Add inbox search over cached mail

- A search icon in the inbox app bar opens an in-bar search field (autofocused, with a
  Back/close handler); typing filters the message list by sender, address, subject, and
  snippet (case-insensitive), within the current account filter.
- Filtering is reactive over the cached list, so results update live as mail syncs, and
  a "No results" state shows when nothing matches.
- assemble/test/lint green; verified on the Android 17 emulator — searching "IMAP"
  narrowed three messages to the two whose subject matched, and a non-matching query
  showed the empty state.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

README.md

@@ -14,8 +14,8 @@ experience with power-user features tucked under an **Advanced Settings** group.
 > contacts autocomplete that sends over SMTP, plus reply; **on-device new-mail
 > notifications** (no push service) with persisted settings; **instant push** via a
 > foreground **IMAP IDLE** service; **attachments** — downloaded on demand and opened in a
-> system viewer; and **multiple accounts** — a unified inbox with per-account filtering.
-> Outlook Graph send and search are upcoming.
+> system viewer; **multiple accounts** — a unified inbox with per-account filtering; and
+> **search** across cached mail. Outlook Graph send is upcoming.
 
 ## Features (target MVP)
 

app/src/main/kotlin/org/libremail/ui/mailbox/MailboxScreen.kt

@@ -2,6 +2,7 @@
 package org.libremail.ui.mailbox
 
 import android.text.format.DateUtils
+import androidx.activity.compose.BackHandler
 import androidx.compose.foundation.background
 import androidx.compose.foundation.clickable
 import androidx.compose.foundation.horizontalScroll
@@ -20,15 +21,19 @@ import androidx.compose.foundation.lazy.LazyColumn
 import androidx.compose.foundation.lazy.items
 import androidx.compose.foundation.rememberScrollState
 import androidx.compose.foundation.shape.CircleShape
+import androidx.compose.foundation.text.BasicTextField
 import androidx.compose.material.icons.Icons
+import androidx.compose.material.icons.filled.Close
 import androidx.compose.material.icons.filled.Edit
 import androidx.compose.material.icons.filled.Email
+import androidx.compose.material.icons.filled.Search
 import androidx.compose.material3.Button
 import androidx.compose.material3.ExperimentalMaterial3Api
 import androidx.compose.material3.ExtendedFloatingActionButton
 import androidx.compose.material3.FilterChip
 import androidx.compose.material3.HorizontalDivider
 import androidx.compose.material3.Icon
+import androidx.compose.material3.IconButton
 import androidx.compose.material3.MaterialTheme
 import androidx.compose.material3.Scaffold
 import androidx.compose.material3.SnackbarHost
@@ -43,6 +48,9 @@ import androidx.compose.runtime.remember
 import androidx.compose.ui.Alignment
 import androidx.compose.ui.Modifier
 import androidx.compose.ui.draw.clip
+import androidx.compose.ui.focus.FocusRequester
+import androidx.compose.ui.focus.focusRequester
+import androidx.compose.ui.graphics.SolidColor
 import androidx.compose.ui.res.stringResource
 import androidx.compose.ui.text.font.FontWeight
 import androidx.compose.ui.text.style.TextOverflow
@@ -66,10 +74,14 @@ fun MailboxScreen(
     val accounts by viewModel.accounts.collectAsStateWithLifecycle()
     val selectedAccountId by viewModel.selectedAccountId.collectAsStateWithLifecycle()
     val hasAccounts by viewModel.hasAccounts.collectAsStateWithLifecycle()
+    val searchActive by viewModel.searchActive.collectAsStateWithLifecycle()
+    val searchQuery by viewModel.searchQuery.collectAsStateWithLifecycle()
     val isRefreshing by viewModel.isRefreshing.collectAsStateWithLifecycle()
     val error by viewModel.error.collectAsStateWithLifecycle()
     val snackbarHostState = remember { SnackbarHostState() }
 
+    BackHandler(enabled = searchActive) { viewModel.closeSearch() }
+
     LaunchedEffect(error) {
         error?.let {
             snackbarHostState.showSnackbar(it)
@@ -78,7 +90,31 @@ fun MailboxScreen(
     }
 
     Scaffold(
-        topBar = { TopAppBar(title = { Text(stringResource(R.string.title_mailbox)) }) },
+        topBar = {
+            TopAppBar(
+                title = {
+                    if (searchActive) {
+                        SearchField(query = searchQuery, onQueryChange = viewModel::onSearchQuery)
+                    } else {
+                        Text(stringResource(R.string.title_mailbox))
+                    }
+                },
+                navigationIcon = {
+                    if (searchActive) {
+                        IconButton(onClick = viewModel::closeSearch) {
+                            Icon(Icons.Filled.Close, contentDescription = stringResource(R.string.search_close))
+                        }
+                    }
+                },
+                actions = {
+                    if (hasAccounts && !searchActive) {
+                        IconButton(onClick = viewModel::openSearch) {
+                            Icon(Icons.Filled.Search, contentDescription = stringResource(R.string.search))
+                        }
+                    }
+                },
+            )
+        },
         bottomBar = {
             org.libremail.ui.LibreMailBottomBar(
                 current = org.libremail.ui.TopDest.MAILBOX,
@@ -115,7 +151,13 @@ fun MailboxScreen(
                     ) {
                         LazyColumn(modifier = Modifier.fillMaxSize()) {
                             if (messages.isEmpty()) {
-                                item { NoMessagesState(Modifier.fillParentMaxSize()) }
+                                item {
+                                    if (searchActive && searchQuery.isNotBlank()) {
+                                        NoResultsState(Modifier.fillParentMaxSize())
+                                    } else {
+                                        NoMessagesState(Modifier.fillParentMaxSize())
+                                    }
+                                }
                             } else {
                                 items(messages, key = { it.id }) { message ->
                                     MessageRow(
@@ -134,6 +176,30 @@ fun MailboxScreen(
     }
 }
 
+@Composable
+private fun SearchField(query: String, onQueryChange: (String) -> Unit) {
+    val focusRequester = remember { FocusRequester() }
+    BasicTextField(
+        value = query,
+        onValueChange = onQueryChange,
+        singleLine = true,
+        textStyle = MaterialTheme.typography.titleLarge.copy(color = MaterialTheme.colorScheme.onSurface),
+        cursorBrush = SolidColor(MaterialTheme.colorScheme.primary),
+        modifier = Modifier.fillMaxWidth().focusRequester(focusRequester),
+        decorationBox = { innerTextField ->
+            if (query.isEmpty()) {
+                Text(
+                    stringResource(R.string.search_hint),
+                    style = MaterialTheme.typography.titleLarge,
+                    color = MaterialTheme.colorScheme.onSurfaceVariant,
+                )
+            }
+            innerTextField()
+        },
+    )
+    LaunchedEffect(Unit) { focusRequester.requestFocus() }
+}
+
 @Composable
 private fun AccountFilterRow(accounts: List<Account>, selectedId: String?, onSelect: (String?) -> Unit) {
     Row(
@@ -284,6 +350,24 @@ private fun NoMessagesState(modifier: Modifier = Modifier) {
     }
 }
 
+@Composable
+private fun NoResultsState(modifier: Modifier = Modifier) {
+    Column(
+        modifier = modifier.padding(24.dp),
+        horizontalAlignment = Alignment.CenterHorizontally,
+        verticalArrangement = Arrangement.Center,
+    ) {
+        Icon(
+            Icons.Filled.Search,
+            contentDescription = null,
+            modifier = Modifier.size(48.dp),
+            tint = MaterialTheme.colorScheme.onSurfaceVariant,
+        )
+        Spacer(Modifier.height(16.dp))
+        Text(stringResource(R.string.search_no_results), style = MaterialTheme.typography.titleMedium)
+    }
+}
+
 private fun formatTimestamp(millis: Long): String =
     DateUtils.getRelativeTimeSpanString(
         millis,

app/src/main/kotlin/org/libremail/ui/mailbox/MailboxViewModel.kt

@@ -37,9 +37,19 @@ class MailboxViewModel @Inject constructor(
     private val _selectedAccountId = MutableStateFlow<String?>(null)
     val selectedAccountId: StateFlow<String?> = _selectedAccountId.asStateFlow()
 
+    private val _searchActive = MutableStateFlow(false)
+    val searchActive: StateFlow<Boolean> = _searchActive.asStateFlow()
+
+    private val _searchQuery = MutableStateFlow("")
+    val searchQuery: StateFlow<String> = _searchQuery.asStateFlow()
+
     val messages: StateFlow<List<Message>> =
-        combine(mailRepository.observeMessages(), _selectedAccountId) { all, accountId ->
-            if (accountId == null) all else all.filter { it.accountId == accountId }
+        combine(mailRepository.observeMessages(), _selectedAccountId, _searchQuery) { all, accountId, query ->
+            val q = query.trim()
+            all.filter { message ->
+                (accountId == null || message.accountId == accountId) &&
+                    (q.isEmpty() || message.matchesSearch(q))
+            }
         }.stateIn(viewModelScope, SharingStarted.WhileSubscribed(5_000), emptyList())
 
     private val _isRefreshing = MutableStateFlow(false)
@@ -62,6 +72,19 @@ class MailboxViewModel @Inject constructor(
         _selectedAccountId.value = accountId
     }
 
+    fun openSearch() {
+        _searchActive.value = true
+    }
+
+    fun closeSearch() {
+        _searchActive.value = false
+        _searchQuery.value = ""
+    }
+
+    fun onSearchQuery(query: String) {
+        _searchQuery.value = query
+    }
+
     fun refresh() {
         if (_isRefreshing.value) return
         viewModelScope.launch {
@@ -75,3 +98,10 @@ class MailboxViewModel @Inject constructor(
         _error.value = null
     }
 }
+
+/** Local match over the always-populated header fields (and snippet, once a body is cached). */
+private fun Message.matchesSearch(query: String): Boolean =
+    sender.contains(query, ignoreCase = true) ||
+        senderEmail.contains(query, ignoreCase = true) ||
+        subject.contains(query, ignoreCase = true) ||
+        snippet.contains(query, ignoreCase = true)

app/src/main/res/values/strings.xml

@@ -25,6 +25,10 @@
     <!-- Mailbox -->
     <string name="mailbox_empty">No messages yet</string>
     <string name="mailbox_all_accounts">All</string>
+    <string name="search">Search</string>
+    <string name="search_close">Close search</string>
+    <string name="search_hint">Search mail</string>
+    <string name="search_no_results">No results</string>
     <string name="mailbox_pull_to_refresh">Pull down to refresh</string>
     <string name="mailbox_welcome_title">Welcome to LibreMail</string>
     <string name="mailbox_welcome_subtitle">Add an account to start reading your mail.</string>