feat(terminal): text selection + copy (custom model)

Drag to select terminal text and copy it with Ctrl-Shift-C. Built as a
custom selection model (xterm.js-style) rather than native selection,
because the virtual scroll only keeps ~60 rows in the DOM and rebuilds
them every frame — native selection would be destroyed and couldn't span
scrolled-out rows.

core.rs:
- selection_text(start, end) extracts a (row,col)→(row,col) range straight
  from history_rows + screen_cache, so copy is correct across the whole
  buffer regardless of what is currently rendered
- TerminalRow::text_in_cols slices a row by grid columns (using the
  segment `cols` widths), trimming trailing whitespace

component.rs:
- Selection { anchor, head } in logical buffer coords; mousedown/move/up
  drag updates it; point_to_cell maps pixels→cell (padding + scrollTop)
- selection_rects computes per-row highlight rects clipped to the rendered
  window; rendered as an overlay inside the translated rows layer so the
  highlight follows scrolling without splitting text segments
- cell_size signal kept in sync with viewport measurement
- Ctrl-Shift-C copies via navigator.clipboard.write_text; Ctrl-C is left
  untouched (still SIGINT); typing clears the selection

style: .terminal-selection overlay, user-select:none on the grid, rows
above the highlight via z-index.

web-sys: add DomRect, MouseEvent, Navigator, Clipboard.

Adds point_to_cell / selection_rects / selection_text unit tests (16
terminal tests total). Marks P0 done in TERMINAL_ROADMAP.md.

Known follow-up: no auto-scroll when dragging past the viewport edge
(scroll first, then select); wide+combining column slicing is approximate.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

Cargo.toml

@@ -39,11 +39,13 @@ wasm-bindgen = "0.2"
 wasm-bindgen-futures = "0.4"
 web-sys = { version = "0.3", default-features = false, features = [
     "BinaryType",
+    "Clipboard",
     "ClipboardEvent",
     "CloseEvent",
     "console",
     "DataTransfer",
     "Document",
+    "DomRect",
     "DomRectReadOnly",
     "Element",
     "ErrorEvent",
@@ -53,6 +55,8 @@ web-sys = { version = "0.3", default-features = false, features = [
     "KeyboardEvent",
     "Location",
     "MessageEvent",
+    "MouseEvent",
+    "Navigator",
     "ResizeObserver",
     "ResizeObserverEntry",
     "WebSocket",

TERMINAL_ROADMAP.md

@@ -30,28 +30,31 @@
 | alt-screen 滚轮 → 方向键翻页 | `component.rs::handle_wheel` |
 | 基础按键：Ctrl-C/D/L、方向键、Enter/Tab/Esc/Backspace | `component.rs::map_key_to_terminal_input` |
 | 粘贴（Ctrl-V / 浏览器菜单，含 bracketed paste） | `component.rs::handle_paste` / `prepare_paste` |
+| 文本选区 + 复制（自建模型，Ctrl-Shift-C，跨滚动） | `component.rs` 鼠标处理 / `core.rs::selection_text` |
 
 ---
 
 ## 2. 追平项（按优先级）
 
-### P0 — 复制 / 粘贴 + 文本选区 ⭐ 投入产出比最高
+### P0 — 复制 / 粘贴 + 文本选区 ⭐ ✅ 已完成
 
-**现状**：粘贴**已完成**（见下）；选区 / 复制尚未做。
+**现状**：粘贴、选区、复制**全部完成并验证通过**。
 
-**计划实现**：
-1. ~~**粘贴（先做，最简单）**~~ ✅ **已完成**
+**已实现**：
+1. **粘贴** ✅
    - `on:paste`（`ClipboardEvent`）读 `clipboard_data().get_data("text")`，归一换行为 `\r` 后作为 `Input` 发送。
    - bracketed paste：应用开启时（`core.bracketed_paste()`）包进 `ESC[200~ … ESC[201~`。
-   - 实现于 `component.rs::handle_paste` + 纯函数 `prepare_paste`（有单元测试）。
-   - 右键不拦截，走浏览器默认菜单（避免依赖剪贴板读权限）；Ctrl-V 为主路径。
-2. **选区（较复杂，下一步）**
-   - 因为渲染是 DOM（每行一个 `<div>`、每段一个 `<span>`），可优先尝试**浏览器原生选区**：给可见行允许 `user-select: text`，监听 `copy` 事件，从 `window.getSelection()` 取文本。
-   - 但虚拟滚动只渲染可见窗口，跨窗口选区会断 → 需要把「逻辑行号 → 文本」的映射暴露给选区逻辑，从 `TerminalCore` 的 `history_rows + screen_rows` 直接取纯文本（已有 `row` → 文本的能力，测试里 `row_text` 即是）。
-   - MVP 可只支持**可见范围内选区 + 复制**，跨滚动选区列为后续。
-3. **快捷键**：Ctrl-Shift-C / Ctrl-Shift-V（终端惯例，避免和 Ctrl-C 中断冲突）。
+   - 实现于 `component.rs::handle_paste` + 纯函数 `prepare_paste`。
+   - 右键走浏览器默认菜单（避免依赖剪贴板读权限）；Ctrl-V 为主路径。
+2. **选区 + 复制** ✅（自建选区模型，xterm.js 风格）
+   - 选区按**逻辑行列坐标**跟踪（`Selection { anchor, head }`），鼠标 `mousedown/move/up` 拖拽更新；`point_to_cell` 做像素→单元格换算（含 padding/scroll）。
+   - 高亮 overlay：`selection_rects` 算每行矩形，渲染在虚拟滚动层内（共享 translateY，跟随滚动），不拆分文本段。
+   - 复制取 `TerminalCore::selection_text(start, end)` —— 直接从 `history_rows + screen_cache` 数据模型按行列取文本，**跨滚动、输出流动时都正确**（不依赖 DOM）。
+   - **Ctrl-Shift-C** 复制（Ctrl-C 保持 SIGINT）；打字清除选区。
+   - 实现于 `component.rs`（`Selection`/`selection_rects`/`point_to_cell`/鼠标处理）+ `core.rs::selection_text` + `core.rs::TerminalRow::text_in_cols`，均有单元测试。
+3. **快捷键**：Ctrl-Shift-C 复制 / Ctrl-V 粘贴。
 
-**风险**：选区与虚拟滚动的交互是主要难点；建议 MVP 限定可见区，先把粘贴 + 可见区复制跑通。
+**已知后续项（非阻塞）**：拖拽到视窗边缘时**没有自动滚动延伸选区**（需先滚到位再选）；行内 wide+组合字符混排的列切片为近似。
 
 ---
 

app/src/terminal/component.rs

@@ -8,7 +8,8 @@ use wasm_bindgen::closure::Closure;
 use web_sys::js_sys::{Array, Function};
 use web_sys::{
     BinaryType, ClipboardEvent, ErrorEvent, Event, HtmlElement, KeyboardEvent,
-    MessageEvent, ResizeObserver, ResizeObserverEntry, WebSocket, WheelEvent,
+    MessageEvent, MouseEvent, ResizeObserver, ResizeObserverEntry, WebSocket,
+    WheelEvent,
 };
 
 use super::core::{TerminalCore, TerminalRow, TerminalSegment};
@@ -27,6 +28,35 @@ const SCROLL_LINE_HEIGHT: f64 = 18.0;
 /// scrolling doesn't flash blank areas before the next frame arrives.
 const VIRTUAL_OVERSCAN: usize = 5;
 
+/// `.terminal-screen` inner padding in px (CSS `padding: 16px`).  Mouse
+/// coordinates subtract this to map onto the cell grid.
+const TERMINAL_PADDING: f64 = 16.0;
+
+/// A text selection in logical buffer coordinates `(row, col)`.  `anchor` is
+/// where the drag began, `head` follows the pointer; either may be the
+/// top-left depending on drag direction.
+#[derive(Clone, Copy, Debug, PartialEq, Eq)]
+struct Selection {
+    anchor: (usize, usize),
+    head: (usize, usize),
+}
+
+impl Selection {
+    /// (top-left, bottom-right) ordered for rendering / extraction.
+    fn ordered(self) -> ((usize, usize), (usize, usize)) {
+        if self.anchor <= self.head {
+            (self.anchor, self.head)
+        } else {
+            (self.head, self.anchor)
+        }
+    }
+
+    /// True when the selection is empty (anchor == head): nothing to copy.
+    fn is_empty(self) -> bool {
+        self.anchor == self.head
+    }
+}
+
 #[derive(Clone, Copy, Debug, PartialEq, Eq)]
 struct TerminalViewport {
     cols: u16,
@@ -81,6 +111,14 @@ pub fn TerminalPanel() -> impl IntoView {
     // the virtual-scroll render closure knows which window to materialise.
     let scroll_top = RwSignal::new(0_i32);
 
+    // Measured cell size (width, height) in px, kept in sync with the viewport
+    // measurement.  Used to map mouse coordinates onto the logical cell grid.
+    let cell_size = RwSignal::new((DEFAULT_CELL_WIDTH, DEFAULT_CELL_HEIGHT));
+
+    // Active text selection in buffer coords, and whether a drag is in progress.
+    let selection = RwSignal::new(None::<Selection>);
+    let selecting = RwSignal::new(false);
+
     // -- WebSocket lifecycle ------------------------------------------------
 
     Effect::new(move |_| {
@@ -110,6 +148,7 @@ pub fn TerminalPanel() -> impl IntoView {
 
             let viewport = measure_terminal_viewport(open_ref, open_measure);
             open_viewport.set(viewport);
+            cell_size.set(measure_cell_size(open_measure));
 
             open_core
                 .update_untracked(|core| core.resize(viewport.rows, viewport.cols));
@@ -241,6 +280,7 @@ pub fn TerminalPanel() -> impl IntoView {
 
                 if viewport != resize_viewport.get_untracked() {
                     resize_viewport.set(viewport);
+                    cell_size.set(measure_cell_size(resize_measure));
 
                     let mode_val = resize_mode.get_untracked();
                     let st = resize_st.get_untracked();
@@ -283,8 +323,31 @@ pub fn TerminalPanel() -> impl IntoView {
     let handle_keydown = {
         let keydown_mode = view_mode;
         let keydown_prog_scroll = programmatic_scroll_top;
+        let keydown_selection = selection;
+        let keydown_core = core_signal;
 
         move |event: KeyboardEvent| {
+            // Ctrl-Shift-C copies the current selection (Ctrl-C is left alone so
+            // it still sends SIGINT).
+            if event.ctrl_key()
+                && event.shift_key()
+                && matches!(event.key().as_str(), "c" | "C")
+            {
+                if let Some(sel) =
+                    keydown_selection.get_untracked().filter(|s| !s.is_empty())
+                {
+                    let (start, end) = sel.ordered();
+                    let text = keydown_core
+                        .try_with_untracked(|core| {
+                            core.selection_text(start, end)
+                        })
+                        .unwrap_or_default();
+                    copy_to_clipboard(&text);
+                }
+                event.prevent_default();
+                return;
+            }
+
             let Some(socket) = ws_signal.get_untracked() else {
                 return;
             };
@@ -293,6 +356,9 @@ pub fn TerminalPanel() -> impl IntoView {
                 return;
             };
 
+            // Typing replaces a selection, like a normal terminal.
+            keydown_selection.set(None);
+
             if !keydown_mode.get_untracked().is_live() {
                 keydown_mode.set(ViewMode::Live);
                 sync_scroll_to_bottom(terminal_ref, keydown_prog_scroll);
@@ -430,6 +496,75 @@ pub fn TerminalPanel() -> impl IntoView {
         }
     };
 
+    // -- Mouse selection ----------------------------------------------------
+    //
+    // Drag to select a range of terminal text.  Selection is tracked in logical
+    // buffer coordinates (not DOM), so it survives re-renders and works across
+    // rows that have scrolled out of the rendered window.
+    let cell_from_event = move |event: &MouseEvent| -> Option<(usize, usize)> {
+        let element = terminal_ref.get_untracked()?;
+        let rect = element.get_bounding_client_rect();
+        let local_x = f64::from(event.client_x()) - rect.left();
+        let local_y = f64::from(event.client_y()) - rect.top();
+        let (cell_w, cell_h) = cell_size.get_untracked();
+        let cols = current_viewport.get_untracked().cols as usize;
+        let total = core_signal
+            .try_with_untracked(|core| core.total_rows())
+            .unwrap_or(0);
+        Some(point_to_cell(
+            local_x,
+            local_y,
+            f64::from(element.scroll_top()),
+            cell_w,
+            cell_h,
+            cols,
+            total,
+        ))
+    };
+
+    let handle_mousedown = {
+        let down_selection = selection;
+        let down_selecting = selecting;
+        move |event: MouseEvent| {
+            if event.button() != 0 {
+                return; // only left button starts a selection
+            }
+            let Some(cell) = cell_from_event(&event) else {
+                return;
+            };
+            down_selection.set(Some(Selection {
+                anchor: cell,
+                head: cell,
+            }));
+            down_selecting.set(true);
+        }
+    };
+
+    let handle_mousemove = {
+        let move_selection = selection;
+        let move_selecting = selecting;
+        move |event: MouseEvent| {
+            if !move_selecting.get_untracked() {
+                return;
+            }
+            let Some(cell) = cell_from_event(&event) else {
+                return;
+            };
+            move_selection.update(|sel| {
+                if let Some(s) = sel {
+                    s.head = cell;
+                }
+            });
+        }
+    };
+
+    let handle_mouseup = {
+        let up_selecting = selecting;
+        move |_event: MouseEvent| {
+            up_selecting.set(false);
+        }
+    };
+
     let handle_click = move |_| {
         focus_terminal(terminal_ref);
     };
@@ -482,6 +617,9 @@ pub fn TerminalPanel() -> impl IntoView {
                 on:scroll=handle_scroll
                 on:wheel=handle_wheel
                 on:paste=handle_paste
+                on:mousedown=handle_mousedown
+                on:mousemove=handle_mousemove
+                on:mouseup=handle_mouseup
             >
                 <span node_ref=measure_ref class="terminal-measure" aria-hidden="true">
                     {MEASURE_SAMPLE_TEXT}
@@ -489,11 +627,14 @@ pub fn TerminalPanel() -> impl IntoView {
                 <div class="terminal-grid">
                     {move || {
                         // Subscribe to render_tick (frame-coalesced data
-                        // changes), scroll_top (scroll), and view_mode
-                        // (live/history switch).
+                        // changes), scroll_top (scroll), view_mode, selection.
                         let _ = render_tick.get();
                         let is_live = view_mode.get().is_live();
-                        let vp_rows = current_viewport.get_untracked().rows as usize;
+                        let sel = selection.get();
+                        let (cell_w, _cell_h) = cell_size.get();
+                        let vp = current_viewport.get_untracked();
+                        let vp_rows = vp.rows as usize;
+                        let cols = vp.cols as usize;
                         let st = scroll_top.get();
                         // Read core untracked — the core signal itself never
                         // notifies; render_tick is the explicit render trigger.
@@ -504,7 +645,13 @@ pub fn TerminalPanel() -> impl IntoView {
                                 virtual_window(core, is_live, st, vp_rows)
                             })
                             .unwrap_or((0.0, 0.0, Vec::new()));
-                        render_spaced_view(total_px, offset_px, visible)
+                        let window_start =
+                            (offset_px / SCROLL_LINE_HEIGHT).round() as usize;
+                        let window_end = window_start + visible.len();
+                        let rects = selection_rects(
+                            sel, window_start, window_end, cols, cell_w,
+                        );
+                        render_spaced_view(total_px, offset_px, visible, rects)
                     }}
                 </div>
             </div>
@@ -560,6 +707,57 @@ fn virtual_window(
     (total_px, offset_px, core.collect_window(start, end))
 }
 
+/// A highlight rectangle for one selected row, positioned relative to the top
+/// of the rendered (translated) rows layer.
+#[derive(Clone, Copy, Debug)]
+struct SelectionRect {
+    top_px: f64,
+    left_px: f64,
+    width_px: f64,
+}
+
+/// Compute the per-row highlight rects for `sel`, clipped to the rendered
+/// window `[window_start, window_end)`.  Returns empty for no/empty selection.
+fn selection_rects(
+    sel: Option<Selection>,
+    window_start: usize,
+    window_end: usize,
+    cols: usize,
+    cell_w: f64,
+) -> Vec<SelectionRect> {
+    let Some(sel) = sel else {
+        return Vec::new();
+    };
+    if sel.is_empty() {
+        return Vec::new();
+    }
+    let ((sr, sc), (er, ec)) = sel.ordered();
+    let first = sr.max(window_start);
+    let last = er.min(window_end.saturating_sub(1));
+    let mut rects = Vec::new();
+    for r in first..=last {
+        if r >= window_end {
+            break;
+        }
+        let (col_a, col_b) = if sr == er {
+            (sc, ec)
+        } else if r == sr {
+            (sc, cols)
+        } else if r == er {
+            (0, ec)
+        } else {
+            (0, cols)
+        };
+        let col_b = col_b.max(col_a);
+        rects.push(SelectionRect {
+            top_px: (r - window_start) as f64 * SCROLL_LINE_HEIGHT,
+            left_px: col_a as f64 * cell_w,
+            width_px: (col_b - col_a) as f64 * cell_w,
+        });
+    }
+    rects
+}
+
 /// Render the visible rows using absolute positioning inside a fixed-height
 /// container.
 ///
@@ -572,6 +770,7 @@ fn render_spaced_view(
     total_px: f64,
     offset_px: f64,
     visible: Vec<TerminalRow>,
+    rects: Vec<SelectionRect>,
 ) -> impl IntoView {
     view! {
         <div
@@ -583,11 +782,20 @@ fn render_spaced_view(
             class="terminal-virtual-rows"
             style=format!("transform:translateY({offset_px}px);")
         >
+            {rects.into_iter().map(render_selection_rect).collect_view()}
             {visible.into_iter().map(render_terminal_row).collect_view()}
         </div>
     }
 }
 
+fn render_selection_rect(rect: SelectionRect) -> impl IntoView {
+    let style = format!(
+        "top:{}px;left:{}px;width:{}px;height:{}px;",
+        rect.top_px, rect.left_px, rect.width_px, SCROLL_LINE_HEIGHT
+    );
+    view! { <div class="terminal-selection" style=style aria-hidden="true"></div> }
+}
+
 fn render_terminal_row(row: TerminalRow) -> impl IntoView {
     view! {
         <div class="terminal-row">
@@ -826,12 +1034,48 @@ fn measure_cell_size(measure_ref: NodeRef<html::Span>) -> (f64, f64) {
     )
 }
 
+/// Map a pointer position to a logical `(row, col)` cell.
+///
+/// `local_x`/`local_y` are relative to the scroll container's top-left
+/// (clientX/Y minus its bounding rect). Padding is removed, the scroll offset
+/// is added to Y, then the result is divided by the cell size and clamped to
+/// the grid. Pure for unit-testing.
+fn point_to_cell(
+    local_x: f64,
+    local_y: f64,
+    scroll_top: f64,
+    cell_w: f64,
+    cell_h: f64,
+    cols: usize,
+    total_rows: usize,
+) -> (usize, usize) {
+    let x = (local_x - TERMINAL_PADDING).max(0.0);
+    let y = (local_y - TERMINAL_PADDING + scroll_top).max(0.0);
+    let col = (x / cell_w.max(1.0)).floor() as usize;
+    let row = (y / cell_h.max(1.0)).floor() as usize;
+    (
+        row.min(total_rows.saturating_sub(1)),
+        col.min(cols.saturating_sub(1)),
+    )
+}
+
 fn focus_terminal(terminal_ref: NodeRef<html::Div>) {
     if let Some(element) = terminal_ref.get_untracked() {
         let _ = element.focus();
     }
 }
 
+/// Write text to the system clipboard (fire-and-forget).  Called from a user
+/// gesture (Ctrl-Shift-C keydown), which browsers allow without a prompt in
+/// secure contexts (localhost counts as secure).
+fn copy_to_clipboard(text: &str) {
+    if text.is_empty() {
+        return;
+    }
+    let clipboard = window().navigator().clipboard();
+    let _ = clipboard.write_text(text);
+}
+
 // ---------------------------------------------------------------------------
 // Key mapping
 // ---------------------------------------------------------------------------
@@ -931,6 +1175,52 @@ mod tests {
         assert_eq!(wheel_delta_to_rows(100_000.0, 0), 12);
     }
 
+    #[test]
+    fn point_to_cell_maps_pixels_with_padding_and_scroll() {
+        let (cw, ch) = (8.0, 18.0);
+        // Top-left content origin is at (PADDING, PADDING) = (16,16).
+        assert_eq!(point_to_cell(16.0, 16.0, 0.0, cw, ch, 80, 100), (0, 0));
+        // One cell right and one row down.
+        assert_eq!(point_to_cell(16.0 + 8.0, 16.0 + 18.0, 0.0, cw, ch, 80, 100), (1, 1));
+        // Scroll offset shifts the row mapping down.
+        assert_eq!(point_to_cell(16.0, 16.0, 180.0, cw, ch, 80, 100), (10, 0));
+        // Clamped to grid bounds.
+        assert_eq!(point_to_cell(99999.0, 99999.0, 0.0, cw, ch, 80, 100), (99, 79));
+        // Inside the padding clamps to (0,0), never negative.
+        assert_eq!(point_to_cell(0.0, 0.0, 0.0, cw, ch, 80, 100), (0, 0));
+    }
+
+    #[test]
+    fn selection_rects_clip_to_window_and_span_columns() {
+        let cw = 8.0;
+        let cols = 80;
+        // Single-row selection cols 2..6 on row 5, window [0,30).
+        let sel = Some(Selection { anchor: (5, 2), head: (5, 6) });
+        let rects = selection_rects(sel, 0, 30, cols, cw);
+        assert_eq!(rects.len(), 1);
+        assert_eq!(rects[0].top_px, 5.0 * SCROLL_LINE_HEIGHT);
+        assert_eq!(rects[0].left_px, 2.0 * cw);
+        assert_eq!(rects[0].width_px, 4.0 * cw);
+
+        // Multi-row selection rows 4..6: first row partial, middle full, last partial.
+        let sel = Some(Selection { anchor: (4, 10), head: (6, 3) });
+        let rects = selection_rects(sel, 0, 30, cols, cw);
+        assert_eq!(rects.len(), 3);
+        assert_eq!(rects[0].left_px, 10.0 * cw); // first row starts at col 10
+        assert_eq!(rects[1].width_px, cols as f64 * cw); // middle row full width
+        assert_eq!(rects[2].left_px, 0.0); // last row from col 0
+        assert_eq!(rects[2].width_px, 3.0 * cw);
+
+        // Selection entirely above the window → clipped out.
+        let sel = Some(Selection { anchor: (1, 0), head: (2, 5) });
+        assert!(selection_rects(sel, 10, 30, cols, cw).is_empty());
+
+        // Empty selection → no rects.
+        let sel = Some(Selection { anchor: (5, 2), head: (5, 2) });
+        assert!(selection_rects(sel, 0, 30, cols, cw).is_empty());
+        assert!(selection_rects(None, 0, 30, cols, cw).is_empty());
+    }
+
     #[test]
     fn prepare_paste_normalizes_newlines_and_wraps_when_bracketed() {
         // Plain paste: CRLF and LF both become CR, no wrapping.

app/src/terminal/core.rs

@@ -221,6 +221,44 @@ impl TerminalCore {
         out
     }
 
+    /// The logical row at combined index `i` (history first, then screen).
+    fn row_at(&self, i: usize) -> Option<&TerminalRow> {
+        let hist_len = self.history_rows.len();
+        if i < hist_len {
+            self.history_rows.get(i)
+        } else {
+            self.screen_cache.get(i - hist_len)
+        }
+    }
+
+    /// Extract the text covered by a selection from `start` to `end`
+    /// (inclusive of `start`, exclusive of `end.col` on the last row), both in
+    /// `(row, col)` buffer coordinates.  Reads straight from the row data, so it
+    /// works across the whole buffer regardless of what is currently rendered.
+    ///
+    /// Per-row trailing whitespace is trimmed; rows are joined with `\n`.
+    pub fn selection_text(
+        &self,
+        start: (usize, usize),
+        end: (usize, usize),
+    ) -> String {
+        let (start, end) = order_points(start, end);
+        let (sr, sc) = start;
+        let (er, ec) = end;
+        let mut lines: Vec<String> = Vec::new();
+
+        for r in sr..=er {
+            let Some(row) = self.row_at(r) else {
+                continue;
+            };
+            let from = if r == sr { sc } else { 0 };
+            let to = if r == er { ec } else { usize::MAX };
+            lines.push(row.text_in_cols(from, to));
+        }
+
+        lines.join("\n")
+    }
+
     // -- Convenience proxies for terminal metadata (all &self, no mutation) --
 
     pub fn size(&self) -> (u16, u16) {
@@ -324,6 +362,49 @@ pub struct TerminalRow {
     pub segments: Vec<TerminalSegment>,
 }
 
+impl TerminalRow {
+    /// Plain text of the columns in `[from, to)` of this row, with trailing
+    /// whitespace trimmed.  `to` may be `usize::MAX` to mean "to end of row".
+    ///
+    /// Columns are walked using each segment's `cols` (grid-column) width.  For
+    /// normal text one char maps to one column; the mapping is approximate only
+    /// for the rare mix of wide + combining chars in a single selection edge,
+    /// which trailing-trim and cell-accurate highlighting make unnoticeable.
+    pub fn text_in_cols(&self, from: usize, to: usize) -> String {
+        let mut out = String::new();
+        let mut col = 0usize;
+        for seg in &self.segments {
+            let seg_end = col + seg.cols;
+            if seg_end <= from {
+                col = seg_end;
+                continue;
+            }
+            if col >= to {
+                break;
+            }
+            // This segment overlaps [from, to): emit the columns inside range.
+            let chars: Vec<char> = seg.text.chars().collect();
+            for (i, ch) in chars.iter().enumerate() {
+                // Distribute chars across the segment's columns 1:1 (clamped).
+                let ch_col = col + i.min(seg.cols.saturating_sub(1));
+                if ch_col >= from && ch_col < to {
+                    out.push(*ch);
+                }
+            }
+            col = seg_end;
+        }
+        out.trim_end().to_owned()
+    }
+}
+
+/// Order two `(row, col)` points so the first is the top-left of the selection.
+fn order_points(
+    a: (usize, usize),
+    b: (usize, usize),
+) -> ((usize, usize), (usize, usize)) {
+    if a <= b { (a, b) } else { (b, a) }
+}
+
 #[derive(Clone, Debug, PartialEq, Eq)]
 pub struct TerminalSegment {
     pub text: String,
@@ -671,6 +752,32 @@ mod tests {
         assert!(core.collect_window(total + 10, total + 20).is_empty());
     }
 
+    #[test]
+    fn selection_text_extracts_partial_and_multi_row_ranges() {
+        let mut core = TerminalCore::new(24, 80);
+        // Three known lines on screen.
+        core.process(b"hello world\r\n");
+        core.process(b"second line\r\n");
+        core.process(b"third\r\n");
+
+        // Rows 0..2 are the three lines (history empty: all on screen).
+        // Single-row partial: cols 0..5 of row 0 => "hello".
+        assert_eq!(core.selection_text((0, 0), (0, 5)), "hello");
+        // Single-row mid range: cols 6..11 of row 0 => "world".
+        assert_eq!(core.selection_text((0, 6), (0, 11)), "world");
+
+        // Multi-row: from row 0 col 6 to row 2 col 5 =>
+        //   "world" (rest of row 0) + whole row 1 + "third" (start of row 2).
+        let text = core.selection_text((0, 6), (2, 5));
+        assert_eq!(text, "world\nsecond line\nthird");
+
+        // Trailing whitespace within a row is trimmed (cols past content).
+        assert_eq!(core.selection_text((0, 0), (0, 40)), "hello world");
+
+        // Reversed points are normalized.
+        assert_eq!(core.selection_text((0, 5), (0, 0)), "hello");
+    }
+
     #[test]
     fn clear_wipes_history_and_keeps_only_new_prompt() {
         let mut core = TerminalCore::new(24, 80);

style/tailwind.css

@@ -634,9 +634,12 @@
     position: relative;
     display: block;
     min-height: 100%;
+    user-select: none;
   }
 
   .terminal-row {
+    position: relative;
+    z-index: 1;
     height: 18px;
     min-height: 18px;
     max-height: 18px;
@@ -674,6 +677,13 @@
     will-change: transform;
   }
 
+  .terminal-selection {
+    position: absolute;
+    background: rgb(56 189 248 / 30%);
+    pointer-events: none;
+    z-index: 0;
+  }
+
   .terminal-measure {
     position: absolute;
     left: -9999px;