Let a text field select from right to left with the mouse (#236)

Dragging from right to left in a canvas text field only moved the
cursor. The hidden input behind the field got every selection sorted
and without a direction. Its selectionchange echo then handed back the
sorted range, and the anchor jumped to the mouse on the first move.

- KeyboardBridge sets the selection with 'backward' when the focus
  lies before the anchor, and reads selectionDirection when the input
  reports a change.
- TextField passes anchor and focus through unchanged. Its own
  sorting is gone.
- Shift+Left runs through the same path. The cursor should now sit at
  the moving end there too. This is not tested on its own.

Tests:
- ./check.sh: 167 files, 2435 tests, CHECK EXIT 0
- e2e 2: ALL PASSED, 25 checks. New check 2d-ii drags right to left
  in the name field and reads start 0, end 13, direction backward.
- Counter-check without the direction: 2d-ii fails with end 2, the
  reported symptom.
- e2e check total in README goes to 1401 (computed, not run in full).

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

src/ui/KeyboardBridge.ts

@@ -5,7 +5,8 @@
  */
 
 export interface TextEditTarget {
-  onBridgeInput(value: string, selectionStart: number, selectionEnd: number): void;
+  /** `anchor` is where the selection started, `focus` where the caret is; focus < anchor is backward. */
+  onBridgeInput(value: string, anchor: number, focus: number): void;
   /** Called for navigation keys (Enter, Escape, Tab, arrows …). Return true to consume. */
   onBridgeKey(event: KeyboardEvent): boolean;
   onBridgeBlur(): void;
@@ -40,8 +41,14 @@ export class KeyboardBridge {
     document.body.appendChild(input);
     this.input = input;
 
-    const sync = () =>
-      this.target?.onBridgeInput(input.value, input.selectionStart ?? 0, input.selectionEnd ?? 0);
+    // The input keeps its range ordered; the direction says which end is the anchor. Reporting
+    // the ordered range lost the anchor of a right-to-left drag on the first selectionchange.
+    const sync = () => {
+      const start = input.selectionStart ?? 0;
+      const end = input.selectionEnd ?? 0;
+      const backward = input.selectionDirection === 'backward';
+      this.target?.onBridgeInput(input.value, backward ? end : start, backward ? start : end);
+    };
     input.addEventListener('input', sync);
     input.addEventListener('keyup', sync);
     document.addEventListener('selectionchange', () => {
@@ -62,17 +69,12 @@ export class KeyboardBridge {
   }
 
   /** Mirrors the field's value into the input and grabs DOM focus. */
-  attach(
-    target: TextEditTarget,
-    value: string,
-    selectionStart = value.length,
-    selectionEnd = selectionStart,
-  ): void {
+  attach(target: TextEditTarget, value: string, anchor = value.length, focus = anchor): void {
     this.suppressBlur = true;
     this.target = target;
     this.input.value = value;
     this.input.focus({ preventScroll: true });
-    this.input.setSelectionRange(selectionStart, selectionEnd);
+    this.select(anchor, focus);
     this.suppressBlur = false;
   }
 
@@ -83,9 +85,14 @@ export class KeyboardBridge {
   }
 
   /** Pushes a value the canvas side changed into the input, so the next keystroke edits that text. */
-  setValue(value: string, selectionStart = value.length, selectionEnd = selectionStart): void {
+  setValue(value: string, anchor = value.length, focus = anchor): void {
     this.input.value = value;
-    if (document.activeElement === this.input) this.input.setSelectionRange(selectionStart, selectionEnd);
+    if (document.activeElement === this.input) this.select(anchor, focus);
+  }
+
+  private select(anchor: number, focus: number): void {
+    const direction = focus < anchor ? 'backward' : 'forward';
+    this.input.setSelectionRange(Math.min(anchor, focus), Math.max(anchor, focus), direction);
   }
 
   /** Ignored when another field attached meanwhile, so a late blur cannot steal it. */

src/ui/widgets/TextField.ts

@@ -167,23 +167,18 @@ export class TextField extends Widget implements TextEditTarget {
   private setSelection(start: number, end: number, pushToBridge: boolean): void {
     this.selStart = clamp(start, 0, this.valueText.length);
     this.selEnd = clamp(end, 0, this.valueText.length);
-    if (pushToBridge && this.editing) {
-      // The DOM only takes an ordered range; selStart/selEnd keep the anchor/focus order a
-      // drag selection needs.
-      const lo = Math.min(this.selStart, this.selEnd);
-      const hi = Math.max(this.selStart, this.selEnd);
-      ui().keyboard.setValue(this.valueText, lo, hi);
-    }
+    // selStart/selEnd are anchor/focus; the bridge keeps that order across its selectionchange echo.
+    if (pushToBridge && this.editing) ui().keyboard.setValue(this.valueText, this.selStart, this.selEnd);
     this.caretVisible = true;
     this.invalidate();
   }
 
   /** Adopts the input's value and selection verbatim; fires `onInput` only when the text changed. */
-  onBridgeInput(value: string, selectionStart: number, selectionEnd: number): void {
+  onBridgeInput(value: string, anchor: number, focus: number): void {
     const changed = value !== this.valueText;
     this.valueText = value;
-    this.selStart = selectionStart;
-    this.selEnd = selectionEnd;
+    this.selStart = anchor;
+    this.selEnd = focus;
     this.caretVisible = true;
     this.invalidate();
     if (changed) this.onInput?.(value);