Replace Match Row with Match Cell (Cmd+M)

- New 'Match Cell' command selects all cells in the sheet whose value
  equals the current cell's value (non-contiguous selection)
- Added state.selectedCells (Set of 'r,c' keys) for scatter selection
- isCellSelected checks selectedCells first, then falls back to
  rectangular selection
- getSelectedData/clearSelectedCells handle non-contiguous selections
- Cmd+M keyboard shortcut mapped
- Match selection cleared on click, arrow movement, or Escape

Co-authored-by: Shelley <shelley@exe.dev>

commands.go

@@ -33,7 +33,7 @@ func (c *CommandRegistry) GetCommands() []Command {
 		{ID: "sort-asc", Name: "Sort A-Z", Shortcut: ""},
 		{ID: "sort-desc", Name: "Sort Z-A", Shortcut: ""},
 		{ID: "sort-advanced", Name: "Sort Advanced", Shortcut: ""},
-		{ID: "match-row", Name: "Match Row", Shortcut: ""},
+		{ID: "match-cell", Name: "Match Cell", Shortcut: "Cmd+M"},
 		{ID: "delete-row", Name: "Delete Row", Shortcut: "Cmd+Backspace"},
 	}
 }

frontend/src/main.js

@@ -7,6 +7,7 @@ const state = {
     filePath: '',
     cursor: { row: 0, col: 0 },
     selection: null, // { startRow, startCol, endRow, endCol }
+    selectedCells: null, // Set of "r,c" strings for non-contiguous selection (Match Cell)
     colWidths: [],   // pixel widths per column
     isSelecting: false,
     editingHeader: -1,
@@ -53,6 +54,10 @@ function cellRefStr(r, c) {
     return colLabel(c) + (r + 1);
 }
 
+function clearMatchSelection() {
+    state.selectedCells = null;
+}
+
 function normalizeSelection() {
     if (!state.selection) return null;
     const { startRow, startCol, endRow, endCol } = state.selection;
@@ -65,6 +70,7 @@ function normalizeSelection() {
 }
 
 function isCellSelected(r, c) {
+    if (state.selectedCells) return state.selectedCells.has(`${r},${c}`);
     const sel = normalizeSelection();
     if (!sel) return r === state.cursor.row && c === state.cursor.col;
     return r >= sel.r1 && r <= sel.r2 && c >= sel.c1 && c <= sel.c2;
@@ -345,6 +351,8 @@ tableBody.addEventListener('mousedown', (e) => {
         commitFormulaBar();
     }
 
+    clearMatchSelection();
+
     if (e.shiftKey) {
         // Extend selection
         state.selection = {
@@ -384,6 +392,7 @@ document.addEventListener('mouseup', () => {
 
 // ===== Keyboard navigation =====
 function moveCursor(dr, dc, shift) {
+    clearMatchSelection();
     if (shift) {
         if (!state.selection) {
             state.selection = {
@@ -470,6 +479,11 @@ document.addEventListener('keydown', (e) => {
         executeCommand('open');
         return;
     }
+    if (meta && e.key === 'm') {
+        e.preventDefault();
+        executeCommand('match-cell');
+        return;
+    }
 
     // Arrow keys
     if (e.key === 'ArrowUp') { e.preventDefault(); moveCursor(-1, 0, e.shiftKey); return; }
@@ -508,6 +522,7 @@ document.addEventListener('keydown', (e) => {
     // Escape clears selection
     if (e.key === 'Escape') {
         state.selection = null;
+        clearMatchSelection();
         updateSelectionClasses();
         return;
     }
@@ -556,6 +571,29 @@ function cancelFormulaBar() {
 
 // ===== Selection data extraction =====
 function getSelectedData() {
+    // Non-contiguous match selection: collect bounding box
+    if (state.selectedCells && state.selectedCells.size > 0) {
+        let minR = Infinity, maxR = -1, minC = Infinity, maxC = -1;
+        for (const key of state.selectedCells) {
+            const [r, c] = key.split(',').map(Number);
+            if (r < minR) minR = r;
+            if (r > maxR) maxR = r;
+            if (c < minC) minC = c;
+            if (c > maxC) maxC = c;
+        }
+        const headers = [];
+        for (let c = minC; c <= maxC; c++) headers.push(state.headers[c] || '');
+        const rows = [];
+        for (let r = minR; r <= maxR; r++) {
+            const row = [];
+            for (let c = minC; c <= maxC; c++) {
+                row.push(state.selectedCells.has(`${r},${c}`) ? getCellValue(r, c) : '');
+            }
+            rows.push(row);
+        }
+        return { headers, rows, isSingleCol: minC === maxC };
+    }
+
     const sel = normalizeSelection();
     if (!sel) {
         return {
@@ -584,6 +622,14 @@ function getSelectedData() {
 }
 
 function clearSelectedCells() {
+    if (state.selectedCells && state.selectedCells.size > 0) {
+        for (const key of state.selectedCells) {
+            const [r, c] = key.split(',').map(Number);
+            setCellValue(r, c, '');
+        }
+        render();
+        return;
+    }
     const sel = normalizeSelection();
     if (!sel) {
         setCellValue(state.cursor.row, state.cursor.col, '');
@@ -622,7 +668,7 @@ async function loadCommands() {
             { ID: 'sort-asc', Name: 'Sort A-Z', Shortcut: '' },
             { ID: 'sort-desc', Name: 'Sort Z-A', Shortcut: '' },
             { ID: 'sort-advanced', Name: 'Sort Advanced', Shortcut: '' },
-            { ID: 'match-row', Name: 'Match Row', Shortcut: '' },
+            { ID: 'match-cell', Name: 'Match Cell', Shortcut: 'Cmd+M' },
             { ID: 'delete-row', Name: 'Delete Row', Shortcut: 'Cmd+Backspace' },
         ];
     }
@@ -729,7 +775,7 @@ async function executeCommand(id) {
         case 'sort-asc': doSort(true); break;
         case 'sort-desc': doSort(false); break;
         case 'sort-advanced': openSortAdvanced(); break;
-        case 'match-row': doMatchRow(); break;
+        case 'match-cell': doMatchCell(); break;
         case 'delete-row': doDeleteRow(); break;
     }
 }
@@ -945,33 +991,24 @@ function doInsertColRight() {
 }
 
 // ===== Match & Delete Row =====
-function doMatchRow() {
-    const col = state.cursor.col;
-    const val = getCellValue(state.cursor.row, col);
-    const matchingRows = [];
+function doMatchCell() {
+    const val = getCellValue(state.cursor.row, state.cursor.col);
+    const matched = new Set();
     for (let r = 0; r < state.rows.length; r++) {
-        if ((state.rows[r][col] || '') === val) {
-            matchingRows.push(r);
+        for (let c = 0; c < state.headers.length; c++) {
+            if ((state.rows[r][c] || '') === val) {
+                matched.add(`${r},${c}`);
             }
         }
-    if (matchingRows.length === 0) {
-        setStatus('No matching rows');
+    }
+    if (matched.size === 0) {
+        setStatus('No matching cells');
         return;
     }
-    // Select from first to last matching row, spanning all columns
-    const first = matchingRows[0];
-    const last = matchingRows[matchingRows.length - 1];
-    state.cursor = { row: first, col: 0 };
-    state.selection = {
-        startRow: first,
-        startCol: 0,
-        endRow: last,
-        endCol: state.headers.length - 1,
-    };
+    state.selection = null;
+    state.selectedCells = matched;
     updateSelectionClasses();
-    scrollCursorIntoView();
-    const colName = state.headers[col] || colLabel(col);
-    setStatus(`${matchingRows.length} row(s) matching ${colName} = "${val}"`);
+    setStatus(`${matched.size} cell(s) matching "${val}"`);
 }
 
 function doDeleteRow() {