fix(dashboard): gate mobile scroll-lock to iOS so Android keyboard stays open

The body scroll-lock applied while the keyboard is up in main chat was an
iOS-specific workaround for visualViewport drift. On Android Chrome the same
mutation does the opposite of what we want — applying position:fixed to body
while the soft keyboard is opening causes Chrome to treat it as a focus-
target relayout and dismiss the keyboard instantly, making the main chat
composer unusable on Android.

useMobileScrollLock now early-returns on non-iOS user agents. Android Chrome
doesn't need it: with interactive-widget=resizes-content the layout viewport
shrinks with the keyboard, so there's no drift to compensate for.

Adds an Android-UA test case that asserts the lock is a no-op there.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

.changeset/android-chat-keyboard-dismiss.md

@@ -0,0 +1,9 @@
+---
+"@fusion/dashboard": patch
+---
+
+fix(dashboard): stop ChatView's body scroll-lock from instantly dismissing the Android soft keyboard
+
+The body scroll-lock applied while the keyboard is open in main chat was an iOS-specific workaround for visualViewport drift. On Android Chrome it does the opposite of what we want — mutating `body { position: fixed; ... }` while the keyboard is opening causes Chrome to treat it as a focus-target relayout and immediately dismisses the keyboard, making the main chat composer unusable on Android.
+
+`useMobileScrollLock` is now gated to iOS UAs. Android Chrome doesn't need it (with `interactive-widget=resizes-content` the layout viewport shrinks with the keyboard, so no drift compensation is required).

packages/dashboard/app/hooks/__tests__/useMobileScrollLock.test.ts

@@ -6,6 +6,7 @@ describe("useMobileScrollLock", () => {
   let savedInnerWidth: number;
   let savedMaxTouchPoints: number;
   let savedOntouchstart: typeof window.ontouchstart;
+  let savedUserAgent: string;
   let scrollSpy: ReturnType<typeof vi.fn>;
 
   beforeEach(() => {
@@ -13,6 +14,7 @@ describe("useMobileScrollLock", () => {
     savedInnerWidth = window.innerWidth;
     savedMaxTouchPoints = navigator.maxTouchPoints;
     savedOntouchstart = window.ontouchstart;
+    savedUserAgent = navigator.userAgent;
     document.documentElement.style.cssText = "";
     document.body.style.cssText = "";
     scrollSpy = vi.fn();
@@ -24,6 +26,7 @@ describe("useMobileScrollLock", () => {
     Object.defineProperty(window, "innerWidth", { value: savedInnerWidth, writable: true, configurable: true });
     Object.defineProperty(navigator, "maxTouchPoints", { value: savedMaxTouchPoints, configurable: true });
     Object.defineProperty(window, "ontouchstart", { value: savedOntouchstart, writable: true, configurable: true });
+    Object.defineProperty(navigator, "userAgent", { value: savedUserAgent, configurable: true });
     document.documentElement.style.cssText = "";
     document.body.style.cssText = "";
     _resetLockState();
@@ -33,6 +36,21 @@ describe("useMobileScrollLock", () => {
     (window as unknown as { ontouchstart: unknown }).ontouchstart = null;
     Object.defineProperty(navigator, "maxTouchPoints", { value: 5, configurable: true });
     Object.defineProperty(window, "innerWidth", { value: 375, writable: true, configurable: true });
+    // Hook is iOS-gated; default fixture uses an iPhone UA.
+    Object.defineProperty(navigator, "userAgent", {
+      value: "Mozilla/5.0 (iPhone; CPU iPhone OS 16_0 like Mac OS X) AppleWebKit/605.1.15",
+      configurable: true,
+    });
+  }
+
+  function makeAndroid() {
+    (window as unknown as { ontouchstart: unknown }).ontouchstart = null;
+    Object.defineProperty(navigator, "maxTouchPoints", { value: 5, configurable: true });
+    Object.defineProperty(window, "innerWidth", { value: 388, writable: true, configurable: true });
+    Object.defineProperty(navigator, "userAgent", {
+      value: "Mozilla/5.0 (Linux; Android 13; Pixel 7) AppleWebKit/537.36",
+      configurable: true,
+    });
   }
 
   function makeDesktop() {
@@ -60,6 +78,14 @@ describe("useMobileScrollLock", () => {
     expect(scrollSpy).not.toHaveBeenCalled();
   });
 
+  it("does nothing on Android (avoids dismissing the soft keyboard)", () => {
+    makeAndroid();
+    renderHook(() => useMobileScrollLock(true));
+    expect(document.body.style.position).toBe("");
+    expect(document.documentElement.style.overflow).toBe("");
+    expect(scrollSpy).not.toHaveBeenCalled();
+  });
+
   it("restores prior styles and scroll position on cleanup", () => {
     makeMobile();
     document.body.style.position = "relative";

packages/dashboard/app/hooks/useMobileScrollLock.ts

@@ -8,6 +8,27 @@ function isMobileDevice(): boolean {
   return hasTouchScreen && isNarrow;
 }
 
+/**
+ * The scroll lock is an iOS-specific workaround: iOS Safari shifts the layout
+ * viewport on input focus (visualViewport.offsetTop > 0) which pushes the
+ * dashboard off-screen, so we pin body via position:fixed to make it
+ * unscrollable. Android Chrome does NOT need this — and applying the same
+ * fix there is actively harmful: mutating body styles while the soft keyboard
+ * is opening causes Chrome to treat it as a focus-target relayout and
+ * dismisses the keyboard immediately. So we gate the lock to iOS only.
+ *
+ * With `interactive-widget=resizes-content` set on the viewport meta, Android
+ * Chrome shrinks the layout viewport with the keyboard, so no drift
+ * compensation is needed there.
+ */
+function isIOS(): boolean {
+  if (typeof window === "undefined") return false;
+  const ua = navigator.userAgent || "";
+  // iPad on iPadOS 13+ reports as MacIntel + touch — handle that too.
+  return /iPad|iPhone|iPod/.test(ua)
+    || (ua.includes("Macintosh") && navigator.maxTouchPoints > 1);
+}
+
 /**
  * Reference-counted body scroll lock for fullscreen mobile overlays.
  *
@@ -111,7 +132,7 @@ export function _resetLockState(): void {
  */
 export function useMobileScrollLock(enabled: boolean): void {
   useEffect(() => {
-    if (!enabled || !isMobileDevice()) return;
+    if (!enabled || !isMobileDevice() || !isIOS()) return;
     applyLock();
     return () => {
       releaseLock();