android: a Tags screen, so the phone can do more than attach tags to a note

Android could list tags and mint new ones. It could not rename, recolour,
delete or merge one — and since the per-note colour picker was removed with
2949, tag colour is the ONLY colour control in the product, which meant an
Android-only session had no way to change any colour anywhere.

A destination reached from the drawer, not a modal. The web's LabelsModal is
a modal because a desktop can float one over the board; on a phone this is a
place you go to tidy up, and a full screen is what that is.

The manage entry is an action ON the drawer's Tags header rather than a row
in it, so it cannot be mistaken for a sixth lens. The header now renders even
when there are no tags: this screen is where you make the first one, and
hiding the way in until one exists is a door that only appears once you are
already inside.

## The two calls this needed

RENAME and MERGE deliberately do not follow the same rule, and the screen
says so rather than hiding it.

  * A rename that lands on an existing name merges, older survives (3324).
    That path is accident-prone — it is a text field, and a typo reaches it —
    so it needs a rule that cannot depend on which way round it was typed.
    The screen catches the collision against the LIST, not from what the core
    returns: the survivor may be the tag being renamed, so an unchanged id
    afterwards proves nothing. Then it asks before merging.

  * An explicit merge keeps its direction. Here the person is choosing, and
    the direction IS the intent — folding #grocery into #groceries is a
    decision, and overriding it with age would refuse the thing they asked
    for. The price is that the direction has to be unmissable, so the body
    names the tag that stops existing and every row offered is the survivor.

Delete quotes the note count, because "it is on 40 notes" is a different
decision from "delete this tag?". The count comes from `list_labels`, the
only call the core populates one on. It also says that a tag written as #tag
in a body comes back on that note's next edit — deleting the row cannot
un-write the word, and that is better said than discovered.

## The board had to learn something

`Destination.WithLabel` holds an id, and deleting or merging a tag the board
is currently LOOKING at would strand it on a lens that queries a row which no
longer exists — permanently empty, escapable only via the drawer. So
`loadLabels` became `refreshLabels`: public, and it drops back to Notes when
the current lens is gone. A failed listing deliberately does NOT trigger that
fallback — "I could not read the tags" is not evidence that this one went.

Reused rather than rewritten: `ErrorBanner` (the board and editor already
share it), `MenuItem` from Panel.kt (it closes the menu before acting so a
dialog cannot open under a hanging menu), `PlainTextField`, and the
`NOTE_TINTS` palette — the screen consumes it and does not fork a copy.

`default` stays in the palette on purpose: a tag with that colour gets a hue
derived from its name, so it means "let it pick", and removing it would leave
no way back to that.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01K3MMqUtzX1TJgA1oypvm1c

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>