fix(quartz): align NIP-53 Live Activities with spec

- MeetingRoomPresenceEvent (kind 10312) now extends BaseReplaceableEvent
  instead of BaseAddressableEvent. NIP-53 states this kind is a regular
  replaceable event ("presence can only be indicated in one room at a
  time"), and LocalCache already routes it through consumeBaseReplaceable.
  createAddress/createAddressATag/createAddressTag now take only pubKey.

- Add TagArrayBuilder extensions for streaming (30311), meeting space
  (30312) and meeting room (30313) tags, plus build() helpers that assemble
  the required tags per NIP-53.

- Add ProofOfAgreement utility to sign and verify the schnorr proof that
  NIP-53 places in the 5th element of a participant p-tag
  (SHA256 of kind:pubkey:dTag signed by the participant's private key).
  Includes LiveActivitiesEvent.hasValidProof() convenience.

quartz/src/commonMain/kotlin/com/vitorpamplona/quartz/nip53LiveActivities/meetingSpaces/MeetingRoomEvent.kt

@@ -23,6 +23,7 @@ package com.vitorpamplona.quartz.nip53LiveActivities.meetingSpaces
 import androidx.compose.runtime.Immutable
 import com.vitorpamplona.quartz.nip01Core.core.BaseAddressableEvent
 import com.vitorpamplona.quartz.nip01Core.core.HexKey
+import com.vitorpamplona.quartz.nip01Core.core.TagArrayBuilder
 import com.vitorpamplona.quartz.nip01Core.core.any
 import com.vitorpamplona.quartz.nip01Core.hints.AddressHintProvider
 import com.vitorpamplona.quartz.nip01Core.hints.EventHintProvider
@@ -30,10 +31,13 @@ import com.vitorpamplona.quartz.nip01Core.hints.PubKeyHintProvider
 import com.vitorpamplona.quartz.nip01Core.hints.types.AddressHint
 import com.vitorpamplona.quartz.nip01Core.hints.types.EventIdHint
 import com.vitorpamplona.quartz.nip01Core.signers.NostrSigner
+import com.vitorpamplona.quartz.nip01Core.signers.eventTemplate
+import com.vitorpamplona.quartz.nip01Core.tags.dTag.dTag
 import com.vitorpamplona.quartz.nip23LongContent.tags.ImageTag
 import com.vitorpamplona.quartz.nip23LongContent.tags.SummaryTag
 import com.vitorpamplona.quartz.nip23LongContent.tags.TitleTag
 import com.vitorpamplona.quartz.nip31Alts.AltTag
+import com.vitorpamplona.quartz.nip31Alts.alt
 import com.vitorpamplona.quartz.nip53LiveActivities.meetingSpaces.tags.MeetingSpaceTag
 import com.vitorpamplona.quartz.nip53LiveActivities.streaming.tags.CurrentParticipantsTag
 import com.vitorpamplona.quartz.nip53LiveActivities.streaming.tags.EndsTag
@@ -46,6 +50,8 @@ import com.vitorpamplona.quartz.nip53LiveActivities.streaming.tags.StatusTag
 import com.vitorpamplona.quartz.nip53LiveActivities.streaming.tags.StreamingTag
 import com.vitorpamplona.quartz.nip53LiveActivities.streaming.tags.TotalParticipantsTag
 import com.vitorpamplona.quartz.utils.TimeUtils
+import kotlin.uuid.ExperimentalUuidApi
+import kotlin.uuid.Uuid
 
 @Immutable
 class MeetingRoomEvent(
@@ -157,5 +163,24 @@ class MeetingRoomEvent(
             val tags = arrayOf(AltTag.assemble(ALT))
             return signer.sign(createdAt, KIND, tags, "")
         }
+
+        @OptIn(ExperimentalUuidApi::class)
+        fun build(
+            meetingSpace: MeetingSpaceTag,
+            title: String,
+            starts: Long,
+            status: StatusTag.STATUS,
+            dTag: String = Uuid.random().toString(),
+            createdAt: Long = TimeUtils.now(),
+            initializer: TagArrayBuilder<MeetingRoomEvent>.() -> Unit = {},
+        ) = eventTemplate(KIND, "", createdAt) {
+            dTag(dTag)
+            meetingSpace(meetingSpace)
+            title(title)
+            starts(starts)
+            status(status)
+            alt(ALT)
+            initializer()
+        }
     }
 }

quartz/src/commonMain/kotlin/com/vitorpamplona/quartz/nip53LiveActivities/meetingSpaces/MeetingRoomTagArrayBuilderExt.kt

@@ -0,0 +1,68 @@
+/*
+ * 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.
+ */
+@file:JvmName("MeetingRoomTagArrayBuilderExt")
+
+package com.vitorpamplona.quartz.nip53LiveActivities.meetingSpaces
+
+import com.vitorpamplona.quartz.nip01Core.core.HexKey
+import com.vitorpamplona.quartz.nip01Core.core.TagArrayBuilder
+import com.vitorpamplona.quartz.nip01Core.relay.normalizer.NormalizedRelayUrl
+import com.vitorpamplona.quartz.nip23LongContent.tags.ImageTag
+import com.vitorpamplona.quartz.nip23LongContent.tags.SummaryTag
+import com.vitorpamplona.quartz.nip23LongContent.tags.TitleTag
+import com.vitorpamplona.quartz.nip53LiveActivities.meetingSpaces.tags.MeetingSpaceTag
+import com.vitorpamplona.quartz.nip53LiveActivities.streaming.tags.CurrentParticipantsTag
+import com.vitorpamplona.quartz.nip53LiveActivities.streaming.tags.EndsTag
+import com.vitorpamplona.quartz.nip53LiveActivities.streaming.tags.ParticipantTag
+import com.vitorpamplona.quartz.nip53LiveActivities.streaming.tags.StartsTag
+import com.vitorpamplona.quartz.nip53LiveActivities.streaming.tags.StatusTag
+import com.vitorpamplona.quartz.nip53LiveActivities.streaming.tags.TotalParticipantsTag
+import kotlin.jvm.JvmName
+
+fun TagArrayBuilder<MeetingRoomEvent>.meetingSpace(rep: MeetingSpaceTag) = addUnique(rep.toTagArray())
+
+fun TagArrayBuilder<MeetingRoomEvent>.title(title: String) = addUnique(TitleTag.assemble(title))
+
+fun TagArrayBuilder<MeetingRoomEvent>.summary(summary: String) = addUnique(SummaryTag.assemble(summary))
+
+fun TagArrayBuilder<MeetingRoomEvent>.image(imageUrl: String) = addUnique(ImageTag.assemble(imageUrl))
+
+fun TagArrayBuilder<MeetingRoomEvent>.starts(timestamp: Long) = addUnique(StartsTag.assemble(timestamp))
+
+fun TagArrayBuilder<MeetingRoomEvent>.ends(timestamp: Long) = addUnique(EndsTag.assemble(timestamp))
+
+fun TagArrayBuilder<MeetingRoomEvent>.status(status: StatusTag.STATUS) = addUnique(StatusTag.assemble(status))
+
+fun TagArrayBuilder<MeetingRoomEvent>.currentParticipants(count: Int) = addUnique(CurrentParticipantsTag.assemble(count))
+
+fun TagArrayBuilder<MeetingRoomEvent>.totalParticipants(count: Int) = addUnique(TotalParticipantsTag.assemble(count))
+
+fun TagArrayBuilder<MeetingRoomEvent>.participant(
+    pubKey: HexKey,
+    relayHint: NormalizedRelayUrl? = null,
+    role: String? = null,
+    proof: HexKey? = null,
+) = add(ParticipantTag.assemble(pubKey, relayHint?.url, role, proof))
+
+fun TagArrayBuilder<MeetingRoomEvent>.participants(participants: List<ParticipantTag>) =
+    participants.forEach {
+        participant(it.pubKey, it.relayHint, it.role, it.proof)
+    }

quartz/src/commonMain/kotlin/com/vitorpamplona/quartz/nip53LiveActivities/meetingSpaces/MeetingSpaceEvent.kt

@@ -23,12 +23,16 @@ package com.vitorpamplona.quartz.nip53LiveActivities.meetingSpaces
 import androidx.compose.runtime.Immutable
 import com.vitorpamplona.quartz.nip01Core.core.BaseAddressableEvent
 import com.vitorpamplona.quartz.nip01Core.core.HexKey
+import com.vitorpamplona.quartz.nip01Core.core.TagArrayBuilder
 import com.vitorpamplona.quartz.nip01Core.core.any
 import com.vitorpamplona.quartz.nip01Core.hints.PubKeyHintProvider
 import com.vitorpamplona.quartz.nip01Core.signers.NostrSigner
+import com.vitorpamplona.quartz.nip01Core.signers.eventTemplate
+import com.vitorpamplona.quartz.nip01Core.tags.dTag.dTag
 import com.vitorpamplona.quartz.nip23LongContent.tags.ImageTag
 import com.vitorpamplona.quartz.nip23LongContent.tags.SummaryTag
 import com.vitorpamplona.quartz.nip31Alts.AltTag
+import com.vitorpamplona.quartz.nip31Alts.alt
 import com.vitorpamplona.quartz.nip53LiveActivities.meetingSpaces.tags.EndpointUrlTag
 import com.vitorpamplona.quartz.nip53LiveActivities.meetingSpaces.tags.RelayListTag
 import com.vitorpamplona.quartz.nip53LiveActivities.meetingSpaces.tags.RoomNameTag
@@ -36,6 +40,8 @@ import com.vitorpamplona.quartz.nip53LiveActivities.meetingSpaces.tags.ServiceUr
 import com.vitorpamplona.quartz.nip53LiveActivities.meetingSpaces.tags.StatusTag
 import com.vitorpamplona.quartz.nip53LiveActivities.streaming.tags.ParticipantTag
 import com.vitorpamplona.quartz.utils.TimeUtils
+import kotlin.uuid.ExperimentalUuidApi
+import kotlin.uuid.Uuid
 
 @Immutable
 class MeetingSpaceEvent(
@@ -93,5 +99,24 @@ class MeetingSpaceEvent(
             val tags = arrayOf(AltTag.assemble(ALT))
             return signer.sign(createdAt, KIND, tags, "")
         }
+
+        @OptIn(ExperimentalUuidApi::class)
+        fun build(
+            room: String,
+            status: StatusTag.STATUS,
+            service: String,
+            host: ParticipantTag,
+            dTag: String = Uuid.random().toString(),
+            createdAt: Long = TimeUtils.now(),
+            initializer: TagArrayBuilder<MeetingSpaceEvent>.() -> Unit = {},
+        ) = eventTemplate(KIND, "", createdAt) {
+            dTag(dTag)
+            room(room)
+            status(status)
+            service(service)
+            participant(host.pubKey, host.relayHint, host.role, host.proof)
+            alt(ALT)
+            initializer()
+        }
     }
 }

quartz/src/commonMain/kotlin/com/vitorpamplona/quartz/nip53LiveActivities/meetingSpaces/TagArrayBuilderExt.kt

@@ -0,0 +1,62 @@
+/*
+ * 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.
+ */
+@file:JvmName("MeetingSpaceTagArrayBuilderExt")
+
+package com.vitorpamplona.quartz.nip53LiveActivities.meetingSpaces
+
+import com.vitorpamplona.quartz.nip01Core.core.HexKey
+import com.vitorpamplona.quartz.nip01Core.core.TagArrayBuilder
+import com.vitorpamplona.quartz.nip01Core.relay.normalizer.NormalizedRelayUrl
+import com.vitorpamplona.quartz.nip23LongContent.tags.ImageTag
+import com.vitorpamplona.quartz.nip23LongContent.tags.SummaryTag
+import com.vitorpamplona.quartz.nip53LiveActivities.meetingSpaces.tags.EndpointUrlTag
+import com.vitorpamplona.quartz.nip53LiveActivities.meetingSpaces.tags.RelayListTag
+import com.vitorpamplona.quartz.nip53LiveActivities.meetingSpaces.tags.RoomNameTag
+import com.vitorpamplona.quartz.nip53LiveActivities.meetingSpaces.tags.ServiceUrlTag
+import com.vitorpamplona.quartz.nip53LiveActivities.meetingSpaces.tags.StatusTag
+import com.vitorpamplona.quartz.nip53LiveActivities.streaming.tags.ParticipantTag
+import kotlin.jvm.JvmName
+
+fun TagArrayBuilder<MeetingSpaceEvent>.room(name: String) = addUnique(RoomNameTag.assemble(name))
+
+fun TagArrayBuilder<MeetingSpaceEvent>.summary(summary: String) = addUnique(SummaryTag.assemble(summary))
+
+fun TagArrayBuilder<MeetingSpaceEvent>.image(imageUrl: String) = addUnique(ImageTag.assemble(imageUrl))
+
+fun TagArrayBuilder<MeetingSpaceEvent>.status(status: StatusTag.STATUS) = addUnique(StatusTag.assemble(status))
+
+fun TagArrayBuilder<MeetingSpaceEvent>.service(url: String) = addUnique(ServiceUrlTag.assemble(url))
+
+fun TagArrayBuilder<MeetingSpaceEvent>.endpoint(url: String) = addUnique(EndpointUrlTag.assemble(url))
+
+fun TagArrayBuilder<MeetingSpaceEvent>.relays(urls: List<NormalizedRelayUrl>) = addUnique(RelayListTag.assemble(urls))
+
+fun TagArrayBuilder<MeetingSpaceEvent>.participant(
+    pubKey: HexKey,
+    relayHint: NormalizedRelayUrl? = null,
+    role: String? = null,
+    proof: HexKey? = null,
+) = add(ParticipantTag.assemble(pubKey, relayHint?.url, role, proof))
+
+fun TagArrayBuilder<MeetingSpaceEvent>.participants(participants: List<ParticipantTag>) =
+    participants.forEach {
+        participant(it.pubKey, it.relayHint, it.role, it.proof)
+    }

quartz/src/commonMain/kotlin/com/vitorpamplona/quartz/nip53LiveActivities/presence/MeetingRoomPresenceEvent.kt

@@ -22,7 +22,7 @@ package com.vitorpamplona.quartz.nip53LiveActivities.presence
 
 import androidx.compose.runtime.Immutable
 import com.vitorpamplona.quartz.nip01Core.core.Address
-import com.vitorpamplona.quartz.nip01Core.core.BaseAddressableEvent
+import com.vitorpamplona.quartz.nip01Core.core.BaseReplaceableEvent
 import com.vitorpamplona.quartz.nip01Core.core.HexKey
 import com.vitorpamplona.quartz.nip01Core.core.TagArrayBuilder
 import com.vitorpamplona.quartz.nip01Core.hints.AddressHintProvider
@@ -43,7 +43,7 @@ class MeetingRoomPresenceEvent(
     tags: Array<Array<String>>,
     content: String,
     sig: HexKey,
-) : BaseAddressableEvent(id, pubKey, createdAt, KIND, tags, content, sig),
+) : BaseReplaceableEvent(id, pubKey, createdAt, KIND, tags, content, sig),
     AddressHintProvider {
     override fun addressHints(): List<AddressHint> = tags.mapNotNull(MeetingSpaceTag::parseAsHint)
 
@@ -57,20 +57,11 @@ class MeetingRoomPresenceEvent(
         const val KIND = 10312
         const val ALT = "Room Presence tag"
 
-        fun createAddress(
+        fun createAddress(pubKey: HexKey): Address = Address(KIND, pubKey, FIXED_D_TAG)
-            pubKey: HexKey,
-            dtag: String,
-        ): Address = Address(KIND, pubKey, dtag)
 
-        fun createAddressATag(
+        fun createAddressATag(pubKey: HexKey): ATag = ATag(KIND, pubKey, FIXED_D_TAG, null)
-            pubKey: HexKey,
-            dtag: String,
-        ): ATag = ATag(KIND, pubKey, dtag, null)
 
-        fun createAddressTag(
+        fun createAddressTag(pubKey: HexKey): String = Address.assemble(KIND, pubKey, FIXED_D_TAG)
-            pubKey: HexKey,
-            dtag: String,
-        ): String = Address.assemble(KIND, pubKey, dtag)
 
         fun build(
             root: MeetingRoomEvent,

quartz/src/commonMain/kotlin/com/vitorpamplona/quartz/nip53LiveActivities/streaming/LiveActivitiesEvent.kt

@@ -23,15 +23,19 @@ package com.vitorpamplona.quartz.nip53LiveActivities.streaming
 import androidx.compose.runtime.Immutable
 import com.vitorpamplona.quartz.nip01Core.core.BaseAddressableEvent
 import com.vitorpamplona.quartz.nip01Core.core.HexKey
+import com.vitorpamplona.quartz.nip01Core.core.TagArrayBuilder
 import com.vitorpamplona.quartz.nip01Core.core.any
 import com.vitorpamplona.quartz.nip01Core.hints.EventHintProvider
 import com.vitorpamplona.quartz.nip01Core.hints.PubKeyHintProvider
 import com.vitorpamplona.quartz.nip01Core.hints.types.EventIdHint
 import com.vitorpamplona.quartz.nip01Core.signers.NostrSigner
+import com.vitorpamplona.quartz.nip01Core.signers.eventTemplate
+import com.vitorpamplona.quartz.nip01Core.tags.dTag.dTag
 import com.vitorpamplona.quartz.nip23LongContent.tags.ImageTag
 import com.vitorpamplona.quartz.nip23LongContent.tags.SummaryTag
 import com.vitorpamplona.quartz.nip23LongContent.tags.TitleTag
 import com.vitorpamplona.quartz.nip31Alts.AltTag
+import com.vitorpamplona.quartz.nip31Alts.alt
 import com.vitorpamplona.quartz.nip53LiveActivities.streaming.tags.CurrentParticipantsTag
 import com.vitorpamplona.quartz.nip53LiveActivities.streaming.tags.EndsTag
 import com.vitorpamplona.quartz.nip53LiveActivities.streaming.tags.ParticipantTag
@@ -43,6 +47,8 @@ import com.vitorpamplona.quartz.nip53LiveActivities.streaming.tags.StatusTag
 import com.vitorpamplona.quartz.nip53LiveActivities.streaming.tags.StreamingTag
 import com.vitorpamplona.quartz.nip53LiveActivities.streaming.tags.TotalParticipantsTag
 import com.vitorpamplona.quartz.utils.TimeUtils
+import kotlin.uuid.ExperimentalUuidApi
+import kotlin.uuid.Uuid
 
 @Immutable
 class LiveActivitiesEvent(
@@ -154,5 +160,16 @@ class LiveActivitiesEvent(
             val tags = arrayOf(AltTag.assemble(ALT))
             return signer.sign(createdAt, KIND, tags, "")
         }
+
+        @OptIn(ExperimentalUuidApi::class)
+        fun build(
+            dTag: String = Uuid.random().toString(),
+            createdAt: Long = TimeUtils.now(),
+            initializer: TagArrayBuilder<LiveActivitiesEvent>.() -> Unit = {},
+        ) = eventTemplate(KIND, "", createdAt) {
+            dTag(dTag)
+            alt(ALT)
+            initializer()
+        }
     }
 }

quartz/src/commonMain/kotlin/com/vitorpamplona/quartz/nip53LiveActivities/streaming/ProofOfAgreement.kt

@@ -0,0 +1,114 @@
+/*
+ * 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.nip53LiveActivities.streaming
+
+import com.vitorpamplona.quartz.nip01Core.core.Address
+import com.vitorpamplona.quartz.nip01Core.core.HexKey
+import com.vitorpamplona.quartz.nip01Core.core.hexToByteArrayOrNull
+import com.vitorpamplona.quartz.nip01Core.core.toHexKey
+import com.vitorpamplona.quartz.nip01Core.crypto.Nip01Crypto
+import com.vitorpamplona.quartz.nip53LiveActivities.streaming.tags.ParticipantTag
+import com.vitorpamplona.quartz.utils.sha256.sha256
+
+/**
+ * NIP-53 Proof of Agreement to Participate.
+ *
+ * The proof is a schnorr signature by the participant's private key over the
+ * SHA256 of the event's addressable `a` tag value (`kind:pubkey:dTag`), encoded as hex.
+ *
+ * See: https://github.com/nostr-protocol/nips/blob/master/53.md#proof-of-agreement-to-participate
+ */
+object ProofOfAgreement {
+    /**
+     * Computes the SHA256 digest over the canonical `kind:pubkey:dTag` string.
+     * This is the message that the participant's private key signs.
+     */
+    fun digest(
+        eventKind: Int,
+        eventAuthor: HexKey,
+        eventDTag: String,
+    ): ByteArray = sha256(Address.assemble(eventKind, eventAuthor, eventDTag).encodeToByteArray())
+
+    fun digest(address: Address): ByteArray = digest(address.kind, address.pubKeyHex, address.dTag)
+
+    /**
+     * Signs the proof using the participant's private key (schnorr over the SHA256
+     * digest of the event's `a` tag value). Returns the hex-encoded signature.
+     *
+     * Only usable by the participant — requires access to their raw private key
+     * (e.g. from a local `NostrSignerInternal`). External signers (NIP-46, NIP-55)
+     * do not expose a raw-bytes sign API so they cannot produce this proof.
+     */
+    fun sign(
+        participantPrivKey: ByteArray,
+        eventKind: Int,
+        eventAuthor: HexKey,
+        eventDTag: String,
+    ): HexKey = Nip01Crypto.sign(digest(eventKind, eventAuthor, eventDTag), participantPrivKey).toHexKey()
+
+    /**
+     * Verifies that [proof] is a valid schnorr signature by [participantPubKey] over
+     * SHA256(`kind:pubkey:dTag`). Returns `false` if the proof is malformed, the
+     * pubkey is invalid, or the signature doesn't match.
+     */
+    fun verify(
+        proof: HexKey,
+        participantPubKey: HexKey,
+        eventKind: Int,
+        eventAuthor: HexKey,
+        eventDTag: String,
+    ): Boolean {
+        val signature = proof.hexToByteArrayOrNull() ?: return false
+        if (signature.size != 64) return false
+        val pubKey = participantPubKey.hexToByteArrayOrNull() ?: return false
+        if (pubKey.size != 32) return false
+
+        return runCatching {
+            Nip01Crypto.verify(signature, digest(eventKind, eventAuthor, eventDTag), pubKey)
+        }.getOrDefault(false)
+    }
+
+    fun verify(
+        proof: HexKey,
+        participantPubKey: HexKey,
+        address: Address,
+    ): Boolean = verify(proof, participantPubKey, address.kind, address.pubKeyHex, address.dTag)
+
+    /**
+     * Verifies a participant tag's proof against its owning [LiveActivitiesEvent].
+     * Returns `false` if the tag has no proof or the proof is invalid.
+     */
+    fun verify(
+        tag: ParticipantTag,
+        event: LiveActivitiesEvent,
+    ): Boolean {
+        val proof = tag.proof ?: return false
+        return verify(proof, tag.pubKey, event.address())
+    }
+}
+
+/**
+ * Convenience: check whether a participant's proof of agreement is valid for this event.
+ * Useful for UI that wants to distinguish "verified" participants from "invited" ones
+ * (per NIP-53: "Clients MAY only display participants if the proof is available or
+ * MAY display participants as 'invited' if the proof is not available").
+ */
+fun LiveActivitiesEvent.hasValidProof(participant: ParticipantTag): Boolean = ProofOfAgreement.verify(participant, this)

quartz/src/commonMain/kotlin/com/vitorpamplona/quartz/nip53LiveActivities/streaming/TagArrayBuilderExt.kt

@@ -0,0 +1,74 @@
+/*
+ * 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.nip53LiveActivities.streaming
+
+import com.vitorpamplona.quartz.nip01Core.core.HexKey
+import com.vitorpamplona.quartz.nip01Core.core.TagArrayBuilder
+import com.vitorpamplona.quartz.nip01Core.relay.normalizer.NormalizedRelayUrl
+import com.vitorpamplona.quartz.nip23LongContent.tags.ImageTag
+import com.vitorpamplona.quartz.nip23LongContent.tags.SummaryTag
+import com.vitorpamplona.quartz.nip23LongContent.tags.TitleTag
+import com.vitorpamplona.quartz.nip53LiveActivities.streaming.tags.CurrentParticipantsTag
+import com.vitorpamplona.quartz.nip53LiveActivities.streaming.tags.EndsTag
+import com.vitorpamplona.quartz.nip53LiveActivities.streaming.tags.ParticipantTag
+import com.vitorpamplona.quartz.nip53LiveActivities.streaming.tags.PinnedEventTag
+import com.vitorpamplona.quartz.nip53LiveActivities.streaming.tags.RecordingTag
+import com.vitorpamplona.quartz.nip53LiveActivities.streaming.tags.RelayListTag
+import com.vitorpamplona.quartz.nip53LiveActivities.streaming.tags.StartsTag
+import com.vitorpamplona.quartz.nip53LiveActivities.streaming.tags.StatusTag
+import com.vitorpamplona.quartz.nip53LiveActivities.streaming.tags.StreamingTag
+import com.vitorpamplona.quartz.nip53LiveActivities.streaming.tags.TotalParticipantsTag
+
+fun TagArrayBuilder<LiveActivitiesEvent>.title(title: String) = addUnique(TitleTag.assemble(title))
+
+fun TagArrayBuilder<LiveActivitiesEvent>.summary(summary: String) = addUnique(SummaryTag.assemble(summary))
+
+fun TagArrayBuilder<LiveActivitiesEvent>.image(imageUrl: String) = addUnique(ImageTag.assemble(imageUrl))
+
+fun TagArrayBuilder<LiveActivitiesEvent>.streaming(url: String) = addUnique(StreamingTag.assemble(url))
+
+fun TagArrayBuilder<LiveActivitiesEvent>.recording(url: String) = addUnique(RecordingTag.assemble(url))
+
+fun TagArrayBuilder<LiveActivitiesEvent>.starts(timestamp: Long) = addUnique(StartsTag.assemble(timestamp))
+
+fun TagArrayBuilder<LiveActivitiesEvent>.ends(timestamp: Long) = addUnique(EndsTag.assemble(timestamp))
+
+fun TagArrayBuilder<LiveActivitiesEvent>.status(status: StatusTag.STATUS) = addUnique(StatusTag.assemble(status))
+
+fun TagArrayBuilder<LiveActivitiesEvent>.currentParticipants(count: Int) = addUnique(CurrentParticipantsTag.assemble(count))
+
+fun TagArrayBuilder<LiveActivitiesEvent>.totalParticipants(count: Int) = addUnique(TotalParticipantsTag.assemble(count))
+
+fun TagArrayBuilder<LiveActivitiesEvent>.participant(
+    pubKey: HexKey,
+    relayHint: NormalizedRelayUrl? = null,
+    role: String? = null,
+    proof: HexKey? = null,
+) = add(ParticipantTag.assemble(pubKey, relayHint?.url, role, proof))
+
+fun TagArrayBuilder<LiveActivitiesEvent>.participants(participants: List<ParticipantTag>) =
+    participants.forEach {
+        participant(it.pubKey, it.relayHint, it.role, it.proof)
+    }
+
+fun TagArrayBuilder<LiveActivitiesEvent>.relays(urls: List<NormalizedRelayUrl>) = addUnique(RelayListTag.assemble(urls))
+
+fun TagArrayBuilder<LiveActivitiesEvent>.pinned(eventId: HexKey) = add(PinnedEventTag.assemble(eventId))

quartz/src/commonTest/kotlin/com/vitorpamplona/quartz/nip53LiveActivities/meetingSpaces/MeetingSpaceEventBuildTest.kt

@@ -0,0 +1,102 @@
+/*
+ * 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.nip53LiveActivities.meetingSpaces
+
+import com.vitorpamplona.quartz.nip01Core.core.Address
+import com.vitorpamplona.quartz.nip53LiveActivities.meetingSpaces.tags.MeetingSpaceTag
+import com.vitorpamplona.quartz.nip53LiveActivities.meetingSpaces.tags.StatusTag
+import com.vitorpamplona.quartz.nip53LiveActivities.streaming.tags.ParticipantTag
+import kotlin.test.Test
+import kotlin.test.assertEquals
+import kotlin.test.assertNotNull
+import com.vitorpamplona.quartz.nip53LiveActivities.streaming.tags.StatusTag as StreamStatusTag
+
+class MeetingSpaceEventBuildTest {
+    private val host = "aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa"
+
+    @Test
+    fun meetingSpaceBuildAssemblesRequiredTags() {
+        val template =
+            MeetingSpaceEvent.build(
+                room = "Main Hall",
+                status = StatusTag.STATUS.OPEN,
+                service = "https://meet.example.com/hall",
+                host = ParticipantTag(host, null, "Host", null),
+                dTag = "main-hall",
+                createdAt = 1_700_000_000L,
+            ) {
+                summary("The big room")
+                image("https://example.com/hall.png")
+                endpoint("https://api.example.com/hall")
+            }
+
+        assertEquals(MeetingSpaceEvent.KIND, template.kind)
+        val byName = template.tags.groupBy { it[0] }
+
+        assertEquals("main-hall", byName["d"]?.single()?.get(1))
+        assertEquals("Main Hall", byName["room"]?.single()?.get(1))
+        assertEquals("open", byName["status"]?.single()?.get(1))
+        assertEquals("https://meet.example.com/hall", byName["service"]?.single()?.get(1))
+        assertEquals("https://api.example.com/hall", byName["endpoint"]?.single()?.get(1))
+        assertEquals("The big room", byName["summary"]?.single()?.get(1))
+        assertEquals("https://example.com/hall.png", byName["image"]?.single()?.get(1))
+        assertEquals(MeetingSpaceEvent.ALT, byName["alt"]?.single()?.get(1))
+
+        val hostTag = byName["p"]?.single()
+        assertNotNull(hostTag)
+        assertEquals(host, hostTag[1])
+        assertEquals("Host", hostTag[3])
+    }
+
+    @Test
+    fun meetingRoomBuildReferencesParentSpace() {
+        val spaceAddress = Address(MeetingSpaceEvent.KIND, host, "main-hall")
+        val template =
+            MeetingRoomEvent.build(
+                meetingSpace = MeetingSpaceTag(spaceAddress),
+                title = "Annual Meeting",
+                starts = 1_700_000_000L,
+                status = StreamStatusTag.STATUS.PLANNED,
+                dTag = "annual-2026",
+                createdAt = 1_700_000_000L,
+            ) {
+                ends(1_700_003_600L)
+                currentParticipants(10)
+                totalParticipants(100)
+            }
+
+        assertEquals(MeetingRoomEvent.KIND, template.kind)
+        val byName = template.tags.groupBy { it[0] }
+
+        assertEquals("annual-2026", byName["d"]?.single()?.get(1))
+        assertEquals("Annual Meeting", byName["title"]?.single()?.get(1))
+        assertEquals("1700000000", byName["starts"]?.single()?.get(1))
+        assertEquals("1700003600", byName["ends"]?.single()?.get(1))
+        assertEquals("planned", byName["status"]?.single()?.get(1))
+        assertEquals("10", byName["current_participants"]?.single()?.get(1))
+        assertEquals("100", byName["total_participants"]?.single()?.get(1))
+        assertEquals(MeetingRoomEvent.ALT, byName["alt"]?.single()?.get(1))
+
+        val aTag = byName["a"]?.single()
+        assertNotNull(aTag)
+        assertEquals("${MeetingSpaceEvent.KIND}:$host:main-hall", aTag[1])
+    }
+}

quartz/src/commonTest/kotlin/com/vitorpamplona/quartz/nip53LiveActivities/presence/MeetingRoomPresenceEventTest.kt

@@ -0,0 +1,69 @@
+/*
+ * 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.nip53LiveActivities.presence
+
+import kotlin.test.Test
+import kotlin.test.assertEquals
+
+class MeetingRoomPresenceEventTest {
+    private val participant = "aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa"
+
+    @Test
+    fun kind10312IsReplaceable() {
+        val event =
+            MeetingRoomPresenceEvent(
+                id = "0".repeat(64),
+                pubKey = participant,
+                createdAt = 1_700_000_000L,
+                tags =
+                    arrayOf(
+                        arrayOf("a", "30313:${"b".repeat(64)}:annual-2026"),
+                        arrayOf("hand", "1"),
+                    ),
+                content = "",
+                sig = "0".repeat(128),
+            )
+
+        // Per NIP-53, kind 10312 is a regular replaceable event: "presence can only
+        // be indicated in one room at a time". Replaceable events have a fixed empty
+        // d-tag regardless of what's in the event tags.
+        assertEquals("", event.dTag())
+        assertEquals("${MeetingRoomPresenceEvent.KIND}:$participant:", event.addressTag())
+    }
+
+    @Test
+    fun createAddressKeysByPubKeyOnly() {
+        val a = MeetingRoomPresenceEvent.createAddress(participant)
+        assertEquals(MeetingRoomPresenceEvent.KIND, a.kind)
+        assertEquals(participant, a.pubKeyHex)
+        assertEquals("", a.dTag)
+
+        val aTag = MeetingRoomPresenceEvent.createAddressATag(participant)
+        assertEquals(MeetingRoomPresenceEvent.KIND, aTag.kind)
+        assertEquals(participant, aTag.pubKeyHex)
+        assertEquals("", aTag.dTag)
+
+        assertEquals(
+            "${MeetingRoomPresenceEvent.KIND}:$participant:",
+            MeetingRoomPresenceEvent.createAddressTag(participant),
+        )
+    }
+}

quartz/src/commonTest/kotlin/com/vitorpamplona/quartz/nip53LiveActivities/streaming/LiveActivitiesEventBuildTest.kt

@@ -0,0 +1,97 @@
+/*
+ * 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.nip53LiveActivities.streaming
+
+import com.vitorpamplona.quartz.nip53LiveActivities.streaming.tags.StatusTag
+import kotlin.test.Test
+import kotlin.test.assertContentEquals
+import kotlin.test.assertEquals
+import kotlin.test.assertNotNull
+import kotlin.test.assertTrue
+
+class LiveActivitiesEventBuildTest {
+    private val host = "aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa"
+    private val guest = "bbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbb"
+
+    @Test
+    fun buildAssemblesAllRequiredAndOptionalTags() {
+        val template =
+            LiveActivitiesEvent.build(dTag = "my-stream", createdAt = 1_700_000_000L) {
+                title("My Stream")
+                summary("A live event")
+                image("https://example.com/img.png")
+                streaming("https://example.com/stream.m3u8")
+                starts(1_700_000_000L)
+                status(StatusTag.STATUS.LIVE)
+                currentParticipants(42)
+                totalParticipants(100)
+                participant(host, role = "Host")
+                participant(guest, role = "Speaker")
+            }
+
+        assertEquals(LiveActivitiesEvent.KIND, template.kind)
+        assertEquals("", template.content)
+
+        val tagsByName = template.tags.groupBy { it[0] }
+
+        assertEquals("my-stream", tagsByName["d"]?.single()?.get(1))
+        assertEquals("My Stream", tagsByName["title"]?.single()?.get(1))
+        assertEquals("A live event", tagsByName["summary"]?.single()?.get(1))
+        assertEquals("https://example.com/img.png", tagsByName["image"]?.single()?.get(1))
+        assertEquals("https://example.com/stream.m3u8", tagsByName["streaming"]?.single()?.get(1))
+        assertEquals("1700000000", tagsByName["starts"]?.single()?.get(1))
+        assertEquals("live", tagsByName["status"]?.single()?.get(1))
+        assertEquals("42", tagsByName["current_participants"]?.single()?.get(1))
+        assertEquals("100", tagsByName["total_participants"]?.single()?.get(1))
+        assertEquals(LiveActivitiesEvent.ALT, tagsByName["alt"]?.single()?.get(1))
+
+        // Per NIP-53, role lives at index 3 of the p-tag; a missing relay must be
+        // represented as an empty string placeholder, not dropped.
+        val pTags = tagsByName["p"] ?: emptyList()
+        assertEquals(2, pTags.size)
+        assertContentEquals(arrayOf("p", host, "", "Host"), pTags[0])
+        assertContentEquals(arrayOf("p", guest, "", "Speaker"), pTags[1])
+    }
+
+    @Test
+    fun buildAllowsMultiplePinnedAndHashtagsWithoutClobbering() {
+        val template =
+            LiveActivitiesEvent.build(dTag = "my-stream") {
+                title("title")
+                pinned("1".repeat(64))
+                pinned("2".repeat(64))
+            }
+
+        val pinned = template.tags.filter { it[0] == "pinned" }
+        assertEquals(2, pinned.size)
+    }
+
+    @Test
+    fun buildUsesRandomDTagWhenNotProvided() {
+        val a = LiveActivitiesEvent.build { title("a") }
+        val b = LiveActivitiesEvent.build { title("b") }
+        val aDTag = a.tags.first { it[0] == "d" }[1]
+        val bDTag = b.tags.first { it[0] == "d" }[1]
+        assertNotNull(aDTag)
+        assertTrue(aDTag.isNotEmpty())
+        assertTrue(aDTag != bDTag, "random dTag should differ between builds")
+    }
+}

quartz/src/commonTest/kotlin/com/vitorpamplona/quartz/nip53LiveActivities/streaming/ProofOfAgreementTest.kt

@@ -0,0 +1,204 @@
+/*
+ * 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.nip53LiveActivities.streaming
+
+import com.vitorpamplona.quartz.nip01Core.core.Address
+import com.vitorpamplona.quartz.nip01Core.core.toHexKey
+import com.vitorpamplona.quartz.nip01Core.crypto.KeyPair
+import com.vitorpamplona.quartz.nip53LiveActivities.streaming.tags.ParticipantTag
+import kotlin.test.Test
+import kotlin.test.assertFalse
+import kotlin.test.assertTrue
+
+class ProofOfAgreementTest {
+    private val dummySig = "0".repeat(128)
+
+    @Test
+    fun roundTripSignAndVerify() {
+        val host = KeyPair()
+        val participant = KeyPair()
+        val hostHex = host.pubKey.toHexKey()
+        val participantHex = participant.pubKey.toHexKey()
+        val dTag = "my-stream"
+
+        val proof =
+            ProofOfAgreement.sign(
+                participantPrivKey = participant.privKey!!,
+                eventKind = LiveActivitiesEvent.KIND,
+                eventAuthor = hostHex,
+                eventDTag = dTag,
+            )
+
+        assertTrue(
+            ProofOfAgreement.verify(
+                proof = proof,
+                participantPubKey = participantHex,
+                eventKind = LiveActivitiesEvent.KIND,
+                eventAuthor = hostHex,
+                eventDTag = dTag,
+            ),
+        )
+    }
+
+    @Test
+    fun verifyFailsForDifferentAddress() {
+        val host = KeyPair()
+        val participant = KeyPair()
+        val hostHex = host.pubKey.toHexKey()
+        val participantHex = participant.pubKey.toHexKey()
+
+        val proof =
+            ProofOfAgreement.sign(
+                participantPrivKey = participant.privKey!!,
+                eventKind = LiveActivitiesEvent.KIND,
+                eventAuthor = hostHex,
+                eventDTag = "one",
+            )
+
+        assertFalse(
+            ProofOfAgreement.verify(
+                proof = proof,
+                participantPubKey = participantHex,
+                eventKind = LiveActivitiesEvent.KIND,
+                eventAuthor = hostHex,
+                eventDTag = "another",
+            ),
+        )
+    }
+
+    @Test
+    fun verifyFailsForWrongParticipantKey() {
+        val host = KeyPair()
+        val participant = KeyPair()
+        val imposter = KeyPair()
+        val hostHex = host.pubKey.toHexKey()
+
+        val proof =
+            ProofOfAgreement.sign(
+                participantPrivKey = participant.privKey!!,
+                eventKind = LiveActivitiesEvent.KIND,
+                eventAuthor = hostHex,
+                eventDTag = "stream",
+            )
+
+        assertFalse(
+            ProofOfAgreement.verify(
+                proof = proof,
+                participantPubKey = imposter.pubKey.toHexKey(),
+                eventKind = LiveActivitiesEvent.KIND,
+                eventAuthor = hostHex,
+                eventDTag = "stream",
+            ),
+        )
+    }
+
+    @Test
+    fun verifyFailsForMalformedProof() {
+        assertFalse(
+            ProofOfAgreement.verify(
+                proof = "not-hex",
+                participantPubKey = "a".repeat(64),
+                eventKind = LiveActivitiesEvent.KIND,
+                eventAuthor = "a".repeat(64),
+                eventDTag = "x",
+            ),
+        )
+        assertFalse(
+            ProofOfAgreement.verify(
+                proof = "ab",
+                participantPubKey = "a".repeat(64),
+                eventKind = LiveActivitiesEvent.KIND,
+                eventAuthor = "a".repeat(64),
+                eventDTag = "x",
+            ),
+        )
+    }
+
+    @Test
+    fun verifyAgainstLiveActivitiesEvent() {
+        val host = KeyPair()
+        val participant = KeyPair()
+        val hostHex = host.pubKey.toHexKey()
+        val participantHex = participant.pubKey.toHexKey()
+        val dTag = "event-d"
+
+        val proof =
+            ProofOfAgreement.sign(
+                participantPrivKey = participant.privKey!!,
+                eventKind = LiveActivitiesEvent.KIND,
+                eventAuthor = hostHex,
+                eventDTag = dTag,
+            )
+
+        val event =
+            LiveActivitiesEvent(
+                id = "0".repeat(64),
+                pubKey = hostHex,
+                createdAt = 1_700_000_000L,
+                tags =
+                    arrayOf(
+                        arrayOf("d", dTag),
+                        arrayOf("p", participantHex, "", "Speaker", proof),
+                        arrayOf("p", "c".repeat(64), "", "Speaker"),
+                    ),
+                content = "",
+                sig = dummySig,
+            )
+
+        val verifiedTag = event.participants().first { it.pubKey == participantHex }
+        val unverifiedTag = event.participants().first { it.pubKey == "c".repeat(64) }
+
+        assertTrue(event.hasValidProof(verifiedTag))
+        assertFalse(event.hasValidProof(unverifiedTag), "missing proof must not be treated as valid")
+    }
+
+    @Test
+    fun digestMatchesAddressForm() {
+        // digest(kind, pubkey, dtag) must agree with digest(Address)
+        val hostHex = "a".repeat(64)
+        val d1 = ProofOfAgreement.digest(LiveActivitiesEvent.KIND, hostHex, "abc")
+        val d2 = ProofOfAgreement.digest(Address(LiveActivitiesEvent.KIND, hostHex, "abc"))
+        assertTrue(d1.contentEquals(d2))
+    }
+
+    @Test
+    fun tagWithoutProofFailsVerification() {
+        val host = KeyPair()
+        val participant = KeyPair()
+
+        val event =
+            LiveActivitiesEvent(
+                id = "0".repeat(64),
+                pubKey = host.pubKey.toHexKey(),
+                createdAt = 1_700_000_000L,
+                tags = arrayOf(arrayOf("d", "d"), arrayOf("p", participant.pubKey.toHexKey())),
+                content = "",
+                sig = dummySig,
+            )
+
+        assertFalse(
+            ProofOfAgreement.verify(
+                tag = ParticipantTag(participant.pubKey.toHexKey(), null, null, null),
+                event = event,
+            ),
+        )
+    }
+}