fix(react-core): preserve cache across layout toggles and reject zero-width entries

Self-inflicted resizes (compact↔expanded) were clearing the cache before
the ignoreResizeRef guard, forcing a full re-measurement on the very next
keystroke. Move the guard ahead of invalidation so layout toggles keep the
cache warm — container dimensions don't change during these transitions.

Also reject compactWidth <= 0 from being cached, preventing a zero-width
entry from silently disabling text-width expansion until the next resize.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

Author: mxmzb

packages/react-core/src/v2/components/chat/CopilotChatInput.tsx

@@ -706,6 +706,8 @@ export function CopilotChatInput({
       0,
     );
 
+    if (compactWidth <= 0) return null;
+
     const result = { compactWidth };
     containerCacheRef.current = result;
     return result;
@@ -857,15 +859,17 @@ export function CopilotChatInput({
     ]);
 
     const scheduleEvaluation = (invalidateCache: boolean) => {
-      if (invalidateCache) {
-        containerCacheRef.current = null;
-      }
-
       if (ignoreResizeRef.current) {
         ignoreResizeRef.current = false;
+        // Self-inflicted resize from a layout toggle — container dimensions
+        // are unchanged, so keep the cache warm.
         return;
       }
 
+      if (invalidateCache) {
+        containerCacheRef.current = null;
+      }
+
       if (typeof window === "undefined") {
         evaluateLayout();
         return;

packages/react-core/src/v2/components/chat/__tests__/CopilotChatInput.test.tsx

@@ -1462,7 +1462,7 @@ describe("CopilotChatInput", () => {
       expect(addRectSpy).toHaveBeenCalled();
     });
 
-    it("invalidates cache but skips re-evaluation during layout toggle (ignoreResizeRef path)", async () => {
+    it("keeps cache warm during layout toggle (ignoreResizeRef path)", async () => {
       const { container } = renderWithProvider(
         <CopilotChatInput onSubmitMessage={mockOnSubmitMessage} />,
       );
@@ -1487,10 +1487,10 @@ describe("CopilotChatInput", () => {
       });
 
       // Simulate observer firing from the layout toggle.
-      // The guard consumes ignoreResizeRef; cache is invalidated but no re-eval loop.
+      // Self-inflicted resize: ignoreResizeRef is consumed, cache stays warm.
       triggerAllResizeObservers();
 
-      // Go back to short text — cache was invalidated, so updateContainerCache must rebuild.
+      // Go back to short text — cache should still be warm from before the toggle.
       const grid = container.querySelector("div.cpk\\:grid") as HTMLElement;
       const addContainer = grid.children[0] as HTMLElement;
       const addRectSpy = vi.fn(
@@ -1508,8 +1508,8 @@ describe("CopilotChatInput", () => {
         );
       });
 
-      // Confirms cache was invalidated (needed getBoundingClientRect to rebuild)
-      expect(addRectSpy).toHaveBeenCalled();
+      // Cache was NOT invalidated — no getBoundingClientRect needed
+      expect(addRectSpy).not.toHaveBeenCalled();
     });
   });