feat: add compose signature pre-filled in text-based post screens

Adds a Signature field to Compose Settings (global UI settings, DataStore
persisted). When opening any text-based composer — new note, reply, quote,
poll, NIP-22 comment (reply/hashtag/geohash/url), or a new long-form
article — the signature is appended to the message with a blank line,
keeping the cursor at the start so the user types above it.

Drafts, forks, and version edits are skipped since their content already
carries (or deliberately omits) a signature, and an untouched
signature-only message is treated as blank so closing the composer never
auto-saves a junk draft.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01Vq4JQPB9m62nJ8Vdp7xVLN

amethyst/src/main/java/com/vitorpamplona/amethyst/model/UiSettings.kt

@@ -57,6 +57,7 @@ data class UiSettings(
     val accentColor: AccentColorType = AccentColorType.PURPLE,
     val fontFamily: FontFamilyType = FontFamilyType.SYSTEM,
     val fontSize: FontSizeType = FontSizeType.NORMAL,
+    val composeSignature: String = "",
 )
 
 enum class ThemeType(

amethyst/src/main/java/com/vitorpamplona/amethyst/model/UiSettingsFlow.kt

@@ -57,6 +57,7 @@ class UiSettingsFlow(
     val accentColor: MutableStateFlow<AccentColorType> = MutableStateFlow(AccentColorType.PURPLE),
     val fontFamily: MutableStateFlow<FontFamilyType> = MutableStateFlow(FontFamilyType.SYSTEM),
     val fontSize: MutableStateFlow<FontSizeType> = MutableStateFlow(FontSizeType.NORMAL),
+    val composeSignature: MutableStateFlow<String> = MutableStateFlow(""),
 ) {
     val listOfFlows: List<Flow<Any?>> =
         listOf<Flow<Any?>>(
@@ -88,6 +89,7 @@ class UiSettingsFlow(
             accentColor,
             fontFamily,
             fontSize,
+            composeSignature,
         )
 
     // emits at every change in any of the propertyes.
@@ -123,6 +125,7 @@ class UiSettingsFlow(
                 flows[25] as AccentColorType,
                 flows[26] as FontFamilyType,
                 flows[27] as FontSizeType,
+                flows[28] as String,
             )
         }
 
@@ -156,6 +159,7 @@ class UiSettingsFlow(
             accentColor.value,
             fontFamily.value,
             fontSize.value,
+            composeSignature.value,
         )
 
     fun update(torSettings: UiSettings): Boolean {
@@ -273,6 +277,10 @@ class UiSettingsFlow(
             fontSize.tryEmit(torSettings.fontSize)
             any = true
         }
+        if (composeSignature.value != torSettings.composeSignature) {
+            composeSignature.tryEmit(torSettings.composeSignature)
+            any = true
+        }
 
         return any
     }
@@ -326,6 +334,7 @@ class UiSettingsFlow(
                 MutableStateFlow(uiSettings.accentColor),
                 MutableStateFlow(uiSettings.fontFamily),
                 MutableStateFlow(uiSettings.fontSize),
+                MutableStateFlow(uiSettings.composeSignature),
             )
     }
 }

amethyst/src/main/java/com/vitorpamplona/amethyst/model/preferences/UISharedPreferences.kt

@@ -126,6 +126,7 @@ class UiSharedPreferences(
         val UI_ACCENT_COLOR = stringPreferencesKey("ui.accent_color")
         val UI_FONT_FAMILY = stringPreferencesKey("ui.font_family")
         val UI_FONT_SIZE = stringPreferencesKey("ui.font_size")
+        val UI_COMPOSE_SIGNATURE = stringPreferencesKey("ui.compose_signature")
 
         suspend fun uiPreferences(context: Context): UiSettings? =
             try {
@@ -166,6 +167,7 @@ class UiSharedPreferences(
                     accentColor = preferences[UI_ACCENT_COLOR]?.let { AccentColorType.valueOf(it) } ?: AccentColorType.PURPLE,
                     fontFamily = preferences[UI_FONT_FAMILY]?.let { FontFamilyType.valueOf(it) } ?: FontFamilyType.SYSTEM,
                     fontSize = preferences[UI_FONT_SIZE]?.let { FontSizeType.valueOf(it) } ?: FontSizeType.NORMAL,
+                    composeSignature = preferences[UI_COMPOSE_SIGNATURE] ?: "",
                 )
             } catch (e: Exception) {
                 if (e is CancellationException) throw e
@@ -218,6 +220,7 @@ class UiSharedPreferences(
                     preferences[UI_ACCENT_COLOR] = sharedSettings.accentColor.name
                     preferences[UI_FONT_FAMILY] = sharedSettings.fontFamily.name
                     preferences[UI_FONT_SIZE] = sharedSettings.fontSize.name
+                    preferences[UI_COMPOSE_SIGNATURE] = sharedSettings.composeSignature
                 }
             } catch (e: Exception) {
                 if (e is CancellationException) throw e

amethyst/src/main/java/com/vitorpamplona/amethyst/ui/note/nip22Comments/CommentPostViewModel.kt

@@ -34,6 +34,7 @@ import androidx.lifecycle.viewModelScope
 import com.vitorpamplona.amethyst.Amethyst
 import com.vitorpamplona.amethyst.R
 import com.vitorpamplona.amethyst.commons.model.nip30CustomEmojis.EmojiPackState
+import com.vitorpamplona.amethyst.commons.ui.text.appendSignature
 import com.vitorpamplona.amethyst.commons.ui.text.currentWord
 import com.vitorpamplona.amethyst.commons.ui.text.insertUrlAtCursor
 import com.vitorpamplona.amethyst.commons.ui.text.replaceCurrentWord
@@ -160,6 +161,10 @@ open class CommentPostViewModel :
     var externalIdentity by mutableStateOf<ExternalId?>(null)
     var replyingTo: Note? by mutableStateOf(null)
 
+    // The signature pre-filled by applySignature(), so an untouched signature-only
+    // message is treated as blank instead of auto-saved as a junk draft.
+    private var appliedSignature: String? = null
+
     val iMetaAttachments = IMetaAttachments()
     var nip95attachments by mutableStateOf<List<Pair<FileStorageEvent, FileStorageHeaderEvent>>>(
         emptyList(),
@@ -407,6 +412,20 @@ open class CommentPostViewModel :
         urlPreviews.update(message.text.toString())
     }
 
+    /**
+     * Pre-fills the signature from Compose Settings at the end of the message. Skipped by
+     * callers when loading a draft (the draft content already carries — or deliberately
+     * omits — a signature).
+     */
+    fun applySignature() {
+        val signature = accountViewModel.settings.composeSignature()
+        if (signature.isEmpty()) return
+
+        appliedSignature = signature
+        message.appendSignature(signature)
+        urlPreviews.update(message.text.toString())
+    }
+
     private fun loadFromDraft(draft: Note) {
         val draftEvent = draft.event ?: return
         if (draftEvent !is CommentEvent) return
@@ -513,7 +532,8 @@ open class CommentPostViewModel :
     }
 
     suspend fun sendDraftSync() {
-        if (message.text.toString().isBlank()) {
+        val text = message.text.toString()
+        if (text.isBlank() || text.trim() == appliedSignature) {
             accountViewModel.account.deleteDraftIgnoreErrors(draftNote)
         } else if (accountViewModel.settings.automaticallyCreateDrafts()) {
             val attachments = mutableSetOf<Event>()

amethyst/src/main/java/com/vitorpamplona/amethyst/ui/note/nip22Comments/GenericCommentPostScreen.kt

@@ -136,6 +136,9 @@ fun ReplyCommentPostScreen(
                 postViewModel.selectImage(persistentListOf(SelectedMedia(it, mediaType)))
             }
         }
+        if (draftId == null) {
+            postViewModel.applySignature()
+        }
     }
 
     GenericCommentPostScreen(postViewModel, accountViewModel, nav)

amethyst/src/main/java/com/vitorpamplona/amethyst/ui/screen/UiSettingsState.kt

@@ -135,6 +135,8 @@ class UiSettingsState(
 
     fun automaticallyCreateDrafts() = uiSettingsFlow.automaticallyCreateDrafts.value == BooleanType.ALWAYS
 
+    fun composeSignature() = uiSettingsFlow.composeSignature.value.trim()
+
     fun isImmersiveScrollingActive() = uiSettingsFlow.automaticallyHideNavigationBars.value == BooleanType.ALWAYS
 
     fun showProfilePictures() = showProfilePictures.value

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

@@ -140,6 +140,9 @@ fun LongFormPostScreen(
         val draft = draftId?.let { accountViewModel.getNoteIfExists(it) }
         val version = versionId?.let { accountViewModel.getNoteIfExists(it) }
         postViewModel.load(draft, version)
+        if (draftId == null && versionId == null) {
+            postViewModel.applySignature()
+        }
     }
 
     WatchAndLoadMyEmojiList(accountViewModel)

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

@@ -35,6 +35,7 @@ import androidx.lifecycle.viewModelScope
 import com.vitorpamplona.amethyst.Amethyst
 import com.vitorpamplona.amethyst.R
 import com.vitorpamplona.amethyst.commons.model.nip30CustomEmojis.EmojiPackState.EmojiMedia
+import com.vitorpamplona.amethyst.commons.ui.text.appendSignature
 import com.vitorpamplona.amethyst.commons.ui.text.currentWord
 import com.vitorpamplona.amethyst.commons.ui.text.insertUrlAtCursor
 import com.vitorpamplona.amethyst.commons.ui.text.replaceCurrentWord
@@ -151,6 +152,10 @@ class LongFormPostViewModel :
         }
     }
 
+    // The signature pre-filled by applySignature(), so an untouched signature-only
+    // body is treated as blank instead of auto-saved as a junk draft.
+    private var appliedSignature: String? = null
+
     var title by mutableStateOf(TextFieldValue(""))
     var summary by mutableStateOf(TextFieldValue(""))
     var coverImageUrl by mutableStateOf("")
@@ -271,6 +276,19 @@ class LongFormPostViewModel :
         }
     }
 
+    /**
+     * Pre-fills the signature from Compose Settings at the end of the article body. Skipped
+     * by callers when loading a draft or editing an existing version (the content already
+     * carries — or deliberately omits — a signature).
+     */
+    fun applySignature() {
+        val signature = accountViewModel.settings.composeSignature()
+        if (signature.isEmpty()) return
+
+        appliedSignature = signature
+        message.appendSignature(signature)
+    }
+
     private fun loadFromDraft(draft: Note) {
         val draftEvent = draft.event ?: return
         if (draftEvent is LongTextNoteEvent) {
@@ -355,7 +373,8 @@ class LongFormPostViewModel :
     }
 
     suspend fun sendDraftSync() {
-        if (message.text.toString().isBlank() && title.text.isBlank()) {
+        val text = message.text.toString()
+        if ((text.isBlank() || text.trim() == appliedSignature) && title.text.isBlank()) {
             accountViewModel.account.deleteDraftIgnoreErrors(draftNote)
         } else if (accountViewModel.settings.automaticallyCreateDrafts()) {
             val template = createTemplate() ?: return

amethyst/src/main/java/com/vitorpamplona/amethyst/ui/screen/loggedIn/geohash/GeoHashPostScreen.kt

@@ -76,6 +76,9 @@ fun GeoHashPostScreen(
                 postViewModel.selectImage(persistentListOf(SelectedMedia(it, mediaType)))
             }
         }
+        if (draftId == null) {
+            postViewModel.applySignature()
+        }
     }
 
     GenericCommentPostScreen(postViewModel, accountViewModel, nav)

amethyst/src/main/java/com/vitorpamplona/amethyst/ui/screen/loggedIn/hashtag/HashtagPostScreen.kt

@@ -76,6 +76,9 @@ fun HashtagPostScreen(
                 postViewModel.selectImage(persistentListOf(SelectedMedia(it, mediaType)))
             }
         }
+        if (draftId == null) {
+            postViewModel.applySignature()
+        }
     }
 
     GenericCommentPostScreen(postViewModel, accountViewModel, nav)

amethyst/src/main/java/com/vitorpamplona/amethyst/ui/screen/loggedIn/home/ShortNotePostScreen.kt

@@ -180,6 +180,9 @@ fun ShortNotePostScreen(
                 postViewModel.selectImage(persistentListOf(SelectedMedia(it, mediaType)))
             }
         }
+        if (draftId == null && forkId == null) {
+            postViewModel.applySignature()
+        }
     }
 
     DisposableEffect(nav, activity) {

amethyst/src/main/java/com/vitorpamplona/amethyst/ui/screen/loggedIn/home/ShortNotePostViewModel.kt

@@ -36,6 +36,7 @@ import androidx.lifecycle.viewModelScope
 import com.vitorpamplona.amethyst.Amethyst
 import com.vitorpamplona.amethyst.R
 import com.vitorpamplona.amethyst.commons.model.nip30CustomEmojis.EmojiPackState.EmojiMedia
+import com.vitorpamplona.amethyst.commons.ui.text.appendSignature
 import com.vitorpamplona.amethyst.commons.ui.text.currentWord
 import com.vitorpamplona.amethyst.commons.ui.text.insertUrlAtCursor
 import com.vitorpamplona.amethyst.commons.ui.text.replaceCurrentWord
@@ -209,6 +210,10 @@ open class ShortNotePostViewModel :
     var originalNote: Note? by mutableStateOf(null)
     var forkedFromNote: Note? by mutableStateOf(null)
 
+    // The signature pre-filled by applySignature(), so an untouched signature-only
+    // message is treated as blank instead of auto-saved as a junk draft.
+    private var appliedSignature: String? = null
+
     var pTags by mutableStateOf<List<User>?>(null)
     var eTags by mutableStateOf<List<Note>?>(null)
 
@@ -609,6 +614,20 @@ open class ShortNotePostViewModel :
         urlPreviews.update(message.text.toString())
     }
 
+    /**
+     * Pre-fills the signature from Compose Settings at the end of the message. Skipped by
+     * callers when loading a draft or forking (the existing content already carries — or
+     * deliberately omits — a signature).
+     */
+    fun applySignature() {
+        val signature = accountViewModel.settings.composeSignature()
+        if (signature.isEmpty()) return
+
+        appliedSignature = signature
+        message.appendSignature(signature)
+        urlPreviews.update(message.text.toString())
+    }
+
     private fun loadFromDraft(draft: Note) {
         val draftEvent = draft.event ?: return
         if (draftEvent is TextNoteEvent) {
@@ -974,7 +993,8 @@ open class ShortNotePostViewModel :
     }
 
     suspend fun sendDraftSync() {
-        if (message.text.toString().isBlank()) {
+        val text = message.text.toString()
+        if (text.isBlank() || text.trim() == appliedSignature) {
             accountViewModel.account.deleteDraftIgnoreErrors(draftNote)
         } else if (accountViewModel.settings.automaticallyCreateDrafts()) {
             val attachments = mutableSetOf<Event>()

amethyst/src/main/java/com/vitorpamplona/amethyst/ui/screen/loggedIn/polls/PollPostScreen.kt

@@ -51,6 +51,9 @@ fun PollPostScreen(
             postViewModel.onMessageChanged()
         }
         postViewModel.wantsPoll = true
+        if (draftId == null) {
+            postViewModel.applySignature()
+        }
     }
 
     NewPostScreenInner(postViewModel, accountViewModel, nav)

amethyst/src/main/java/com/vitorpamplona/amethyst/ui/screen/loggedIn/settings/ComposeSettingsScreen.kt

@@ -23,11 +23,14 @@ package com.vitorpamplona.amethyst.ui.screen.loggedIn.settings
 import androidx.annotation.StringRes
 import androidx.compose.foundation.layout.Arrangement
 import androidx.compose.foundation.layout.Column
+import androidx.compose.foundation.layout.fillMaxWidth
 import androidx.compose.foundation.layout.padding
 import androidx.compose.foundation.rememberScrollState
 import androidx.compose.foundation.verticalScroll
+import androidx.compose.material3.OutlinedTextField
 import androidx.compose.material3.Scaffold
 import androidx.compose.material3.Switch
+import androidx.compose.material3.Text
 import androidx.compose.runtime.Composable
 import androidx.compose.runtime.collectAsState
 import androidx.compose.runtime.getValue
@@ -109,10 +112,30 @@ fun ComposeSettingsContent(
             )
             SettingsDivider()
             AddClientTagTile(accountViewModel)
+            SettingsDivider()
+            SignatureTile(sharedPrefs.composeSignature)
         }
     }
 }
 
+@Composable
+private fun SignatureTile(flow: MutableStateFlow<String>) {
+    val value by flow.collectAsState()
+
+    SettingsBlockTile(
+        icon = MaterialSymbols.EditNote,
+        title = stringRes(R.string.compose_signature_setting_title),
+        description = stringRes(R.string.compose_signature_setting_description),
+    ) {
+        OutlinedTextField(
+            value = value,
+            onValueChange = { flow.tryEmit(it) },
+            placeholder = { Text(stringRes(R.string.compose_signature_setting_hint)) },
+            modifier = Modifier.fillMaxWidth(),
+        )
+    }
+}
+
 @Composable
 private fun AddClientTagTile(accountViewModel: AccountViewModel) {
     val addClientTag by accountViewModel.account.settings.syncedSettings.security

amethyst/src/main/java/com/vitorpamplona/amethyst/ui/screen/loggedIn/url/UrlPostScreen.kt

@@ -78,6 +78,9 @@ fun UrlPostScreen(
                 postViewModel.selectImage(persistentListOf(SelectedMedia(it, mediaType)))
             }
         }
+        if (draftId == null) {
+            postViewModel.applySignature()
+        }
     }
 
     GenericCommentPostScreen(postViewModel, accountViewModel, nav)

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

@@ -1782,7 +1782,7 @@
     <string name="ots_explorer_search_keywords" translatable="false">opentimestamps, timestamp, ots, proof</string>
     <string name="namecoin_search_keywords" translatable="false">namecoin, dns, identity, name</string>
     <string name="calendar_reminder_search_keywords" translatable="false">calendar, events, reminders, rsvp</string>
-    <string name="compose_search_keywords" translatable="false">draft, posting, editor, auto-save</string>
+    <string name="compose_search_keywords" translatable="false">draft, posting, editor, auto-save, signature</string>
     <string name="reactions_settings_search_keywords" translatable="false">emoji, reactions, like</string>
     <string name="bottom_bar_search_keywords" translatable="false">navigation, tabs, nav bar</string>
     <string name="home_tabs_search_keywords" translatable="false">tabs, feeds, threads, conversations</string>
@@ -3622,6 +3622,9 @@
     <string name="compose_settings">Compose Settings</string>
     <string name="auto_create_drafts_setting_title">Automatically create drafts</string>
     <string name="auto_create_drafts_setting_description">Saves a draft event automatically when you type or leave a composer with unsent text and sends to your private outbox relays.</string>
+    <string name="compose_signature_setting_title">Signature</string>
+    <string name="compose_signature_setting_description">Added at the end of the message when opening a new post, reply, quote, or article. Leave empty to disable.</string>
+    <string name="compose_signature_setting_hint">Your signature</string>
     <string name="ai_writing_use_this">Use This</string>
     <string name="ai_writing_dismiss">Dismiss</string>
     <string name="ai_tone_correct">Correct</string>

commons/src/commonMain/kotlin/com/vitorpamplona/amethyst/commons/ui/text/TextFieldStateExtensions.kt

@@ -32,6 +32,21 @@ fun TextFieldState.setTextAndPlaceCursorAtBeginning(text: String) {
     }
 }
 
+/**
+ * Appends [signature] to the end of the field, separated by a blank line, keeping the
+ * cursor where it was so the user starts typing above it. No-op when the signature is
+ * already present, so re-running a screen's load logic never duplicates it.
+ */
+fun TextFieldState.appendSignature(signature: String) {
+    if (text.contains(signature)) return
+    edit {
+        val cursor = selection
+        append("\n\n")
+        append(signature)
+        selection = cursor
+    }
+}
+
 fun TextFieldState.insertUrlAtCursor(url: String) {
     edit {
         var toInsert = url.trim()

commons/src/commonTest/kotlin/com/vitorpamplona/amethyst/commons/ui/text/AppendSignatureTest.kt

@@ -0,0 +1,60 @@
+/*
+ * Copyright (c) 2025 Vitor Pamplona
+ *
+ * Permission is hereby granted, free of charge, to any person obtaining a copy of
+ * this software and associated documentation files (the "Software"), to deal in
+ * the Software without restriction, including without limitation the rights to use,
+ * copy, modify, merge, publish, distribute, sublicense, and/or sell copies of the
+ * Software, and to permit persons to whom the Software is furnished to do so,
+ * subject to the following conditions:
+ *
+ * The above copyright notice and this permission notice shall be included in all
+ * copies or substantial portions of the Software.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+ * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY, FITNESS
+ * FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR
+ * COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN
+ * AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION
+ * WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.
+ */
+package com.vitorpamplona.amethyst.commons.ui.text
+
+import androidx.compose.foundation.text.input.TextFieldState
+import kotlin.test.Test
+import kotlin.test.assertEquals
+
+class AppendSignatureTest {
+    @Test
+    fun appendsToEmptyFieldKeepingCursorAtStart() {
+        val state = TextFieldState()
+
+        state.appendSignature("— me")
+
+        assertEquals("\n\n— me", state.text.toString())
+        assertEquals(0, state.selection.start)
+        assertEquals(0, state.selection.end)
+    }
+
+    @Test
+    fun appendsAfterExistingContentKeepingCursor() {
+        val state = TextFieldState("nostr:quote")
+        state.setTextAndPlaceCursorAtBeginning("nostr:quote")
+
+        state.appendSignature("— me")
+
+        assertEquals("nostr:quote\n\n— me", state.text.toString())
+        assertEquals(0, state.selection.start)
+        assertEquals(0, state.selection.end)
+    }
+
+    @Test
+    fun doesNotDuplicateWhenSignatureAlreadyPresent() {
+        val state = TextFieldState()
+
+        state.appendSignature("— me")
+        state.appendSignature("— me")
+
+        assertEquals("\n\n— me", state.text.toString())
+    }
+}