Remove the drag-right-to-go-back gesture

The screen no longer follows a horizontal drag. Back is the arrow at the
top left and the platform's own edge gesture, both unchanged.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>

app/androidApp/src/main/kotlin/com/example/aiapp/AppRoot.kt

@@ -198,21 +198,17 @@ fun AppRoot(
             // row key. Only reachable since a notification can move straight from one session to
             // another; every other way here passes through [Screen.Main], which disposes it anyway.
             key(here.summary.id) {
-                // The gesture goes on a box around the screen rather than inside it, so it is the
-                // outermost thing in the tree and everything within has already had its chance at
-                // the drag. See [swipeBack]. No imePadding here, for the reason above.
-                Box(Modifier.swipeBack(goToMain)) {
-                    SessionScreen(
-                        settings = current,
-                        summary = here.summary,
-                        onBack = goToMain,
-                        share = share,
-                        onShareTaken = { share = null },
-                    )
-                }
+                // No imePadding here, for the reason above.
+                SessionScreen(
+                    settings = current,
+                    summary = here.summary,
+                    onBack = goToMain,
+                    share = share,
+                    onShareTaken = { share = null },
+                )
             }
         is Screen.Spawn ->
-            Box(Modifier.imePadding().swipeBack(goToMain)) {
+            Box(Modifier.imePadding()) {
                 SpawnScreen(
                     settings = current,
                     onSpawned = { spawned ->
@@ -223,7 +219,7 @@ fun AppRoot(
                 )
             }
         is Screen.Settings ->
-            Box(Modifier.imePadding().swipeBack(goToMain)) {
+            Box(Modifier.imePadding()) {
                 SettingsScreen(
                     existing = current,
                     onSaved = { saved ->

app/androidApp/src/main/kotlin/com/example/aiapp/SwipeBack.kt

@@ -1,70 +0,0 @@
-package com.example.aiapp
-
-import androidx.compose.animation.core.Animatable
-import androidx.compose.foundation.gestures.Orientation
-import androidx.compose.foundation.gestures.draggable
-import androidx.compose.foundation.gestures.rememberDraggableState
-import androidx.compose.runtime.Composable
-import androidx.compose.runtime.remember
-import androidx.compose.runtime.rememberCoroutineScope
-import androidx.compose.ui.Modifier
-import androidx.compose.ui.graphics.graphicsLayer
-import androidx.compose.ui.platform.LocalDensity
-import androidx.compose.ui.unit.Dp
-import androidx.compose.ui.unit.dp
-import kotlinx.coroutines.launch
-
-/**
- * Dragging the screen to the right to step back to the one behind it.
- *
- * The platform's own back gesture is a swipe from the very edge, and only from there; on a phone
- * held in one hand the way back from a session is either that narrow strip or the arrow at the top
- * left, which is the far corner from the thumb. This is the same movement from anywhere on the
- * screen.
- *
- * **It loses every argument.** The gesture is a plain horizontal [draggable] on the outside of the
- * screen, so anything inside that wants horizontal drags has already taken them by the time this
- * would see them: pointer events reach the innermost node first, and a drag a child has consumed
- * never crosses this modifier's touch slop. That is what keeps a wide code fence, a table scrolled
- * sideways or a text selection working -- they are the components the reader meant, and this is
- * only what is left over. Vertical drags are not its orientation, so the transcript scrolls
- * untouched.
- *
- * The screen follows the finger rather than jumping at the end, because a gesture with no feedback
- * cannot be aborted: the reader has to be able to see it starting and change their mind. Released
- * short of [SWIPE_BACK_TRAVEL] it slides back and nothing happens. Right rather than left, and only
- * right, since there is nothing forward of these screens to go to.
- */
-@Composable
-fun Modifier.swipeBack(onBack: () -> Unit): Modifier {
-    val offset = remember { Animatable(0f) }
-    val scope = rememberCoroutineScope()
-    val travel = with(LocalDensity.current) { SWIPE_BACK_TRAVEL.toPx() }
-    return draggable(
-            state =
-                rememberDraggableState { delta ->
-                    // Rightward only: a leftward drag stays at zero rather than lifting the
-                    // screen off its left edge, which would look like a gesture that does
-                    // something and does not.
-                    scope.launch { offset.snapTo((offset.value + delta).coerceAtLeast(0f)) }
-                },
-            orientation = Orientation.Horizontal,
-            onDragStopped = {
-                if (offset.value >= travel) {
-                    onBack()
-                    // Straight back rather than animated: the screen this was moving is being
-                    // replaced, and animating it home first would show the old one sliding back
-                    // into place after the new one had arrived.
-                    offset.snapTo(0f)
-                } else {
-                    offset.animateTo(0f)
-                }
-            },
-        )
-        // Read inside the block, so following the finger is a draw-phase change and costs no
-        // recomposition of the screen being dragged.
-        .graphicsLayer { translationX = offset.value }
-}
-
-/** How far the screen has to be pulled for letting go to mean "back" rather than "never mind". */
-private val SWIPE_BACK_TRAVEL: Dp = 96.dp