt. If the accumulator exceeds debt,
+  // the excess is stale — e.g., moveFocus cleared virtualFocusRow without
+  // trimming the accumulator, orphaning entries the pop above can never
+  // reach because oldDebt was ALREADY 0. Truncate to debt (keeping the
+  // newest = closest-to-on-screen entries). Check newDebt (not oldDebt):
+  // captureScrolledRows runs BEFORE this shift in the real flow (ink.tsx),
+  // so at entry the accumulator is populated but oldDebt is still 0 —
+  // that's the normal establish-debt path, not stale.
+  if (s.scrolledOffAbove.length > newAboveDebt) {
+    // Above pushes newest at END → keep END.
+    s.scrolledOffAbove =
+      newAboveDebt > 0 ? s.scrolledOffAbove.slice(-newAboveDebt) : []
+    s.scrolledOffAboveSW =
+      newAboveDebt > 0 ? s.scrolledOffAboveSW.slice(-newAboveDebt) : []
+  }
+  if (s.scrolledOffBelow.length > newBelowDebt) {
+    // Below unshifts newest at FRONT → keep FRONT.
+    s.scrolledOffBelow = s.scrolledOffBelow.slice(0, newBelowDebt)
+    s.scrolledOffBelowSW = s.scrolledOffBelowSW.slice(0, newBelowDebt)
+  }
+  // Clamp col depends on which EDGE (not dRow direction): virtual tracking
+  // means a top-clamped point can stay top-clamped during a dRow>0 reverse
+  // shift — dRow-based clampCol would give it the bottom col.
+  const shift = (p: Point, vRow: number): Point => {
+    if (vRow < minRow) return { col: 0, row: minRow }
+    if (vRow > maxRow) return { col: width - 1, row: maxRow }
+    return { col: p.col, row: vRow }
+  }
+  s.anchor = shift(s.anchor, vAnchor)
+  s.focus = shift(s.focus, vFocus)
+  s.virtualAnchorRow =
+    vAnchor < minRow || vAnchor > maxRow ? vAnchor : undefined
+  s.virtualFocusRow = vFocus < minRow || vFocus > maxRow ? vFocus : undefined
+  // anchorSpan not virtual-tracked: it's for word/line extend-on-drag,
+  // irrelevant to the keyboard-scroll round-trip case.
+  if (s.anchorSpan) {
+    const sp = (p: Point): Point => {
+      const r = p.row + dRow
+      if (r < minRow) return { col: 0, row: minRow }
+      if (r > maxRow) return { col: width - 1, row: maxRow }
+      return { col: p.col, row: r }
+    }
+    s.anchorSpan = {
+      lo: sp(s.anchorSpan.lo),
+      hi: sp(s.anchorSpan.hi),
+      kind: s.anchorSpan.kind,
+    }
+  }
+}
+
+/**
+ * Shift the anchor row by dRow, clamped to [minRow, maxRow]. Used during
+ * drag-to-scroll: when the ScrollBox scrolls by N rows, the content that
+ * was under the anchor is now at a different viewport row, so the anchor
+ * must follow it. Focus is left unchanged (it stays at the mouse position).
+ */
+export function shiftAnchor(
+  s: SelectionState,
+  dRow: number,
+  minRow: number,
+  maxRow: number,
+): void {
+  if (!s.anchor) return
+  // Same virtual-row tracking as shiftSelection/shiftSelectionForFollow: the
+  // drag→follow transition hands off to shiftSelectionForFollow, which reads
+  // (virtualAnchorRow ?? anchor.row). Without this, drag-phase clamping
+  // leaves virtual undefined → follow initializes from the already-clamped
+  // row, under-counting total drift → shiftSelection's invariant-restore
+  // prematurely clears valid drag-phase accumulator entries.
+  const raw = (s.virtualAnchorRow ?? s.anchor.row) + dRow
+  s.anchor = { col: s.anchor.col, row: clamp(raw, minRow, maxRow) }
+  s.virtualAnchorRow = raw < minRow || raw > maxRow ? raw : undefined
+  // anchorSpan not virtual-tracked (word/line extend, irrelevant to
+  // keyboard-scroll round-trip) — plain clamp from current row.
+  if (s.anchorSpan) {
+    const shift = (p: Point): Point => ({
+      col: p.col,
+      row: clamp(p.row + dRow, minRow, maxRow),
+    })
+    s.anchorSpan = {
+      lo: shift(s.anchorSpan.lo),
+      hi: shift(s.anchorSpan.hi),
+      kind: s.anchorSpan.kind,
+    }
+  }
+}
+
+/**
+ * Shift the whole selection (anchor + focus + anchorSpan) by dRow, clamped
+ * to [minRow, maxRow]. Used when sticky/auto-follow scrolls the ScrollBox
+ * while a selection is active — native terminal behavior is for the
+ * highlight to walk up the screen with the text (not stay at the same
+ * screen position).
+ *
+ * Differs from shiftAnchor: during drag-to-scroll, focus tracks the live
+ * mouse position and only anchor follows the text. During streaming-follow,
+ * the selection is text-anchored at both ends — both must move. The
+ * isDragging check in ink.tsx picks which shift to apply.
+ *
+ * If both ends would shift strictly BELOW minRow (unclamped), the selected
+ * text has scrolled entirely off the top. Clear it — otherwise a single
+ * inverted cell lingers at the viewport top as a ghost (native terminals
+ * drop the selection when it leaves scrollback). Landing AT minRow is
+ * still valid: that cell holds the correct text. Returns true if the
+ * selection was cleared so the caller can notify React-land subscribers
+ * (useHasSelection) — the caller is inside onRender so it can't use
+ * notifySelectionChange (recursion), must fire listeners directly.
+ */
+export function shiftSelectionForFollow(
+  s: SelectionState,
+  dRow: number,
+  minRow: number,
+  maxRow: number,
+): boolean {
+  if (!s.anchor) return false
+  // Mirror shiftSelection: compute raw (unclamped) positions from virtual
+  // if set, else current. This handles BOTH the update path (virtual already
+  // set from a prior keyboard scroll) AND the initialize path (first clamp
+  // happens HERE via follow-scroll, no prior keyboard scroll). Without the
+  // initialize path, follow-scroll-first leaves virtual undefined even
+  // though the clamp below occurred → a later PgUp computes debt from the
+  // clamped row instead of the true pre-clamp row and never pops the
+  // accumulator — getSelectedText double-counts the off-screen rows.
+  const rawAnchor = (s.virtualAnchorRow ?? s.anchor.row) + dRow
+  const rawFocus = s.focus
+    ? (s.virtualFocusRow ?? s.focus.row) + dRow
+    : undefined
+  if (rawAnchor < minRow && rawFocus !== undefined && rawFocus < minRow) {
+    clearSelection(s)
+    return true
+  }
+  // Clamp from raw, not p.row+dRow — so a virtual position coming back
+  // in-bounds lands at the TRUE position, not the stale clamped one.
+  s.anchor = { col: s.anchor.col, row: clamp(rawAnchor, minRow, maxRow) }
+  if (s.focus && rawFocus !== undefined) {
+    s.focus = { col: s.focus.col, row: clamp(rawFocus, minRow, maxRow) }
+  }
+  s.virtualAnchorRow =
+    rawAnchor < minRow || rawAnchor > maxRow ? rawAnchor : undefined
+  s.virtualFocusRow =
+    rawFocus !== undefined && (rawFocus < minRow || rawFocus > maxRow)
+      ? rawFocus
+      : undefined
+  // anchorSpan not virtual-tracked (word/line extend, irrelevant to
+  // keyboard-scroll round-trip) — plain clamp from current row.
+  if (s.anchorSpan) {
+    const shift = (p: Point): Point => ({
+      col: p.col,
+      row: clamp(p.row + dRow, minRow, maxRow),
+    })
+    s.anchorSpan = {
+      lo: shift(s.anchorSpan.lo),
+      hi: shift(s.anchorSpan.hi),
+      kind: s.anchorSpan.kind,
+    }
+  }
+  return false
+}
+
+export function hasSelection(s: SelectionState): boolean {
+  return s.anchor !== null && s.focus !== null
+}
+
+/**
+ * Normalized selection bounds: start is always before end in reading order.
+ * Returns null if no active selection.
+ */
+export function selectionBounds(s: SelectionState): {
+  start: { col: number; row: number }
+  end: { col: number; row: number }
+} | null {
+  if (!s.anchor || !s.focus) return null
+  return comparePoints(s.anchor, s.focus) <= 0
+    ? { start: s.anchor, end: s.focus }
+    : { start: s.focus, end: s.anchor }
+}
+
+/**
+ * Check if a cell at (col, row) is within the current selection range.
+ * Used by the renderer to apply inverse style.
+ */
+export function isCellSelected(
+  s: SelectionState,
+  col: number,
+  row: number,
+): boolean {
+  const b = selectionBounds(s)
+  if (!b) return false
+  const { start, end } = b
+  if (row < start.row || row > end.row) return false
+  if (row === start.row && col < start.col) return false
+  if (row === end.row && col > end.col) return false
+  return true
+}
+
+/** Extract text from one screen row. When the next row is a soft-wrap
+ *  continuation (screen.softWrap[row+1]>0), clamp to that content-end
+ *  column and skip the trailing trim so the word-separator space survives
+ *  the join. See Screen.softWrap for why the clamp is necessary. */
+function extractRowText(
+  screen: Screen,
+  row: number,
+  colStart: number,
+  colEnd: number,
+): string {
+  const noSelect = screen.noSelect
+  const rowOff = row * screen.width
+  const contentEnd = row + 1 < screen.height ? screen.softWrap[row + 1]! : 0
+  const lastCol = contentEnd > 0 ? Math.min(colEnd, contentEnd - 1) : colEnd
+  let line = ''
+  for (let col = colStart; col <= lastCol; col++) {
+    // Skip cells marked noSelect (gutters, line numbers, diff sigils).
+    // Check before cellAt to avoid the decode cost for excluded cells.
+    if (noSelect[rowOff + col] === 1) continue
+    const cell = cellAt(screen, col, row)
+    if (!cell) continue
+    // Skip spacer tails (second half of wide chars) — the head already
+    // contains the full grapheme. SpacerHead is a blank at line-end.
+    if (
+      cell.width === CellWidth.SpacerTail ||
+      cell.width === CellWidth.SpacerHead
+    ) {
+      continue
+    }
+    line += cell.char
+  }
+  return contentEnd > 0 ? line : line.replace(/\s+$/, '')
+}
+
+/** Accumulator for selected text that merges soft-wrapped rows back
+ *  into logical lines. push(text, sw) appends a newline before text
+ *  only when sw=false (i.e. the row starts a new logical line). Rows
+ *  with sw=true are concatenated onto the previous row. */
+function joinRows(
+  lines: string[],
+  text: string,
+  sw: boolean | undefined,
+): void {
+  if (sw && lines.length > 0) {
+    lines[lines.length - 1] += text
+  } else {
+    lines.push(text)
+  }
+}
+
+/**
+ * Extract text from the screen buffer within the selection range.
+ * Rows are joined with newlines unless the screen's softWrap bitmap
+ * marks a row as a word-wrap continuation — those rows are concatenated
+ * onto the previous row so the copied text matches the logical source
+ * line, not the visual wrapped layout. Trailing whitespace on the last
+ * fragment of each logical line is trimmed. Wide-char spacer cells are
+ * skipped. Rows that scrolled out of the viewport during drag-to-scroll
+ * are joined back in from the scrolledOffAbove/Below accumulators along
+ * with their captured softWrap bits.
+ */
+export function getSelectedText(s: SelectionState, screen: Screen): string {
+  const b = selectionBounds(s)
+  if (!b) return ''
+  const { start, end } = b
+  const sw = screen.softWrap
+  const lines: string[] = []
+
+  for (let i = 0; i < s.scrolledOffAbove.length; i++) {
+    joinRows(lines, s.scrolledOffAbove[i]!, s.scrolledOffAboveSW[i])
+  }
+
+  for (let row = start.row; row <= end.row; row++) {
+    const rowStart = row === start.row ? start.col : 0
+    const rowEnd = row === end.row ? end.col : screen.width - 1
+    joinRows(lines, extractRowText(screen, row, rowStart, rowEnd), sw[row]! > 0)
+  }
+
+  for (let i = 0; i < s.scrolledOffBelow.length; i++) {
+    joinRows(lines, s.scrolledOffBelow[i]!, s.scrolledOffBelowSW[i])
+  }
+
+  return lines.join('\n')
+}
+
+/**
+ * Capture text from rows about to scroll out of the viewport during
+ * drag-to-scroll, BEFORE scrollBy overwrites them. Only the rows that
+ * intersect the selection are captured, using the selection's col bounds
+ * for the anchor-side boundary row. After capturing the anchor row, the
+ * anchor.col AND anchorSpan cols are reset to the full-width boundary so
+ * subsequent captures and the final getSelectedText don't re-apply a stale
+ * col constraint to content that's no longer under the original anchor.
+ * Both span cols are reset (not just the near side): after a blocked
+ * reversal the drag can flip direction, and extendSelection then reads the
+ * OPPOSITE span side — which would otherwise still hold the original word
+ * boundary and truncate one subsequently-captured row.
+ *
+ * side='above': rows scrolling out the top (dragging down, anchor=start).
+ * side='below': rows scrolling out the bottom (dragging up, anchor=end).
+ */
+export function captureScrolledRows(
+  s: SelectionState,
+  screen: Screen,
+  firstRow: number,
+  lastRow: number,
+  side: 'above' | 'below',
+): void {
+  const b = selectionBounds(s)
+  if (!b || firstRow > lastRow) return
+  const { start, end } = b
+  // Intersect [firstRow, lastRow] with [start.row, end.row]. Rows outside
+  // the selection aren't captured — they weren't selected.
+  const lo = Math.max(firstRow, start.row)
+  const hi = Math.min(lastRow, end.row)
+  if (lo > hi) return
+
+  const width = screen.width
+  const sw = screen.softWrap
+  const captured: string[] = []
+  const capturedSW: boolean[] = []
+  for (let row = lo; row <= hi; row++) {
+    const colStart = row === start.row ? start.col : 0
+    const colEnd = row === end.row ? end.col : width - 1
+    captured.push(extractRowText(screen, row, colStart, colEnd))
+    capturedSW.push(sw[row]! > 0)
+  }
+
+  if (side === 'above') {
+    // Newest rows go at the bottom of the above-accumulator (closest to
+    // the on-screen content in reading order).
+    s.scrolledOffAbove.push(...captured)
+    s.scrolledOffAboveSW.push(...capturedSW)
+    // We just captured the top of the selection. The anchor (=start when
+    // dragging down) is now pointing at content that will scroll out; its
+    // col constraint was applied to the captured row. Reset to col 0 so
+    // the NEXT tick and the final getSelectedText read the full row.
+    if (s.anchor && s.anchor.row === start.row && lo === start.row) {
+      s.anchor = { col: 0, row: s.anchor.row }
+      if (s.anchorSpan) {
+        s.anchorSpan = {
+          kind: s.anchorSpan.kind,
+          lo: { col: 0, row: s.anchorSpan.lo.row },
+          hi: { col: width - 1, row: s.anchorSpan.hi.row },
+        }
+      }
+    }
+  } else {
+    // Newest rows go at the TOP of the below-accumulator — they're
+    // closest to the on-screen content.
+    s.scrolledOffBelow.unshift(...captured)
+    s.scrolledOffBelowSW.unshift(...capturedSW)
+    if (s.anchor && s.anchor.row === end.row && hi === end.row) {
+      s.anchor = { col: width - 1, row: s.anchor.row }
+      if (s.anchorSpan) {
+        s.anchorSpan = {
+          kind: s.anchorSpan.kind,
+          lo: { col: 0, row: s.anchorSpan.lo.row },
+          hi: { col: width - 1, row: s.anchorSpan.hi.row },
+        }
+      }
+    }
+  }
+}
+
+/**
+ * Apply the selection overlay directly to the screen buffer by changing
+ * the style of every cell in the selection range. Called after the
+ * renderer produces the Frame but before the diff — the normal diffEach
+ * then picks up the restyled cells as ordinary changes, so LogUpdate
+ * stays a pure diff engine with no selection awareness.
+ *
+ * Uses a SOLID selection background (theme-provided via StylePool.
+ * setSelectionBg) that REPLACES each cell's bg while PRESERVING its fg —
+ * matches native terminal selection. Previously SGR-7 inverse (swapped
+ * fg/bg per cell), which fragmented badly over syntax-highlighted text:
+ * every distinct fg color became a different bg stripe.
+ *
+ * Uses StylePool caches so on drag the only work per cell is a Map
+ * lookup + packed-int write.
+ */
+export function applySelectionOverlay(
+  screen: Screen,
+  selection: SelectionState,
+  stylePool: StylePool,
+): void {
+  const b = selectionBounds(selection)
+  if (!b) return
+  const { start, end } = b
+  const width = screen.width
+  const noSelect = screen.noSelect
+  for (let row = start.row; row <= end.row && row < screen.height; row++) {
+    const colStart = row === start.row ? start.col : 0
+    const colEnd = row === end.row ? Math.min(end.col, width - 1) : width - 1
+    const rowOff = row * width
+    for (let col = colStart; col <= colEnd; col++) {
+      const idx = rowOff + col
+      // Skip noSelect cells — gutters stay visually unchanged so it's
+      // clear they're not part of the copy. Surrounding selectable cells
+      // still highlight so the selection extent remains visible.
+      if (noSelect[idx] === 1) continue
+      const cell = cellAtIndex(screen, idx)
+      setCellStyleId(screen, col, row, stylePool.withSelectionBg(cell.styleId))
+    }
+  }
+}