Merge pull request #3593 from vitorpamplona/claude/nip-51-compliance-review-vwhyvn

Add hashtag muting support via NIP-51

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

@@ -4734,6 +4734,14 @@ class Account(
         sendMyPublicAndPrivateOutbox(muteList.showWord(word))
     }
 
+    suspend fun hideHashtag(hashtag: String) {
+        sendMyPublicAndPrivateOutbox(muteList.hideHashtag(hashtag))
+    }
+
+    suspend fun showHashtag(hashtag: String) {
+        muteList.showHashtag(hashtag)?.let { sendMyPublicAndPrivateOutbox(it) }
+    }
+
     suspend fun hideUser(pubkeyHex: HexKey) {
         sendMyPublicAndPrivateOutbox(muteList.hideUser(pubkeyHex))
     }

amethyst/src/main/java/com/vitorpamplona/amethyst/model/nip51Lists/HiddenUsersState.kt

@@ -25,6 +25,7 @@ import com.vitorpamplona.amethyst.model.AccountSettings
 import com.vitorpamplona.amethyst.service.checkNotInMainThread
 import com.vitorpamplona.quartz.nip01Core.core.HexKey
 import com.vitorpamplona.quartz.nip51Lists.muteList.tags.EventTag
+import com.vitorpamplona.quartz.nip51Lists.muteList.tags.HashtagTag
 import com.vitorpamplona.quartz.nip51Lists.muteList.tags.MuteTag
 import com.vitorpamplona.quartz.nip51Lists.muteList.tags.UserTag
 import com.vitorpamplona.quartz.nip51Lists.muteList.tags.WordTag
@@ -57,6 +58,7 @@ class HiddenUsersState(
     ): LiveHiddenUsers {
         val hiddenUsers = blockList.mapNotNullTo(mutableSetOf()) { if (it is UserTag) it.pubKey else null } + muteList.mapNotNull { if (it is UserTag) it.pubKey else null }
         val hiddenWords = blockList.mapNotNullTo(mutableSetOf()) { if (it is WordTag) it.word else null } + muteList.mapNotNull { if (it is WordTag) it.word else null }
+        val hiddenHashtags = blockList.mapNotNullTo(mutableSetOf()) { if (it is HashtagTag) it.hashtag.lowercase() else null } + muteList.mapNotNull { if (it is HashtagTag) it.hashtag.lowercase() else null }
         val mutedThreads = muteList.mapNotNullTo(mutableSetOf()) { if (it is EventTag) it.eventId else null }
 
         return LiveHiddenUsers(
@@ -67,6 +69,7 @@ class HiddenUsersState(
             hiddenUsers = hiddenUsers,
             spammers = transientHiddenUsers,
             hiddenWords = hiddenWords,
+            hiddenHashtags = hiddenHashtags,
             maxHashtagLimit = maxHashtagLimit,
             mutedThreads = mutedThreads,
         )

amethyst/src/main/java/com/vitorpamplona/amethyst/model/nip51Lists/muteList/MuteListState.kt

@@ -29,6 +29,7 @@ import com.vitorpamplona.quartz.nip01Core.core.HexKey
 import com.vitorpamplona.quartz.nip01Core.signers.NostrSigner
 import com.vitorpamplona.quartz.nip51Lists.muteList.MuteListEvent
 import com.vitorpamplona.quartz.nip51Lists.muteList.tags.EventTag
+import com.vitorpamplona.quartz.nip51Lists.muteList.tags.HashtagTag
 import com.vitorpamplona.quartz.nip51Lists.muteList.tags.MuteTag
 import com.vitorpamplona.quartz.nip51Lists.muteList.tags.UserTag
 import com.vitorpamplona.quartz.nip51Lists.muteList.tags.WordTag
@@ -142,6 +143,39 @@ class MuteListState(
         }
     }
 
+    suspend fun hideHashtag(hashtag: String): MuteListEvent {
+        val muteList = getMuteList()
+
+        return if (muteList != null) {
+            MuteListEvent.add(
+                earlierVersion = muteList,
+                mute = HashtagTag(hashtag),
+                isPrivate = true,
+                signer = signer,
+            )
+        } else {
+            MuteListEvent.create(
+                mute = HashtagTag(hashtag),
+                isPrivate = true,
+                signer = signer,
+            )
+        }
+    }
+
+    suspend fun showHashtag(hashtag: String): MuteListEvent? {
+        val muteList = getMuteList()
+
+        return if (muteList != null) {
+            MuteListEvent.remove(
+                earlierVersion = muteList,
+                mute = HashtagTag(hashtag),
+                signer = signer,
+            )
+        } else {
+            null
+        }
+    }
+
     suspend fun hideThread(rootHex: HexKey): MuteListEvent {
         val muteList = getMuteList()
         return if (muteList != null) {

amethyst/src/main/java/com/vitorpamplona/amethyst/service/relayClient/reqCommand/user/UserObservers.kt

@@ -396,6 +396,33 @@ fun observeUserIsFollowingHashtag(
     return flow.collectAsStateWithLifecycle(hashtag in accountViewModel.account.hashtagList.flow.value)
 }
 
+@SuppressLint("StateFlowValueCalledInComposition")
+@OptIn(ExperimentalCoroutinesApi::class, FlowPreview::class)
+@Composable
+fun observeUserIsMutingHashtag(
+    hashtag: String,
+    accountViewModel: AccountViewModel,
+): State<Boolean> {
+    // Subscribe in the LocalCache for changes that arrive in the device
+    val flow =
+        remember(accountViewModel, hashtag) {
+            accountViewModel.account.hiddenUsers.flow
+                .mapLatest { it.isHashtagHidden(hashtag) }
+                .onStart {
+                    emit(
+                        accountViewModel.account.hiddenUsers.flow.value
+                            .isHashtagHidden(hashtag),
+                    )
+                }.distinctUntilChanged()
+                .flowOn(Dispatchers.IO)
+        }
+
+    return flow.collectAsStateWithLifecycle(
+        accountViewModel.account.hiddenUsers.flow.value
+            .isHashtagHidden(hashtag),
+    )
+}
+
 @SuppressLint("StateFlowValueCalledInComposition")
 @OptIn(ExperimentalCoroutinesApi::class, FlowPreview::class)
 @Composable

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

@@ -1693,6 +1693,10 @@ class AccountViewModel(
 
     fun hideWord(word: String) = launchSigner { account.hideWord(word) }
 
+    fun hideHashtag(tag: String) = launchSigner { account.hideHashtag(tag) }
+
+    fun showHashtag(tag: String) = launchSigner { account.showHashtag(tag) }
+
     fun isLoggedUser(pubkeyHex: HexKey?): Boolean = account.signer.pubKey == pubkeyHex
 
     fun isLoggedUser(user: User?): Boolean = isLoggedUser(user?.pubkeyHex)

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

@@ -25,15 +25,26 @@ import androidx.compose.foundation.clickable
 import androidx.compose.foundation.layout.Arrangement
 import androidx.compose.foundation.layout.Row
 import androidx.compose.foundation.layout.fillMaxWidth
+import androidx.compose.foundation.layout.size
+import androidx.compose.material3.DropdownMenu
+import androidx.compose.material3.DropdownMenuItem
+import androidx.compose.material3.IconButton
 import androidx.compose.material3.Text
 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.text.font.FontWeight
+import androidx.compose.ui.unit.dp
 import androidx.lifecycle.viewmodel.compose.viewModel
 import com.vitorpamplona.amethyst.R
+import com.vitorpamplona.amethyst.commons.icons.symbols.Icon
+import com.vitorpamplona.amethyst.commons.icons.symbols.MaterialSymbols
 import com.vitorpamplona.amethyst.service.relayClient.reqCommand.user.observeUserIsFollowingHashtag
+import com.vitorpamplona.amethyst.service.relayClient.reqCommand.user.observeUserIsMutingHashtag
 import com.vitorpamplona.amethyst.ui.feeds.WatchLifecycleAndUpdateModel
 import com.vitorpamplona.amethyst.ui.layouts.DisappearingScaffold
 import com.vitorpamplona.amethyst.ui.navigation.bottombars.FabBottomBarPadded
@@ -46,6 +57,7 @@ import com.vitorpamplona.amethyst.ui.screen.loggedIn.hashtag.dal.HashtagFeedView
 import com.vitorpamplona.amethyst.ui.screen.loggedIn.hashtag.datasource.HashtagFilterAssemblerSubscription
 import com.vitorpamplona.amethyst.ui.screen.loggedIn.profile.FollowButton
 import com.vitorpamplona.amethyst.ui.screen.loggedIn.profile.UnfollowButton
+import com.vitorpamplona.amethyst.ui.stringRes
 import com.vitorpamplona.amethyst.ui.theme.StdPadding
 
 @Composable
@@ -172,4 +184,57 @@ fun HashtagActionOptions(
             }
         }
     }
+
+    HashtagMuteMenu(tag, accountViewModel)
+}
+
+@Composable
+fun HashtagMuteMenu(
+    tag: String,
+    accountViewModel: AccountViewModel,
+) {
+    var menuOpen by remember { mutableStateOf(false) }
+    val isMuted by observeUserIsMutingHashtag(tag, accountViewModel)
+
+    IconButton(onClick = { menuOpen = true }) {
+        Icon(
+            symbol = MaterialSymbols.MoreVert,
+            contentDescription = stringRes(R.string.more_options),
+            modifier = Modifier.size(22.dp),
+        )
+    }
+
+    DropdownMenu(expanded = menuOpen, onDismissRequest = { menuOpen = false }) {
+        if (isMuted) {
+            DropdownMenuItem(
+                text = { Text(stringRes(R.string.unmute_hashtag)) },
+                onClick = {
+                    menuOpen = false
+                    if (!accountViewModel.isWriteable()) {
+                        accountViewModel.toastManager.toast(
+                            R.string.read_only_user,
+                            R.string.login_with_a_private_key_to_be_able_to_show_word,
+                        )
+                    } else {
+                        accountViewModel.showHashtag(tag)
+                    }
+                },
+            )
+        } else {
+            DropdownMenuItem(
+                text = { Text(stringRes(R.string.mute_hashtag)) },
+                onClick = {
+                    menuOpen = false
+                    if (!accountViewModel.isWriteable()) {
+                        accountViewModel.toastManager.toast(
+                            R.string.read_only_user,
+                            R.string.login_with_a_private_key_to_be_able_to_hide_word,
+                        )
+                    } else {
+                        accountViewModel.hideHashtag(tag)
+                    }
+                },
+            )
+        }
+    }
 }

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

@@ -2331,6 +2331,8 @@
 
     <string name="hidden_words">Hidden Words</string>
     <string name="hide_new_word_label">Hide new word or sentence</string>
+    <string name="mute_hashtag">Mute hashtag</string>
+    <string name="unmute_hashtag">Unmute hashtag</string>
     <string name="settings_muted_threads_title">Muted threads</string>
     <string name="settings_muted_threads_empty">No muted threads</string>
     <string name="settings_muted_threads_unknown">Unknown thread · %1$s</string>

commons/src/commonMain/kotlin/com/vitorpamplona/amethyst/commons/model/IAccount.kt

@@ -61,11 +61,15 @@ data class LiveHiddenUsers(
     val spammers: Set<String> = emptySet(),
     val hiddenWords: Set<String> = emptySet(),
     val mutedThreads: Set<String> = emptySet(),
+    // Lowercased hashtags (without the leading '#') the user has muted via NIP-51 `"t"` entries.
+    val hiddenHashtags: Set<String> = emptySet(),
     val maxHashtagLimit: Int = 8,
 ) {
     fun isUserHidden(userHex: String) = hiddenUsers.contains(userHex) || spammers.contains(userHex)
 
     fun isThreadMuted(rootHex: String) = mutedThreads.contains(rootHex)
+
+    fun isHashtagHidden(hashtag: String) = hiddenHashtags.contains(hashtag.lowercase())
 }
 
 /**

commons/src/commonMain/kotlin/com/vitorpamplona/amethyst/commons/model/Note.kt

@@ -1309,6 +1309,12 @@ open class Note(
             }
         }
 
+        if (accountChoices.hiddenHashtags.isNotEmpty()) {
+            if (thisEvent.anyHashTag { it.lowercase() in accountChoices.hiddenHashtags }) {
+                return true
+            }
+        }
+
         if (accountChoices.hiddenWordsCase.isNotEmpty()) {
             if (thisEvent is BaseThreadedEvent && thisEvent.content.containsAny(accountChoices.hiddenWordsCase)) {
                 return true

commons/src/commonTest/kotlin/com/vitorpamplona/amethyst/commons/model/NoteIsHiddenForTest.kt

@@ -90,4 +90,33 @@ class NoteIsHiddenForTest {
 
         assertTrue(note.isHiddenFor(choices), "Note whose author is hidden must still be hidden")
     }
+
+    private fun tTag(hashtag: String) = arrayOf("t", hashtag)
+
+    @Test
+    fun note_withMutedHashtag_isHidden() {
+        val event = textNoteEvent(id = replyId, eTags = arrayOf(tTag("bitcoin")))
+        val note = Note(replyId).also { it.event = event }
+        val choices = noHidden.copy(hiddenHashtags = setOf("bitcoin"))
+
+        assertTrue(note.isHiddenFor(choices), "Note tagged with a muted hashtag must be hidden")
+    }
+
+    @Test
+    fun note_withMutedHashtag_isCaseInsensitive() {
+        val event = textNoteEvent(id = replyId, eTags = arrayOf(tTag("Bitcoin")))
+        val note = Note(replyId).also { it.event = event }
+        val choices = noHidden.copy(hiddenHashtags = setOf("bitcoin"))
+
+        assertTrue(note.isHiddenFor(choices), "Muted-hashtag matching must ignore case")
+    }
+
+    @Test
+    fun note_withoutMutedHashtag_isNotHidden() {
+        val event = textNoteEvent(id = replyId, eTags = arrayOf(tTag("nostr")))
+        val note = Note(replyId).also { it.event = event }
+        val choices = noHidden.copy(hiddenHashtags = setOf("bitcoin"))
+
+        assertFalse(note.isHiddenFor(choices), "Note without the muted hashtag must not be hidden")
+    }
 }

quartz/src/commonMain/kotlin/com/vitorpamplona/quartz/experimental/profileGallery/GalleryListEvent.kt

@@ -1,150 +0,0 @@
-/*
- * 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.quartz.experimental.profileGallery
-
-import androidx.compose.runtime.Immutable
-import com.vitorpamplona.quartz.nip01Core.core.HexKey
-import com.vitorpamplona.quartz.nip01Core.signers.NostrSigner
-import com.vitorpamplona.quartz.nip01Core.tags.aTag.ATag
-import com.vitorpamplona.quartz.nip51Lists.PrivateTagArrayEvent
-import com.vitorpamplona.quartz.utils.TimeUtils
-
-@Deprecated("Replaced by NIP-68")
-@Immutable
-class GalleryListEvent(
-    id: HexKey,
-    pubKey: HexKey,
-    createdAt: Long,
-    tags: Array<Array<String>>,
-    content: String,
-    sig: HexKey,
-) : PrivateTagArrayEvent(id, pubKey, createdAt, KIND, tags, content, sig) {
-    @Suppress("DEPRECATION")
-    companion object {
-        const val KIND = 10011
-        const val GALLERY_TAG_NAME = "url"
-
-        suspend fun addEvent(
-            earlierVersion: GalleryListEvent?,
-            eventId: HexKey,
-            url: String,
-            relay: String?,
-            signer: NostrSigner,
-            createdAt: Long = TimeUtils.now(),
-        ) = addTag(earlierVersion, GALLERY_TAG_NAME, eventId, url, relay, signer, createdAt)
-
-        suspend fun addTag(
-            earlierVersion: GalleryListEvent?,
-            tagName: String,
-            eventId: HexKey,
-            url: String,
-            relay: String?,
-            signer: NostrSigner,
-            createdAt: Long = TimeUtils.now(),
-        ): GalleryListEvent {
-            val tags = arrayOf(tagName, url, eventId)
-            if (relay != null) {
-                tags + relay
-            }
-
-            return add(
-                earlierVersion,
-                arrayOf(tags),
-                signer,
-                createdAt,
-            )
-        }
-
-        suspend fun add(
-            earlierVersion: GalleryListEvent?,
-            listNewTags: Array<Array<String>>,
-            signer: NostrSigner,
-            createdAt: Long = TimeUtils.now(),
-        ): GalleryListEvent =
-            create(
-                content = earlierVersion?.content ?: "",
-                tags = listNewTags.plus(earlierVersion?.tags ?: arrayOf()),
-                signer = signer,
-                createdAt = createdAt,
-            )
-
-        suspend fun removeEvent(
-            earlierVersion: GalleryListEvent,
-            eventId: HexKey,
-            url: String,
-            signer: NostrSigner,
-            createdAt: Long = TimeUtils.now(),
-        ) = removeTag(earlierVersion, GALLERY_TAG_NAME, eventId, url, signer, createdAt)
-
-        suspend fun removeReplaceable(
-            earlierVersion: GalleryListEvent,
-            aTag: ATag,
-            url: String,
-            signer: NostrSigner,
-            createdAt: Long = TimeUtils.now(),
-        ) = removeTag(earlierVersion, GALLERY_TAG_NAME, aTag.toTag(), url, signer, createdAt)
-
-        private suspend fun removeTag(
-            earlierVersion: GalleryListEvent,
-            tagName: String,
-            eventId: HexKey,
-            url: String,
-            signer: NostrSigner,
-            createdAt: Long = TimeUtils.now(),
-        ): GalleryListEvent =
-            create(
-                content = earlierVersion.content,
-                tags =
-                    earlierVersion.tags
-                        .filter { it.size <= 1 || !(it[0] == tagName && it[1] == url && it[2] == eventId) }
-                        .toTypedArray(),
-                signer = signer,
-                createdAt = createdAt,
-            )
-
-        suspend fun create(
-            content: String,
-            tags: Array<Array<String>>,
-            signer: NostrSigner,
-            createdAt: Long = TimeUtils.now(),
-        ): GalleryListEvent = signer.sign(createdAt, KIND, tags, content)
-    }
-
-    @Immutable
-    data class GalleryUrl(
-        val url: String,
-        val id: String,
-        val relay: String?,
-    ) {
-        fun encode(): String = ":$url:$id:$relay"
-
-        companion object {
-            fun decode(encodedGallerySetup: String): GalleryUrl? {
-                val galleryParts = encodedGallerySetup.split(":", limit = 3)
-                return if (galleryParts.size > 3) {
-                    GalleryUrl(galleryParts[1], galleryParts[2], galleryParts[3])
-                } else {
-                    null
-                }
-            }
-        }
-    }
-}

quartz/src/commonMain/kotlin/com/vitorpamplona/quartz/nip51Lists/muteList/TagArrayExt.kt

@@ -22,6 +22,7 @@ package com.vitorpamplona.quartz.nip51Lists.muteList
 
 import com.vitorpamplona.quartz.nip01Core.core.TagArray
 import com.vitorpamplona.quartz.nip51Lists.muteList.tags.EventTag
+import com.vitorpamplona.quartz.nip51Lists.muteList.tags.HashtagTag
 import com.vitorpamplona.quartz.nip51Lists.muteList.tags.MuteTag
 import com.vitorpamplona.quartz.nip51Lists.muteList.tags.UserTag
 import com.vitorpamplona.quartz.nip51Lists.muteList.tags.WordTag
@@ -43,3 +44,9 @@ fun TagArray.mutedThreads() = mapNotNull(EventTag::parse)
 fun TagArray.mutedThreadIds() = mapNotNull(EventTag::parseId)
 
 fun TagArray.mutedThreadIdSet() = mapNotNullTo(mutableSetOf(), EventTag::parseId)
+
+fun TagArray.mutedHashtags() = mapNotNull(HashtagTag::parse)
+
+fun TagArray.mutedHashtagIds() = mapNotNull(HashtagTag::parseId)
+
+fun TagArray.mutedHashtagIdSet() = mapNotNullTo(mutableSetOf(), HashtagTag::parseId)

quartz/src/commonMain/kotlin/com/vitorpamplona/quartz/nip51Lists/muteList/tags/HashtagTag.kt

@@ -0,0 +1,67 @@
+/*
+ * 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.quartz.nip51Lists.muteList.tags
+
+import androidx.compose.runtime.Immutable
+import com.vitorpamplona.quartz.nip01Core.core.has
+import com.vitorpamplona.quartz.utils.arrayOfNotNull
+import com.vitorpamplona.quartz.utils.ensure
+
+/**
+ * NIP-51 mute-list hashtag entry (`"t"`). Hides notes that carry the given
+ * hashtag. Per NIP-24, `t` values are conventionally lowercased.
+ */
+@Immutable
+class HashtagTag(
+    val hashtag: String,
+) : MuteTag {
+    override fun toTagArray() = assemble(hashtag)
+
+    override fun toTagIdOnly() = assemble(hashtag)
+
+    companion object {
+        const val TAG_NAME = "t"
+
+        fun isTagged(tag: Array<String>) = tag.has(1) && tag[0] == TAG_NAME && tag[1].isNotEmpty()
+
+        fun isTagged(
+            tag: Array<String>,
+            hashtag: String,
+        ) = tag.has(1) && tag[0] == TAG_NAME && tag[1] == hashtag
+
+        fun parse(tag: Array<String>): HashtagTag? {
+            ensure(tag.has(1)) { return null }
+            ensure(tag[0] == TAG_NAME) { return null }
+            ensure(tag[1].isNotEmpty()) { return null }
+
+            return HashtagTag(tag[1])
+        }
+
+        fun parseId(tag: Array<String>): String? {
+            ensure(tag.has(1)) { return null }
+            ensure(tag[0] == TAG_NAME) { return null }
+            ensure(tag[1].isNotEmpty()) { return null }
+            return tag[1]
+        }
+
+        fun assemble(hashtag: String) = arrayOfNotNull(TAG_NAME, hashtag)
+    }
+}

quartz/src/commonMain/kotlin/com/vitorpamplona/quartz/nip51Lists/muteList/tags/MuteTag.kt

@@ -28,8 +28,8 @@ sealed interface MuteTag {
     fun toTagIdOnly(): Tag
 
     companion object {
-        fun isTagged(tag: Array<String>) = WordTag.isTagged(tag) || UserTag.isTagged(tag) || EventTag.isTagged(tag)
+        fun isTagged(tag: Array<String>) = WordTag.isTagged(tag) || UserTag.isTagged(tag) || EventTag.isTagged(tag) || HashtagTag.isTagged(tag)
 
-        fun parse(tag: Array<String>): MuteTag? = WordTag.parse(tag) ?: UserTag.parse(tag) ?: EventTag.parse(tag)
+        fun parse(tag: Array<String>): MuteTag? = WordTag.parse(tag) ?: UserTag.parse(tag) ?: EventTag.parse(tag) ?: HashtagTag.parse(tag)
     }
 }

quartz/src/commonTest/kotlin/com/vitorpamplona/quartz/nip51Lists/muteList/tags/HashtagTagTest.kt

@@ -0,0 +1,81 @@
+/*
+ * 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.quartz.nip51Lists.muteList.tags
+
+import kotlin.test.Test
+import kotlin.test.assertEquals
+import kotlin.test.assertFalse
+import kotlin.test.assertNotNull
+import kotlin.test.assertNull
+import kotlin.test.assertTrue
+
+class HashtagTagTest {
+    private val hashtag = "bitcoin"
+
+    @Test fun isTagged_acceptsHashtag() {
+        assertTrue(HashtagTag.isTagged(arrayOf("t", hashtag)))
+    }
+
+    @Test fun isTagged_rejectsEmpty() {
+        assertFalse(HashtagTag.isTagged(arrayOf("t", "")))
+    }
+
+    @Test fun isTagged_rejectsWrongPrefix() {
+        assertFalse(HashtagTag.isTagged(arrayOf("word", hashtag)))
+    }
+
+    @Test fun parse_extractsHashtag() {
+        val tag = assertNotNull(HashtagTag.parse(arrayOf("t", hashtag)))
+        assertEquals(hashtag, tag.hashtag)
+    }
+
+    @Test fun parse_rejectsEmpty() {
+        assertNull(HashtagTag.parse(arrayOf("t", "")))
+    }
+
+    @Test fun parse_rejectsWrongPrefix() {
+        assertNull(HashtagTag.parse(arrayOf("p", hashtag)))
+    }
+
+    @Test fun parseId_extractsValue() {
+        assertEquals(hashtag, HashtagTag.parseId(arrayOf("t", hashtag)))
+    }
+
+    @Test fun toTagArray_roundTrips() {
+        val parsed = assertNotNull(HashtagTag.parse(HashtagTag(hashtag).toTagArray()))
+        assertEquals(hashtag, parsed.hashtag)
+    }
+
+    @Test fun muteTagCompanion_parsesHashtagTag() {
+        val parsed = assertNotNull(MuteTag.parse(arrayOf("t", hashtag)))
+        assertTrue(parsed is HashtagTag)
+    }
+
+    @Test fun muteTagCompanion_isTaggedRecognizesHashtagTag() {
+        assertTrue(MuteTag.isTagged(arrayOf("t", hashtag)))
+    }
+
+    @Test fun muteTagCompanion_doesNotConfuseHashtagWithWord() {
+        // "t" must parse as a hashtag, not a word; "word" must parse as a word.
+        assertTrue(MuteTag.parse(arrayOf("t", hashtag)) is HashtagTag)
+        assertTrue(MuteTag.parse(arrayOf("word", hashtag)) is WordTag)
+    }
+}