diff --git a/bitchat/App/ConversationStore.swift b/bitchat/App/ConversationStore.swift
index 4e752b9b..f7fff03a 100644
--- a/bitchat/App/ConversationStore.swift
+++ b/bitchat/App/ConversationStore.swift
@@ -64,10 +64,25 @@ final class Conversation: ObservableObject, Identifiable {
         return messages[index]
     }
 
+    /// All message IDs currently in this conversation (unordered).
+    var messageIDs: Dictionary<String, Int>.Keys {
+        indexByMessageID.keys
+    }
+
     // MARK: Store-internal mutations
 
+    /// Result of an ordered insert. `trimmedMessageIDs` reports messages
+    /// evicted by the cap so the store can keep its message-ID →
+    /// conversation map exact.
+    fileprivate struct InsertResult {
+        let inserted: Bool
+        let trimmedMessageIDs: [String]
+
+        static let duplicate = InsertResult(inserted: false, trimmedMessageIDs: [])
+    }
+
     fileprivate enum UpsertOutcome {
-        case appended
+        case appended(trimmedMessageIDs: [String])
         case updated
     }
 
@@ -75,9 +90,9 @@ final class Conversation: ObservableObject, Identifiable {
     /// Fast path appends when the timestamp is >= the current tail;
     /// otherwise a binary search finds the upper-bound insertion point so
     /// arrival order is preserved among equal timestamps.
-    /// Returns `false` if a message with the same ID already exists.
-    fileprivate func insert(_ message: BitchatMessage) -> Bool {
-        guard indexByMessageID[message.id] == nil else { return false }
+    /// Reports `inserted: false` if a message with the same ID already exists.
+    fileprivate func insert(_ message: BitchatMessage) -> InsertResult {
+        guard indexByMessageID[message.id] == nil else { return .duplicate }
 
         if let last = messages.last, message.timestamp < last.timestamp {
             let index = insertionIndex(for: message.timestamp)
@@ -88,8 +103,7 @@ final class Conversation: ObservableObject, Identifiable {
             indexByMessageID[message.id] = messages.count - 1
         }
 
-        trimIfNeeded()
-        return true
+        return InsertResult(inserted: true, trimmedMessageIDs: trimIfNeeded())
     }
 
     /// Replace-or-append by message ID. An existing message keeps its
@@ -100,14 +114,14 @@ final class Conversation: ObservableObject, Identifiable {
             messages[index] = message
             return .updated
         }
-        _ = insert(message)
-        return .appended
+        let result = insert(message)
+        return .appended(trimmedMessageIDs: result.trimmedMessageIDs)
     }
 
     /// Applies a delivery status keyed by message ID, honoring the
-    /// no-downgrade rule (mirrors `ChatDeliveryCoordinator.shouldSkipUpdate`):
-    /// equal statuses are skipped, and `.read` is never downgraded to
-    /// `.delivered` or `.sent`.
+    /// no-downgrade rule (the SOLE enforcement point — every delivery
+    /// update flows through the store): equal statuses are skipped, and
+    /// `.read` is never downgraded to `.delivered` or `.sent`.
     /// Returns `true` when the status was applied.
     fileprivate func applyDeliveryStatus(_ status: DeliveryStatus, forMessageID messageID: String) -> Bool {
         guard let index = indexByMessageID[messageID] else { return false }
@@ -197,14 +211,17 @@ final class Conversation: ObservableObject, Identifiable {
         }
     }
 
-    private func trimIfNeeded() {
-        guard messages.count > cap else { return }
+    /// Trims oldest messages over the cap; returns the trimmed message IDs.
+    private func trimIfNeeded() -> [String] {
+        guard messages.count > cap else { return [] }
         let overflow = messages.count - cap
-        for message in messages.prefix(overflow) {
-            indexByMessageID.removeValue(forKey: message.id)
+        let trimmedIDs = messages.prefix(overflow).map(\.id)
+        for id in trimmedIDs {
+            indexByMessageID.removeValue(forKey: id)
         }
         messages.removeFirst(overflow)
         reindex(from: 0)
+        return trimmedIDs
     }
 }
 
@@ -242,6 +259,19 @@ final class ConversationStore: ObservableObject {
 
     private(set) var conversationsByID: [ConversationID: Conversation] = [:]
 
+    /// Store-level message-ID → conversation-membership map for ID-only
+    /// lookups (delivery receipts arrive with a message ID, not a
+    /// conversation). Maintained incrementally at every mutation point —
+    /// all mutation is centralized in the intent API below, so the map is
+    /// exact, never scanned or rebuilt.
+    ///
+    /// The value is a `Set` because a private message can legitimately live
+    /// in TWO direct conversations: step 2's raw per-peer keying mirrors a
+    /// message into both the stable-key and ephemeral-peer chats
+    /// (`mirrorToEphemeralIfNeeded`). A delivery update must reach both
+    /// copies.
+    private var conversationIDsByMessageID: [String: Set<ConversationID>] = [:]
+
     let changes = PassthroughSubject<ConversationChange, Never>()
 
     // MARK: Intent API
@@ -264,7 +294,10 @@ final class ConversationStore: ObservableObject {
     @discardableResult
     func append(_ message: BitchatMessage, to id: ConversationID) -> Bool {
         let conversation = conversation(for: id)
-        guard conversation.insert(message) else { return false }
+        let result = conversation.insert(message)
+        guard result.inserted else { return false }
+        registerMessageID(message.id, in: id)
+        unregisterMessageIDs(result.trimmedMessageIDs, from: id)
         changes.send(.appended(id, message))
         return true
     }
@@ -273,7 +306,9 @@ final class ConversationStore: ObservableObject {
     func upsertByID(_ message: BitchatMessage, in id: ConversationID) {
         let conversation = conversation(for: id)
         switch conversation.upsert(message) {
-        case .appended:
+        case .appended(let trimmedMessageIDs):
+            registerMessageID(message.id, in: id)
+            unregisterMessageIDs(trimmedMessageIDs, from: id)
             changes.send(.appended(id, message))
         case .updated:
             changes.send(.updated(id, messageID: message.id))
@@ -293,6 +328,44 @@ final class ConversationStore: ObservableObject {
         return true
     }
 
+    /// Applies a delivery status to EVERY conversation containing
+    /// `messageID` (ID-only — delivery receipts don't know conversations;
+    /// mirrored private copies live in two direct chats). Returns `false`
+    /// when the message is unknown or no copy changed (equal status or
+    /// downgrade — read beats delivered beats sent).
+    ///
+    /// `BitchatMessage` is a reference type, so mirrored copies sharing one
+    /// instance are updated by the first apply; subsequent conversations
+    /// skip as already-equal (state stays correct everywhere, the
+    /// `.statusChanged` event fires for the conversation that applied).
+    @discardableResult
+    func setDeliveryStatus(_ status: DeliveryStatus, forMessageID messageID: String) -> Bool {
+        guard let ids = conversationIDsByMessageID[messageID] else { return false }
+        var applied = false
+        for id in ids where setDeliveryStatus(status, forMessageID: messageID, in: id) {
+            applied = true
+        }
+        return applied
+    }
+
+    /// Current delivery status of `messageID` in whichever conversation
+    /// holds it (mirrored copies share status — see `setDeliveryStatus`).
+    func deliveryStatus(forMessageID messageID: String) -> DeliveryStatus? {
+        guard let ids = conversationIDsByMessageID[messageID] else { return nil }
+        for id in ids {
+            if let status = conversationsByID[id]?.message(withID: messageID)?.deliveryStatus {
+                return status
+            }
+        }
+        return nil
+    }
+
+    /// Every conversation currently containing `messageID` (empty when the
+    /// message is unknown).
+    func conversationIDs(forMessageID messageID: String) -> Set<ConversationID> {
+        conversationIDsByMessageID[messageID] ?? []
+    }
+
     func markRead(_ id: ConversationID) {
         guard unreadConversations.contains(id) else { return }
         unreadConversations.remove(id)
@@ -329,7 +402,13 @@ final class ConversationStore: ObservableObject {
 
         let destinationConversation = conversation(for: destination)
         for message in sourceConversation.messages {
-            _ = destinationConversation.insert(message)
+            let result = destinationConversation.insert(message)
+            guard result.inserted else { continue }
+            registerMessageID(message.id, in: destination)
+            unregisterMessageIDs(result.trimmedMessageIDs, from: destination)
+        }
+        for messageID in sourceConversation.messageIDs {
+            unregisterMessageID(messageID, from: source)
         }
 
         let wasUnread = unreadConversations.contains(source)
@@ -359,6 +438,7 @@ final class ConversationStore: ObservableObject {
               let removed = conversation.remove(messageID: messageID) else {
             return nil
         }
+        unregisterMessageID(messageID, from: id)
         changes.send(.messageRemoved(id, messageID: messageID))
         return removed
     }
@@ -368,7 +448,9 @@ final class ConversationStore: ObservableObject {
     /// conversation is consistent. No-op for unknown conversations.
     func removeMessages(from id: ConversationID, where predicate: (BitchatMessage) -> Bool) {
         guard let conversation = conversationsByID[id] else { return }
-        for messageID in conversation.removeAll(where: predicate) {
+        let removedIDs = conversation.removeAll(where: predicate)
+        unregisterMessageIDs(removedIDs, from: id)
+        for messageID in removedIDs {
             changes.send(.messageRemoved(id, messageID: messageID))
         }
     }
@@ -377,6 +459,9 @@ final class ConversationStore: ObservableObject {
     /// its unread/selection state) alive.
     func clear(_ id: ConversationID) {
         guard let conversation = conversationsByID[id] else { return }
+        for messageID in conversation.messageIDs {
+            unregisterMessageID(messageID, from: id)
+        }
         conversation.clearMessages()
         changes.send(.cleared(id))
     }
@@ -384,7 +469,10 @@ final class ConversationStore: ObservableObject {
     /// Removes a conversation entirely, including unread state; clears the
     /// selection if it pointed at the removed conversation.
     func removeConversation(_ id: ConversationID) {
-        guard conversationsByID.removeValue(forKey: id) != nil else { return }
+        guard let conversation = conversationsByID.removeValue(forKey: id) else { return }
+        for messageID in conversation.messageIDs {
+            unregisterMessageID(messageID, from: id)
+        }
         conversationIDs.removeAll { $0 == id }
         unreadConversations.remove(id)
         if selectedConversationID == id {
@@ -400,6 +488,7 @@ final class ConversationStore: ObservableObject {
         conversationsByID.removeAll()
         conversationIDs.removeAll()
         unreadConversations.removeAll()
+        conversationIDsByMessageID.removeAll()
         if selectedConversationID != nil {
             selectedConversationID = nil
         }
@@ -411,6 +500,26 @@ final class ConversationStore: ObservableObject {
 
     // MARK: Internals
 
+    private func registerMessageID(_ messageID: String, in id: ConversationID) {
+        conversationIDsByMessageID[messageID, default: []].insert(id)
+    }
+
+    private func unregisterMessageID(_ messageID: String, from id: ConversationID) {
+        guard var ids = conversationIDsByMessageID[messageID] else { return }
+        ids.remove(id)
+        if ids.isEmpty {
+            conversationIDsByMessageID.removeValue(forKey: messageID)
+        } else {
+            conversationIDsByMessageID[messageID] = ids
+        }
+    }
+
+    private func unregisterMessageIDs(_ messageIDs: [String], from id: ConversationID) {
+        for messageID in messageIDs {
+            unregisterMessageID(messageID, from: id)
+        }
+    }
+
     private static func cap(for id: ConversationID) -> Int {
         switch id {
         case .mesh:
@@ -471,13 +580,23 @@ extension ConversationStore {
     }
 
     /// `true` when any direct conversation contains a message with `messageID`
-    /// (O(1) per conversation via the incremental ID index).
+    /// (O(1) via the store-level message-ID → conversation map).
     func directConversationsContainMessage(withID messageID: String) -> Bool {
+        conversationIDs(forMessageID: messageID).contains { id in
+            if case .direct = id { return true }
+            return false
+        }
+    }
+
+    /// Message IDs across all direct conversations (read-receipt pruning
+    /// keeps only receipts whose messages still exist).
+    func directMessageIDs() -> Set<String> {
+        var messageIDs = Set<String>()
         for (id, conversation) in conversationsByID {
             guard case .direct = id else { continue }
-            if conversation.containsMessage(withID: messageID) { return true }
+            messageIDs.formUnion(conversation.messageIDs)
         }
-        return false
+        return messageIDs
     }
 
     /// Removes every direct conversation (panic clear).
@@ -501,12 +620,10 @@ extension ConversationStore {
     /// message, if any.
     @discardableResult
     func removePublicMessage(withID messageID: String) -> BitchatMessage? {
-        for (id, conversation) in conversationsByID {
+        for id in conversationIDs(forMessageID: messageID) {
             switch id {
             case .mesh, .geohash:
-                if conversation.containsMessage(withID: messageID) {
-                    return removeMessage(withID: messageID, from: id)
-                }
+                return removeMessage(withID: messageID, from: id)
             case .direct:
                 continue
             }
diff --git a/bitchat/ViewModels/ChatDeliveryCoordinator.swift b/bitchat/ViewModels/ChatDeliveryCoordinator.swift
index 8acf7bec..f2fc13c0 100644
--- a/bitchat/ViewModels/ChatDeliveryCoordinator.swift
+++ b/bitchat/ViewModels/ChatDeliveryCoordinator.swift
@@ -12,18 +12,19 @@ import Foundation
 /// coordinators off their `unowned let viewModel: ChatViewModel` back-refs.
 @MainActor
 protocol ChatDeliveryContext: AnyObject {
-    /// Get-only derived views of the `ConversationStore`. `BitchatMessage`
-    /// is a reference type, so the public-timeline status patch below writes
-    /// through the shared message objects; step 4 replaces this with
-    /// `setDeliveryStatus(for:in:)` store intents.
-    var messages: [BitchatMessage] { get }
-    var privateChats: [PeerID: [BitchatMessage]] { get }
     var isStartupPhase: Bool { get }
-    /// Applies a delivery status to a private message by ID (single-writer
-    /// store intent; full delivery migration is step 4). Returns `false`
-    /// when the message is unknown or the update would downgrade the status.
+    /// Applies a delivery status to every copy of the message across
+    /// conversations (`ConversationStore` intent, ID-only: the store's
+    /// message-ID → conversation map resolves which conversations hold the
+    /// message, including mirrored ephemeral/stable private copies). The
+    /// no-downgrade rule is enforced in the store. Returns `false` when the
+    /// message is unknown or no copy changed.
     @discardableResult
-    func setPrivateDeliveryStatus(_ status: DeliveryStatus, forMessageID messageID: String, peerID: PeerID) -> Bool
+    func setDeliveryStatus(_ status: DeliveryStatus, forMessageID messageID: String) -> Bool
+    /// Current delivery status of the message in whichever conversation holds it.
+    func deliveryStatus(forMessageID messageID: String) -> DeliveryStatus?
+    /// Message IDs across all direct conversations (read-receipt pruning).
+    func privateMessageIDs() -> Set<String>
     /// Drops every recorded read receipt whose message ID is not in `validMessageIDs`.
     /// Returns the number of receipts removed. (Single mutation path for the
     /// owner's `sentReadReceipts`; this coordinator never reads the raw set.)
@@ -35,6 +36,19 @@ protocol ChatDeliveryContext: AnyObject {
 }
 
 extension ChatViewModel: ChatDeliveryContext {
+    @discardableResult
+    func setDeliveryStatus(_ status: DeliveryStatus, forMessageID messageID: String) -> Bool {
+        conversations.setDeliveryStatus(status, forMessageID: messageID)
+    }
+
+    func deliveryStatus(forMessageID messageID: String) -> DeliveryStatus? {
+        conversations.deliveryStatus(forMessageID: messageID)
+    }
+
+    func privateMessageIDs() -> Set<String> {
+        conversations.directMessageIDs()
+    }
+
     func notifyUIChanged() {
         objectWillChange.send()
     }
@@ -44,14 +58,12 @@ extension ChatViewModel: ChatDeliveryContext {
     }
 }
 
+/// Thin mapper from delivery events (read receipts, transport delivery
+/// callbacks) onto `ConversationStore` delivery intents, plus read-receipt
+/// retention cleanup. The store's message-ID → conversation map replaces the
+/// positional `messageLocationIndex` this coordinator used to maintain.
 final class ChatDeliveryCoordinator {
     private unowned let context: any ChatDeliveryContext
-    private var messageLocationIndex: [String: Set<MessageLocation>] = [:]
-    private var indexedPublicMessageCount = 0
-    private var indexedPublicTailMessageID: String?
-    private var indexedPrivateMessageCounts: [PeerID: Int] = [:]
-    private var indexedPrivateTailMessageIDs: [PeerID: String] = [:]
-    private var hasBuiltMessageLocationIndex = false
 
     init(context: any ChatDeliveryContext) {
         self.context = context
@@ -59,15 +71,9 @@ final class ChatDeliveryCoordinator {
 
     @MainActor
     func cleanupOldReadReceipts() {
-        guard !context.isStartupPhase, !context.privateChats.isEmpty else {
-            return
-        }
-
-        let validMessageIDs = Set(
-            context.privateChats.values.flatMap { messages in
-                messages.map(\.id)
-            }
-        )
+        guard !context.isStartupPhase else { return }
+        let validMessageIDs = context.privateMessageIDs()
+        guard !validMessageIDs.isEmpty else { return }
 
         let removedCount = context.pruneSentReadReceipts(keeping: validMessageIDs)
         if removedCount > 0 {
@@ -90,9 +96,7 @@ final class ChatDeliveryCoordinator {
 
     @MainActor
     func deliveryStatus(for messageID: String) -> DeliveryStatus? {
-        withValidLocations(for: messageID) { locations in
-            locations.lazy.compactMap { self.deliveryStatus(at: $0) }.first
-        }
+        context.deliveryStatus(forMessageID: messageID)
     }
 
     @MainActor
@@ -106,222 +110,10 @@ final class ChatDeliveryCoordinator {
             break
         }
 
-        var didUpdateStatus = false
-        let locations = withValidLocations(for: messageID) { $0 }
-        guard !locations.isEmpty else { return false }
-
-        for location in locations {
-            guard case .publicTimeline(let index) = location,
-                  index < context.messages.count,
-                  context.messages[index].id == messageID else {
-                continue
-            }
-
-            let currentStatus = context.messages[index].deliveryStatus
-            if !shouldSkipUpdate(currentStatus: currentStatus, newStatus: status) {
-                context.messages[index].deliveryStatus = status
-                didUpdateStatus = true
-            }
-        }
-
-        for location in locations {
-            guard case .privateChat(let peerID, let index) = location,
-                  let chatMessages = context.privateChats[peerID],
-                  index < chatMessages.count,
-                  chatMessages[index].id == messageID else {
-                continue
-            }
-
-            let currentStatus = chatMessages[index].deliveryStatus
-            guard !shouldSkipUpdate(currentStatus: currentStatus, newStatus: status) else { continue }
-
-            if context.setPrivateDeliveryStatus(status, forMessageID: messageID, peerID: peerID) {
-                didUpdateStatus = true
-            }
-        }
-
-        if didUpdateStatus {
-            context.notifyUIChanged()
-        }
-
-        return didUpdateStatus
-    }
-}
-
-private extension ChatDeliveryCoordinator {
-    enum MessageLocation: Hashable {
-        case publicTimeline(index: Int)
-        case privateChat(peerID: PeerID, index: Int)
-    }
-
-    func shouldSkipUpdate(currentStatus: DeliveryStatus?, newStatus: DeliveryStatus) -> Bool {
-        guard let currentStatus else { return false }
-        if currentStatus == newStatus { return true }
-
-        switch (currentStatus, newStatus) {
-        case (.read, .delivered), (.read, .sent):
-            return true
-        default:
+        guard context.setDeliveryStatus(status, forMessageID: messageID) else {
             return false
         }
-    }
-
-    @MainActor
-    func withValidLocations<T>(
-        for messageID: String,
-        _ body: (Set<MessageLocation>) -> T
-    ) -> T {
-        let didRebuildIndex = refreshMessageLocationIndexForGrowth()
-
-        if let locations = messageLocationIndex[messageID],
-           locations.allSatisfy({ isLocation($0, validFor: messageID) }) {
-            return body(locations)
-        }
-
-        guard !didRebuildIndex else {
-            return body(messageLocationIndex[messageID] ?? [])
-        }
-
-        if messageLocationIndex[messageID] == nil {
-            return body([])
-        }
-
-        rebuildMessageLocationIndex()
-        return body(messageLocationIndex[messageID] ?? [])
-    }
-
-    @MainActor
-    func deliveryStatus(at location: MessageLocation) -> DeliveryStatus? {
-        switch location {
-        case .publicTimeline(let index):
-            guard index < context.messages.count else { return nil }
-            return context.messages[index].deliveryStatus
-        case .privateChat(let peerID, let index):
-            guard let messages = context.privateChats[peerID],
-                  index < messages.count else {
-                return nil
-            }
-            return messages[index].deliveryStatus
-        }
-    }
-
-    @MainActor
-    func isLocation(_ location: MessageLocation, validFor messageID: String) -> Bool {
-        switch location {
-        case .publicTimeline(let index):
-            return index < context.messages.count
-                && context.messages[index].id == messageID
-        case .privateChat(let peerID, let index):
-            guard let messages = context.privateChats[peerID],
-                  index < messages.count else {
-                return false
-            }
-            return messages[index].id == messageID
-        }
-    }
-
-    @MainActor
-    @discardableResult
-    func refreshMessageLocationIndexForGrowth() -> Bool {
-        guard hasBuiltMessageLocationIndex else {
-            rebuildMessageLocationIndex()
-            return true
-        }
-
-        if context.messages.count < indexedPublicMessageCount {
-            rebuildMessageLocationIndex()
-            return true
-        }
-
-        if context.messages.count == indexedPublicMessageCount,
-           context.messages.last?.id != indexedPublicTailMessageID {
-            rebuildMessageLocationIndex()
-            return true
-        }
-
-        if context.messages.count > indexedPublicMessageCount {
-            // Growth is only a pure append if the previously indexed tail kept
-            // its position; a middle insertion (out-of-order timestamp arrival)
-            // shifts it and invalidates every indexed location after the
-            // insertion point.
-            if indexedPublicMessageCount > 0,
-               context.messages[indexedPublicMessageCount - 1].id != indexedPublicTailMessageID {
-                rebuildMessageLocationIndex()
-                return true
-            }
-            for index in indexedPublicMessageCount..<context.messages.count {
-                add(.publicTimeline(index: index), for: context.messages[index].id)
-            }
-            indexedPublicMessageCount = context.messages.count
-            indexedPublicTailMessageID = context.messages.last?.id
-        }
-
-        let currentPeerIDs = Set(context.privateChats.keys)
-        if !Set(indexedPrivateMessageCounts.keys).isSubset(of: currentPeerIDs) {
-            rebuildMessageLocationIndex()
-            return true
-        }
-
-        for (peerID, messages) in context.privateChats {
-            let indexedCount = indexedPrivateMessageCounts[peerID] ?? 0
-            if messages.count < indexedCount {
-                rebuildMessageLocationIndex()
-                return true
-            }
-
-            if messages.count == indexedCount,
-               messages.last?.id != indexedPrivateTailMessageIDs[peerID] {
-                rebuildMessageLocationIndex()
-                return true
-            }
-
-            guard messages.count > indexedCount else { continue }
-            // Same append-only check as the public timeline above.
-            if indexedCount > 0,
-               messages[indexedCount - 1].id != indexedPrivateTailMessageIDs[peerID] {
-                rebuildMessageLocationIndex()
-                return true
-            }
-            for index in indexedCount..<messages.count {
-                add(.privateChat(peerID: peerID, index: index), for: messages[index].id)
-            }
-            indexedPrivateMessageCounts[peerID] = messages.count
-            if let tailID = messages.last?.id {
-                indexedPrivateTailMessageIDs[peerID] = tailID
-            } else {
-                indexedPrivateTailMessageIDs.removeValue(forKey: peerID)
-            }
-        }
-
-        return false
-    }
-
-    @MainActor
-    func rebuildMessageLocationIndex() {
-        messageLocationIndex.removeAll(keepingCapacity: true)
-
-        for (index, message) in context.messages.enumerated() {
-            add(.publicTimeline(index: index), for: message.id)
-        }
-        indexedPublicMessageCount = context.messages.count
-        indexedPublicTailMessageID = context.messages.last?.id
-
-        indexedPrivateMessageCounts.removeAll(keepingCapacity: true)
-        indexedPrivateTailMessageIDs.removeAll(keepingCapacity: true)
-        for (peerID, messages) in context.privateChats {
-            for (index, message) in messages.enumerated() {
-                add(.privateChat(peerID: peerID, index: index), for: message.id)
-            }
-            indexedPrivateMessageCounts[peerID] = messages.count
-            if let tailID = messages.last?.id {
-                indexedPrivateTailMessageIDs[peerID] = tailID
-            }
-        }
-
-        hasBuiltMessageLocationIndex = true
-    }
-
-    func add(_ location: MessageLocation, for messageID: String) {
-        messageLocationIndex[messageID, default: []].insert(location)
+        context.notifyUIChanged()
+        return true
     }
 }
diff --git a/bitchatTests/ChatViewModelDeliveryStatusTests.swift b/bitchatTests/ChatViewModelDeliveryStatusTests.swift
index ecebdae3..bf859abb 100644
--- a/bitchatTests/ChatViewModelDeliveryStatusTests.swift
+++ b/bitchatTests/ChatViewModelDeliveryStatusTests.swift
@@ -304,7 +304,7 @@ struct ChatViewModelDeliveryStatusTests {
     }
 
     @Test @MainActor
-    func deliveryStatus_indexRefreshesAfterPrivateChatReorder() async {
+    func deliveryStatus_survivesPrivateChatReorder() async {
         let (viewModel, transport) = makeTestableViewModel()
         let peerID = PeerID(str: "0102030405060708")
         let messageID = "reordered-msg-1"
@@ -335,8 +335,8 @@ struct ChatViewModelDeliveryStatusTests {
         #expect(isSent(viewModel.deliveryCoordinator.deliveryStatus(for: messageID)))
 
         // A late arrival with an older timestamp is inserted before the
-        // target by the store, shifting its position and invalidating the
-        // delivery coordinator's location index.
+        // target by the store, shifting its position; the store's ID-keyed
+        // indexes must keep the target updatable.
         viewModel.seedPrivateChat([olderMessage], for: peerID)
         #expect(viewModel.privateChats[peerID]?.map(\.id) == ["older-msg", messageID])
 
@@ -383,16 +383,31 @@ struct ChatViewModelDeliveryStatusTests {
 // MARK: - Mock Delivery Context
 
 /// Lightweight stand-in for `ChatDeliveryContext` proving that
-/// `ChatDeliveryCoordinator` is testable without constructing a `ChatViewModel`.
+/// `ChatDeliveryCoordinator` is testable without constructing a
+/// `ChatViewModel`: the delivery surface forwards to a real
+/// `ConversationStore` (the coordinator is a thin mapper over store
+/// intents), and assertions read store state.
 @MainActor
 private final class MockChatDeliveryContext: ChatDeliveryContext {
-    var messages: [BitchatMessage] = []
-    var privateChats: [PeerID: [BitchatMessage]] = [:]
+    let store = ConversationStore()
     var sentReadReceipts: Set<String> = []
     var isStartupPhase = false
     private(set) var notifyUIChangedCount = 0
     private(set) var markedDeliveredMessageIDs: [String] = []
 
+    @discardableResult
+    func setDeliveryStatus(_ status: DeliveryStatus, forMessageID messageID: String) -> Bool {
+        store.setDeliveryStatus(status, forMessageID: messageID)
+    }
+
+    func deliveryStatus(forMessageID messageID: String) -> DeliveryStatus? {
+        store.deliveryStatus(forMessageID: messageID)
+    }
+
+    func privateMessageIDs() -> Set<String> {
+        store.directMessageIDs()
+    }
+
     func pruneSentReadReceipts(keeping validMessageIDs: Set<String>) -> Int {
         let oldCount = sentReadReceipts.count
         sentReadReceipts = sentReadReceipts.intersection(validMessageIDs)
@@ -406,29 +421,19 @@ private final class MockChatDeliveryContext: ChatDeliveryContext {
     func markMessageDelivered(_ messageID: String) {
         markedDeliveredMessageIDs.append(messageID)
     }
-
-    @discardableResult
-    func setPrivateDeliveryStatus(_ status: DeliveryStatus, forMessageID messageID: String, peerID: PeerID) -> Bool {
-        guard var chat = privateChats[peerID],
-              let index = chat.firstIndex(where: { $0.id == messageID }) else {
-            return false
-        }
-        if Conversation.shouldSkipStatusUpdate(current: chat[index].deliveryStatus, new: status) {
-            return false
-        }
-        chat[index].deliveryStatus = status
-        privateChats[peerID] = chat
-        return true
-    }
 }
 
 @MainActor
-private func makePrivateMessage(id: String, status: DeliveryStatus) -> BitchatMessage {
+private func makePrivateMessage(
+    id: String,
+    status: DeliveryStatus,
+    timestamp: Date = Date()
+) -> BitchatMessage {
     BitchatMessage(
         id: id,
         sender: "me",
         content: "Test message",
-        timestamp: Date(),
+        timestamp: timestamp,
         isRelay: false,
         isPrivate: true,
         recipientNickname: "Peer",
@@ -437,10 +442,28 @@ private func makePrivateMessage(id: String, status: DeliveryStatus) -> BitchatMe
     )
 }
 
+@MainActor
+private func makePublicMessage(
+    id: String,
+    status: DeliveryStatus,
+    timestamp: Date = Date()
+) -> BitchatMessage {
+    BitchatMessage(
+        id: id,
+        sender: "me",
+        content: "Public message",
+        timestamp: timestamp,
+        isRelay: false,
+        isPrivate: false,
+        deliveryStatus: status
+    )
+}
+
 // MARK: - Coordinator Tests Against Mock Context
 
 /// Exercises `ChatDeliveryCoordinator` against `MockChatDeliveryContext` —
-/// the exemplar for the narrow-dependency coordinator pattern.
+/// the exemplar for the narrow-dependency coordinator pattern. State is
+/// seeded into and asserted against the mock's `ConversationStore`.
 struct ChatDeliveryCoordinatorContextTests {
 
     @Test @MainActor
@@ -449,7 +472,7 @@ struct ChatDeliveryCoordinatorContextTests {
         let coordinator = ChatDeliveryCoordinator(context: context)
         let peerID = PeerID(str: "0102030405060708")
         let messageID = "mock-msg-1"
-        context.privateChats[peerID] = [makePrivateMessage(id: messageID, status: .sent)]
+        context.store.append(makePrivateMessage(id: messageID, status: .sent), to: .directPeer(peerID))
 
         let didUpdate = coordinator.updateMessageDeliveryStatus(
             messageID,
@@ -457,7 +480,7 @@ struct ChatDeliveryCoordinatorContextTests {
         )
 
         #expect(didUpdate)
-        #expect(isDelivered(context.privateChats[peerID]?.first?.deliveryStatus))
+        #expect(isDelivered(context.store.conversation(for: .directPeer(peerID)).message(withID: messageID)?.deliveryStatus))
         #expect(context.notifyUIChangedCount == 1)
         #expect(context.markedDeliveredMessageIDs == [messageID])
     }
@@ -468,13 +491,16 @@ struct ChatDeliveryCoordinatorContextTests {
         let coordinator = ChatDeliveryCoordinator(context: context)
         let peerID = PeerID(str: "0102030405060708")
         let messageID = "mock-msg-2"
-        context.privateChats[peerID] = [makePrivateMessage(id: messageID, status: .delivered(to: "Peer", at: Date()))]
+        context.store.append(
+            makePrivateMessage(id: messageID, status: .delivered(to: "Peer", at: Date())),
+            to: .directPeer(peerID)
+        )
 
         coordinator.didReceiveReadReceipt(
             ReadReceipt(originalMessageID: messageID, readerID: peerID, readerNickname: "Peer")
         )
 
-        #expect(isRead(context.privateChats[peerID]?.first?.deliveryStatus))
+        #expect(isRead(coordinator.deliveryStatus(for: messageID)))
         #expect(context.notifyUIChangedCount == 1)
         #expect(context.markedDeliveredMessageIDs == [messageID])
     }
@@ -483,22 +509,12 @@ struct ChatDeliveryCoordinatorContextTests {
     func sentStatus_doesNotMarkDeliveredAndUnknownMessageDoesNotNotify() async {
         let context = MockChatDeliveryContext()
         let coordinator = ChatDeliveryCoordinator(context: context)
-        context.messages = [
-            BitchatMessage(
-                id: "public-mock-1",
-                sender: "me",
-                content: "Public message",
-                timestamp: Date(),
-                isRelay: false,
-                isPrivate: false,
-                deliveryStatus: .sending
-            )
-        ]
+        context.store.append(makePublicMessage(id: "public-mock-1", status: .sending), to: .mesh)
 
         // .sent is not a confirmed receipt — must not reach markMessageDelivered.
         let didUpdate = coordinator.updateMessageDeliveryStatus("public-mock-1", status: .sent)
         #expect(didUpdate)
-        #expect(isSent(context.messages.first?.deliveryStatus))
+        #expect(isSent(context.store.conversation(for: .mesh).message(withID: "public-mock-1")?.deliveryStatus))
         #expect(context.markedDeliveredMessageIDs.isEmpty)
         #expect(context.notifyUIChangedCount == 1)
 
@@ -508,57 +524,98 @@ struct ChatDeliveryCoordinatorContextTests {
         #expect(context.notifyUIChangedCount == 1)
     }
 
+    // The old positional `messageLocationIndex` could go stale when a late
+    // arrival was inserted mid-array (count grew but indexed locations
+    // shifted). The store's per-conversation ID index is reindexed inside the
+    // same mutation, so staleness is structurally impossible — these tests
+    // pin the equivalent behavior through the new path: after out-of-order
+    // insertion, updates keyed by ID still land on the right messages.
+
     @Test @MainActor
-    func middleInsertedMessage_isFoundAfterIndexWasBuilt() async {
+    func middleInsertedMessage_isStillUpdatableByID() async {
         let context = MockChatDeliveryContext()
         let coordinator = ChatDeliveryCoordinator(context: context)
-        let makePublic = { (id: String) in
-            BitchatMessage(
-                id: id,
-                sender: "me",
-                content: "Public message",
-                timestamp: Date(),
-                isRelay: false,
-                isPrivate: false,
-                deliveryStatus: .sending
-            )
-        }
-        context.messages = [makePublic("public-a"), makePublic("public-b")]
+        context.store.append(
+            makePublicMessage(id: "public-a", status: .sending, timestamp: Date(timeIntervalSince1970: 10)),
+            to: .mesh
+        )
+        context.store.append(
+            makePublicMessage(id: "public-b", status: .sending, timestamp: Date(timeIntervalSince1970: 30)),
+            to: .mesh
+        )
 
-        // Build the incremental index.
         #expect(coordinator.updateMessageDeliveryStatus("public-a", status: .sent))
 
-        // Out-of-order arrival: PublicMessagePipeline inserts by timestamp,
-        // so the count grows while the tail ID stays the same.
-        context.messages.insert(makePublic("public-mid"), at: 1)
+        // Out-of-order arrival: the store inserts by timestamp, shifting the
+        // tail's position.
+        context.store.append(
+            makePublicMessage(id: "public-mid", status: .sending, timestamp: Date(timeIntervalSince1970: 20)),
+            to: .mesh
+        )
+        let mesh = context.store.conversation(for: .mesh)
+        #expect(mesh.messages.map(\.id) == ["public-a", "public-mid", "public-b"])
 
-        // The inserted message must be locatable, and the shifted tail must
-        // not be updated through a stale index entry.
+        // Both the inserted message and the shifted tail stay updatable.
         #expect(coordinator.updateMessageDeliveryStatus("public-mid", status: .sent))
-        #expect(isSent(context.messages[1].deliveryStatus))
+        #expect(isSent(mesh.message(withID: "public-mid")?.deliveryStatus))
         #expect(coordinator.updateMessageDeliveryStatus("public-b", status: .sent))
-        #expect(isSent(context.messages[2].deliveryStatus))
+        #expect(isSent(mesh.message(withID: "public-b")?.deliveryStatus))
     }
 
     @Test @MainActor
-    func middleInsertedPrivateMessage_isFoundAfterIndexWasBuilt() async {
+    func middleInsertedPrivateMessage_isStillUpdatableByID() async {
         let context = MockChatDeliveryContext()
         let coordinator = ChatDeliveryCoordinator(context: context)
         let peerID = PeerID(str: "0102030405060708")
-        context.privateChats[peerID] = [
-            makePrivateMessage(id: "pm-a", status: .sending),
-            makePrivateMessage(id: "pm-b", status: .sending)
-        ]
+        let conversationID = ConversationID.directPeer(peerID)
+        context.store.append(
+            makePrivateMessage(id: "pm-a", status: .sending, timestamp: Date(timeIntervalSince1970: 10)),
+            to: conversationID
+        )
+        context.store.append(
+            makePrivateMessage(id: "pm-b", status: .sending, timestamp: Date(timeIntervalSince1970: 30)),
+            to: conversationID
+        )
 
         #expect(coordinator.updateMessageDeliveryStatus("pm-a", status: .sent))
 
-        // Timestamp re-sort (sanitizeChat) can place a late arrival mid-array.
-        context.privateChats[peerID]?.insert(makePrivateMessage(id: "pm-mid", status: .sending), at: 1)
+        // A late arrival with an older timestamp lands mid-array.
+        context.store.append(
+            makePrivateMessage(id: "pm-mid", status: .sending, timestamp: Date(timeIntervalSince1970: 20)),
+            to: conversationID
+        )
+        let chat = context.store.conversation(for: conversationID)
+        #expect(chat.messages.map(\.id) == ["pm-a", "pm-mid", "pm-b"])
 
         #expect(coordinator.updateMessageDeliveryStatus("pm-mid", status: .sent))
-        #expect(isSent(context.privateChats[peerID]?[1].deliveryStatus))
+        #expect(isSent(chat.message(withID: "pm-mid")?.deliveryStatus))
         #expect(coordinator.updateMessageDeliveryStatus("pm-b", status: .sent))
-        #expect(isSent(context.privateChats[peerID]?[2].deliveryStatus))
+        #expect(isSent(chat.message(withID: "pm-b")?.deliveryStatus))
+    }
+
+    @Test @MainActor
+    func mirroredPrivateCopies_bothReceiveDeliveryUpdate() async {
+        let context = MockChatDeliveryContext()
+        let coordinator = ChatDeliveryCoordinator(context: context)
+        let stablePeerID = PeerID(str: String(repeating: "ab", count: 32))
+        let ephemeralPeerID = PeerID(str: "0102030405060708")
+        let messageID = "mirrored-mock-1"
+
+        // Step 2's keying mirrors a private message into both the stable-key
+        // and ephemeral-peer conversations (distinct copies here to prove
+        // per-conversation application, not shared-reference aliasing).
+        context.store.append(makePrivateMessage(id: messageID, status: .sent), to: .directPeer(stablePeerID))
+        context.store.append(makePrivateMessage(id: messageID, status: .sent), to: .directPeer(ephemeralPeerID))
+
+        let didUpdate = coordinator.updateMessageDeliveryStatus(
+            messageID,
+            status: .delivered(to: "Peer", at: Date())
+        )
+
+        #expect(didUpdate)
+        #expect(isDelivered(context.store.conversation(for: .directPeer(stablePeerID)).message(withID: messageID)?.deliveryStatus))
+        #expect(isDelivered(context.store.conversation(for: .directPeer(ephemeralPeerID)).message(withID: messageID)?.deliveryStatus))
+        #expect(context.markedDeliveredMessageIDs == [messageID])
     }
 
     @Test @MainActor
@@ -566,7 +623,7 @@ struct ChatDeliveryCoordinatorContextTests {
         let context = MockChatDeliveryContext()
         let coordinator = ChatDeliveryCoordinator(context: context)
         let peerID = PeerID(str: "0102030405060708")
-        context.privateChats[peerID] = [makePrivateMessage(id: "keep-receipt", status: .sent)]
+        context.store.append(makePrivateMessage(id: "keep-receipt", status: .sent), to: .directPeer(peerID))
         context.sentReadReceipts = ["keep-receipt", "drop-receipt"]
 
         // Startup phase: cleanup must be a no-op.
diff --git a/bitchatTests/ConversationStoreTests.swift b/bitchatTests/ConversationStoreTests.swift
index 8535cc57..3cd0f225 100644
--- a/bitchatTests/ConversationStoreTests.swift
+++ b/bitchatTests/ConversationStoreTests.swift
@@ -562,4 +562,159 @@ struct ConversationStoreTests {
         #expect(!conversation.containsMessage(withID: "one"))
         #expect(store.append(makeMessage(id: "one", timestamp: 2000), to: id))
     }
+
+    // MARK: - Store-level message-ID → conversation map (ID-only delivery)
+
+    @Test("ID map tracks append, upsert, and removal")
+    @MainActor
+    func messageIDMapTracksAppendAndRemoval() {
+        let store = ConversationStore()
+        let direct = makeDirectConversationID("aa")
+
+        #expect(store.conversationIDs(forMessageID: "m1").isEmpty)
+
+        store.append(makeMessage(id: "m1", timestamp: 1), to: .mesh)
+        #expect(store.conversationIDs(forMessageID: "m1") == [.mesh])
+
+        // Upsert-as-append registers; upsert-in-place does not duplicate.
+        store.upsertByID(makeMessage(id: "d1", timestamp: 1, isPrivate: true), in: direct)
+        store.upsertByID(makeMessage(id: "d1", timestamp: 1, isPrivate: true, deliveryStatus: .sent), in: direct)
+        #expect(store.conversationIDs(forMessageID: "d1") == [direct])
+
+        store.removeMessage(withID: "m1", from: .mesh)
+        #expect(store.conversationIDs(forMessageID: "m1").isEmpty)
+
+        store.removeMessages(from: direct, where: { $0.id == "d1" })
+        #expect(store.conversationIDs(forMessageID: "d1").isEmpty)
+    }
+
+    @Test("ID map handles multi-conversation membership (mirrored private copies)")
+    @MainActor
+    func messageIDMapHandlesMirroredCopies() {
+        let store = ConversationStore()
+        let stable = makeDirectConversationID("stable")
+        let ephemeral = makeDirectConversationID("ephemeral")
+
+        // Step 2's keying mirrors one private message into the stable-key
+        // AND ephemeral-peer conversations (distinct copies here to prove
+        // per-conversation bookkeeping).
+        store.upsertByID(makeMessage(id: "dm-1", timestamp: 1, isPrivate: true, deliveryStatus: .sent), in: stable)
+        store.upsertByID(makeMessage(id: "dm-1", timestamp: 1, isPrivate: true, deliveryStatus: .sent), in: ephemeral)
+        #expect(store.conversationIDs(forMessageID: "dm-1") == [stable, ephemeral])
+
+        // An ID-only delivery update reaches BOTH copies.
+        #expect(store.setDeliveryStatus(.delivered(to: "bob", at: Date()), forMessageID: "dm-1"))
+        for id in [stable, ephemeral] {
+            guard case .delivered = store.conversation(for: id).message(withID: "dm-1")?.deliveryStatus else {
+                Issue.record("expected .delivered in \(id)")
+                return
+            }
+        }
+
+        // Removing one copy keeps the other resolvable.
+        store.removeMessage(withID: "dm-1", from: ephemeral)
+        #expect(store.conversationIDs(forMessageID: "dm-1") == [stable])
+    }
+
+    @Test("ID-only setDeliveryStatus enforces no-downgrade and unknown IDs")
+    @MainActor
+    func idOnlyDeliveryStatusRules() {
+        let store = ConversationStore()
+        let direct = makeDirectConversationID("aa")
+        store.append(
+            makeMessage(id: "dm-1", timestamp: 1, isPrivate: true, deliveryStatus: .read(by: "bob", at: Date())),
+            to: direct
+        )
+
+        // Unknown message.
+        #expect(!store.setDeliveryStatus(.sent, forMessageID: "missing"))
+        #expect(store.deliveryStatus(forMessageID: "missing") == nil)
+
+        // Downgrade from .read is refused; status is readable by ID alone.
+        #expect(!store.setDeliveryStatus(.delivered(to: "bob", at: Date()), forMessageID: "dm-1"))
+        guard case .read = store.deliveryStatus(forMessageID: "dm-1") else {
+            Issue.record("expected .read to survive the downgrade attempt")
+            return
+        }
+    }
+
+    @Test("ID map follows migration between conversations")
+    @MainActor
+    func messageIDMapFollowsMigration() {
+        let store = ConversationStore()
+        let source = makeDirectConversationID("ephemeral")
+        let destination = makeDirectConversationID("stable")
+        store.append(makeMessage(id: "dm-1", timestamp: 1, isPrivate: true), to: source)
+        store.append(makeMessage(id: "dm-2", timestamp: 2, isPrivate: true), to: source)
+        // Already present in the destination: migration dedups, and the map
+        // must not retain a stale source membership.
+        store.append(makeMessage(id: "dm-2", timestamp: 2, isPrivate: true), to: destination)
+
+        store.migrateConversation(from: source, to: destination)
+
+        #expect(store.conversationIDs(forMessageID: "dm-1") == [destination])
+        #expect(store.conversationIDs(forMessageID: "dm-2") == [destination])
+        // Delivery updates keep flowing after the handoff.
+        #expect(store.setDeliveryStatus(.sent, forMessageID: "dm-1"))
+    }
+
+    @Test("ID map drops trimmed messages")
+    @MainActor
+    func messageIDMapDropsTrimmedMessages() {
+        let store = ConversationStore()
+        let id = ConversationID.geohash("u4pruyd")
+        let conversation = store.conversation(for: id)
+        store.append(makeMessage(id: "first", timestamp: 1), to: id)
+        for index in 0..<conversation.cap {
+            store.append(makeMessage(id: "filler-\(index)", timestamp: 2 + TimeInterval(index)), to: id)
+        }
+
+        // "first" fell off the cap: the map must forget it.
+        #expect(store.conversationIDs(forMessageID: "first").isEmpty)
+        #expect(!store.setDeliveryStatus(.sent, forMessageID: "first"))
+        // Survivors stay resolvable.
+        #expect(store.conversationIDs(forMessageID: "filler-0") == [id])
+    }
+
+    @Test("ID map is emptied by clear, removeConversation, and clearAll")
+    @MainActor
+    func messageIDMapClearedWithConversations() {
+        let store = ConversationStore()
+        let direct = makeDirectConversationID("aa")
+        store.append(makeMessage(id: "m1", timestamp: 1), to: .mesh)
+        store.append(makeMessage(id: "d1", timestamp: 1, isPrivate: true), to: direct)
+
+        store.clear(.mesh)
+        #expect(store.conversationIDs(forMessageID: "m1").isEmpty)
+        #expect(store.conversationIDs(forMessageID: "d1") == [direct])
+
+        store.removeConversation(direct)
+        #expect(store.conversationIDs(forMessageID: "d1").isEmpty)
+
+        store.append(makeMessage(id: "m2", timestamp: 2), to: .mesh)
+        store.clearAll()
+        #expect(store.conversationIDs(forMessageID: "m2").isEmpty)
+    }
+
+    @Test("shared message instance across conversations stays consistent")
+    @MainActor
+    func sharedInstanceMirroredCopiesStayConsistent() {
+        let store = ConversationStore()
+        let stable = makeDirectConversationID("stable")
+        let ephemeral = makeDirectConversationID("ephemeral")
+        // The production mirroring path upserts the SAME BitchatMessage
+        // instance (reference type) into both conversations.
+        let message = makeMessage(id: "dm-1", timestamp: 1, isPrivate: true, deliveryStatus: .sent)
+        store.upsertByID(message, in: stable)
+        store.upsertByID(message, in: ephemeral)
+
+        #expect(store.setDeliveryStatus(.delivered(to: "bob", at: Date()), forMessageID: "dm-1"))
+
+        for id in [stable, ephemeral] {
+            guard case .delivered = store.conversation(for: id).message(withID: "dm-1")?.deliveryStatus else {
+                Issue.record("expected .delivered in \(id)")
+                return
+            }
+        }
+    }
 }
diff --git a/bitchatTests/Performance/PerformanceBaselineTests.swift b/bitchatTests/Performance/PerformanceBaselineTests.swift
index 007f0402..88189b27 100644
--- a/bitchatTests/Performance/PerformanceBaselineTests.swift
+++ b/bitchatTests/Performance/PerformanceBaselineTests.swift
@@ -194,26 +194,18 @@ final class PerformanceBaselineTests: XCTestCase {
         reportThroughput("gcs.buildAndDecode", samples: samples, operations: repsPerPass, unit: "filters")
     }
 
-    // MARK: - 4a. Delivery location index (incremental path)
+    // MARK: - 4a. Delivery status updates through the coordinator (store path)
 
-    /// `ChatDeliveryCoordinator.updateMessageDeliveryStatus` against a warm
-    /// location index: 2000 public + 50x40 private messages, 500 status
-    /// updates per pass. Statuses alternate sent <-> delivered so every call
-    /// performs a real update (never the skip path).
+    /// `ChatDeliveryCoordinator.updateMessageDeliveryStatus` over the
+    /// `ConversationStore`'s message-ID → conversation map: 2000 public
+    /// (split mesh + geohash to stay under the per-conversation cap) + 50x40
+    /// private messages, 500 status updates per pass. Statuses alternate
+    /// sent <-> delivered so every call performs a real update (never the
+    /// skip path).
     func testDeliveryStatusIncrementalUpdates() {
         let context = PerfDeliveryContext.makeCorpus(publicCount: 2000, peerCount: 50, messagesPerPeer: 40)
         let coordinator = ChatDeliveryCoordinator(context: context)
-        // Warm the index so the measure block exercises the incremental path.
-        XCTAssertTrue(coordinator.updateMessageDeliveryStatus(context.messages[0].id, status: .sent))
-
-        // 250 public + 250 private IDs spread across the corpus.
-        var targetIDs: [String] = []
-        for i in stride(from: 0, to: 2000, by: 8) { targetIDs.append(context.messages[i].id) }
-        let peerIDs = context.privateChats.keys.sorted { $0.id < $1.id }
-        for (offset, peer) in peerIDs.enumerated() where offset < 25 {
-            guard let chat = context.privateChats[peer] else { continue }
-            for i in stride(from: 0, to: chat.count, by: 4) { targetIDs.append(chat[i].id) }
-        }
+        let targetIDs = context.makeTargetIDs(publicTargets: 250, privateTargets: 250)
         XCTAssertEqual(targetIDs.count, 500)
 
         let fixedDate = Date(timeIntervalSince1970: 1_700_000_000)
@@ -235,46 +227,38 @@ final class PerformanceBaselineTests: XCTestCase {
         reportThroughput("delivery.incrementalUpdate", samples: samples, operations: targetIDs.count, unit: "updates")
     }
 
-    // MARK: - 4b. Delivery location index (rebuild path)
+    // MARK: - 4b. Delivery status updates against the store directly
 
-    /// The expensive path: a non-append insertion (out-of-order arrival at
-    /// the head of the timeline) invalidates the index, so the next status
-    /// update triggers a full rebuild over ~4000 message locations.
-    func testDeliveryStatusIndexRebuild() {
+    /// `ConversationStore.setDeliveryStatus(_:forMessageID:)` at the same
+    /// scale as 4a, without the coordinator/context wrapping — the store-side
+    /// cost of an ID-only delivery update (map lookup + per-conversation
+    /// ID-index apply + change emission). Replaces the deleted
+    /// `delivery.indexRebuild` benchmark: the positional location index and
+    /// its rebuild path no longer exist; the store's ID indexes are
+    /// maintained inside each mutation, so there is no rebuild to measure.
+    func testDeliveryStatusStoreUpdates() {
         let context = PerfDeliveryContext.makeCorpus(publicCount: 2000, peerCount: 50, messagesPerPeer: 40)
-        let coordinator = ChatDeliveryCoordinator(context: context)
-        // Warm the index before the first insertion invalidates it.
-        XCTAssertTrue(coordinator.updateMessageDeliveryStatus(context.messages[0].id, status: .sent))
+        let store = context.store
+        let targetIDs = context.makeTargetIDs(publicTargets: 250, privateTargets: 250)
+        XCTAssertEqual(targetIDs.count, 500)
 
-        // Pre-built head insertions, one consumed per measure pass.
-        let insertions: [BitchatMessage] = (0..<32).map { i in
-            BitchatMessage(
-                id: "insert-\(i)",
-                sender: "alice",
-                content: "out-of-order arrival \(i)",
-                timestamp: Date(timeIntervalSince1970: 1_690_000_000),
-                isRelay: false
-            )
-        }
-        let probeID = context.messages[1000].id
         let fixedDate = Date(timeIntervalSince1970: 1_700_000_000)
-        var pass = 0
         var toggle = false
         var samples: [TimeInterval] = []
 
         measure {
-            precondition(pass < insertions.count, "add more pre-built insertions")
-            context.messages.insert(insertions[pass], at: 0)
-            pass += 1
             toggle.toggle()
             let status: DeliveryStatus = toggle ? .delivered(to: "peer", at: fixedDate) : .sent
             let start = Date()
-            let updated = coordinator.updateMessageDeliveryStatus(probeID, status: status)
+            var updated = 0
+            for id in targetIDs where store.setDeliveryStatus(status, forMessageID: id) {
+                updated += 1
+            }
             samples.append(Date().timeIntervalSince(start))
-            XCTAssertTrue(updated)
+            XCTAssertEqual(updated, targetIDs.count)
         }
 
-        reportThroughput("delivery.indexRebuild", samples: samples, operations: 1, unit: "rebuilds")
+        reportThroughput("delivery.storeUpdate", samples: samples, operations: targetIDs.count, unit: "updates")
     }
 
     // MARK: - 5. Message formatting
@@ -638,50 +622,63 @@ private final class PerfNostrContext: ChatNostrContext {
 
 // MARK: - Mock ChatDeliveryContext
 
+/// Minimal `ChatDeliveryContext` over a real `ConversationStore` (the
+/// coordinator is a thin mapper onto store intents, so the measured cost is
+/// the store's ID-map delivery path).
 @MainActor
 private final class PerfDeliveryContext: ChatDeliveryContext {
-    var messages: [BitchatMessage] = []
-    var privateChats: [PeerID: [BitchatMessage]] = [:]
+    let store = ConversationStore()
     var sentReadReceipts: Set<String> = []
     var isStartupPhase: Bool { false }
+    private var publicIDs: [String] = []
+    private var privateIDsByPeer: [(peerID: PeerID, messageIDs: [String])] = []
+
     func notifyUIChanged() {}
     func markMessageDelivered(_ messageID: String) {}
 
+    @discardableResult
+    func setDeliveryStatus(_ status: DeliveryStatus, forMessageID messageID: String) -> Bool {
+        store.setDeliveryStatus(status, forMessageID: messageID)
+    }
+
+    func deliveryStatus(forMessageID messageID: String) -> DeliveryStatus? {
+        store.deliveryStatus(forMessageID: messageID)
+    }
+
+    func privateMessageIDs() -> Set<String> {
+        store.directMessageIDs()
+    }
+
     func pruneSentReadReceipts(keeping validMessageIDs: Set<String>) -> Int {
         let oldCount = sentReadReceipts.count
         sentReadReceipts = sentReadReceipts.intersection(validMessageIDs)
         return oldCount - sentReadReceipts.count
     }
 
-    @discardableResult
-    func setPrivateDeliveryStatus(_ status: DeliveryStatus, forMessageID messageID: String, peerID: PeerID) -> Bool {
-        guard var chat = privateChats[peerID],
-              let index = chat.firstIndex(where: { $0.id == messageID }) else {
-            return false
-        }
-        chat[index].deliveryStatus = status
-        privateChats[peerID] = chat
-        return true
-    }
-
-    /// 2000 public + `peerCount` x `messagesPerPeer` private messages with
-    /// deterministic IDs and timestamps.
+    /// `publicCount` public messages (split evenly between mesh and one
+    /// geohash conversation so the corpus stays under the per-conversation
+    /// cap) + `peerCount` x `messagesPerPeer` private messages, seeded into
+    /// the store with deterministic IDs and timestamps.
     static func makeCorpus(publicCount: Int, peerCount: Int, messagesPerPeer: Int) -> PerfDeliveryContext {
         let context = PerfDeliveryContext()
         let base = Date(timeIntervalSince1970: 1_700_000_000)
-        context.messages = (0..<publicCount).map { i in
-            BitchatMessage(
+        let geohashID = ConversationID.geohash("u4pruyd")
+        for i in 0..<publicCount {
+            let message = BitchatMessage(
                 id: "pub-\(i)",
                 sender: "peer\(i % 20)",
                 content: "public message number \(i)",
                 timestamp: base.addingTimeInterval(Double(i)),
                 isRelay: false
             )
+            context.store.append(message, to: i % 2 == 0 ? .mesh : geohashID)
+            context.publicIDs.append(message.id)
         }
         for p in 0..<peerCount {
             let peerID = PeerID(str: String(format: "%016x", 0xA000_0000 + p))
-            context.privateChats[peerID] = (0..<messagesPerPeer).map { i in
-                BitchatMessage(
+            var messageIDs: [String] = []
+            for i in 0..<messagesPerPeer {
+                let message = BitchatMessage(
                     id: "dm-\(p)-\(i)",
                     sender: "peer\(p)",
                     content: "private message \(i) for peer \(p)",
@@ -691,10 +688,32 @@ private final class PerfDeliveryContext: ChatDeliveryContext {
                     recipientNickname: "me",
                     senderPeerID: peerID
                 )
+                context.store.append(message, to: .directPeer(peerID))
+                messageIDs.append(message.id)
             }
+            context.privateIDsByPeer.append((peerID, messageIDs))
         }
         return context
     }
+
+    /// Deterministic update targets spread across the corpus: `publicTargets`
+    /// public IDs plus `privateTargets` private IDs.
+    func makeTargetIDs(publicTargets: Int, privateTargets: Int) -> [String] {
+        var targetIDs: [String] = []
+        let publicStride = max(1, publicIDs.count / publicTargets)
+        for i in stride(from: 0, to: publicIDs.count, by: publicStride) where targetIDs.count < publicTargets {
+            targetIDs.append(publicIDs[i])
+        }
+        var privateCount = 0
+        outer: for (_, messageIDs) in privateIDsByPeer {
+            for i in stride(from: 0, to: messageIDs.count, by: 4) {
+                guard privateCount < privateTargets else { break outer }
+                targetIDs.append(messageIDs[i])
+                privateCount += 1
+            }
+        }
+        return targetIDs
+    }
 }
 
 // MARK: - End-to-end pipeline fixture
diff --git a/docs/CONVERSATION-STORE-DESIGN.md b/docs/CONVERSATION-STORE-DESIGN.md
index 7f63342e..aa34b406 100644
--- a/docs/CONVERSATION-STORE-DESIGN.md
+++ b/docs/CONVERSATION-STORE-DESIGN.md
@@ -1,9 +1,11 @@
 # Conversation Store: Single Source of Truth
 
-**Status:** Steps 1–3 implemented (additive store, private cutover, public
-cutover; `PublicTimelineStore` deleted). Baselines recorded in
+**Status:** Steps 1–4 implemented (additive store, private cutover, public
+cutover, delivery via store; `PublicTimelineStore` and
+`ChatDeliveryCoordinator.messageLocationIndex` deleted). Baselines recorded in
 `bitchatTests/Performance/PerformanceBaselineTests.swift` (`pipeline.privateIngest`,
-`pipeline.publicIngest`, `store.append`).
+`pipeline.publicIngest`, `store.append`, `delivery.incrementalUpdate`,
+`delivery.storeUpdate`).
 
 ---