feat(dees-table): add opt-in flash highlighting for updated table cells

changelog.md

@@ -1,5 +1,13 @@
 # Changelog
 
+## 2026-04-08 - 3.70.0 - feat(dees-table)
+add opt-in flash highlighting for updated table cells
+
+- introduces highlight-updates and highlight-duration properties for diff-based cell update highlighting
+- adds a warning banner when flash highlighting is enabled without rowKey
+- keeps selection stable across data refreshes and avoids flashing user-edited cells
+- includes a live demo showcasing flashing updates and reduced-motion support
+
 ## 2026-04-08 - 3.69.1 - fix(ui)
 refine heading emphasis and animate app dashboard subview expansion
 

ts_web/00_commitinfo_data.ts

@@ -3,6 +3,6 @@
  */
 export const commitinfo = {
   name: '@design.estate/dees-catalog',
-  version: '3.69.1',
+  version: '3.70.0',
   description: 'A comprehensive library that provides dynamic web components for building sophisticated and modern web applications using JavaScript and TypeScript.'
 }

ts_web/elements/00group-dataview/dees-table/dees-table.demo.ts

@@ -1,6 +1,7 @@
 import { type ITableAction } from './dees-table.js';
 import * as plugins from '../../00plugins.js';
 import { html, css, cssManager } from '@design.estate/dees-element';
+import '@design.estate/dees-wcctools/demotools';
 
 interface ITableDemoData {
   date: string;
@@ -742,6 +743,71 @@ export const demoFunc = () => html`
           ] as ITableAction[]}
         ></dees-table>
       </div>
+
+      <dees-demowrapper .runAfterRender=${async (elementArg: HTMLElement) => {
+        const tableEl = elementArg.querySelector('#demoLiveFlash') as any;
+        if (!tableEl) return;
+        // Guard against double-start if runAfterRender fires more than once
+        // (e.g. across hot-reload cycles).
+        if (tableEl.__liveFlashTimerId) {
+          window.clearInterval(tableEl.__liveFlashTimerId);
+        }
+        const tick = () => {
+          if (!Array.isArray(tableEl.data) || tableEl.data.length === 0) return;
+          const next = tableEl.data.map((r: any) => ({ ...r }));
+          const count = 1 + Math.floor(Math.random() * 3);
+          for (let i = 0; i < count; i++) {
+            const idx = Math.floor(Math.random() * next.length);
+            const delta = +((Math.random() * 2 - 1) * 3).toFixed(2);
+            const newPrice = Math.max(1, +(next[idx].price + delta).toFixed(2));
+            next[idx] = {
+              ...next[idx],
+              price: newPrice,
+              change: delta,
+              updatedAt: new Date().toLocaleTimeString(),
+            };
+          }
+          tableEl.data = next;
+        };
+        tableEl.__liveFlashTimerId = window.setInterval(tick, 1500);
+      }}>
+        <div class="demo-section">
+          <h2 class="demo-title">Live Updates with Flash Highlighting</h2>
+          <p class="demo-description">
+            Opt-in cell-flash via <code>highlight-updates="flash"</code>. The ticker below mutates
+            random rows every 1.5s and reassigns <code>.data</code>. Updated cells briefly flash
+            amber and fade out. Requires <code>rowKey</code> (here <code>"symbol"</code>). Honors
+            <code>prefers-reduced-motion</code>. Row selection persists across updates — click a
+            row, then watch it stay selected as the data churns.
+          </p>
+          <dees-table
+            id="demoLiveFlash"
+            .rowKey=${'symbol'}
+            highlight-updates="flash"
+            .selectionMode=${'multi'}
+            heading1="Live Market Feed"
+            heading2="Flashing cells indicate updated values"
+            .columns=${[
+              { key: 'symbol', header: 'Symbol', sortable: true },
+              { key: 'price', header: 'Price', sortable: true },
+              { key: 'change', header: 'Δ', sortable: true },
+              { key: 'updatedAt', header: 'Updated' },
+            ]}
+            .data=${[
+              { symbol: 'AAPL', price: 182.52, change: 0, updatedAt: '—' },
+              { symbol: 'MSFT', price: 414.18, change: 0, updatedAt: '—' },
+              { symbol: 'GOOG', price: 168.74, change: 0, updatedAt: '—' },
+              { symbol: 'AMZN', price: 186.13, change: 0, updatedAt: '—' },
+              { symbol: 'TSLA', price: 248.50, change: 0, updatedAt: '—' },
+              { symbol: 'NVDA', price: 877.35, change: 0, updatedAt: '—' },
+              { symbol: 'META', price: 492.96, change: 0, updatedAt: '—' },
+              { symbol: 'NFLX', price: 605.88, change: 0, updatedAt: '—' },
+              { symbol: 'AMD',  price: 165.24, change: 0, updatedAt: '—' },
+              { symbol: 'INTC', price:  42.15, change: 0, updatedAt: '—' },
+            ]}
+          ></dees-table>
+        </div>
+      </dees-demowrapper>
     </div>
   </div>
 `;

ts_web/elements/00group-dataview/dees-table/dees-table.ts

@@ -214,6 +214,30 @@ export class DeesTable<T> extends DeesElement {
   @property({ type: Number, attribute: 'virtual-overscan' })
   accessor virtualOverscan: number = 8;
 
+  /**
+   * Opt-in visual indication of cell-value changes across data updates.
+   *
+   * - `'none'` (default): no diffing, zero overhead.
+   * - `'flash'`: when `data` is reassigned to a new array reference, diff the
+   *   new rows against the previous snapshot and briefly flash any cells
+   *   whose resolved value changed. Equality is strict `===`; object-valued
+   *   cells are compared by reference. The currently-edited cell is never
+   *   flashed. User-initiated cell edits do not flash.
+   *
+   * Requires `rowKey` to be set — without it, the feature silently no-ops
+   * and renders a visible dev warning banner. Honors `prefers-reduced-motion`
+   * (fades are replaced with a static background hint of the same duration).
+   */
+  @property({ type: String, attribute: 'highlight-updates' })
+  accessor highlightUpdates: 'none' | 'flash' = 'none';
+
+  /**
+   * Duration of the flash animation in milliseconds. Fed into the
+   * `--dees-table-flash-duration` CSS variable on the host.
+   */
+  @property({ type: Number, attribute: 'highlight-duration' })
+  accessor highlightDuration: number = 900;
+
   /**
    * When set, the table renders inside a fixed-height scroll container
    * (`max-height: var(--table-max-height, 360px)`) and the header sticks
@@ -268,6 +292,23 @@ export class DeesTable<T> extends DeesElement {
   @state()
   private accessor __floatingActive: boolean = false;
 
+  // ─── Flash-on-update state (only populated when highlightUpdates === 'flash') ──
+  /** rowId → set of colKey strings currently flashing. */
+  @state()
+  private accessor __flashingCells: Map<string, Set<string>> = new Map();
+
+  /** rowId → (colKey → last-seen resolved cell value). Populated per diff pass. */
+  private __prevSnapshot?: Map<string, Map<string, unknown>>;
+
+  /** Single shared timer that clears __flashingCells after highlightDuration ms. */
+  private __flashClearTimer?: ReturnType<typeof setTimeout>;
+
+  /** Monotonic counter bumped each flash batch so directives.keyed recreates the cell node and restarts the animation. */
+  private __flashTick: number = 0;
+
+  /** One-shot console.warn gate for missing rowKey in flash mode. */
+  private __flashWarnedNoRowKey: boolean = false;
+
   // ─── Render memoization ──────────────────────────────────────────────
   // These caches let render() short-circuit when the relevant inputs
   // (by reference) haven't changed. They are NOT @state — mutating them
@@ -557,6 +598,15 @@ export class DeesTable<T> extends DeesElement {
           </div>
         </div>
         <div class="headingSeparation"></div>
+        ${this.highlightUpdates === 'flash' && !this.rowKey
+          ? html`<div class="flashConfigWarning" role="alert">
+              <dees-icon .icon=${'lucide:triangleAlert'}></dees-icon>
+              <span>
+                <code>highlight-updates="flash"</code> requires
+                <code>rowKey</code> to be set. Flash is disabled.
+              </span>
+            </div>`
+          : html``}
         <div class="searchGrid hidden">
           <dees-input-text
             .label=${'lucene syntax search'}
@@ -606,9 +656,13 @@ export class DeesTable<T> extends DeesElement {
                   ${useVirtual && topSpacerHeight > 0
                     ? html`<tr aria-hidden="true" style="height:${topSpacerHeight}px"><td></td></tr>`
                     : html``}
-                  ${renderRows.map((itemArg, sliceIdx) => {
+                  ${directives.repeat(
+                    renderRows,
+                    (itemArg, sliceIdx) => `${this.getRowId(itemArg)}::${renderStart + sliceIdx}`,
+                    (itemArg, sliceIdx) => {
                     const rowIndex = renderStart + sliceIdx;
                     const rowId = this.getRowId(itemArg);
+                    const flashSet = this.__flashingCells.get(rowId);
                     return html`
                       <tr
                         data-row-idx=${rowIndex}
@@ -640,6 +694,7 @@ export class DeesTable<T> extends DeesElement {
                             const isEditing =
                               this.__editingCell?.rowId === rowId &&
                               this.__editingCell?.colKey === editKey;
+                            const isFlashing = !!flashSet?.has(editKey);
                             const cellClasses = [
                               isEditable ? 'editable' : '',
                               isFocused && !isEditing ? 'focused' : '',
@@ -647,14 +702,22 @@ export class DeesTable<T> extends DeesElement {
                             ]
                               .filter(Boolean)
                               .join(' ');
+                            const innerHtml = html`<div
+                              class=${isFlashing ? 'innerCellContainer flashing' : 'innerCellContainer'}
+                            >
+                              ${isEditing ? this.renderCellEditor(itemArg, col) : content}
+                            </div>`;
                             return html`
                               <td
                                 class=${cellClasses}
                                 data-col-key=${editKey}
                               >
-                                <div class="innerCellContainer">
+                                ${isFlashing
-                                  ${isEditing ? this.renderCellEditor(itemArg, col) : content}
+                                  ? directives.keyed(
-                                </div>
+                                      `${rowId}:${editKey}:${this.__flashTick}`,
+                                      innerHtml
+                                    )
+                                  : innerHtml}
                               </td>
                             `;
                           })}
@@ -685,7 +748,8 @@ export class DeesTable<T> extends DeesElement {
                           }
                         })()}
                       </tr>`;
-                  })}
+                  }
+                  )}
                   ${useVirtual && bottomSpacerHeight > 0
                     ? html`<tr aria-hidden="true" style="height:${bottomSpacerHeight}px"><td></td></tr>`
                     : html``}
@@ -801,7 +865,7 @@ export class DeesTable<T> extends DeesElement {
                 const key = String(col.key);
                 if (col.filterable === false) return html`<th></th>`;
                 return html`<th>
-                  <input type="text" placeholder="Filter..." .value=${this.columnFilters[key] || ''}
+                  <input type="text" placeholder="Filter..." data-col-key=${key} .value=${this.columnFilters[key] || ''}
                     @input=${(e: Event) => this.setColumnFilter(key, (e.target as HTMLInputElement).value)} />
                 </th>`;
               })}
@@ -957,6 +1021,84 @@ export class DeesTable<T> extends DeesElement {
     if (fh) fh.classList.remove('active');
   }
 
+  /**
+   * If a filter `<input>` inside the floating-header clone currently has
+   * focus, copy its value, caret, and selection range onto the matching
+   * input in the real header, then focus that real input. This lets the
+   * user keep typing uninterrupted when filter input causes the table to
+   * shrink below the viewport stick line and the floating header has to
+   * unmount.
+   *
+   * Safe to call at any time — it is a no-op unless an input inside the
+   * floating header is focused and has a `data-col-key` attribute that
+   * matches a real-header input.
+   */
+  private __transferFocusToRealHeader(): void {
+    const fh = this.__floatingHeaderEl;
+    if (!fh) return;
+    const active = this.shadowRoot?.activeElement as HTMLElement | null;
+    if (!active || !fh.contains(active)) return;
+    const colKey = active.getAttribute('data-col-key');
+    if (!colKey) return;
+    const fromInput = active as HTMLInputElement;
+    const real = this.shadowRoot?.querySelector(
+      `.tableScroll > table > thead input[data-col-key="${CSS.escape(colKey)}"]`
+    ) as HTMLInputElement | null;
+    if (!real || real === fromInput) return;
+    const selStart = fromInput.selectionStart;
+    const selEnd = fromInput.selectionEnd;
+    const selDir = fromInput.selectionDirection as any;
+    real.focus({ preventScroll: true });
+    try {
+      if (selStart != null && selEnd != null) {
+        real.setSelectionRange(selStart, selEnd, selDir || undefined);
+      }
+    } catch {
+      /* setSelectionRange throws on unsupported input types — ignore */
+    }
+  }
+
+  /**
+   * Symmetric counterpart to `__transferFocusToRealHeader`. When the
+   * floating header has just activated and a real-header filter input
+   * was focused (and is now scrolled off-screen behind the floating
+   * clone), move focus to the clone's matching input so the user keeps
+   * typing in the visible one.
+   *
+   * Called from `__syncFloatingHeader` inside the post-activation
+   * `updateComplete` callback — by then the clone subtree exists in the
+   * DOM and can receive focus.
+   */
+  private __transferFocusToFloatingHeader(): void {
+    const fh = this.__floatingHeaderEl;
+    if (!fh || !this.__floatingActive) return;
+    const active = this.shadowRoot?.activeElement as HTMLElement | null;
+    if (!active) return;
+    // Only handle focus that lives in the real header (not already in the clone).
+    const realThead = this.shadowRoot?.querySelector(
+      '.tableScroll > table > thead'
+    ) as HTMLElement | null;
+    if (!realThead || !realThead.contains(active)) return;
+    const colKey = active.getAttribute('data-col-key');
+    if (!colKey) return;
+    const fromInput = active as HTMLInputElement;
+    const clone = fh.querySelector(
+      `input[data-col-key="${CSS.escape(colKey)}"]`
+    ) as HTMLInputElement | null;
+    if (!clone || clone === fromInput) return;
+    const selStart = fromInput.selectionStart;
+    const selEnd = fromInput.selectionEnd;
+    const selDir = fromInput.selectionDirection as any;
+    clone.focus({ preventScroll: true });
+    try {
+      if (selStart != null && selEnd != null) {
+        clone.setSelectionRange(selStart, selEnd, selDir || undefined);
+      }
+    } catch {
+      /* ignore */
+    }
+  }
+
   // ─── Virtualization ─────────────────────────────────────────────────
 
   /**
@@ -1062,6 +1204,15 @@ export class DeesTable<T> extends DeesElement {
     const shouldBeActive = tableRect.top < stick.top && distance > 0;
 
     if (shouldBeActive !== this.__floatingActive) {
+      if (!shouldBeActive) {
+        // Before we flag the clone for unmount, hand off any focused
+        // filter input to its counterpart in the real header. This is the
+        // "user is typing in a sticky filter input, filter shrinks the
+        // table so the floating header hides" case — without this
+        // handoff the user's focus (and caret position) would be lost
+        // when the clone unmounts.
+        this.__transferFocusToRealHeader();
+      }
       this.__floatingActive = shouldBeActive;
       fh.classList.toggle('active', shouldBeActive);
       if (!shouldBeActive) {
@@ -1072,8 +1223,14 @@ export class DeesTable<T> extends DeesElement {
       }
       if (shouldBeActive) {
         // Clone subtree doesn't exist yet — wait for the next render to
-        // materialize it, then complete geometry sync.
+        // materialize it, then complete geometry sync. Additionally, if a
-        this.updateComplete.then(() => this.__syncFloatingHeader());
+        // real-header filter input was focused when we activated, hand
+        // off to the clone once it exists so the user keeps typing in
+        // the visible (floating) input.
+        this.updateComplete.then(() => {
+          this.__syncFloatingHeader();
+          this.__transferFocusToFloatingHeader();
+        });
         return;
       }
     }
@@ -1127,6 +1284,10 @@ export class DeesTable<T> extends DeesElement {
   public async disconnectedCallback() {
     super.disconnectedCallback();
     this.teardownFloatingHeader();
+    if (this.__flashClearTimer) {
+      clearTimeout(this.__flashClearTimer);
+      this.__flashClearTimer = undefined;
+    }
   }
 
   public async firstUpdated() {
@@ -1134,9 +1295,141 @@ export class DeesTable<T> extends DeesElement {
     // table markup actually exists (it only renders when data.length > 0).
   }
 
+  /**
+   * Runs before each render. Drives two independent concerns:
+   *
+   * 1. **Selection rebind** — when `data` is reassigned to a fresh array
+   *    (typical live-data pattern), `selectedDataRow` still points at the
+   *    stale row object from the old array. We re-resolve it by rowKey so
+   *    consumers of `selectedDataRow` (footer indicator, header/footer
+   *    actions, copy fallback) see the live reference. `selectedIds`,
+   *    `__focusedCell`, `__editingCell`, `__selectionAnchorId` are all
+   *    keyed by string rowId and persist automatically — no change needed.
+   *    This runs regardless of `highlightUpdates` — it is a baseline
+   *    correctness fix for live data.
+   *
+   * 2. **Flash diff** — when `highlightUpdates === 'flash'`, diff the new
+   *    data against `__prevSnapshot` and populate `__flashingCells` with
+   *    the (rowId, colKey) pairs whose resolved cell value changed. A
+   *    single shared timer clears `__flashingCells` after
+   *    `highlightDuration` ms. Skipped if `rowKey` is missing (with a
+   *    one-shot console.warn; the render surface also shows a warning
+   *    banner).
+   */
+  public willUpdate(changedProperties: Map<string | number | symbol, unknown>): void {
+    // --- Phase 1: selection rebind (always runs) ---
+    if (changedProperties.has('data') && this.selectedDataRow && this.rowKey) {
+      const prevId = this.getRowId(this.selectedDataRow);
+      let found: T | undefined;
+      for (const row of this.data) {
+        if (this.getRowId(row) === prevId) {
+          found = row;
+          break;
+        }
+      }
+      if (found) {
+        if (found !== this.selectedDataRow) this.selectedDataRow = found;
+      } else {
+        this.selectedDataRow = undefined as unknown as T;
+      }
+    }
+
+    // --- Phase 2: flash diff ---
+    if (this.highlightUpdates !== 'flash') {
+      // Mode was toggled off (or never on) — drop any lingering state so
+      // re-enabling later starts with a clean slate.
+      if (this.__prevSnapshot || this.__flashingCells.size > 0) {
+        this.__prevSnapshot = undefined;
+        if (this.__flashingCells.size > 0) this.__flashingCells = new Map();
+        if (this.__flashClearTimer) {
+          clearTimeout(this.__flashClearTimer);
+          this.__flashClearTimer = undefined;
+        }
+      }
+      return;
+    }
+    if (!this.rowKey) {
+      if (!this.__flashWarnedNoRowKey) {
+        this.__flashWarnedNoRowKey = true;
+        console.warn(
+          '[dees-table] highlightUpdates="flash" requires `rowKey` to be set. Flash is disabled. ' +
+          'Set the rowKey property/attribute to a stable identifier on your row data (e.g. `rowKey="id"`).'
+        );
+      }
+      return;
+    }
+    if (!changedProperties.has('data')) return;
+
+    const effectiveColumns = this.__getEffectiveColumns();
+    const visibleCols = effectiveColumns.filter((c) => !c.hidden);
+    const nextSnapshot = new Map<string, Map<string, unknown>>();
+    const newlyFlashing = new Map<string, Set<string>>();
+
+    for (const row of this.data) {
+      const rowId = this.getRowId(row);
+      const cellMap = new Map<string, unknown>();
+      for (const col of visibleCols) {
+        cellMap.set(String(col.key), getCellValueFn(row, col, this.displayFunction));
+      }
+      nextSnapshot.set(rowId, cellMap);
+
+      const prevCells = this.__prevSnapshot?.get(rowId);
+      if (!prevCells) continue; // new row — not an "update"
+      for (const [colKey, nextVal] of cellMap) {
+        if (prevCells.get(colKey) !== nextVal) {
+          // Don't flash the cell the user is actively editing.
+          if (
+            this.__editingCell &&
+            this.__editingCell.rowId === rowId &&
+            this.__editingCell.colKey === colKey
+          ) continue;
+          let set = newlyFlashing.get(rowId);
+          if (!set) {
+            set = new Set();
+            newlyFlashing.set(rowId, set);
+          }
+          set.add(colKey);
+        }
+      }
+    }
+
+    const hadPrev = !!this.__prevSnapshot;
+    this.__prevSnapshot = nextSnapshot;
+    if (!hadPrev) return; // first time seeing data — no flashes
+
+    if (newlyFlashing.size === 0) return;
+
+    // Merge with any in-flight flashes from a rapid second update so a cell
+    // that changes twice before its animation ends gets a single clean
+    // restart (via __flashTick / directives.keyed) instead of stacking.
+    for (const [rowId, cols] of newlyFlashing) {
+      const existing = this.__flashingCells.get(rowId);
+      if (existing) {
+        for (const c of cols) existing.add(c);
+      } else {
+        this.__flashingCells.set(rowId, cols);
+      }
+    }
+    this.__flashTick++;
+    // Reactivity nudge: we've mutated the Map in place, so give Lit a fresh
+    // reference so the @state change fires for render.
+    this.__flashingCells = new Map(this.__flashingCells);
+    if (this.__flashClearTimer) clearTimeout(this.__flashClearTimer);
+    this.__flashClearTimer = setTimeout(() => {
+      this.__flashingCells = new Map();
+      this.__flashClearTimer = undefined;
+    }, Math.max(0, this.highlightDuration));
+  }
+
   public async updated(changedProperties: Map<string | number | symbol, unknown>): Promise<void> {
     super.updated(changedProperties);
 
+    // Feed highlightDuration into the CSS variable so JS and CSS stay in
+    // sync via a single source of truth.
+    if (changedProperties.has('highlightDuration')) {
+      this.style.setProperty('--dees-table-flash-duration', `${this.highlightDuration}ms`);
+    }
+
     // Only re-measure column widths when the data or schema actually changed
     // (or on first paint). `determineColumnWidths` is the single biggest
     // first-paint cost — it forces multiple layout flushes per row.
@@ -2090,6 +2383,10 @@ export class DeesTable<T> extends DeesElement {
     }
     if (parsed !== oldValue) {
       (item as any)[col.key] = parsed;
+      // Keep the flash-diff snapshot in sync so the next external update
+      // does not see this user edit as an external change (which would
+      // otherwise flash the cell the user just typed into).
+      this.__recordCellInSnapshot(item, col);
       this.dispatchEvent(
         new CustomEvent('cellEdit', {
           detail: { row: item, key, oldValue, newValue: parsed },
@@ -2103,6 +2400,24 @@ export class DeesTable<T> extends DeesElement {
     this.requestUpdate();
   }
 
+  /**
+   * Updates the flash diff snapshot for a single cell to match its current
+   * resolved value. Called from `commitCellEdit` so a user-initiated edit
+   * does not register as an external change on the next diff pass.
+   * No-op when flash mode is off or no snapshot exists yet.
+   */
+  private __recordCellInSnapshot(item: T, col: Column<T>): void {
+    if (this.highlightUpdates !== 'flash' || !this.__prevSnapshot) return;
+    if (!this.rowKey) return;
+    const rowId = this.getRowId(item);
+    let cellMap = this.__prevSnapshot.get(rowId);
+    if (!cellMap) {
+      cellMap = new Map();
+      this.__prevSnapshot.set(rowId, cellMap);
+    }
+    cellMap.set(String(col.key), getCellValueFn(item, col, this.displayFunction));
+  }
+
   /** Renders the appropriate dees-input-* component for this column. */
   private renderCellEditor(item: T, col: Column<T>): TemplateResult {
     const raw = (item as any)[col.key];

ts_web/elements/00group-dataview/dees-table/styles.ts

@@ -373,6 +373,72 @@ export const tableStyles: CSSResult[] = [
         line-height: 24px;
       }
 
+      /* ---- Cell flash highlighting (opt-in via highlight-updates="flash") ----
+         Bloomberg/TradingView-style: the text itself briefly takes an accent
+         color then fades back to the default. No background tint, no layout
+         shift, no weight change. Readable, modern, subtle.
+         Consumers can override per instance:
+           dees-table#myTable { --dees-table-flash-color: hsl(142 76% 40%); }
+      */
+      :host {
+        --dees-table-flash-color: ${cssManager.bdTheme(
+          'hsl(32 95% 44%)',
+          'hsl(45 93% 62%)'
+        )};
+        --dees-table-flash-easing: cubic-bezier(0.22, 0.61, 0.36, 1);
+      }
+
+      .innerCellContainer.flashing {
+        animation: dees-table-cell-flash
+                   var(--dees-table-flash-duration, 900ms)
+                   var(--dees-table-flash-easing);
+      }
+
+      /* Hold the accent color briefly, then fade back to the theme's default
+         text color. Inherits to child text and to SVG icons that use
+         currentColor. Cells with explicit color overrides in renderers are
+         intentionally unaffected. */
+      @keyframes dees-table-cell-flash {
+        0%,
+        35% { color: var(--dees-table-flash-color); }
+        100% { color: var(--dees-color-text-primary); }
+      }
+
+      @media (prefers-reduced-motion: reduce) {
+        .innerCellContainer.flashing {
+          animation: none;
+          color: var(--dees-table-flash-color);
+        }
+      }
+
+      /* Dev-time warning banner shown when highlight-updates="flash" but
+         rowKey is missing. Consumers should never ship this to production. */
+      .flashConfigWarning {
+        display: flex;
+        align-items: center;
+        gap: 8px;
+        margin: 8px 16px 0;
+        padding: 8px 12px;
+        border-left: 3px solid ${cssManager.bdTheme('hsl(38 92% 50%)', 'hsl(48 96% 63%)')};
+        background: ${cssManager.bdTheme('hsl(48 96% 89% / 0.6)', 'hsl(48 96% 30% / 0.15)')};
+        color: ${cssManager.bdTheme('hsl(32 81% 29%)', 'hsl(48 96% 80%)')};
+        font-size: 12px;
+        line-height: 1.4;
+        border-radius: 4px;
+      }
+      .flashConfigWarning dees-icon {
+        width: 14px;
+        height: 14px;
+        flex: 0 0 auto;
+      }
+      .flashConfigWarning code {
+        padding: 1px 4px;
+        border-radius: 3px;
+        background: ${cssManager.bdTheme('hsl(0 0% 100% / 0.6)', 'hsl(0 0% 0% / 0.3)')};
+        font-family: ${cssGeistFontFamily};
+        font-size: 11px;
+      }
+
       /* Editable cell affordances */
       td.editable {
         cursor: text;