Only absorb blank space when fully visible on keyboard open

Fix Android keyboard close/open asymmetry and apply binary blank absorption

Two changes to the Android useChatKeyboard hook:

1. Apply the same binary blank absorption from the iOS fix: only absorb
   blank space when fully visible (visibleFraction >= 1), otherwise
   shift content by the full keyboard amount. Previously Android used
   linear scaling which caused partial occlusion when blank was
   partially visible.

2. Fix close animation overshooting on non-inverted lists. The close
   path was computing the theoretical scroll displacement (keyboard
   height minus blank absorption) to undo the open shift. But when
   the open shift was clamped by maxScroll, the theoretical value
   exceeded the actual shift, causing close to move content down
   more than open moved it up.

   Record the actual scroll displacement at the end of the open
   animation (scroll.value - offsetBeforeScroll) and use that for
   the close calculation. This makes open/close symmetric regardless
   of clamping.

Author: trcoffman

src/components/KeyboardChatScrollView/useChatKeyboard/__tests__/blankSize.ios.spec.ts

@@ -133,10 +133,10 @@ describe("blankSize — iOS inverted + always", () => {
 });
 
 describe("blankSize — iOS persistent behavior", () => {
-  it("full absorption on close: uses actualTotalPadding for snap", () => {
+  it("partial visibility on close: uses actualTotalPadding for snap", () => {
     // Scroll near end so blank is partially visible
     // (pastContentEnd = 1000+800-1500 = 300, fraction = 300/500 = 0.6)
-    // blankAbsorbed = 500*0.6 = 300, scrollEff = max(0, 300-300) = 0 → full absorption
+    // Partial visibility → no absorption → content shifts normally
     mockSize.value = { width: 390, height: 1500 };
     mockOffset.value = 1000;
     const { result } = render({
@@ -145,9 +145,11 @@ describe("blankSize — iOS persistent behavior", () => {
       blankSize: sv(500),
     });
 
-    // Open keyboard — fully absorbed, position preserved
+    // Open keyboard — partial visibility, no absorption, content shifts
+    // computeIOSContentOffset(1000, 300, 1500, 800, false, 500)
+    //   maxScroll = max(1500-800+500, 0) = 1200 → min(1300, 1200) = 1200
     handlers.onStart({ height: KEYBOARD });
-    expect(result.current.contentOffsetY!.value).toBe(1000);
+    expect(result.current.contentOffsetY!.value).toBe(1200);
 
     // Close keyboard — persistent + at end → snap using actualTotalPadding
     handlers.onStart({ height: 0 });
@@ -189,10 +191,10 @@ describe("blankSize — iOS never behavior", () => {
 });
 
 describe("blankSize — iOS whenAtEnd behavior", () => {
-  it("full absorption prevents shift even when at end", () => {
+  it("partial visibility shifts content normally when at end", () => {
     // Scroll near end so blank is partially visible
     // (pastContentEnd = 1000+800-1500 = 300, fraction = 300/500 = 0.6)
-    // blankAbsorbed = 500*0.6 = 300, scrollEff = max(0, 300-300) = 0 → full absorption
+    // Partial visibility → no absorption → content shifts normally
     mockSize.value = { width: 390, height: 1500 };
     mockOffset.value = 1000;
     const { result } = render({
@@ -204,7 +206,9 @@ describe("blankSize — iOS whenAtEnd behavior", () => {
     handlers.onStart({ height: KEYBOARD });
 
     expect(result.current.padding.value).toBe(KEYBOARD);
-    // blankAbsorbed=300, scrollEff=0 → contentOffsetY = scroll.value
-    expect(result.current.contentOffsetY!.value).toBe(1000);
+    // blankAbsorbed=0 (partial visibility), scrollEff=300
+    // computeIOSContentOffset(1000, 300, 1500, 800, false, 500)
+    //   maxScroll = 1200 → min(1300, 1200) = 1200
+    expect(result.current.contentOffsetY!.value).toBe(1200);
   });
 });

src/components/KeyboardChatScrollView/useChatKeyboard/index.ios.ts

@@ -96,8 +96,9 @@ function useChatKeyboard(
           inverted,
         );
         const blankAbsorbed =
-          getBlankAbsorbed(blankSize.value, extraContentPadding.value) *
-          visibleFraction;
+          visibleFraction >= 1
+            ? getBlankAbsorbed(blankSize.value, extraContentPadding.value)
+            : 0;
         const scrollEff = getScrollEffective(effective, blankAbsorbed);
         const actualTotalPadding = Math.max(
           blankSize.value,

src/components/KeyboardChatScrollView/useChatKeyboard/index.ts

@@ -49,6 +49,7 @@ function useChatKeyboard(
   const targetKeyboardHeight = useSharedValue(0);
   const closing = useSharedValue(false);
   const blankFractionOnOpen = useSharedValue(0);
+  const actualOpenShift = useSharedValue(0);
   const {
     layout,
     size,
@@ -116,8 +117,9 @@ function useChatKeyboard(
           inverted,
         );
         const blankAbsorbed =
-          getBlankAbsorbed(blankSize.value, extraContentPadding.value) *
-          visibleFraction;
+          visibleFraction >= 1
+            ? getBlankAbsorbed(blankSize.value, extraContentPadding.value)
+            : 0;
         const scrollEff = getScrollEffective(effective, blankAbsorbed);
 
         if (inverted && e.duration === -1) {
@@ -127,7 +129,7 @@ function useChatKeyboard(
           return;
         } else if (e.height > 0) {
           // Android: keyboard opening — set padding + capture scroll position
-          blankFractionOnOpen.value = visibleFraction;
+          blankFractionOnOpen.value = visibleFraction >= 1 ? 1 : 0;
           padding.value = effective;
           offsetBeforeScroll.value = scroll.value;
 
@@ -148,17 +150,9 @@ function useChatKeyboard(
           } else {
             // Preserve "whenAtEnd" sentinel: if open didn't shift, close shouldn't either
             if (offsetBeforeScroll.value !== -1) {
-              // Non-inverted: undo only the actual scroll displacement
-              // (accounting for blank absorption at open time)
-              const prevBlankAbsorbed =
-                getBlankAbsorbed(blankSize.value, extraContentPadding.value) *
-                blankFractionOnOpen.value;
-              const prevScrollEff = getScrollEffective(
-                padding.value,
-                prevBlankAbsorbed,
-              );
-
-              offsetBeforeScroll.value = scroll.value - prevScrollEff;
+              // Use the actual displacement recorded at end of open animation
+              // (not the theoretical value) so close is symmetric with open
+              offsetBeforeScroll.value = scroll.value - actualOpenShift.value;
             }
           }
         }
@@ -319,6 +313,11 @@ function useChatKeyboard(
           );
 
           scrollTo(scrollViewRef, 0, target, false);
+
+          // Track actual (clamped) displacement during open for symmetric close
+          if (!closing.value) {
+            actualOpenShift.value = target - offsetBeforeScroll.value;
+          }
         }
       },
       onEnd: (e) => {
@@ -335,6 +334,11 @@ function useChatKeyboard(
         );
 
         padding.value = effective;
+
+        // Record actual scroll displacement so close can be symmetric
+        if (effective > 0 && offsetBeforeScroll.value !== -1) {
+          actualOpenShift.value = scroll.value - offsetBeforeScroll.value;
+        }
       },
     },
     [inverted, keyboardLiftBehavior, freeze, offset],