Add formula "point mode": click/drag a cell to insert its reference

Excel/Numbers-style reference picking: while editing a formula (buffer
starts with "="), a click on any grid cell -- in the same table or a
completely different one -- inserts its reference at the caret instead of
changing the selection; a drag inserts/grows a range reference live as you
drag. A further click/drag before typing anything replaces the just-inserted
reference; typing anything (";" to separate SUM() arguments included, but
not special-cased -- any character ends the window, same as Excel) makes the
next click append a fresh one instead.

- document.ts: whichever editor is open (in-cell editor or formula bar)
  registers a small handle (home tableId + read/replace the buffer);
  pointClick()/pointDrag() insert or replace a reference into it, qualifying
  with `Name!` (quoted if needed) when the clicked table differs from the
  editor's own. formulaPointModeActive() gates it on the buffer being a
  formula; noteFormulaTyped() (wired to real typing, not the programmatic
  inserts) ends the "replace" window.
- TableGrid.vue: onCellMouseDown checks point mode before its normal
  selection/edit handling, tracking a drag the same way normal selection
  does; dblclick during point mode no longer hijacks into editing that cell.
- FormulaBar.vue: registers on focus, same click/drag targeting works from
  there without disturbing the grid's own selection.

Verified interactively against the dev server with Playwright, including a
real bug the store-level tests (a mocked editor handle, no real DOM) missed
entirely: preventDefault() alone kept focus on the editor, but the mousedown
still bubbled to CanvasObject.vue's own handler, which selects/brings the
clicked table to front -- closing the very editor being pointed into. Fixed
with stopPropagation() alongside it. After that fix: same-table and
cross-table click/drag both insert correctly-qualified references, a second
click replaces before typing and appends after, and the live selection/
active object are untouched by a point-mode click.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>

src/components/TableGrid.vue

@@ -415,6 +415,17 @@ function startDrag(mode: 'replace' | 'additive') {
 }
 function onCellMouseDown(e: MouseEvent, c: number, r: number) {
   if (e.button !== 0) return;
+  if (store.formulaPointModeActive()) {
+    e.preventDefault(); // keep focus on the formula editor -- must not blur/commit it
+    // ... and don't let it bubble to the canvas object's own mousedown
+    // (CanvasObject.vue selects/brings-to-front the clicked table on any
+    // mousedown; a point-mode click must stay invisible to that, same as
+    // Excel doesn't change your object selection while you're just picking
+    // a reference for a formula elsewhere).
+    e.stopPropagation();
+    startPointDrag(c, r);
+    return;
+  }
   if (editing.value) commitEdit();
   clearFlow();
   lastPointer = { x: e.clientX, y: e.clientY };
@@ -451,6 +462,37 @@ function onDragUp() {
   window.removeEventListener('blur', onDragUp);
 }
 
+// ---- formula "point mode" (click/drag a cell to insert its reference) ---
+let pointDragStart: { c: number; r: number } | null = null;
+function startPointDrag(c: number, r: number) {
+  pointDragStart = { c, r };
+  store.pointClick(props.tableId, c, r);
+  window.addEventListener('mousemove', onPointDragMove, true);
+  window.addEventListener('mouseup', onPointDragUp, true);
+  window.addEventListener('blur', onPointDragUp);
+}
+function onPointDragMove(e: MouseEvent) {
+  if (!pointDragStart) return;
+  if (e.buttons === 0) {
+    onPointDragUp(); // a mouseup we never saw -- self-heal a stuck drag
+    return;
+  }
+  const hit = cellFromPoint(e.clientX, e.clientY);
+  if (!hit) return;
+  if (hit.c === pointDragStart.c && hit.r === pointDragStart.r) {
+    store.pointClick(props.tableId, hit.c, hit.r);
+  } else {
+    store.pointDrag(props.tableId, pointDragStart.c, pointDragStart.r, hit.c, hit.r);
+  }
+}
+function onPointDragUp() {
+  if (!pointDragStart) return;
+  pointDragStart = null;
+  window.removeEventListener('mousemove', onPointDragMove, true);
+  window.removeEventListener('mouseup', onPointDragUp, true);
+  window.removeEventListener('blur', onPointDragUp);
+}
+
 // ---- fill handle (drag to copy/fill, Excel/Numbers-style) ---------------
 /** Small square at the selection's bottom-right corner; dragging it repeats
  *  the selection's cells (values, formulas -- reference-adjusted like a
@@ -624,9 +666,35 @@ function resizeEditor() {
   ta.style.height = Math.min(mirror.offsetHeight, EDIT_MAX_H) + 'px';
 }
 
+/** Lets the store insert a reference into this editor when the user clicks
+ *  a grid cell mid-formula ("point mode") -- see store.pointClick/pointDrag. */
+function formulaEditorHandle() {
+  return {
+    tableId: props.tableId,
+    getState: () => {
+      const el = editInput.value;
+      return {
+        text: editValue.value,
+        start: el?.selectionStart ?? editValue.value.length,
+        end: el?.selectionEnd ?? editValue.value.length,
+      };
+    },
+    replace: (start: number, end: number, value: string) => {
+      editValue.value = editValue.value.slice(0, start) + value + editValue.value.slice(end);
+      nextTick(() => {
+        const el = editInput.value;
+        el?.focus();
+        el?.setSelectionRange(start + value.length, start + value.length);
+        resizeEditor();
+      });
+    },
+  };
+}
+
 function beginEdit(c: number, r: number, initial?: string) {
   editing.value = { col: c, row: r };
   editValue.value = initial ?? store.cellInput(props.tableId, c, r);
+  store.registerFormulaEditor(formulaEditorHandle());
   nextTick(() => {
     const el = editInput.value;
     if (!el) return;
@@ -642,11 +710,13 @@ function commitEdit() {
   const { col, row } = editing.value;
   store.setCellInput(props.tableId, col, row, editValue.value);
   editing.value = null;
+  store.registerFormulaEditor(null);
   focusRoot();
   setTimeout(() => (committing = false), 0);
 }
 function cancelEdit() {
   editing.value = null;
+  store.registerFormulaEditor(null);
   focusRoot();
 }
 function onEditKeydown(e: KeyboardEvent) {
@@ -709,6 +779,18 @@ function toggleReferenceLock() {
 function onEditBlur() {
   if (!committing && editing.value) commitEdit();
 }
+/** Actual typing (not a point-mode click inserting a reference programmatically)
+ *  ends the "next click replaces the last reference" window. */
+function onEditInput() {
+  resizeEditor();
+  store.noteFormulaTyped();
+}
+/** Clicking inside the field to reposition the caret should also end that
+ *  window (mousedown so it fires before any selection change is read). */
+function onEditMousedown(e: MouseEvent) {
+  e.stopPropagation();
+  store.noteFormulaTyped();
+}
 
 // ---- keyboard navigation (Excel-like) ------------------------
 function onKeydown(e: KeyboardEvent) {
@@ -889,6 +971,7 @@ const totalWidth = computed(() => {
 
 onBeforeUnmount(() => {
   onDragUp();
+  onPointDragUp();
   onFillDragUp();
   onResizeUp();
   onRowResizeUp();
@@ -960,7 +1043,7 @@ defineExpose({
               }"
               :style="cellStyle(c - 1, r - 1)"
               @mousedown="onCellMouseDown($event, c - 1, r - 1)"
-              @dblclick="beginEdit(c - 1, r - 1)"
+              @dblclick="!store.formulaPointModeActive() && beginEdit(c - 1, r - 1)"
             >
               <div
                 class="cell-content"
@@ -998,9 +1081,9 @@ defineExpose({
         spellcheck="false"
         rows="1"
         @keydown="onEditKeydown"
-        @input="resizeEditor"
+        @input="onEditInput"
         @blur="onEditBlur"
-        @mousedown.stop
+        @mousedown="onEditMousedown"
       />
       <div v-if="editing" ref="editMirrorEl" class="cell-input-mirror" :style="editMirrorStyle" aria-hidden="true" />
     </div>