fix(compose): preserve mentions atomically against IME word-recomposition

Microsoft SwiftKey re-enters word-edit mode over a previously-committed
display token after autocorrect-on-space, then issues setComposingText
with a shortened version. Compose's auto-derived offset mapping for
OutputTransformation uses identity inside a wedge, so the IME's
replacement only overwrites the leading characters of the underlying
@npub1... bech32, leaving an orphan tail that no longer matches the
mention regex. The wedge collapses, the orphan bech32 becomes visible,
and the cursor lands in the middle of it. Gboard never enters word-edit
mode for previously-committed tokens, so it doesn't trigger this.

Add MentionPreservingInputTransformation that runs on every input
change and reverts any edit whose original-text range partially
intersects a complete mention without fully covering it. The mention
stays atomic; the IME re-reads the unchanged buffer and moves on.
Wire it into all OutputTransformation-using fields: chats, new note,
group DM, public channel, public message, classifieds, long-form.

https://claude.ai/code/session_01LVmmGa3Npuv2d1eeYm9BdZ

amethyst/src/main/java/com/vitorpamplona/amethyst/ui/actions/MentionPreservingInputTransformation.kt

@@ -0,0 +1,76 @@
+/*
+ * Copyright (c) 2025 Vitor Pamplona
+ *
+ * Permission is hereby granted, free of charge, to any person obtaining a copy of
+ * this software and associated documentation files (the "Software"), to deal in
+ * the Software without restriction, including without limitation the rights to use,
+ * copy, modify, merge, publish, distribute, sublicense, and/or sell copies of the
+ * Software, and to permit persons to whom the Software is furnished to do so,
+ * subject to the following conditions:
+ *
+ * The above copyright notice and this permission notice shall be included in all
+ * copies or substantial portions of the Software.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+ * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY, FITNESS
+ * FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR
+ * COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN
+ * AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION
+ * WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.
+ */
+package com.vitorpamplona.amethyst.ui.actions
+
+import androidx.compose.foundation.text.input.InputTransformation
+import androidx.compose.foundation.text.input.TextFieldBuffer
+
+/**
+ * Rejects any edit that partially modifies a previously-complete Nostr mention
+ * (`@npub1…`, `nostr:npub1…`, `@nprofile1…`, `nostr:nprofile1…`).
+ *
+ * Background: when an `OutputTransformation` collapses an underlying npub into a
+ * short `@DisplayName`, Compose's auto-derived offset mapping uses identity inside
+ * the wedge. Some IMEs — notably Microsoft SwiftKey — re-enter "word edit mode"
+ * over a previously-committed display token after autocorrect-on-space, then issue
+ * `setComposingText` with a shortened version. Because the mapping is identity
+ * inside the wedge, the IME's replacement only overwrites the leading characters
+ * of the underlying bech32, leaving an orphan tail that no longer matches the
+ * mention regex. The wedge collapses, the orphan bech32 becomes visible, and the
+ * cursor lands in the middle of it. Gboard never enters this state because it
+ * does not recompose previously-committed tokens.
+ *
+ * This guard runs on every input change. If the change's original-text range
+ * partially intersects a complete mention but does not fully cover it, the entire
+ * change is reverted. The mention stays atomic; the IME re-reads the unchanged
+ * buffer and moves on.
+ */
+object MentionPreservingInputTransformation : InputTransformation {
+    private val mentionRegex =
+        Regex("(?:@|nostr:)(?:npub1[a-z0-9]{58}|nprofile1[a-z0-9]+)")
+
+    override fun TextFieldBuffer.transformInput() {
+        val changeCount = changes.changeCount
+        if (changeCount == 0) return
+
+        val original = originalText.toString()
+        if (original.isEmpty()) return
+
+        val mentions = mentionRegex.findAll(original).toList()
+        if (mentions.isEmpty()) return
+
+        for (i in 0 until changeCount) {
+            val origRange = changes.getOriginalRange(i)
+            val origStart = origRange.min
+            val origEnd = origRange.max
+            for (mention in mentions) {
+                val mStart = mention.range.first
+                val mEndExclusive = mention.range.last + 1
+                val overlaps = origStart < mEndExclusive && origEnd > mStart
+                val fullyCovers = origStart <= mStart && origEnd >= mEndExclusive
+                if (overlaps && !fullyCovers) {
+                    revertAllChanges()
+                    return
+                }
+            }
+        }
+    }
+}

amethyst/src/main/java/com/vitorpamplona/amethyst/ui/note/creators/messagefield/MessageField.kt

@@ -40,6 +40,7 @@ import androidx.compose.ui.platform.LocalSoftwareKeyboardController
 import androidx.compose.ui.text.input.KeyboardCapitalization
 import androidx.compose.ui.text.style.TextDirection
 import androidx.compose.ui.unit.dp
+import com.vitorpamplona.amethyst.ui.actions.MentionPreservingInputTransformation
 import com.vitorpamplona.amethyst.ui.actions.UrlUserTagOutputTransformation
 import com.vitorpamplona.amethyst.ui.components.ThinPaddingTextField
 import com.vitorpamplona.amethyst.ui.stringRes
@@ -70,6 +71,7 @@ fun MessageField(
         state = viewModel.message,
         onTextChanged = viewModel::onMessageChanged,
         onContentReceived = onContentReceived,
+        inputTransformation = MentionPreservingInputTransformation,
         keyboardOptions =
             KeyboardOptions.Default.copy(
                 capitalization = KeyboardCapitalization.Sentences,

amethyst/src/main/java/com/vitorpamplona/amethyst/ui/screen/loggedIn/chats/privateDM/send/NewGroupDMScreen.kt

@@ -77,6 +77,7 @@ import com.vitorpamplona.amethyst.commons.richtext.EncryptedMediaUrlVideo
 import com.vitorpamplona.amethyst.commons.richtext.MediaUrlImage
 import com.vitorpamplona.amethyst.commons.richtext.MediaUrlVideo
 import com.vitorpamplona.amethyst.commons.richtext.RichTextParser
+import com.vitorpamplona.amethyst.ui.actions.MentionPreservingInputTransformation
 import com.vitorpamplona.amethyst.ui.actions.UrlUserTagOutputTransformation
 import com.vitorpamplona.amethyst.ui.actions.uploads.SelectFromFiles
 import com.vitorpamplona.amethyst.ui.actions.uploads.SelectFromGallery
@@ -530,6 +531,7 @@ fun SendDirectMessageTo(
             ThinPaddingTextField(
                 state = postViewModel.toUsers,
                 onTextChanged = postViewModel::onToUsersChanged,
+                inputTransformation = MentionPreservingInputTransformation,
                 modifier =
                     Modifier
                         .weight(1f)
@@ -572,6 +574,7 @@ fun SendDirectMessageTo(
             ThinPaddingTextField(
                 state = postViewModel.subject,
                 onTextChanged = { postViewModel.onSubjectChanged() },
+                inputTransformation = MentionPreservingInputTransformation,
                 modifier = Modifier.fillMaxWidth(),
                 placeholder = {
                     Text(

amethyst/src/main/java/com/vitorpamplona/amethyst/ui/screen/loggedIn/chats/privateDM/send/PrivateMessageEditFieldRow.kt

@@ -53,6 +53,7 @@ import androidx.lifecycle.viewmodel.compose.viewModel
 import com.vitorpamplona.amethyst.R
 import com.vitorpamplona.amethyst.model.LocalCache
 import com.vitorpamplona.amethyst.model.User
+import com.vitorpamplona.amethyst.ui.actions.MentionPreservingInputTransformation
 import com.vitorpamplona.amethyst.ui.actions.StrippingFailureDialog
 import com.vitorpamplona.amethyst.ui.actions.UrlUserTagOutputTransformation
 import com.vitorpamplona.amethyst.ui.actions.uploads.SelectFromGallery
@@ -203,6 +204,7 @@ fun EditField(
     ThinPaddingTextField(
         state = channelScreenModel.message,
         onTextChanged = { channelScreenModel.onMessageChanged() },
+        inputTransformation = MentionPreservingInputTransformation,
         keyboardOptions = PostKeyboard,
         shape = EditFieldBorder,
         modifier = Modifier.fillMaxWidth(),

amethyst/src/main/java/com/vitorpamplona/amethyst/ui/screen/loggedIn/chats/publicChannels/send/EditFieldRow.kt

@@ -37,6 +37,7 @@ import androidx.compose.ui.text.input.KeyboardCapitalization
 import androidx.compose.ui.text.style.TextDirection
 import androidx.compose.ui.unit.dp
 import com.vitorpamplona.amethyst.R
+import com.vitorpamplona.amethyst.ui.actions.MentionPreservingInputTransformation
 import com.vitorpamplona.amethyst.ui.actions.StrippingFailureDialog
 import com.vitorpamplona.amethyst.ui.actions.UrlUserTagOutputTransformation
 import com.vitorpamplona.amethyst.ui.actions.uploads.SelectFromGallery
@@ -116,6 +117,7 @@ fun EditFieldRow(
         ThinPaddingTextField(
             state = channelScreenModel.message,
             onTextChanged = { channelScreenModel.onMessageChanged() },
+            inputTransformation = MentionPreservingInputTransformation,
             keyboardOptions =
                 KeyboardOptions.Default.copy(
                     capitalization = KeyboardCapitalization.Sentences,

amethyst/src/main/java/com/vitorpamplona/amethyst/ui/screen/loggedIn/discover/nip23LongForm/LongFormPostScreen.kt

@@ -84,6 +84,7 @@ import com.vitorpamplona.amethyst.commons.icons.symbols.Icon
 import com.vitorpamplona.amethyst.commons.icons.symbols.MaterialSymbols
 import com.vitorpamplona.amethyst.commons.model.EmptyTagList
 import com.vitorpamplona.amethyst.ui.actions.StrippingFailureDialog
+import com.vitorpamplona.amethyst.ui.actions.MentionPreservingInputTransformation
 import com.vitorpamplona.amethyst.ui.actions.UrlUserTagOutputTransformation
 import com.vitorpamplona.amethyst.ui.actions.uploads.GallerySelectSingle
 import com.vitorpamplona.amethyst.ui.actions.uploads.SelectFromFiles
@@ -381,6 +382,7 @@ private fun MarkdownPostScreenBody(
                     ThinPaddingTextField(
                         state = postViewModel.message,
                         onTextChanged = postViewModel::onMessageChanged,
+                        inputTransformation = MentionPreservingInputTransformation,
                         modifier =
                             Modifier
                                 .fillMaxWidth()

amethyst/src/main/java/com/vitorpamplona/amethyst/ui/screen/loggedIn/discover/nip99Classifieds/SellProduct.kt

@@ -49,6 +49,7 @@ import androidx.compose.ui.tooling.preview.Preview
 import androidx.compose.ui.unit.dp
 import coil3.compose.AsyncImage
 import com.vitorpamplona.amethyst.R
+import com.vitorpamplona.amethyst.ui.actions.MentionPreservingInputTransformation
 import com.vitorpamplona.amethyst.ui.actions.UrlUserTagOutputTransformation
 import com.vitorpamplona.amethyst.ui.components.TextSpinner
 import com.vitorpamplona.amethyst.ui.components.ThinPaddingTextField
@@ -111,6 +112,7 @@ fun SellProduct(postViewModel: NewProductViewModel) {
             ThinPaddingTextField(
                 state = postViewModel.title,
                 onTextChanged = { postViewModel.onTitleChanged() },
+                inputTransformation = MentionPreservingInputTransformation,
                 modifier = Modifier.fillMaxWidth(),
                 placeholder = {
                     Text(
@@ -311,6 +313,7 @@ fun SellProduct(postViewModel: NewProductViewModel) {
             ThinPaddingTextField(
                 state = postViewModel.locationText,
                 onTextChanged = { postViewModel.onLocationChanged() },
+                inputTransformation = MentionPreservingInputTransformation,
                 modifier = Modifier.fillMaxWidth(),
                 placeholder = {
                     Text(

amethyst/src/main/java/com/vitorpamplona/amethyst/ui/screen/loggedIn/notifications/publicMessages/NewPublicMessageScreen.kt

@@ -56,6 +56,7 @@ import androidx.compose.ui.unit.dp
 import androidx.lifecycle.viewmodel.compose.viewModel
 import com.vitorpamplona.amethyst.R
 import com.vitorpamplona.amethyst.ui.actions.StrippingFailureDialog
+import com.vitorpamplona.amethyst.ui.actions.MentionPreservingInputTransformation
 import com.vitorpamplona.amethyst.ui.actions.UrlUserTagOutputTransformation
 import com.vitorpamplona.amethyst.ui.actions.uploads.SelectFromFiles
 import com.vitorpamplona.amethyst.ui.actions.uploads.SelectFromGallery
@@ -417,6 +418,7 @@ fun SendDirectMessageTo(
             ThinPaddingTextField(
                 state = postViewModel.toUsers,
                 onTextChanged = postViewModel::onToUsersChanged,
+                inputTransformation = MentionPreservingInputTransformation,
                 modifier =
                     Modifier
                         .weight(1f)