Implement fit-mode rendering contract with container sizing and pane re-fit

src/app/services/chart-renderer.ts

@@ -14,6 +14,17 @@ import type { Config } from 'vega-lite';
 export interface RenderHandle {
   /** Finalize the underlying Vega view and clear the node. */
   destroy(): void;
+  /**
+   * Re-fit the chart to its container's current size (spec §04 Responsiveness).
+   *
+   * Vega-Lite compiles `"container"` sizing to width/height signals that re-read
+   * `containerSize()` ONLY on a `window:resize` event (nothing observes the
+   * element, and `view.resize()` alone re-runs layout with the stale size). So a
+   * pane drag — which fires no window resize — needs us to synthesize that event.
+   * Doing it this way also means only the container-bound dimensions re-fit
+   * (fixed ones have no such handler), which is exactly right for Width/Height.
+   */
+  resize(): void;
 }
 
 /** Embed a prepared spec into `node`. Non-negotiable: no actions menu, SVG output. */
@@ -33,5 +44,12 @@ export async function renderSpec(
       result.view.finalize();
       node.replaceChildren();
     },
+    resize() {
+      // Synthesize the window:resize the container signals listen for (see the
+      // interface doc). The view re-reads containerSize() and re-renders itself;
+      // a finalized view has already removed its listener, so this is a safe
+      // no-op after destroy().
+      if (typeof window !== 'undefined') window.dispatchEvent(new Event('resize'));
+    },
   };
 }