fix(chat): stabilize Facebook keyboard fallback

src/app/chat/hooks/__tests__/chat-keyboard-geometry.test.ts

@@ -9,6 +9,7 @@ import {
 
 const baseline: ChatKeyboardViewportBaseline = {
   layoutHeight: 800,
+  layoutWidth: 390,
   visualHeight: 760,
 };
 
@@ -82,9 +83,42 @@ describe("resolveChatKeyboardInset", () => {
 });
 
 describe("resolveChatKeyboardFallbackInset", () => {
-  it("scales with viewport height and remains bounded", () => {
-    expect(resolveChatKeyboardFallbackInset(500)).toBe(276);
-    expect(resolveChatKeyboardFallbackInset(800)).toBe(352);
-    expect(resolveChatKeyboardFallbackInset(1_200)).toBe(396);
+  it.each([
+    [{ layoutWidth: 320, layoutHeight: 568 }, 256],
+    [{ layoutWidth: 360, layoutHeight: 640 }, 285],
+    [{ layoutWidth: 390, layoutHeight: 844 }, 316],
+    [{ layoutWidth: 430, layoutHeight: 932 }, 347],
+  ])("fits common viewport %o", (viewport, expectedInset) => {
+    expect(resolveChatKeyboardFallbackInset(viewport)).toBe(expectedInset);
+  });
+
+  it("stays stable across tall viewports with the same width", () => {
+    expect(
+      resolveChatKeyboardFallbackInset({
+        layoutWidth: 390,
+        layoutHeight: 760,
+      }),
+    ).toBe(316);
+    expect(
+      resolveChatKeyboardFallbackInset({
+        layoutWidth: 390,
+        layoutHeight: 900,
+      }),
+    ).toBe(316);
+  });
+
+  it("keeps the keyboard estimate within its bounds", () => {
+    expect(
+      resolveChatKeyboardFallbackInset({
+        layoutWidth: 300,
+        layoutHeight: 400,
+      }),
+    ).toBe(256);
+    expect(
+      resolveChatKeyboardFallbackInset({
+        layoutWidth: 600,
+        layoutHeight: 1_000,
+      }),
+    ).toBe(356);
   });
 });

src/app/chat/hooks/__tests__/use-chat-keyboard-avoidance.test.tsx

@@ -44,6 +44,7 @@ describe("useChatKeyboardAvoidance", () => {
   let visualViewport: MockVisualViewport;
   let virtualKeyboard: MockVirtualKeyboard;
   let innerHeight: number;
+  let innerWidth: number;
 
   beforeEach(() => {
     vi.useFakeTimers();
@@ -52,12 +53,17 @@ describe("useChatKeyboardAvoidance", () => {
     vi.mocked(BrowserDetector.isFacebookInAppBrowser).mockReturnValue(true);
     vi.mocked(PlatformDetector.isAndroid).mockReturnValue(true);
     innerHeight = 800;
+    innerWidth = 390;
     visualViewport = new MockVisualViewport();
     virtualKeyboard = new MockVirtualKeyboard();
     Object.defineProperty(window, "innerHeight", {
       configurable: true,
       get: () => innerHeight,
     });
+    Object.defineProperty(window, "innerWidth", {
+      configurable: true,
+      get: () => innerWidth,
+    });
     Object.defineProperty(window, "visualViewport", {
       configurable: true,
       value: visualViewport,
@@ -89,16 +95,16 @@ describe("useChatKeyboardAvoidance", () => {
     vi.unstubAllGlobals();
   });
 
-  it("uses a one-shot Facebook fallback after 250ms without polling", () => {
+  it("uses a one-shot Facebook fallback after 150ms without polling", () => {
     const intervalSpy = vi.spyOn(window, "setInterval");
     renderHarness(root, false);
     renderHarness(root, true);
 
-    act(() => vi.advanceTimersByTime(249));
+    act(() => vi.advanceTimersByTime(149));
     expect(getBottomInset(container)).toBe("");
 
     act(() => vi.advanceTimersByTime(1));
-    expect(getBottomInset(container)).toBe("352px");
+    expect(getBottomInset(container)).toBe("316px");
     expect(intervalSpy).not.toHaveBeenCalled();
   });
 
@@ -112,7 +118,7 @@ describe("useChatKeyboardAvoidance", () => {
     act(() => {
       visualViewport.dispatchEvent(new Event("resize"));
       virtualKeyboard.dispatchEvent(new Event("geometrychange"));
-      vi.advanceTimersByTime(250);
+      vi.advanceTimersByTime(150);
     });
 
     expect(getBottomInset(container)).toBe("");
@@ -126,7 +132,7 @@ describe("useChatKeyboardAvoidance", () => {
     visualViewport.height = 460;
     act(() => {
       visualViewport.dispatchEvent(new Event("resize"));
-      vi.advanceTimersByTime(250);
+      vi.advanceTimersByTime(150);
     });
 
     expect(getBottomInset(container)).toBe("");
@@ -172,7 +178,7 @@ describe("useChatKeyboardAvoidance", () => {
     visualViewport.height = 500;
     act(() => {
       window.dispatchEvent(new Event("resize"));
-      vi.advanceTimersByTime(250);
+      vi.advanceTimersByTime(150);
     });
 
     expect(getBottomInset(container)).toBe("0px");
@@ -181,23 +187,23 @@ describe("useChatKeyboardAvoidance", () => {
   it("allows a delayed real viewport signal to replace the fallback", () => {
     renderHarness(root, false);
     renderHarness(root, true);
-    act(() => vi.advanceTimersByTime(250));
-    expect(getBottomInset(container)).toBe("352px");
+    act(() => vi.advanceTimersByTime(150));
+    expect(getBottomInset(container)).toBe("316px");
 
-    visualViewport.height = 460;
+    visualViewport.height = 500;
     act(() => {
       visualViewport.dispatchEvent(new Event("resize"));
       vi.advanceTimersByTime(0);
     });
 
-    expect(getBottomInset(container)).toBe("316px");
+    expect(getBottomInset(container)).toBe("276px");
   });
 
   it("removes the local inset when focus leaves", () => {
     renderHarness(root, false);
     renderHarness(root, true);
-    act(() => vi.advanceTimersByTime(250));
-    expect(getBottomInset(container)).toBe("352px");
+    act(() => vi.advanceTimersByTime(150));
+    expect(getBottomInset(container)).toBe("316px");
 
     renderHarness(root, false);
 

src/app/chat/hooks/chat-keyboard-geometry.ts

@@ -1,17 +1,24 @@
 export const CHAT_KEYBOARD_VISIBLE_THRESHOLD_PX = 80;
 export const CHAT_KEYBOARD_ZOOM_THRESHOLD = 1.05;
 export const CHAT_KEYBOARD_TARGET_GAP_PX = 16;
-export const CHAT_KEYBOARD_FALLBACK_RATIO = 0.42;
-export const CHAT_KEYBOARD_FALLBACK_MIN_PX = 260;
-export const CHAT_KEYBOARD_FALLBACK_MAX_PX = 380;
+export const CHAT_KEYBOARD_FALLBACK_WIDTH_RATIO = 0.77;
+export const CHAT_KEYBOARD_FALLBACK_HEIGHT_RATIO = 0.42;
+export const CHAT_KEYBOARD_FALLBACK_MIN_PX = 240;
+export const CHAT_KEYBOARD_FALLBACK_MAX_PX = 340;
 
 const CHAT_KEYBOARD_MAX_INSET_RATIO = 0.55;
 
 export interface ChatKeyboardViewportBaseline {
   layoutHeight: number;
+  layoutWidth: number;
   visualHeight: number;
 }
 
+export type ChatKeyboardFallbackViewport = Pick<
+  ChatKeyboardViewportBaseline,
+  "layoutHeight" | "layoutWidth"
+>;
+
 export interface ChatKeyboardViewportSnapshot {
   layoutHeight: number;
   visualHeight: number;
@@ -80,13 +87,17 @@ export function resolveChatKeyboardInset(
 }
 
 export function resolveChatKeyboardFallbackInset(
-  layoutHeight: number,
+  viewport: ChatKeyboardFallbackViewport,
 ): number {
+  const widthEstimate =
+    viewport.layoutWidth * CHAT_KEYBOARD_FALLBACK_WIDTH_RATIO;
+  const heightLimit =
+    viewport.layoutHeight * CHAT_KEYBOARD_FALLBACK_HEIGHT_RATIO;
   const estimatedKeyboardHeight = Math.min(
     CHAT_KEYBOARD_FALLBACK_MAX_PX,
     Math.max(
       CHAT_KEYBOARD_FALLBACK_MIN_PX,
-      Math.round(layoutHeight * CHAT_KEYBOARD_FALLBACK_RATIO),
+      Math.round(Math.min(widthEstimate, heightLimit)),
     ),
   );
 

src/app/chat/hooks/use-chat-keyboard-avoidance.ts

@@ -196,7 +196,7 @@ export function useChatKeyboardAvoidance({
       }
       fallbackApplied = true;
       applyBottomInset(
-        resolveChatKeyboardFallbackInset(baseline.layoutHeight),
+        resolveChatKeyboardFallbackInset(baseline),
         "fallback",
       );
     }, CHAT_KEYBOARD_FALLBACK_DELAY_MS);
@@ -221,6 +221,7 @@ export function useChatKeyboardAvoidance({
 function readViewportBaseline(): ChatKeyboardViewportBaseline {
   return {
     layoutHeight: window.innerHeight,
+    layoutWidth: window.innerWidth,
     visualHeight: window.visualViewport?.height ?? window.innerHeight,
   };
 }