fix(completion): keep the menu inside the pane it belongs to

The menu was anchored under the word being completed and capped at a flat
480px, with nothing checking that 480px was there. In a split — two panes
side by side is the ordinary case — it was not: the box ran past the
pane's right edge and the overflow was clipped, so a row read "switch
Switch bra" with the sentence stopping at the divider.

That clip is also what the description elision exists to prevent. The
budget is measured against the menu's width, so with the width unchecked
it kept eliding to 480px and the ellipsis it added landed outside the
pane. The one signal that the text had been cut was the first thing lost.

Cap the width at the grid and pull the box back inside — which is what
the history menu two functions down has always done — and hand the real
width to `description_budget` so what it elides is what fits. A wide pane
behaves as before: the menu stays under the word until it would hang over
the edge. A pane narrower than the menu pins it to the left, the same
place the history menu sits.

Verified in a dev window, split in two: "git sw" now shows "switch Switch
branches" whole, and unsplit the menu still opens under the word.

src/terminal/view.rs

@@ -4727,7 +4727,18 @@ impl TerminalView {
         let srow = srow.saturating_sub(self.input_scroll_rows());
 
         const MAX_ROWS: usize = 10;
-        let total_rows = self.terminal.term.lock().screen_lines();
+        let (total_rows, total_cols) = {
+            let term = self.terminal.term.lock();
+            (term.screen_lines(), term.columns())
+        };
+        // How wide the menu ends up, decided before the rows so their
+        // descriptions can be elided against it. A menu wider than the pane
+        // has its right-hand column clipped by the pane, and the clip takes
+        // the ellipsis with it — which is exactly the mid-word cut the
+        // ellipsis exists to prevent. The history menu below already caps
+        // itself to the grid this way.
+        let grid_w = self.cell_width * (total_cols as f32);
+        let menu_w = px(COMPLETION_MENU_MAX_W).min(grid_w);
         let (place_above, visible, first) = menu_layout(
             total_rows,
             srow,
@@ -4755,7 +4766,7 @@ impl TerminalView {
             } else {
                 cand.text.clone()
             };
-            let budget = description_budget(cell, label.chars().count());
+            let budget = description_budget(cell, label.chars().count(), menu_w.as_f32());
             div()
                 .h(lh)
                 .flex()
@@ -4797,7 +4808,12 @@ impl TerminalView {
         let menu_h = self.line_height * (line_count as f32) + px(10.);
 
         let gap = px(6.);
-        let x = px(GRID_PAD_X) + self.cell_width * (scol as f32);
+        // Anchored under the word being completed, then pulled back inside the
+        // pane if that would hang it over the right edge.
+        let anchor = px(GRID_PAD_X) + self.cell_width * (scol as f32);
+        let x = anchor
+            .min(px(GRID_PAD_X) + grid_w - menu_w)
+            .max(px(GRID_PAD_X));
         let y = if place_above {
             px(GRID_PAD_Y) + self.line_height * (srow as f32) - menu_h - gap
         } else {
@@ -4812,8 +4828,8 @@ impl TerminalView {
                 .flex()
                 .flex_col()
                 .py_1()
-                .min_w(px(120.))
-                .max_w(px(COMPLETION_MENU_MAX_W))
+                .min_w(px(120.).min(menu_w))
+                .max_w(menu_w)
                 .overflow_hidden()
                 .bg(theme.popover)
                 .border_1()
@@ -5595,12 +5611,17 @@ const COMPLETION_MENU_MAX_W: f32 = 480.;
 /// had been cut. The row spends its width on `px_2` either side, the kind
 /// icon, the gap after it and the margin before the description; whatever is
 /// left, in cells, is the description's.
-fn description_budget(cell_width: f32, label_cells: usize) -> usize {
+///
+/// `menu_w` is the width the menu actually got, not the width it would like:
+/// in a pane narrower than [`COMPLETION_MENU_MAX_W`] the menu is capped to the
+/// grid, and a budget measured against the larger number puts the ellipsis
+/// past the edge — which is the same mid-word cut, only harder to see.
+fn description_budget(cell_width: f32, label_cells: usize, menu_w: f32) -> usize {
     const ROW_CHROME: f32 = 8. + 8. + 16. + 6. + 8.;
     if cell_width <= 0. {
         return 0;
     }
-    let free = COMPLETION_MENU_MAX_W - ROW_CHROME - label_cells as f32 * cell_width;
+    let free = menu_w - ROW_CHROME - label_cells as f32 * cell_width;
     (free / cell_width).floor().max(0.) as usize
 }
 
@@ -5796,9 +5817,9 @@ mod tests {
         assert!(!out.contains(" …"), "{out:?}");
     }
     use super::{
-        LoopbackPlan, RawInput, SelectEndCopy, Typeahead, WheelRoute, clipboard_paste_text,
-        compose_notification_title, cwd_is_on_host, display_width, is_typeahead_interrupt,
-        loopback_plan, observe_typeahead_for_owner,
+        COMPLETION_MENU_MAX_W, LoopbackPlan, RawInput, SelectEndCopy, Typeahead, WheelRoute,
+        clipboard_paste_text, compose_notification_title, cwd_is_on_host, display_width,
+        is_typeahead_interrupt, loopback_plan, observe_typeahead_for_owner,
     };
     use super::{SCROLL_ANIM_FRAME, scroll_anim_step};
     use super::{
@@ -6938,14 +6959,19 @@ mod tests {
 
     #[test]
     fn the_description_budget_is_what_the_name_leaves_of_the_menu() {
+        const W: f32 = COMPLETION_MENU_MAX_W;
         // A 9px cell: 46px of row chrome, so a bare row leaves (480-46)/9 cells.
-        assert_eq!(description_budget(9., 0), 48);
+        assert_eq!(description_budget(9., 0, W), 48);
         // Every cell the name takes is one the description does not get.
-        assert_eq!(description_budget(9., 10), 38);
+        assert_eq!(description_budget(9., 10, W), 38);
         // A name that fills the menu on its own leaves nothing, and never
         // underflows into a huge budget.
-        assert_eq!(description_budget(9., 200), 0);
-        assert_eq!(description_budget(0., 10), 0);
+        assert_eq!(description_budget(9., 200, W), 0);
+        assert_eq!(description_budget(0., 10, W), 0);
+        // A pane too narrow for the full menu shrinks the budget with it,
+        // instead of eliding to a width the menu never got.
+        assert!(description_budget(9., 10, 240.) < description_budget(9., 10, W));
+        assert_eq!(description_budget(9., 10, 240.), 11);
     }
 
     #[test]