fix(messaging): reduce composer recomposition and typing jank

feature/messaging/build.gradle.kts

@@ -34,6 +34,7 @@ kotlin {
 
             implementation(libs.androidx.paging.common)
             implementation(libs.androidx.paging.compose)
+            implementation(libs.kotlinx.collections.immutable)
 
             // JetBrains Material 3 Adaptive (multiplatform ListDetailPaneScaffold)
             implementation(libs.jetbrains.compose.material3.adaptive)

feature/messaging/src/commonMain/kotlin/org/meshtastic/feature/messaging/Message.kt

@@ -82,6 +82,9 @@ import androidx.compose.ui.tooling.preview.PreviewLightDark
 import androidx.compose.ui.unit.dp
 import androidx.lifecycle.compose.collectAsStateWithLifecycle
 import androidx.paging.compose.collectAsLazyPagingItems
+import kotlinx.collections.immutable.ImmutableMap
+import kotlinx.collections.immutable.persistentMapOf
+import kotlinx.collections.immutable.toPersistentMap
 import kotlinx.coroutines.launch
 import org.jetbrains.compose.resources.stringResource
 import org.meshtastic.core.common.util.HomoglyphCharacterStringTransformer
@@ -99,7 +102,6 @@ import org.meshtastic.core.resources.type_a_message
 import org.meshtastic.core.resources.unknown_channel
 import org.meshtastic.core.ui.component.InlineStyle
 import org.meshtastic.core.ui.component.SharedContactDialog
-import org.meshtastic.core.ui.component.inlineMarkdownStyleRanges
 import org.meshtastic.core.ui.component.smartScrollToIndex
 import org.meshtastic.core.ui.icon.MeshtasticIcons
 import org.meshtastic.core.ui.icon.Send
@@ -150,6 +152,13 @@ fun MessageScreen(
     val focusManager = LocalFocusManager.current
 
     val nodes by viewModel.nodeList.collectAsStateWithLifecycle()
+    val mentionCandidates by remember {
+        derivedStateOf {
+            nodes
+                .associate { it.user.id to MentionCandidate(it.user.id, it.user.long_name, it.user.short_name) }
+                .toPersistentMap()
+        }
+    }
     val ourNode by viewModel.ourNodeInfo.collectAsStateWithLifecycle()
     val connectionState by viewModel.connectionState.collectAsStateWithLifecycle()
     val channels by viewModel.channels.collectAsStateWithLifecycle()
@@ -435,7 +444,7 @@ fun MessageScreen(
                     isEnabled = connectionState is ConnectionState.Connected,
                     isHomoglyphEncodingEnabled = homoglyphEncodingEnabled,
                     textFieldState = messageInputState,
-                    nodes = nodes,
+                    mentionCandidates = mentionCandidates,
                     onSendMessage = {
                         val messageText = messageInputState.text.toString().trim { it.isWhitespace() }
                         if (messageText.isNotEmpty()) {
@@ -531,12 +540,132 @@ internal fun currentMentionQuery(text: String, selection: TextRange): MentionQue
     return MentionQuery(at, cursor, query)
 }
 
-private fun Node.matchesMention(query: String): Boolean {
-    if (query.isEmpty()) return true
-    val q = query.lowercase()
-    return user.long_name.lowercase().contains(q) ||
-        user.short_name.lowercase().contains(q) ||
-        user.id.lowercase().contains(q)
+/**
+ * Lightweight mention target — contains only fields that affect composer presentation. A telemetry-only [Node] change
+ * leaves a [MentionCandidate] unchanged so the composable's recomposition scope stays narrow. Normalized fields are
+ * cached once so matching does not allocate three lowercase strings per candidate on every keystroke.
+ */
+internal data class MentionCandidate(val id: String, val longName: String, val shortName: String) {
+    private val normalizedId = id.lowercase()
+    private val normalizedLongName = longName.lowercase()
+    private val normalizedShortName = shortName.lowercase()
+
+    fun matchesNormalizedQuery(query: String): Boolean =
+        normalizedLongName.contains(query) || normalizedShortName.contains(query) || normalizedId.contains(query)
+}
+
+internal fun matchingMentionCandidates(
+    candidates: Collection<MentionCandidate>,
+    query: String,
+    limit: Int = MENTION_SUGGESTION_LIMIT,
+): List<MentionCandidate> = when {
+    limit <= 0 -> emptyList()
+
+    query.isEmpty() -> candidates.take(limit)
+
+    else -> {
+        val normalizedQuery = query.lowercase()
+        candidates.asSequence().filter { it.matchesNormalizedQuery(normalizedQuery) }.take(limit).toList()
+    }
+}
+
+/** Regex-backed inline-markdown style ranges for the live TextField path — avoids the IntelliJ GFM parser. */
+private val LIVE_BOLD = Regex("\\*\\*([^*]+)\\*\\*")
+private val LIVE_ITALIC = Regex("(?<!\\*)\\*([^*]+)\\*(?!\\*)") // single *, not part of **
+private val LIVE_STRIKE = Regex("~~([^~]+)~~")
+private val LIVE_CODE = Regex("`([^`]+)`")
+
+internal data class LiveStyleSpan(val range: IntRange, val style: InlineStyle)
+
+/**
+ * Detects live-markdown spans in [source] using simple regex patterns instead of a full GFM AST parser.
+ *
+ * The live composer intentionally previews only asterisk emphasis, strikethrough, and inline code. Underscore emphasis
+ * remains raw while editing, but the sent message still uses the full Markdown renderer.
+ */
+internal fun liveInlineMarkdownStyleRanges(source: String): List<LiveStyleSpan> {
+    if (!source.any { it in LIVE_STYLE_DELIMITER_SET }) return emptyList()
+    val codeMatches = LIVE_CODE.findAll(source).toList()
+    // Returns true when either delimiter boundary of this match falls inside a code span. Markdown entirely inside
+    // code, or malformed markdown crossing a code boundary, must not add styling. A code span nested inside outer
+    // emphasis is still allowed, so outer bold text can retain both its bold span and an inner code span.
+    val isBlockedByCodeSpan: (MatchResult) -> Boolean = { match ->
+        codeMatches.any { codeMatch -> match.range.first in codeMatch.range || match.range.last in codeMatch.range }
+    }
+    return buildList {
+        LIVE_BOLD.findAll(source).filterNot(isBlockedByCodeSpan).forEach {
+            add(LiveStyleSpan(it.groups[1]!!.range, InlineStyle.Bold))
+        }
+        LIVE_ITALIC.findAll(source).filterNot(isBlockedByCodeSpan).forEach {
+            add(LiveStyleSpan(it.groups[1]!!.range, InlineStyle.Italic))
+        }
+        LIVE_STRIKE.findAll(source).filterNot(isBlockedByCodeSpan).forEach {
+            add(LiveStyleSpan(it.groups[1]!!.range, InlineStyle.Strikethrough))
+        }
+        codeMatches.forEach { add(LiveStyleSpan(it.groups[1]!!.range, InlineStyle.Code)) }
+    }
+        .sortedWith(compareBy<LiveStyleSpan>({ it.range.first }, { it.range.last }, { it.style.ordinal }))
+}
+
+private val LIVE_STYLE_DELIMITER_SET = setOf('*', '~', '`')
+
+internal data class MentionReplacement(val range: IntRange, val text: String)
+
+internal data class MentionOutputPlan(val replacements: List<MentionReplacement>, val styleSpans: List<LiveStyleSpan>)
+
+/**
+ * Builds presentation edits from the immutable source buffer. Markdown is parsed before friendly-name replacement so
+ * display names containing `*`, `~`, or backticks cannot introduce formatting that was not present in the stored text.
+ */
+internal fun mentionOutputPlan(source: String, candidatesById: Map<String, MentionCandidate>): MentionOutputPlan {
+    val replacements =
+        MENTION_TOKEN_REGEX.findAll(source)
+            .mapNotNull { match ->
+                val candidate = candidatesById[match.groupValues[1]] ?: return@mapNotNull null
+                MentionReplacement(match.range, "@" + candidate.longName.ifEmpty { candidate.shortName })
+            }
+            .toList()
+    val styleSpans = remapStyleSpans(liveInlineMarkdownStyleRanges(source), replacements)
+    return MentionOutputPlan(replacements, styleSpans)
+}
+
+/** Remaps source-buffer style ranges through non-overlapping mention replacements. */
+internal fun remapStyleSpans(spans: List<LiveStyleSpan>, replacements: List<MentionReplacement>): List<LiveStyleSpan> {
+    if (spans.isEmpty() || replacements.isEmpty()) return spans
+    val sortedReplacements = replacements.sortedBy { it.range.first }
+    return spans.mapNotNull { span ->
+        val start = remapBoundary(span.range.first, sortedReplacements, preferReplacementEnd = false)
+        val endExclusive = remapBoundary(span.range.last + 1, sortedReplacements, preferReplacementEnd = true)
+        if (start >= endExclusive) null else span.copy(range = start until endExclusive)
+    }
+}
+
+private fun remapBoundary(
+    sourceOffset: Int,
+    replacements: List<MentionReplacement>,
+    preferReplacementEnd: Boolean,
+): Int {
+    var delta = 0
+    var mappedOffset: Int? = null
+    val iterator = replacements.iterator()
+    while (iterator.hasNext() && mappedOffset == null) {
+        val replacement = iterator.next()
+        val sourceStart = replacement.range.first
+        val sourceEndExclusive = replacement.range.last + 1
+        mappedOffset =
+            when {
+                sourceOffset <= sourceStart -> sourceOffset + delta
+
+                sourceOffset < sourceEndExclusive ->
+                    sourceStart + delta + if (preferReplacementEnd) replacement.text.length else 0
+
+                else -> {
+                    delta += replacement.text.length - (sourceEndExclusive - sourceStart)
+                    null
+                }
+            }
+    }
+    return mappedOffset ?: sourceOffset + delta
 }
 
 /**
@@ -545,13 +674,18 @@ private fun Node.matchesMention(query: String): Boolean {
  * and the raw markdown delimiters, so the bytes sent are unchanged.
  */
 @OptIn(ExperimentalFoundationApi::class)
-private fun mentionOutputTransformation(nodesById: Map<String, Node>) = OutputTransformation {
-    for (match in MENTION_TOKEN_REGEX.findAll(toString()).toList().asReversed()) {
-        val node = nodesById[match.groupValues[1]] ?: continue
-        replace(match.range.first, match.range.last + 1, "@" + node.user.long_name.ifEmpty { node.user.short_name })
+private fun mentionOutputTransformation(candidatesById: Map<String, MentionCandidate>) = OutputTransformation {
+    val source = toString()
+    // Fast path: plain text with no mention tokens or markdown delimiters — skip all scanning.
+    val hasMention = source.indexOf('@') >= 0
+    val needsStyle = hasMention || source.any { it in LIVE_STYLE_DELIMITER_SET }
+    if (!needsStyle) return@OutputTransformation
+
+    val plan = mentionOutputPlan(source, candidatesById)
+    for (replacement in plan.replacements.asReversed()) {
+        replace(replacement.range.first, replacement.range.last + 1, replacement.text)
     }
-    // Live markdown styling over the (mention-substituted) buffer. Delimiters stay visible; only spans are added.
-    for (span in inlineMarkdownStyleRanges(toString())) {
+    for (span in plan.styleSpans) {
         val spanStyle =
             when (span.style) {
                 InlineStyle.Bold -> SpanStyle(fontWeight = FontWeight.Bold)
@@ -569,7 +703,8 @@ private fun mentionOutputTransformation(nodesById: Map<String, Node>) = OutputTr
  *
  * @param isEnabled Whether the input field should be enabled.
  * @param textFieldState The [TextFieldState] managing the input's text.
- * @param nodes Known nodes, used for the `@`-mention autocomplete and friendly-name display.
+ * @param mentionCandidates Identity-stable node-id → mention entry. Only changes when a node's id or display name
+ *   changes — telemetry-only updates leave this map structurally identical, preventing recomposition churn.
  * @param modifier The modifier for this composable.
  * @param maxByteSize The maximum allowed size of the message in bytes.
  * @param onSendMessage Callback invoked when the send button is pressed or send IME action is triggered.
@@ -580,7 +715,7 @@ private fun MessageInput(
     isEnabled: Boolean,
     isHomoglyphEncodingEnabled: Boolean,
     textFieldState: TextFieldState,
-    nodes: List<Node>,
+    mentionCandidates: ImmutableMap<String, MentionCandidate>,
     modifier: Modifier = Modifier,
     maxByteSize: Int = MESSAGE_CHARACTER_LIMIT_BYTES,
     onSendMessage: () -> Unit,
@@ -603,24 +738,23 @@ private fun MessageInput(
     val isOverLimit = currentByteLength > maxByteSize
     val canSend = !isOverLimit && currentText.isNotEmpty() && isEnabled
 
-    val nodesById = remember(nodes) { nodes.associateBy { it.user.id } }
-    val mentionOutput = remember(nodesById) { mentionOutputTransformation(nodesById) }
+    val mentionOutput = remember(mentionCandidates) { mentionOutputTransformation(mentionCandidates) }
     val mentionQuery by
         remember(textFieldState) {
             derivedStateOf { currentMentionQuery(textFieldState.text.toString(), textFieldState.selection) }
         }
     val suggestions =
-        remember(mentionQuery, nodes) {
-            val query = mentionQuery?.query ?: return@remember emptyList<Node>()
-            nodes.filter { it.matchesMention(query) }.take(MENTION_SUGGESTION_LIMIT)
+        remember(mentionQuery, mentionCandidates) {
+            val query = mentionQuery?.query ?: return@remember emptyList<MentionCandidate>()
+            matchingMentionCandidates(mentionCandidates.values, query)
         }
 
     // While the mention popup is open, Enter / send completes the top suggestion instead of sending a raw @query.
     val mentionActive = mentionQuery != null && suggestions.isNotEmpty()
-    fun insertMention(node: Node) {
+    fun insertMention(candidate: MentionCandidate) {
         val q = mentionQuery ?: return
         textFieldState.edit {
-            val insert = "@${node.user.id} "
+            val insert = "@${candidate.id} "
             replace(q.start, q.end, insert)
             selection = TextRange(q.start + insert.length)
         }
@@ -698,27 +832,29 @@ private fun MessageInput(
 }
 
 @Composable
-private fun MentionSuggestions(suggestions: List<Node>, onPick: (Node) -> Unit) {
+private fun MentionSuggestions(suggestions: List<MentionCandidate>, onPick: (MentionCandidate) -> Unit) {
     Surface(
         modifier = Modifier.fillMaxWidth().padding(horizontal = 8.dp),
         tonalElevation = 3.dp,
         shape = RoundedCornerShape(12.dp),
     ) {
         Column {
-            suggestions.forEach { node ->
+            suggestions.forEach { candidate ->
                 Row(
                     modifier =
-                    Modifier.fillMaxWidth().clickable { onPick(node) }.padding(horizontal = 12.dp, vertical = 8.dp),
+                    Modifier.fillMaxWidth()
+                        .clickable { onPick(candidate) }
+                        .padding(horizontal = 12.dp, vertical = 8.dp),
                     verticalAlignment = Alignment.CenterVertically,
                     horizontalArrangement = Arrangement.spacedBy(8.dp),
                 ) {
                     Text(
-                        text = node.user.short_name,
+                        text = candidate.shortName,
                         style = MaterialTheme.typography.labelLarge,
                         fontWeight = FontWeight.Bold,
                     )
                     Text(
-                        text = node.user.long_name,
+                        text = candidate.longName,
                         style = MaterialTheme.typography.bodyMedium,
                         maxLines = 1,
                         overflow = TextOverflow.Ellipsis,
@@ -732,29 +868,30 @@ private fun MentionSuggestions(suggestions: List<Node>, onPick: (Node) -> Unit)
 @PreviewLightDark
 @Composable
 fun MessageInputPreview() {
+    val mentionCandidates = persistentMapOf<String, MentionCandidate>()
     AppTheme {
         Surface {
             Column(modifier = Modifier.padding(8.dp)) {
                 MessageInput(
                     isEnabled = true,
                     isHomoglyphEncodingEnabled = false,
-                    nodes = emptyList(),
+                    mentionCandidates = mentionCandidates,
                     textFieldState = rememberTextFieldState("Hello"),
                     onSendMessage = {},
                 )
                 Spacer(Modifier.size(16.dp))
                 MessageInput(
                     isEnabled = false,
                     isHomoglyphEncodingEnabled = false,
-                    nodes = emptyList(),
+                    mentionCandidates = mentionCandidates,
                     textFieldState = rememberTextFieldState("Disabled"),
                     onSendMessage = {},
                 )
                 Spacer(Modifier.size(16.dp))
                 MessageInput(
                     isEnabled = true,
                     isHomoglyphEncodingEnabled = false,
-                    nodes = emptyList(),
+                    mentionCandidates = mentionCandidates,
                     textFieldState =
                     rememberTextFieldState(
                         "A very long message that might exceed the byte limit " +
@@ -768,7 +905,7 @@ fun MessageInputPreview() {
                 MessageInput(
                     isEnabled = true,
                     isHomoglyphEncodingEnabled = false,
-                    nodes = emptyList(),
+                    mentionCandidates = mentionCandidates,
                     textFieldState = rememberTextFieldState("こんにちは世界"), // Hello World in Japanese
                     onSendMessage = {},
                     maxByteSize = 10,

feature/messaging/src/commonMain/kotlin/org/meshtastic/feature/messaging/MessageViewModel.kt

@@ -22,6 +22,8 @@ import androidx.lifecycle.viewModelScope
 import androidx.paging.PagingData
 import androidx.paging.cachedIn
 import kotlinx.coroutines.FlowPreview
+import kotlinx.coroutines.Job
+import kotlinx.coroutines.delay
 import kotlinx.coroutines.flow.Flow
 import kotlinx.coroutines.flow.MutableStateFlow
 import kotlinx.coroutines.flow.StateFlow
@@ -34,6 +36,7 @@ import kotlinx.coroutines.flow.flatMapLatest
 import kotlinx.coroutines.flow.flow
 import kotlinx.coroutines.flow.flowOf
 import kotlinx.coroutines.flow.update
+import kotlinx.coroutines.launch
 import org.koin.core.annotation.KoinViewModel
 import org.meshtastic.core.common.util.currentLocaleCode
 import org.meshtastic.core.common.util.ioDispatcher
@@ -108,13 +111,28 @@ class MessageViewModel(
     private val _draftMessage = MutableStateFlow(savedStateHandle.get<String>("draftMessage") ?: "")
     val draftMessage: StateFlow<String> = _draftMessage.asStateFlow()
 
+    private var pendingDraftPersistence: Job? = null
+
+    /**
+     * Updates the in-memory draft immediately. The durable [SavedStateHandle] write is debounced by
+     * [DRAFT_PERSISTENCE_DELAY_MS] — rapid edits cancel the prior pending flush, so only the trailing value persists.
+     * On process death within the debounce window the last ≤[DRAFT_PERSISTENCE_DELAY_MS] of typing is not durably
+     * saved; this is a conscious trade-off to avoid per-keystroke jank.
+     */
     fun setDraftMessage(text: String) {
         _draftMessage.value = text
-        savedStateHandle["draftMessage"] = text
+        pendingDraftPersistence?.cancel()
+        pendingDraftPersistence =
+            viewModelScope.launch {
+                delay(DRAFT_PERSISTENCE_DELAY_MS)
+                savedStateHandle["draftMessage"] = text
+            }
     }
 
     fun clearDraftMessage() {
         _draftMessage.value = ""
+        pendingDraftPersistence?.cancel()
+        pendingDraftPersistence = null
         savedStateHandle["draftMessage"] = ""
     }
 
@@ -413,5 +431,6 @@ class MessageViewModel(
     companion object {
         private const val SEARCH_DEBOUNCE_MS = 300L
         private const val MIN_SEARCH_LENGTH = 2
+        private const val DRAFT_PERSISTENCE_DELAY_MS = 300L
     }
 }