android/app/src/main/java/com/fabledsword/thoughtsync/MainActivity.kt

@@ -31,6 +31,8 @@ import com.fabledsword.thoughtsync.ui.ForegroundTransitions
 import com.fabledsword.thoughtsync.ui.NoteEditorScreen
 import com.fabledsword.thoughtsync.ui.StoreUnavailableScreen
 import com.fabledsword.thoughtsync.ui.SyncScreen
+import com.fabledsword.thoughtsync.ui.TagsScreen
+import com.fabledsword.thoughtsync.ui.TagsViewModel
 import com.fabledsword.thoughtsync.ui.SyncState
 import com.fabledsword.thoughtsync.ui.SyncViewModel
 import com.fabledsword.thoughtsync.ui.ThoughtSyncTheme
@@ -95,7 +97,7 @@ class MainActivity : ComponentActivity() {
 }
 
 /** Which screen is up. Exactly one at a time. */
-private enum class Screen { BOARD, EDITOR, SYNC }
+private enum class Screen { BOARD, EDITOR, SYNC, TAGS }
 
 /**
  * The whole app, once the store is open.
@@ -104,7 +106,7 @@ private enum class Screen { BOARD, EDITOR, SYNC }
  * both cover the display completely, so keeping the board's two-column grid
  * measuring and recomposing underneath one would be pure waste.
  *
- * Still no navigation library. Three destinations, each entered from exactly one
+ * Still no navigation library. Four destinations, each entered from exactly one
  * place and left by back — a nav graph would be ceremony around an enum, and the
  * state that actually matters (which note is open, whether this device is linked)
  * already lives in view models.
@@ -149,6 +151,13 @@ private fun App(
     // opens the editor on an unsaved draft, so writing a note and editing one are the
     // same surface with the same toolbar.
     var showingSync by rememberSaveable { mutableStateOf(false) }
+    var showingTags by rememberSaveable { mutableStateOf(false) }
+
+    // Tag writes reach the board two ways at once: the drawer lists tags, and the
+    // board may be LOOKING at one that a delete or a merge just removed. Both are
+    // `refreshLabels`, which also leaves a lens whose tag stopped existing.
+    val tags: TagsViewModel =
+        viewModel(factory = TagsViewModel.factory(core, onStoreChanged = board::refreshLabels))
 
     val update: UpdateViewModel = viewModel(factory = UpdateViewModel.factory(core, context))
     val settings = remember(context) { SyncSettings(context) }
@@ -161,6 +170,9 @@ private fun App(
     val screen =
         when {
             showingSync -> Screen.SYNC
+            // Above the editor: tags are reached only from the board's drawer, so
+            // there is never an open note underneath one to go back to.
+            showingTags -> Screen.TAGS
             editing != null -> Screen.EDITOR
             else -> Screen.BOARD
         }
@@ -188,6 +200,18 @@ private fun App(
                 onInstallOutcome = update::consumeInstallOutcome,
             )
 
+        Screen.TAGS ->
+            TagsScreen(
+                state = tags.state,
+                onClose = { showingTags = false },
+                onCreate = tags::create,
+                onRename = tags::rename,
+                onColour = tags::setColour,
+                onDelete = tags::remove,
+                onMerge = tags::merge,
+                onDismissError = tags::dismissError,
+            )
+
         Screen.EDITOR ->
             NoteEditorScreen(
                 // Non-null by construction: `screen` is EDITOR only when it is.
@@ -218,6 +242,7 @@ private fun App(
                         onDismissError = sync::dismissSyncError,
                     ),
                 onOpenSync = { showingSync = true },
+                onManageTags = { showingTags = true },
                 onSearch = board::search,
                 onCompose = board::compose,
                 onToggleItem = board::toggleItem,
@@ -247,6 +272,7 @@ private fun App(
     // The sync screen has no back handler of its own, so one lives here. The
     // editor keeps its own, because it has to save the open note before leaving.
     BackHandler(enabled = showingSync) { showingSync = false }
+    BackHandler(enabled = showingTags) { showingTags = false }
 }
 
 /**

android/app/src/main/java/com/fabledsword/thoughtsync/ui/BoardScreen.kt

@@ -26,6 +26,7 @@ import androidx.compose.foundation.verticalScroll
 import androidx.compose.material.icons.Icons
 import androidx.compose.material.icons.filled.Add
 import androidx.compose.material.icons.filled.Close
+import androidx.compose.material.icons.filled.Edit
 import androidx.compose.material.icons.filled.Menu
 import androidx.compose.material.icons.filled.Search
 import androidx.compose.material3.CircularProgressIndicator
@@ -74,6 +75,7 @@ fun BoardScreen(
     onOpenNote: (Note) -> Unit,
     sync: BoardSync,
     onOpenSync: () -> Unit,
+    onManageTags: () -> Unit,
     onSearch: (String) -> Unit,
     onCompose: () -> Unit,
     onToggleItem: (Note, Int, Boolean) -> Unit,
@@ -138,6 +140,10 @@ fun BoardScreen(
                     onOpenSync()
                     scope.launch { drawerState.close() }
                 },
+                onManageTags = {
+                    onManageTags()
+                    scope.launch { drawerState.close() }
+                },
             )
         },
     ) {
@@ -367,6 +373,7 @@ private fun NavigationDrawer(
     syncSummary: String?,
     onOpen: (Destination) -> Unit,
     onOpenSync: () -> Unit,
+    onManageTags: () -> Unit,
 ) {
     ModalDrawerSheet {
         Column(modifier = Modifier.verticalScroll(rememberScrollState())) {
@@ -380,18 +387,36 @@ private fun NavigationDrawer(
                 DrawerRow(destination, current, onOpen)
             }
 
-            if (labels.isNotEmpty()) {
-                HorizontalDivider(modifier = Modifier.padding(horizontal = 16.dp, vertical = 8.dp))
+            // The header renders even with no tags, unlike the rows below it: the
+            // manage screen is where you go to MAKE the first one, and hiding the
+            // way in until one exists would be a door that appears only once you
+            // are already inside. It is an action ON the section rather than a row
+            // in it, so it cannot be mistaken for one more lens.
+            HorizontalDivider(modifier = Modifier.padding(horizontal = 16.dp, vertical = 8.dp))
+            Row(
+                modifier =
+                    Modifier
+                        .fillMaxWidth()
+                        .padding(start = 28.dp, end = 16.dp, bottom = 4.dp),
+                verticalAlignment = Alignment.CenterVertically,
+            ) {
                 Text(
                     text = stringResource(R.string.nav_labels),
                     style = MaterialTheme.typography.labelMedium,
                     color = MaterialTheme.colorScheme.onSurfaceVariant,
-                    modifier = Modifier.padding(start = 28.dp, bottom = 4.dp),
+                    modifier = Modifier.weight(1f),
                 )
-                labels.forEach { label ->
-                    DrawerRow(Destination.WithLabel(label.id, label.name), current, onOpen)
+                IconButton(onClick = onManageTags) {
+                    Icon(
+                        Icons.Filled.Edit,
+                        contentDescription = stringResource(R.string.tags_manage),
+                        tint = MaterialTheme.colorScheme.onSurfaceVariant,
+                    )
                 }
             }
+            labels.forEach { label ->
+                DrawerRow(Destination.WithLabel(label.id, label.name), current, onOpen)
+            }
 
             HorizontalDivider(modifier = Modifier.padding(horizontal = 16.dp, vertical = 8.dp))
             listOf(Destination.Archive, Destination.Trash).forEach { destination ->

android/app/src/main/java/com/fabledsword/thoughtsync/ui/BoardViewModel.kt

@@ -123,7 +123,7 @@ class BoardViewModel(
 
     init {
         refresh()
-        loadLabels()
+        refreshLabels()
     }
 
     fun open(destination: Destination) {
@@ -162,13 +162,34 @@ class BoardViewModel(
             is Destination.WithLabel -> core.listNotes(query(VIEW_NOTES, labelId = destination.id))
         }
 
-    private fun loadLabels() {
+    /**
+     * Reload the drawer's tags, and leave a lens whose tag no longer exists.
+     *
+     * Public because the Tags screen owns operations this board cannot see: a
+     * delete or a merge removes a tag, and the board may be LOOKING at that tag —
+     * `Destination.WithLabel` holds an id, and a query for a deleted one returns
+     * nothing forever. Without the fallback, tidying up tags could strand the board
+     * on a permanently empty lens whose only escape is the drawer.
+     *
+     * A rename needs no fallback: the id survives, and re-listing gives the drawer
+     * the new name. A rename that MERGED is a delete of one of the two, which this
+     * catches by id like any other.
+     */
+    fun refreshLabels() {
         viewModelScope.launch {
             runCatching { withContext(Dispatchers.IO) { core.listLabels() } }
-                .onSuccess { state = state.copy(labels = it) }
+                .onSuccess { labels ->
+                    state = state.copy(labels = labels)
+                    val lens = state.destination
+                    if (lens is Destination.WithLabel && labels.none { it.id == lens.id }) {
+                        open(Destination.Notes)
+                    }
+                }
                 // A drawer that cannot list labels is a degraded drawer, not a
                 // broken board — the notes are still there. Failing quietly here
-                // beats an error banner over working content.
+                // beats an error banner over working content. The lens is left
+                // alone in this case on purpose: "I could not read the tags" is not
+                // evidence that this one is gone.
                 .onFailure { state = state.copy(labels = emptyList()) }
         }
     }
@@ -387,7 +408,7 @@ class BoardViewModel(
                     }
                     // The drawer lists labels with their note counts, and both
                     // just changed.
-                    loadLabels()
+                    refreshLabels()
                 }
 
             is EditorAction.SetReminder -> edit(id, NoteEdit.RemindAt(action.at))

android/app/src/main/java/com/fabledsword/thoughtsync/ui/TagsScreen.kt

@@ -0,0 +1,584 @@
+package com.fabledsword.thoughtsync.ui
+
+import androidx.compose.foundation.background
+import androidx.compose.foundation.border
+import androidx.compose.foundation.clickable
+import androidx.compose.foundation.isSystemInDarkTheme
+import androidx.compose.foundation.layout.Arrangement
+import androidx.compose.foundation.layout.Box
+import androidx.compose.foundation.layout.Column
+import androidx.compose.foundation.layout.Row
+import androidx.compose.foundation.layout.fillMaxSize
+import androidx.compose.foundation.layout.fillMaxWidth
+import androidx.compose.foundation.layout.imePadding
+import androidx.compose.foundation.layout.padding
+import androidx.compose.foundation.layout.size
+import androidx.compose.foundation.lazy.LazyColumn
+import androidx.compose.foundation.lazy.items
+import androidx.compose.foundation.shape.CircleShape
+import androidx.compose.foundation.text.KeyboardActions
+import androidx.compose.foundation.text.KeyboardOptions
+import androidx.compose.material.icons.Icons
+import androidx.compose.material.icons.automirrored.filled.ArrowBack
+import androidx.compose.material.icons.filled.MoreVert
+import androidx.compose.material3.AlertDialog
+import androidx.compose.material3.DropdownMenu
+import androidx.compose.material3.ExperimentalMaterial3Api
+import androidx.compose.material3.Icon
+import androidx.compose.material3.IconButton
+import androidx.compose.material3.LinearProgressIndicator
+import androidx.compose.material3.MaterialTheme
+import androidx.compose.material3.Scaffold
+import androidx.compose.material3.Text
+import androidx.compose.material3.TextButton
+import androidx.compose.material3.TopAppBar
+import androidx.compose.runtime.Composable
+import androidx.compose.runtime.getValue
+import androidx.compose.runtime.mutableStateOf
+import androidx.compose.runtime.remember
+import androidx.compose.runtime.setValue
+import androidx.compose.ui.Alignment
+import androidx.compose.ui.Modifier
+import androidx.compose.ui.draw.clip
+import androidx.compose.ui.res.stringResource
+import androidx.compose.ui.text.input.ImeAction
+import androidx.compose.ui.unit.dp
+import com.fabledsword.thoughtsync.R
+import com.fabledsword.thoughtsync.core.Label
+
+/** The swatch shown beside a tag, and tapped to change its colour. */
+private val SWATCH = 22.dp
+
+/** What the row's overflow menu is currently asking about. */
+private sealed interface TagDialog {
+    data class Rename(
+        val tag: Label,
+    ) : TagDialog
+
+    /** A rename whose new name another tag already holds — see [RenameDialog]. */
+    data class ConfirmMerge(
+        val tag: Label,
+        val into: Label,
+        val name: String,
+    ) : TagDialog
+
+    data class Merge(
+        val tag: Label,
+    ) : TagDialog
+
+    data class Delete(
+        val tag: Label,
+    ) : TagDialog
+
+    data class Colour(
+        val tag: Label,
+    ) : TagDialog
+}
+
+/**
+ * Tag management: list, create, rename, recolour, delete, merge.
+ *
+ * A destination you go to, not a modal. The web's `LabelsModal.vue` is a modal
+ * because a desktop has room to float one over the board; on a phone this is a
+ * place you visit to tidy up, and a full screen is what that is.
+ *
+ * It is also, since the per-note colour picker was removed, the ONLY colour
+ * control in the product. That is why the swatch is a first-class tap target on
+ * every row rather than something behind the overflow menu.
+ */
+@OptIn(ExperimentalMaterial3Api::class)
+@Composable
+fun TagsScreen(
+    state: TagsState,
+    onClose: () -> Unit,
+    onCreate: (String) -> Unit,
+    onRename: (String, String) -> Unit,
+    onColour: (String, String) -> Unit,
+    onDelete: (String) -> Unit,
+    onMerge: (String, String) -> Unit,
+    onDismissError: () -> Unit,
+) {
+    var dialog by remember { mutableStateOf<TagDialog?>(null) }
+
+    Scaffold(
+        topBar = {
+            TopAppBar(
+                title = { Text(stringResource(R.string.tags_title)) },
+                navigationIcon = {
+                    IconButton(onClick = onClose) {
+                        Icon(
+                            Icons.AutoMirrored.Filled.ArrowBack,
+                            contentDescription = stringResource(R.string.tags_back),
+                        )
+                    }
+                },
+            )
+        },
+    ) { padding ->
+        Column(
+            modifier =
+                Modifier
+                    .fillMaxSize()
+                    .padding(padding)
+                    .imePadding(),
+        ) {
+            // An indeterminate bar rather than blocking the list: a tag write is a
+            // local SQLite call and usually finishes before this is seen at all.
+            if (state.busy) {
+                LinearProgressIndicator(modifier = Modifier.fillMaxWidth())
+            }
+
+            // The same banner the board and the editor use. A third way of saying
+            // "that did not work" would be a third thing to keep consistent.
+            state.error?.let { message ->
+                ErrorBanner(message = message, onDismiss = onDismissError)
+            }
+
+            NewTagField(
+                enabled = !state.busy,
+                onCreate = onCreate,
+            )
+
+            if (!state.loading && state.tags.isEmpty()) {
+                EmptyTags()
+            }
+
+            // weight, NOT fillMaxSize: this has siblings above it, and filling the
+            // whole height would measure the list against space the field and the
+            // banner have already taken — pushing the end of the list off-screen.
+            LazyColumn(modifier = Modifier.weight(1f)) {
+                items(state.tags, key = { it.id }) { tag ->
+                    TagRow(
+                        tag = tag,
+                        enabled = !state.busy,
+                        onColour = { dialog = TagDialog.Colour(tag) },
+                        onRename = { dialog = TagDialog.Rename(tag) },
+                        onMerge = { dialog = TagDialog.Merge(tag) },
+                        onDelete = { dialog = TagDialog.Delete(tag) },
+                    )
+                }
+            }
+        }
+    }
+
+    when (val open = dialog) {
+        null -> Unit
+
+        is TagDialog.Rename ->
+            RenameDialog(
+                tag = open.tag,
+                others = state.tags,
+                onDismiss = { dialog = null },
+                onRename = { name ->
+                    dialog = null
+                    onRename(open.tag.id, name)
+                },
+                // Renaming onto a name another tag holds MERGES the two, and that
+                // cannot be undone by repeating it, so the confirmation replaces
+                // this dialog rather than the rename just happening.
+                onWouldMerge = { into, name -> dialog = TagDialog.ConfirmMerge(open.tag, into, name) },
+            )
+
+        is TagDialog.ConfirmMerge ->
+            ConfirmDialog(
+                title = stringResource(R.string.tags_rename_merges_title, hash(open.into.name)),
+                body = stringResource(R.string.tags_rename_merges_body, hash(open.into.name)),
+                confirm = stringResource(R.string.tags_rename_merges_confirm),
+                onDismiss = { dialog = null },
+                onConfirm = {
+                    dialog = null
+                    onRename(open.tag.id, open.name)
+                },
+            )
+
+        is TagDialog.Merge ->
+            MergeDialog(
+                tag = open.tag,
+                others = state.tags.filter { it.id != open.tag.id },
+                onDismiss = { dialog = null },
+                onMerge = { target ->
+                    dialog = null
+                    onMerge(open.tag.id, target.id)
+                },
+            )
+
+        is TagDialog.Delete ->
+            ConfirmDialog(
+                title = stringResource(R.string.tags_delete_title, hash(open.tag.name)),
+                // The count is the part that makes the consequence real — "it is on
+                // 40 notes" is a different decision from "delete this tag?". It comes
+                // from the LIST, the only call the core populates a count on.
+                body =
+                    open.tag.count
+                        ?.takeIf { it > 0 }
+                        ?.let { stringResource(R.string.tags_delete_body_counted, it) }
+                        ?: stringResource(R.string.tags_delete_body),
+                footnote = stringResource(R.string.tags_delete_from_text),
+                confirm = stringResource(R.string.tags_delete_confirm),
+                onDismiss = { dialog = null },
+                onConfirm = {
+                    dialog = null
+                    onDelete(open.tag.id)
+                },
+            )
+
+        is TagDialog.Colour ->
+            ColourDialog(
+                tag = open.tag,
+                onDismiss = { dialog = null },
+                onPick = { key ->
+                    dialog = null
+                    onColour(open.tag.id, key)
+                },
+            )
+    }
+}
+
+/**
+ * `#` on the name, everywhere it is spoken about.
+ *
+ * The chips already wear it (`NoteCard.kt`, `EditorChrome.kt`) and it is the
+ * reason these are called tags at all — a dialog that said "Delete grocery?" would
+ * be talking about something else.
+ */
+private fun hash(name: String): String = "#$name"
+
+@Composable
+private fun NewTagField(
+    enabled: Boolean,
+    onCreate: (String) -> Unit,
+) {
+    var text by remember { mutableStateOf("") }
+    val submit = {
+        if (text.isNotBlank()) {
+            onCreate(text)
+            text = ""
+        }
+    }
+
+    Row(
+        modifier = Modifier.padding(horizontal = 16.dp, vertical = 8.dp),
+        verticalAlignment = Alignment.CenterVertically,
+        horizontalArrangement = Arrangement.spacedBy(8.dp),
+    ) {
+        PlainTextField(
+            value = text,
+            onValueChange = { text = it },
+            modifier = Modifier.weight(1f),
+            hint = R.string.tags_new_hint,
+            enabled = enabled,
+            singleLine = true,
+            keyboardOptions = KeyboardOptions(imeAction = ImeAction.Done),
+            keyboardActions = KeyboardActions(onDone = { submit() }),
+        )
+        TextButton(onClick = submit, enabled = enabled && text.isNotBlank()) {
+            Text(stringResource(R.string.tags_create))
+        }
+    }
+}
+
+/**
+ * Said out loud rather than left as a blank screen — and it names the `#` route,
+ * because the operator did not know `#tag` extraction existed at all (Scribe
+ * #2949) and this is the natural place to say so.
+ */
+@Composable
+private fun EmptyTags() {
+    Column(
+        modifier = Modifier.padding(horizontal = 16.dp, vertical = 24.dp),
+        verticalArrangement = Arrangement.spacedBy(4.dp),
+    ) {
+        Text(
+            text = stringResource(R.string.tags_empty_title),
+            style = MaterialTheme.typography.titleSmall,
+        )
+        Text(
+            text = stringResource(R.string.tags_empty_body),
+            style = MaterialTheme.typography.bodyMedium,
+            color = MaterialTheme.colorScheme.onSurfaceVariant,
+        )
+    }
+}
+
+@Composable
+private fun TagRow(
+    tag: Label,
+    enabled: Boolean,
+    onColour: () -> Unit,
+    onRename: () -> Unit,
+    onMerge: () -> Unit,
+    onDelete: () -> Unit,
+) {
+    val dark = isSystemInDarkTheme()
+    val tint = labelTintFor(tag.name, tag.color)
+    var menuOpen by remember { mutableStateOf(false) }
+
+    Row(
+        modifier =
+            Modifier
+                .fillMaxWidth()
+                .padding(horizontal = 16.dp, vertical = 10.dp),
+        verticalAlignment = Alignment.CenterVertically,
+        horizontalArrangement = Arrangement.spacedBy(12.dp),
+    ) {
+        Box(
+            modifier =
+                Modifier
+                    .size(SWATCH)
+                    .clip(CircleShape)
+                    .background(tint.chipBackground(dark))
+                    .border(1.dp, tint.chipBorder(dark), CircleShape)
+                    .clickable(enabled = enabled, onClick = onColour),
+        )
+
+        Column(modifier = Modifier.weight(1f)) {
+            Text(
+                text = hash(tag.name),
+                style = MaterialTheme.typography.bodyLarge,
+                color = tint.tagInk(dark),
+            )
+            Text(
+                text = countLabel(tag.count),
+                style = MaterialTheme.typography.labelSmall,
+                color = MaterialTheme.colorScheme.onSurfaceVariant,
+            )
+        }
+
+        Column {
+            IconButton(onClick = { menuOpen = true }, enabled = enabled) {
+                Icon(
+                    Icons.Filled.MoreVert,
+                    contentDescription = stringResource(R.string.tags_actions),
+                )
+            }
+            DropdownMenu(expanded = menuOpen, onDismissRequest = { menuOpen = false }) {
+                // Panel.kt's MenuItem, not a bare DropdownMenuItem: every one of
+                // these raises a dialog, and it closes the menu BEFORE acting so the
+                // dialog cannot open underneath a menu still hanging over it.
+                val close = { menuOpen = false }
+                MenuItem(R.string.tags_rename, close, onRename)
+                MenuItem(R.string.tags_merge, close, onMerge)
+                MenuItem(R.string.tags_delete, close, onDelete)
+            }
+        }
+    }
+}
+
+/**
+ * Zero is its own sentence, not "0 notes".
+ *
+ * A count of null means the core did not populate one — only `list_labels` does —
+ * which is a different thing from a tag with no notes, so it reads as unknown
+ * rather than as empty.
+ */
+@Composable
+private fun countLabel(count: Long?): String =
+    when {
+        count == null -> ""
+        count <= 0L -> stringResource(R.string.tags_count_none)
+        count == 1L -> stringResource(R.string.tags_count_one)
+        else -> stringResource(R.string.tags_count, count.toInt())
+    }
+
+/**
+ * Rename, with the merge caught before it happens.
+ *
+ * The collision is detected HERE, against the list, rather than from what the
+ * core returns: the merge survivor is whichever tag is older, so it may well be
+ * the one being renamed, and an unchanged id afterwards would prove nothing.
+ * Matching is case-insensitive because the core's is.
+ */
+@Composable
+private fun RenameDialog(
+    tag: Label,
+    others: List<Label>,
+    onDismiss: () -> Unit,
+    onRename: (String) -> Unit,
+    onWouldMerge: (Label, String) -> Unit,
+) {
+    var text by remember(tag.id) { mutableStateOf(tag.name) }
+    val trimmed = text.trim()
+    val clash =
+        others.firstOrNull { it.id != tag.id && it.name.equals(trimmed, ignoreCase = true) }
+    val submit = {
+        when {
+            trimmed.isEmpty() -> Unit
+            clash != null -> onWouldMerge(clash, trimmed)
+            else -> onRename(trimmed)
+        }
+    }
+
+    AlertDialog(
+        onDismissRequest = onDismiss,
+        title = { Text(stringResource(R.string.tags_rename_title, hash(tag.name))) },
+        text = {
+            PlainTextField(
+                value = text,
+                onValueChange = { text = it },
+                hint = R.string.tags_new_hint,
+                singleLine = true,
+                keyboardOptions = KeyboardOptions(imeAction = ImeAction.Done),
+                keyboardActions = KeyboardActions(onDone = { submit() }),
+            )
+        },
+        confirmButton = {
+            TextButton(onClick = submit, enabled = trimmed.isNotEmpty()) {
+                Text(stringResource(R.string.tags_rename_confirm))
+            }
+        },
+        dismissButton = {
+            TextButton(onClick = onDismiss) { Text(stringResource(R.string.tags_cancel)) }
+        },
+    )
+}
+
+/**
+ * Merge, with the direction stated and the survivor named.
+ *
+ * Unlike a rename — where the OLDER tag survives so that the outcome cannot
+ * depend on which way round it was typed — this one is deliberate, so the
+ * direction the person chooses IS the intent and is honoured. The price of that
+ * is that the direction has to be unmissable, which is why the body names the tag
+ * that stops existing and every row here is the one that survives.
+ */
+@Composable
+private fun MergeDialog(
+    tag: Label,
+    others: List<Label>,
+    onDismiss: () -> Unit,
+    onMerge: (Label) -> Unit,
+) {
+    val dark = isSystemInDarkTheme()
+
+    AlertDialog(
+        onDismissRequest = onDismiss,
+        title = { Text(stringResource(R.string.tags_merge_title, hash(tag.name))) },
+        text = {
+            Column(verticalArrangement = Arrangement.spacedBy(8.dp)) {
+                Text(
+                    text = stringResource(R.string.tags_merge_body, hash(tag.name)),
+                    style = MaterialTheme.typography.bodyMedium,
+                )
+                if (others.isEmpty()) {
+                    Text(
+                        text = stringResource(R.string.tags_merge_none),
+                        style = MaterialTheme.typography.bodyMedium,
+                        color = MaterialTheme.colorScheme.onSurfaceVariant,
+                    )
+                }
+                others.forEach { other ->
+                    val tint = labelTintFor(other.name, other.color)
+                    Text(
+                        text = hash(other.name),
+                        style = MaterialTheme.typography.bodyLarge,
+                        color = tint.tagInk(dark),
+                        modifier =
+                            Modifier
+                                .fillMaxWidth()
+                                .clickable { onMerge(other) }
+                                .padding(vertical = 8.dp),
+                    )
+                }
+            }
+        },
+        confirmButton = {},
+        dismissButton = {
+            TextButton(onClick = onDismiss) { Text(stringResource(R.string.tags_cancel)) }
+        },
+    )
+}
+
+/**
+ * The palette, and since the per-note picker was removed this is the only place in
+ * the product a colour is chosen.
+ *
+ * Every key from [NOTE_TINTS], `default` included: a tag whose colour is
+ * `default` gets a hue derived from its name (`DerivedTint.kt`), so "default" here
+ * means "let it pick" rather than "grey", and taking it away would leave no way
+ * back to that.
+ */
+@Composable
+private fun ColourDialog(
+    tag: Label,
+    onDismiss: () -> Unit,
+    onPick: (String) -> Unit,
+) {
+    val dark = isSystemInDarkTheme()
+
+    AlertDialog(
+        onDismissRequest = onDismiss,
+        title = { Text(stringResource(R.string.tags_colour_of, hash(tag.name))) },
+        text = {
+            Column(verticalArrangement = Arrangement.spacedBy(4.dp)) {
+                NOTE_TINTS.forEach { (key, tint) ->
+                    Row(
+                        modifier =
+                            Modifier
+                                .fillMaxWidth()
+                                .clickable { onPick(key) }
+                                .padding(vertical = 8.dp),
+                        verticalAlignment = Alignment.CenterVertically,
+                        horizontalArrangement = Arrangement.spacedBy(12.dp),
+                    ) {
+                        Box(
+                            modifier =
+                                Modifier
+                                    .size(SWATCH)
+                                    .clip(CircleShape)
+                                    .background(tint.chipBackground(dark))
+                                    .border(1.dp, tint.chipBorder(dark), CircleShape),
+                        )
+                        Text(
+                            text = tint.label,
+                            style = MaterialTheme.typography.bodyMedium,
+                            color =
+                                if (key == tag.color) {
+                                    MaterialTheme.colorScheme.primary
+                                } else {
+                                    MaterialTheme.colorScheme.onSurface
+                                },
+                        )
+                    }
+                }
+            }
+        },
+        confirmButton = {},
+        dismissButton = {
+            TextButton(onClick = onDismiss) { Text(stringResource(R.string.tags_cancel)) }
+        },
+    )
+}
+
+/** A destructive confirmation: what it is, what it costs, and one way out. */
+@Composable
+private fun ConfirmDialog(
+    title: String,
+    body: String,
+    confirm: String,
+    onDismiss: () -> Unit,
+    onConfirm: () -> Unit,
+    footnote: String? = null,
+) {
+    AlertDialog(
+        onDismissRequest = onDismiss,
+        title = { Text(title) },
+        text = {
+            Column(verticalArrangement = Arrangement.spacedBy(8.dp)) {
+                Text(text = body, style = MaterialTheme.typography.bodyMedium)
+                footnote?.let {
+                    Text(
+                        text = it,
+                        style = MaterialTheme.typography.labelSmall,
+                        color = MaterialTheme.colorScheme.onSurfaceVariant,
+                    )
+                }
+            }
+        },
+        confirmButton = {
+            TextButton(onClick = onConfirm) { Text(confirm) }
+        },
+        dismissButton = {
+            TextButton(onClick = onDismiss) { Text(stringResource(R.string.tags_cancel)) }
+        },
+    )
+}

android/app/src/main/java/com/fabledsword/thoughtsync/ui/TagsViewModel.kt

@@ -0,0 +1,181 @@
+package com.fabledsword.thoughtsync.ui
+
+import androidx.compose.runtime.getValue
+import androidx.compose.runtime.mutableStateOf
+import androidx.compose.runtime.setValue
+import androidx.lifecycle.ViewModel
+import androidx.lifecycle.ViewModelProvider
+import androidx.lifecycle.viewModelScope
+import com.fabledsword.thoughtsync.core.Label
+import com.fabledsword.thoughtsync.core.ThoughtSync
+import kotlinx.coroutines.Dispatchers
+import kotlinx.coroutines.launch
+import kotlinx.coroutines.withContext
+
+/**
+ * Everything the Tags screen renders from.
+ *
+ * [tags] comes from `list_labels`, which is the only call that populates a
+ * `count` — the single-tag returns leave it null by design. So the counts a
+ * confirmation dialog quotes are always the LIST's, never an operation's result.
+ */
+data class TagsState(
+    val loading: Boolean = true,
+    val tags: List<Label> = emptyList(),
+    /** An in-flight write, for disabling the controls that would race it. */
+    val busy: Boolean = false,
+    val error: String? = null,
+)
+
+/**
+ * Create, rename, recolour, delete and merge tags.
+ *
+ * A peer of the web's `LabelsModal.vue`, not a reduced companion — the same six
+ * operations over the same core the desktop uses.
+ *
+ * ## Why every write re-lists
+ *
+ * A tag operation changes more than the row it names. A merge deletes one tag and
+ * moves its notes; a delete changes nothing else's count but removes a drawer
+ * lens; a rename can MERGE (see below) and so can make a different row vanish.
+ * Re-listing after each write costs one cheap local SQLite read and removes a
+ * whole class of "the screen thinks there are still two" bugs. Patching the list
+ * in place would mean re-deriving, in Kotlin, rules the core already owns.
+ *
+ * ## Renaming can merge
+ *
+ * `rename_label` folds two tags together when the new name is one another tag
+ * already holds, and the OLDER row survives (Scribe #3324). So it can return a
+ * tag whose id is not the one passed in, and it can make another tag stop
+ * existing. The screen asks first; this view model does not, because a
+ * confirmation belongs to the surface with a person in front of it.
+ *
+ * ## Threading
+ *
+ * All of these are ordinary blocking FFI into SQLite — no async, no network — so
+ * they take [Dispatchers.IO], exactly like the board's calls. Sync happens later:
+ * the core marks the rows dirty and the next sync carries them.
+ */
+class TagsViewModel(
+    private val core: ThoughtSync,
+    /**
+     * Called after any write that landed.
+     *
+     * The board holds its own snapshot of the tag list for the drawer, and its
+     * current destination may BE one of these tags — deleting or merging that one
+     * leaves it looking at a lens that no longer exists. Wiring the two together
+     * explicitly is less magic than a shared event bus and makes the dependency
+     * visible at the construction site, the same way [SyncViewModel] does it.
+     */
+    private val onStoreChanged: () -> Unit,
+) : ViewModel() {
+    var state by mutableStateOf(TagsState())
+        private set
+
+    init {
+        refresh()
+    }
+
+    fun refresh() {
+        viewModelScope.launch {
+            state =
+                runCatching { withContext(Dispatchers.IO) { core.listLabels() } }
+                    .fold(
+                        onSuccess = { state.copy(tags = it, loading = false, error = null) },
+                        // Unlike the drawer, this screen cannot fail quietly: it is
+                        // the only thing on the display, and an empty list here
+                        // would read as "you have no tags" rather than "I couldn't
+                        // look".
+                        onFailure = { state.copy(loading = false, error = it.describeTagFailure()) },
+                    )
+        }
+    }
+
+    fun create(name: String) {
+        val trimmed = name.trim()
+        if (trimmed.isEmpty()) return
+        // Find-or-create in the core: typing a name that exists in another case
+        // attaches the existing tag rather than minting a near-duplicate.
+        write { it.createLabel(trimmed) }
+    }
+
+    fun rename(
+        id: String,
+        name: String,
+    ) {
+        val trimmed = name.trim()
+        if (trimmed.isEmpty()) return
+        write { it.renameLabel(id, trimmed) }
+    }
+
+    fun setColour(
+        id: String,
+        colour: String,
+    ) = write { it.setLabelColor(id, colour) }
+
+    fun remove(id: String) = write { it.removeLabel(id) }
+
+    /**
+     * Fold [sourceId] into [targetId]. The source stops existing.
+     *
+     * Directional and not undone by repeating it — the caller has to have said
+     * which one survives before this runs, because afterwards there is nothing
+     * left to read the direction from.
+     */
+    fun merge(
+        sourceId: String,
+        targetId: String,
+    ) {
+        if (sourceId == targetId) return
+        write { it.mergeLabels(sourceId, targetId) }
+    }
+
+    fun dismissError() {
+        state = state.copy(error = null)
+    }
+
+    /**
+     * Run one store write, then re-list and tell the board.
+     *
+     * `busy` is cleared in the same assignment that stores the result, so no path
+     * out of here can leave the screen stuck with its controls disabled.
+     */
+    private fun write(block: (ThoughtSync) -> Unit) {
+        if (state.busy) return
+        state = state.copy(busy = true, error = null)
+        viewModelScope.launch {
+            val failure =
+                runCatching { withContext(Dispatchers.IO) { block(core) } }
+                    .exceptionOrNull()
+            val tags =
+                runCatching { withContext(Dispatchers.IO) { core.listLabels() } }
+                    .getOrDefault(state.tags)
+            state =
+                state.copy(
+                    tags = tags,
+                    busy = false,
+                    error = failure?.describeTagFailure(),
+                )
+            // Even a FAILED write can have changed the store — a merge that threw
+            // partway still moved rows — so the board is told either way.
+            onStoreChanged()
+        }
+    }
+
+    companion object {
+        fun factory(
+            core: ThoughtSync,
+            onStoreChanged: () -> Unit,
+        ): ViewModelProvider.Factory =
+            object : ViewModelProvider.Factory {
+                @Suppress("UNCHECKED_CAST")
+                override fun <T : ViewModel> create(modelClass: Class<T>): T = TagsViewModel(core, onStoreChanged) as T
+            }
+    }
+}
+
+/**
+ * The core reports problems as one error type carrying a message meant to be
+ * shown, so the message is used when there is one.
+ */
+private fun Throwable.describeTagFailure(): String = message ?: "Something went wrong."

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

@@ -66,6 +66,51 @@
     <string name="editor_delete_forever_body">It will be removed from this device and from every device you sync with. This cannot be undone.</string>
     <string name="editor_delete_forever_confirm">Delete</string>
 
+    <!-- Tag management. The whole vocabulary is "tag" (see Scribe #2966); the
+         schema still says Label, and no string here needs to know that. -->
+    <string name="tags_manage">Manage tags</string>
+    <string name="tags_title">Tags</string>
+    <string name="tags_back">Back</string>
+    <string name="tags_new_hint">New tag</string>
+    <string name="tags_create">Create</string>
+    <string name="tags_count">%1$d notes</string>
+    <string name="tags_count_one">1 note</string>
+    <string name="tags_count_none">No notes yet</string>
+    <string name="tags_empty_title">No tags yet</string>
+    <string name="tags_empty_body">Create one above, or write a #tag in a note and it becomes one.</string>
+    <string name="tags_actions">More actions</string>
+    <string name="tags_colour">Colour</string>
+    <string name="tags_colour_of">Colour for %1$s</string>
+
+    <string name="tags_rename">Rename</string>
+    <string name="tags_rename_title">Rename %1$s</string>
+    <string name="tags_rename_confirm">Rename</string>
+    <!-- Renaming onto an existing tag merges the two, older survives (Scribe
+         #3324). A merge cannot be undone by repeating it and is reachable here by
+         a typo, so it says so before it happens — same reasoning as #2116. -->
+    <string name="tags_rename_merges_title">Merge with %1$s?</string>
+    <string name="tags_rename_merges_body">A tag called %1$s already exists. Renaming will merge these two into one, carrying every note from both. The notes are kept; one of the two tags stops existing, and that cannot be undone.</string>
+    <string name="tags_rename_merges_confirm">Merge</string>
+
+    <string name="tags_merge">Merge into…</string>
+    <string name="tags_merge_title">Merge %1$s into…</string>
+    <!-- The survivor is named in the button, not just the title: this is the one
+         operation here that repeating does not undo. -->
+    <string name="tags_merge_body">Every note tagged %1$s will be tagged with the one you pick instead, and %1$s will stop existing. The notes are kept.</string>
+    <string name="tags_merge_none">There is no other tag to merge into.</string>
+
+    <string name="tags_delete">Delete</string>
+    <string name="tags_delete_title">Delete %1$s?</string>
+    <string name="tags_delete_body">It will be removed from every note that has it, on every device you sync with. The notes themselves are kept.</string>
+    <string name="tags_delete_body_counted">It is on %1$d notes. It will be removed from all of them, on every device you sync with. The notes themselves are kept.</string>
+    <string name="tags_delete_confirm">Delete</string>
+    <!-- A tag written as #tag in a note's body is owned by that text. Deleting the
+         row cannot un-write the word, so it comes back on that note's next edit —
+         said here rather than left as a surprise. -->
+    <string name="tags_delete_from_text">Tags written as #tag in a note come back when that note is next edited.</string>
+
+    <string name="tags_cancel">Cancel</string>
+
     <!-- Pickers -->
     <string name="label_picker_title">Tags</string>
     <string name="label_new_hint">Type a tag and press enter</string>