feat(base): extend inline embed scroll viewport leftward, anchor first cell with grid padding

Bring back the leftward extension via negative margin-left so the
scroll viewport reaches AppShell.Main's left edge, then offset the
.grid with padding-left = extendLeft so the first cell still lines
up with page-content on load. The extended area becomes scrollable
empty space the user can pan into — same shape as Notion's inline
databases.

Done with one new CSS var (--embed-grid-pad-left) consumed by the
.grid in grid.module.css. Standalone full-page bases never set the
var, so it's a no-op there.

apps/client/src/features/base/components/base-table.tsx

@@ -315,14 +315,16 @@ export function BaseTable({ pageId, embedded }: BaseTableProps) {
   if (!base) return null;
 
   // When embedded inline in a doc page, the parent <NodeViewWrapper>
-  // exposes --embed-extend-r (positive px). We pull the grid's right
-  // edge outward via negative margin-right — box-model: width: auto
-  // becomes parent_width + |margin|, so the box physically grows past
-  // its parent's bounds. Left edge stays at the wrapper's natural
-  // (page-content) position so the table aligns with page text on
-  // load. Toolbar is unchanged.
+  // exposes --embed-extend-l / --embed-extend-r (positive px). We
+  // pull both edges outward via negative margin so the scroll viewport
+  // grows toward AppShell.Main's edges. Initial visual alignment with
+  // page text is preserved by --embed-grid-pad-left, applied to the
+  // .grid in grid.module.css — that padding makes the first cell sit
+  // at page-content-left on load while still letting the user pan
+  // left into the extended viewport. Toolbar is unchanged.
   const gridExtendStyle = embedded
     ? ({
+        marginLeft: "calc(-1 * var(--embed-extend-l, 0px))",
         marginRight: "calc(-1 * var(--embed-extend-r, 0px))",
       } as const)
     : undefined;

apps/client/src/features/base/styles/grid.module.css

@@ -13,6 +13,12 @@
   border: 1px solid
     light-dark(var(--mantine-color-gray-2), var(--mantine-color-dark-4));
   border-radius: var(--mantine-radius-sm);
+  /* When the embed wrapper extends the scroll viewport leftward, this
+   * padding pushes the first cell back to page-content alignment so
+   * the table looks aligned on load. The padded area is part of the
+   * scrollable region — the user can pan left into it. Standalone
+   * full-page bases never set the var, so it's a no-op there. */
+  padding-left: var(--embed-grid-pad-left, 0);
 }
 
 .headerRow {

apps/client/src/features/editor/components/base-embed/base-embed-view.tsx

@@ -6,23 +6,28 @@ import { useBaseQuery } from "@/features/base/queries/base-query";
 
 const SIDE_GUTTER = 8;
 
-// Extend the grid only to the right — toward AppShell.Main's right
-// edge. The left edge stays at the wrapper's natural (page-content)
-// position so the table is visually aligned with the page text on
-// load, matching Notion. Leftward scroll-viewport extension is only
-// meaningful once we add frozen columns that need to lock at the
-// sidebar edge; deferred until then.
+// Extend the scroll viewport on both sides (toward AppShell.Main's
+// edges), but offset the grid content with padding-left = extendLeft
+// so the first cell still lines up with page-content on load. The
+// extra leftward area becomes scrollable empty space the user can
+// pan into — same behavior as Notion's inline databases.
 function applyExtension(wrapper: HTMLDivElement) {
   const rect = wrapper.getBoundingClientRect();
   if (rect.width === 0) return;
 
   const main = wrapper.closest("main") as HTMLElement | null;
-  const targetRight = main
-    ? main.getBoundingClientRect().right - SIDE_GUTTER
+  const mainRect = main?.getBoundingClientRect();
+  const targetLeft = (mainRect?.left ?? 0) + SIDE_GUTTER;
+  const targetRight = mainRect
+    ? mainRect.right - SIDE_GUTTER
     : window.innerWidth - SIDE_GUTTER;
 
+  const extendLeft = Math.max(0, rect.left - targetLeft);
   const extendRight = Math.max(0, targetRight - rect.right);
+
+  wrapper.style.setProperty("--embed-extend-l", `${extendLeft}px`);
   wrapper.style.setProperty("--embed-extend-r", `${extendRight}px`);
+  wrapper.style.setProperty("--embed-grid-pad-left", `${extendLeft}px`);
 }
 
 export function BaseEmbedView({ node }: NodeViewProps) {