feat: optional subject/title field in the ShortNotePostScreen composer

Add a subject line toggled from the composer's bottom row. On a kind-1 note it
becomes a NIP-14 `subject` tag; on a NIP-29 kind-11 group thread it becomes the
`title` (superseding the first-line-as-title heuristic — that stays as the
fallback when the field is left empty). The field is auto-shown for group
threads and labelled "Title" there, "Subject" otherwise.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01B5MLY4hq5LXJ2D5WeLRyXj

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

@@ -45,6 +45,7 @@ import androidx.compose.material3.ExperimentalMaterial3Api
 import androidx.compose.material3.FilterChip
 import androidx.compose.material3.IconButton
 import androidx.compose.material3.MaterialTheme
+import androidx.compose.material3.OutlinedTextField
 import androidx.compose.material3.Scaffold
 import androidx.compose.material3.Surface
 import androidx.compose.material3.Switch
@@ -350,6 +351,26 @@ private fun NewPostScreenBody(
                     )
                 }
 
+                if (postViewModel.wantsSubject) {
+                    OutlinedTextField(
+                        value = postViewModel.subjectText,
+                        onValueChange = { postViewModel.subjectText = it },
+                        singleLine = true,
+                        label = {
+                            Text(
+                                stringRes(
+                                    if (postViewModel.groupThreadTarget != null) {
+                                        R.string.relay_group_thread_title_label
+                                    } else {
+                                        R.string.messages_new_message_subject
+                                    },
+                                ),
+                            )
+                        },
+                        modifier = Modifier.fillMaxWidth().padding(vertical = Size10dp),
+                    )
+                }
+
                 // Only show text input if no voice message is being posted
                 if (postViewModel.voiceMetadata == null && postViewModel.voiceRecording == null) {
                     Row(
@@ -788,6 +809,10 @@ private fun BottomRowActions(
             }
         }
 
+        AddSubjectButton(postViewModel.wantsSubject) {
+            postViewModel.toggleSubject()
+        }
+
         MarkAsSensitiveButton(postViewModel.wantsToMarkAsSensitive) {
             postViewModel.toggleMarkAsSensitive()
         }
@@ -857,6 +882,21 @@ private fun AddPrivateNoteButton(
     }
 }
 
+@Composable
+private fun AddSubjectButton(
+    isActive: Boolean,
+    onClick: () -> Unit,
+) {
+    IconButton(onClick = onClick) {
+        Icon(
+            symbol = MaterialSymbols.AutoMirrored.Article,
+            contentDescription = stringRes(R.string.messages_new_message_subject),
+            modifier = Modifier.height(22.dp),
+            tint = if (isActive) MaterialTheme.colorScheme.primary else MaterialTheme.colorScheme.onBackground,
+        )
+    }
+}
+
 @Composable
 private fun AddPollButton(
     isPollActive: Boolean,

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

@@ -116,6 +116,7 @@ import com.vitorpamplona.quartz.nip10Notes.content.findURLs
 import com.vitorpamplona.quartz.nip10Notes.tags.markedETags
 import com.vitorpamplona.quartz.nip10Notes.tags.notify
 import com.vitorpamplona.quartz.nip10Notes.tags.prepareETagsAsReplyTo
+import com.vitorpamplona.quartz.nip14Subject.subject
 import com.vitorpamplona.quartz.nip18Reposts.quotes.quotes
 import com.vitorpamplona.quartz.nip18Reposts.quotes.taggedQuoteIds
 import com.vitorpamplona.quartz.nip22Comments.CommentEvent
@@ -310,6 +311,11 @@ open class ShortNotePostViewModel :
     override var forwardZapTo = mutableStateOf<SplitBuilder<User>>(SplitBuilder())
     override val forwardZapToEditting = TextFieldState()
 
+    // Optional subject line: a NIP-14 `subject` tag on a kind-1 note, or the `title` of a NIP-29
+    // kind-11 group thread. Toggled from the bottom row; auto-on for group threads.
+    var wantsSubject by mutableStateOf(false)
+    var subjectText by mutableStateOf("")
+
     // NSFW, Sensitive
     var wantsToMarkAsSensitive by mutableStateOf(false)
     var contentWarningDescription by mutableStateOf("")
@@ -504,6 +510,8 @@ open class ShortNotePostViewModel :
     ) {
         val relay = relayUrl?.let { RelayUrlNormalizer.normalizeOrNull(it) }
         groupThreadTarget = if (groupId != null && relay != null) GroupThreadTarget(groupId, listOf(relay)) else null
+        // A thread wants a title, so surface the field by default when composing one.
+        if (groupThreadTarget != null) wantsSubject = true
     }
 
     open fun load(
@@ -1114,12 +1122,14 @@ open class ShortNotePostViewModel :
 
         val threadTarget = groupThreadTarget
         return if (threadTarget != null) {
-            // NIP-29 kind-11 group thread: title = first line, body = the rest (or the whole line
-            // when single-line). Scoped to the group by `h`; the host relay authorizes the write.
+            // NIP-29 kind-11 group thread. The title is the explicit subject field when filled;
+            // otherwise it falls back to the first line (body = the rest). Scoped to the group by
+            // `h`; the host relay authorizes the write.
+            val subject = if (wantsSubject) subjectText.trim() else ""
             val text = tagger.message
             val firstBreak = text.indexOf('\n')
-            val title = (if (firstBreak >= 0) text.substring(0, firstBreak) else text).trim()
-            val body = (if (firstBreak >= 0) text.substring(firstBreak + 1) else text).trim()
+            val title = subject.ifEmpty { (if (firstBreak >= 0) text.substring(0, firstBreak) else text).trim() }
+            val body = if (subject.isNotEmpty()) text.trim() else (if (firstBreak >= 0) text.substring(firstBreak + 1) else text).trim()
 
             ThreadEvent.build(body, title) {
                 hTag(threadTarget.groupId)
@@ -1261,6 +1271,8 @@ open class ShortNotePostViewModel :
                 references(findURLs(tagger.message))
                 quotes(findNostrUris(tagger.message))
 
+                if (wantsSubject && subjectText.isNotBlank()) subject(subjectText.trim())
+
                 geoHash?.let { geohash(it) }
                 localZapRaiserAmount?.let { zapraiser(it) }
                 zapReceiver?.let { zapSplits(it) }
@@ -1434,6 +1446,8 @@ open class ShortNotePostViewModel :
         zapRaiserAmount.value = null
 
         wantsForwardZapTo = false
+        wantsSubject = false
+        subjectText = ""
         wantsToMarkAsSensitive = false
         contentWarningDescription = ""
         wantsToAddGeoHash = false
@@ -1821,6 +1835,12 @@ open class ShortNotePostViewModel :
         draftTag.newVersion()
     }
 
+    fun toggleSubject() {
+        wantsSubject = !wantsSubject
+        if (!wantsSubject) subjectText = ""
+        draftTag.newVersion()
+    }
+
     fun toggleExpirationDate() {
         wantsExpirationDate = !wantsExpirationDate
         if (wantsExpirationDate) {