diff --git a/app/shared/src/commonMain/kotlin/iris/data/ChatStore.kt b/app/shared/src/commonMain/kotlin/iris/data/ChatStore.kt
index eb0c051..a8a19c7 100644
--- a/app/shared/src/commonMain/kotlin/iris/data/ChatStore.kt
+++ b/app/shared/src/commonMain/kotlin/iris/data/ChatStore.kt
@@ -444,6 +444,26 @@ class ChatStore {
         if (changed) _lanes.value = map
     }
 
+    /**
+ * Remove messages by id from every lane (a `message.deleted` frame). The
+ * server is authoritative: the frame carries no lane, and a message id is
+ * unique, so scanning all lanes is both safe and idempotent (a no-op when the
+ * id is absent, e.g. a local-only id another device never had).
+ */
+    fun removeMessages(messageIds: Set<String>) {
+        if (messageIds.isEmpty()) return
+        val map = _lanes.value.toMutableMap()
+        var changed = false
+        for ((lane, list) in map) {
+            val updated = list.filterNot { it.id in messageIds }
+            if (updated != list) {
+                map[lane] = updated
+                changed = true
+            }
+        }
+        if (changed) _lanes.value = map
+    }
+
     /** M7: mark all pending user messages as failed (gateway error frame). */
     fun failPending() {
         val map = _lanes.value.toMutableMap()
diff --git a/app/shared/src/commonMain/kotlin/iris/protocol/Protocol.kt b/app/shared/src/commonMain/kotlin/iris/protocol/Protocol.kt
index 05f6f0e..c7920ed 100644
--- a/app/shared/src/commonMain/kotlin/iris/protocol/Protocol.kt
+++ b/app/shared/src/commonMain/kotlin/iris/protocol/Protocol.kt
@@ -3,6 +3,7 @@ package iris.protocol
 import kotlinx.serialization.SerialName
 import kotlinx.serialization.Serializable
 import kotlinx.serialization.json.Json
+import kotlinx.serialization.json.JsonArray
 import kotlinx.serialization.json.JsonElement
 import kotlinx.serialization.json.JsonObject
 import kotlinx.serialization.json.JsonPrimitive
@@ -41,6 +42,10 @@ const val TYPE_TYPING = "typing"
 const val TYPE_MESSAGE_START = "message.start"
 const val TYPE_MESSAGE_UPDATE = "message.update"
 const val TYPE_MESSAGE_STOP = "message.stop"
+
+// Message deletion (app requests; broadcast to all devices)
+const val TYPE_MESSAGE_DELETE = "message.delete"
+const val TYPE_MESSAGE_DELETED = "message.deleted"
 const val TYPE_TOOL_START = "tool.start"
 const val TYPE_TOOL_PROGRESS = "tool.progress"
 const val TYPE_TOOL_END = "tool.end"
@@ -385,6 +390,14 @@ data class HistoryPayload(
     @SerialName("oldest_message_id") val oldestMessageId: String? = null,
 )
 
+// ── message deletion ──────────────────────────────────────────────────────
+
+/** The message(s) removed from a chat/thread (response + broadcast). */
+@Serializable
+data class MessageDeletedPayload(
+    @SerialName("message_ids") val messageIds: List<String> = emptyList(),
+)
+
 // ── M5: push / notifications ────────────────────────────────────────────
 
 /** Notification kinds (mirror of protocol.NOTIF_*). */
@@ -550,6 +563,24 @@ fun historyFrame(
         },
     )
 
+/** Request deletion of the given message(s) in a chat/thread. The server
+ *  removes them from the outbox and broadcasts `message.deleted`. */
+fun messageDeleteFrame(
+    id: Int,
+    chatId: String,
+    messageIds: List<String>,
+    threadId: String? = null,
+): Frame =
+    Frame(
+        id = id,
+        type = TYPE_MESSAGE_DELETE,
+        chatId = chatId,
+        threadId = threadId,
+        payload = buildJsonObject {
+            put("message_ids", JsonArray(messageIds.map { JsonPrimitive(it) }))
+        },
+    )
+
 // ── M4 frame builders ────────────────────────────────────────────────────
 
 fun mediaUploadStartFrame(
diff --git a/app/shared/src/commonMain/kotlin/iris/state/IrisController.kt b/app/shared/src/commonMain/kotlin/iris/state/IrisController.kt
index 32a0610..463ab5a 100644
--- a/app/shared/src/commonMain/kotlin/iris/state/IrisController.kt
+++ b/app/shared/src/commonMain/kotlin/iris/state/IrisController.kt
@@ -19,6 +19,7 @@ import iris.protocol.HIGH_PRIORITY_NOTIF_KINDS
 import iris.protocol.HistoryMessage
 import iris.protocol.HistoryPayload
 import iris.protocol.MediaOfferPayload
+import iris.protocol.MessageDeletedPayload
 import iris.protocol.MessagePayload
 import iris.protocol.MessageStopPayload
 import iris.protocol.NotificationPayload
@@ -38,6 +39,8 @@ import iris.protocol.TYPE_CHANNEL_RENAMED
 import iris.protocol.TYPE_COMMENTARY
 import iris.protocol.TYPE_MEDIA_OFFER
 import iris.protocol.TYPE_MESSAGE
+import iris.protocol.TYPE_MESSAGE_DELETE
+import iris.protocol.TYPE_MESSAGE_DELETED
 import iris.protocol.TYPE_MESSAGE_START
 import iris.protocol.TYPE_MESSAGE_STOP
 import iris.protocol.TYPE_MESSAGE_UPDATE
@@ -56,6 +59,7 @@ import iris.protocol.channelListFrame
 import iris.protocol.channelRenameFrame
 import iris.protocol.channelSetDefaultFrame
 import iris.protocol.historyFrame
+import iris.protocol.messageDeleteFrame
 import iris.protocol.searchFrame
 import iris.protocol.syncFrame
 import kotlinx.coroutines.CoroutineScope
@@ -367,6 +371,13 @@ class IrisController(
                     TYPE_READ_RECEIPT -> {
                         frame.payloadAs<ReadReceiptPayload>()?.let { chat.markRead(it.messageId) }
                     }
+                    TYPE_MESSAGE_DELETED -> {
+                        // A message was deleted (by this or another device).
+                        // Idempotent: dropping an unknown id is a no-op.
+                        frame.payloadAs<MessageDeletedPayload>()?.let {
+                            chat.removeMessages(it.messageIds.toSet())
+                        }
+                    }
                     TYPE_STATUS -> {
                         frame.payloadAs<StatusPayload>()?.let { _gatewayStatus.value = it.state }
                     }
@@ -539,6 +550,18 @@ class IrisController(
         )
     }
 
+    /** Delete the given message(s) from the current lane (long-press select →
+     *  delete). The server removes them from the outbox and broadcasts
+     *  `message.deleted`; the local cache drops them on that frame (or
+     *  immediately, below, for snappy UX). */
+    fun deleteMessages(messageIds: List<String>) {
+        if (messageIds.isEmpty()) return
+        val lane = chat.currentLane.value
+        val (chatId, threadId) = chat.parseLane(lane)
+        chat.removeMessages(messageIds.toSet())
+        client.sendFrame(messageDeleteFrame(0, chatId, messageIds, threadId))
+    }
+
     // ── M4: attachments (pick -> upload -> send) ──────────────────────────
 
     /** Stage a picked file: upload it, then keep it as a pending attachment. */
diff --git a/app/shared/src/commonMain/kotlin/iris/ui/screens/ChatScreen.kt b/app/shared/src/commonMain/kotlin/iris/ui/screens/ChatScreen.kt
index 543731d..9bb0f5e 100644
--- a/app/shared/src/commonMain/kotlin/iris/ui/screens/ChatScreen.kt
+++ b/app/shared/src/commonMain/kotlin/iris/ui/screens/ChatScreen.kt
@@ -2,6 +2,7 @@ package iris.ui.screens
 
 import androidx.compose.foundation.ExperimentalFoundationApi
 import androidx.compose.foundation.background
+import androidx.compose.foundation.border
 import androidx.compose.foundation.clickable
 import androidx.compose.foundation.combinedClickable
 import androidx.compose.foundation.focusable
@@ -221,6 +222,34 @@ fun ChatScreen(controller: IrisController) {
         // Topic context menu (long-press / right-click): rename / delete a thread.
         var renameThread by remember { mutableStateOf<ChannelInfo?>(null) }
         var deleteThread by remember { mutableStateOf<ChannelInfo?>(null) }
+        // Message selection (long-press / right-click a bubble → multi-select →
+        // delete). The composer is replaced by a selection toolbar while active.
+        var selectionMode by remember { mutableStateOf(false) }
+        var selectedIds by remember { mutableStateOf<Set<String>>(emptySet()) }
+        var showDeleteConfirm by remember { mutableStateOf(false) }
+
+        fun enterSelection(id: String) {
+            selectionMode = true
+            selectedIds = setOf(id)
+        }
+
+        fun toggleSelect(id: String) {
+            selectedIds = if (id in selectedIds) selectedIds - id else selectedIds + id
+            if (selectedIds.isEmpty()) selectionMode = false
+        }
+
+        fun exitSelection() {
+            selectionMode = false
+            selectedIds = emptySet()
+        }
+
+        // Selection is scoped to the lane the messages were viewed in; leaving
+        // that lane (channel / thread switch) clears any in-progress selection
+        // so a later delete can't target the wrong lane.
+        LaunchedEffect(currentLane) {
+            if (selectionMode) exitSelection()
+        }
+
         Column(modifier = Modifier.fillMaxSize()) {
             // Header (M7: avatar + two-line title pill, reference look). Wide
             // panes keep everything on one row; narrow phones move the utility
@@ -355,12 +384,27 @@ fun ChatScreen(controller: IrisController) {
                         when (row) {
                             is ChatRow.Day -> DaySeparator(row.label)
                             is ChatRow.Item -> when (val item = row.item) {
-                                is MessageItem -> MessageBubble(
-                                    msg = item,
-                                    maxWidth = bubbleMaxWidth,
-                                    reasoningAutoCollapse = reasoningAutoCollapse,
-                                    onRetry = { controller.retrySend(item.id) },
-                                )
+                                is MessageItem -> {
+                                    // Only finalized messages are selectable: a
+                                    // streaming bubble has no final id yet and a
+                                    // pending echo isn't on the server to delete.
+                                    val selectable = !item.streaming && !item.pending
+                                    MessageBubble(
+                                        msg = item,
+                                        maxWidth = bubbleMaxWidth,
+                                        reasoningAutoCollapse = reasoningAutoCollapse,
+                                        onRetry = { controller.retrySend(item.id) },
+                                        selectionMode = selectionMode && selectable,
+                                        selected = selectable && item.id in selectedIds,
+                                        onToggleSelect = { if (selectable) toggleSelect(item.id) },
+                                        onLongPress = {
+                                            if (selectable) {
+                                                if (selectionMode) toggleSelect(item.id)
+                                                else enterSelection(item.id)
+                                            }
+                                        },
+                                    )
+                                }
                                 is ToolItem -> if (toolDetail != ToolDetail.NOTHING) ToolCard(item, toolDetail)
                             }
                         }
@@ -444,6 +488,15 @@ fun ChatScreen(controller: IrisController) {
                 }
             }
 
+            // Selection toolbar (replaces the composer while messages are selected).
+            if (selectionMode) {
+                SelectionToolbar(
+                    count = selectedIds.size,
+                    onCancel = { exitSelection() },
+                    onDelete = { showDeleteConfirm = true },
+                )
+            }
+
             // Composer (M7: rounded pill + accent circular send button). Sending is gated
             // on a live socket: sendMessage is a no-op while disconnected, so an
             // ungated send would show a pending bubble that never resolves.
@@ -452,7 +505,7 @@ fun ChatScreen(controller: IrisController) {
                 isConnected && (input.isNotBlank() || attachments.any { it.mediaRef != null && it.error == null })
             val layoutDensity = LocalDensity.current.density
             var textHeightPx by remember { mutableFloatStateOf(0f) }
-            Row(
+            if (!selectionMode) Row(
                 modifier = Modifier
                     .fillMaxWidth()
                     .padding(horizontal = 12.dp, vertical = 8.dp)
@@ -575,6 +628,30 @@ fun ChatScreen(controller: IrisController) {
                     },
                 )
             }
+            // Message selection: confirm deleting the selected message(s).
+            if (showDeleteConfirm) {
+                val n = selectedIds.size
+                AlertDialog(
+                    onDismissRequest = { showDeleteConfirm = false },
+                    title = { Text(if (n == 1) "Delete message?" else "Delete $n messages?") },
+                    text = {
+                        Text(
+                            if (n == 1) "This message will be deleted for all devices."
+                            else "These messages will be deleted for all devices.",
+                        )
+                    },
+                    confirmButton = {
+                        TextButton(onClick = {
+                            showDeleteConfirm = false
+                            controller.deleteMessages(selectedIds.toList())
+                            exitSelection()
+                        }) { Text("Delete") }
+                    },
+                    dismissButton = {
+                        TextButton(onClick = { showDeleteConfirm = false }) { Text("Cancel") }
+                    },
+                )
+            }
         }
     }
 
@@ -1418,8 +1495,18 @@ private fun NotificationBanner(
     }
 }
 
+@OptIn(ExperimentalFoundationApi::class)
 @Composable
-private fun MessageBubble(msg: MessageItem, maxWidth: Dp, reasoningAutoCollapse: Boolean, onRetry: () -> Unit) {
+private fun MessageBubble(
+    msg: MessageItem,
+    maxWidth: Dp,
+    reasoningAutoCollapse: Boolean,
+    onRetry: () -> Unit,
+    selectionMode: Boolean = false,
+    selected: Boolean = false,
+    onToggleSelect: () -> Unit = {},
+    onLongPress: () -> Unit = {},
+) {
     val isUser = msg.role == ROLE_USER
     val isCommentary = msg.isCommentary
     val bubbleColor = when {
@@ -1437,15 +1524,31 @@ private fun MessageBubble(msg: MessageItem, maxWidth: Dp, reasoningAutoCollapse:
         modifier = Modifier.fillMaxWidth(),
         horizontalArrangement = if (isUser) Arrangement.End else Arrangement.Start,
     ) {
+        // Selection check sits on the side away from the bubble (user bubbles
+        // are right-aligned → check on the left; assistant on the left → right).
+        if (isUser && selectionMode) {
+            SelectionCheck(selected)
+            Spacer(modifier = Modifier.width(6.dp))
+        }
         Column(
             modifier = Modifier
                 .widthIn(max = maxWidth)
                 .clip(RoundedCornerShape(14.dp))
-                .background(bubbleColor)
+                .background(if (selected) IrisColors.chipSelected else bubbleColor)
                 .then(
-                    if (isUser && msg.status == MsgStatus.Failed) {
-                        Modifier.clickable { onRetry() }
-                    } else Modifier
+                    // Long-press / right-click enters (or toggles within) message
+                    // selection; a plain tap toggles while selecting, or retries a
+                    // failed user send otherwise. Attached always so the long-press
+                    // affordance exists even outside selection mode.
+                    Modifier
+                        .combinedClickable(
+                            onClick = {
+                                if (selectionMode) onToggleSelect()
+                                else if (isUser && msg.status == MsgStatus.Failed) onRetry()
+                            },
+                            onLongClick = { onLongPress() },
+                        )
+                        .rightClick { onLongPress() }
                 )
                 .padding(horizontal = 12.dp, vertical = 8.dp),
         ) {
@@ -1532,6 +1635,63 @@ private fun MessageBubble(msg: MessageItem, maxWidth: Dp, reasoningAutoCollapse:
                 }
             }
         }
+        if (!isUser && selectionMode) {
+            Spacer(modifier = Modifier.width(6.dp))
+            SelectionCheck(selected)
+        }
+    }
+}
+
+/** Circular selection indicator shown beside a bubble in selection mode. */
+@Composable
+private fun SelectionCheck(selected: Boolean) {
+    Box(
+        modifier = Modifier
+            .size(22.dp)
+            .clip(CircleShape)
+            .background(if (selected) IrisColors.primary else Color.Transparent)
+            .border(
+                width = if (selected) 0.dp else 1.5.dp,
+                color = IrisColors.textDim,
+                shape = CircleShape,
+            ),
+        contentAlignment = Alignment.Center,
+    ) {
+        if (selected) Text("✓", color = Color.White, fontSize = 12.sp)
+    }
+}
+
+/** Toolbar shown in place of the composer while messages are selected. */
+@Composable
+private fun SelectionToolbar(count: Int, onCancel: () -> Unit, onDelete: () -> Unit) {
+    Row(
+        modifier = Modifier
+            .fillMaxWidth()
+            .padding(horizontal = 12.dp, vertical = 8.dp)
+            .clip(RoundedCornerShape(28.dp))
+            .background(IrisColors.surface)
+            .padding(horizontal = 8.dp, vertical = 4.dp),
+        verticalAlignment = Alignment.CenterVertically,
+    ) {
+        HeaderIconButton(onClick = onCancel) {
+            Text("✕", fontSize = 16.sp)
+        }
+        Spacer(modifier = Modifier.width(8.dp))
+        Text(
+            if (count == 1) "1 selected" else "$count selected",
+            style = MaterialTheme.typography.bodyLarge,
+            modifier = Modifier.weight(1f),
+        )
+        Box(
+            modifier = Modifier
+                .clip(RoundedCornerShape(20.dp))
+                .background(if (count > 0) IrisColors.primary else IrisColors.primary.copy(alpha = 0.35f))
+                .clickable(enabled = count > 0) { onDelete() }
+                .padding(horizontal = 16.dp, vertical = 8.dp),
+            contentAlignment = Alignment.Center,
+        ) {
+            Text("🗑 Delete", color = Color.White, fontSize = 14.sp)
+        }
     }
 }
 
diff --git a/docs/04-wire-protocol.md b/docs/04-wire-protocol.md
index 2767aed..a09ec6a 100644
--- a/docs/04-wire-protocol.md
+++ b/docs/04-wire-protocol.md
@@ -63,7 +63,17 @@ Streaming a bubble. `update` carries the **full** current text (app replaces).
 {"type":"message.start","chat_id":"…","payload":{"message_id":"m_9002","role":"assistant"}}
 {"type":"message.update","chat_id":"…","payload":{"message_id":"m_9002","text":"partial…"}}
 {"type":"message.stop","chat_id":"…","payload":{"message_id":"m_9002","final_text":"full…",
-   "reasoning":"…","model":"…","tokens":11}}
+    "reasoning":"…","model":"…","tokens":11}}
+```
+
+### `message.deleted`
+The given message(s) were deleted from a chat/thread. Response to a
+`message.delete` request (`id` set) **and** broadcast to every device so all of
+them drop the message(s) from their cache. Also outboxed, so a device that was
+offline learns of the deletion on its next `sync`.
+```json
+{"type":"message.deleted","id":30,"chat_id":"android:default","thread_id":null,
+ "payload":{"message_ids":["m_9001","m_9002"]}}
 ```
 
 ### `commentary`
@@ -300,6 +310,16 @@ Load a page of messages for a chat/thread (initial open, scroll-up pagination).
 `before_message_id` — return messages older than this (omit for newest page).
 `limit` — max messages (default 50, max 200).
 
+### `message.delete`
+Delete the given message(s) from a chat/thread. The server removes them from the
+outbox (so `history`/`sync` no longer return them) and broadcasts
+`message.deleted` to every device. Idempotent: a message already gone (pruned by
+retention) still yields a `message.deleted` broadcast so live caches drop it.
+```json
+{"type":"message.delete","id":30,"chat_id":"android:default","thread_id":null,
+ "payload":{"message_ids":["m_9001","m_9002"]}}
+```
+
 ### `commands.catalog`
 Fetch the full slash-command catalog (for the `Menü` bottom sheet).
 ```json
@@ -346,10 +366,11 @@ Keepalive. `{"type":"ping","payload":{"ts":1724000000000}}` → `pong`.
 
 - Frames are ordered per connection (TCP/WS). Streaming `message.update` frames
   for a `message_id` are monotonic; the app may coalesce to the latest.
-- Terminal frames (`message`, `message.stop`, `tool.end`, `notification`,
-  `picker.*`, `channel.*`, `agent.busy`, `agent.idle`, `history`,
-  `commands.catalog`, `commands.complete`) are **never dropped** under
-  backpressure; only intermediate `message.update`/`tool.progress` are coalesced.
+- Terminal frames (`message`, `message.stop`, `message.deleted`, `tool.end`,
+  `notification`, `picker.*`, `channel.*`, `agent.busy`, `agent.idle`,
+  `history`, `commands.catalog`, `commands.complete`) are **never dropped**
+  under backpressure; only intermediate `message.update`/`tool.progress` are
+  coalesced.
 - Anything not delivered live goes to the **outbox** and is replayed by `sync`.
 - **Broadcast:** channel directory events (`channel.*`) and read-receipts are
   pushed to **all** connected devices for that gateway (no subscribe step).
diff --git a/docs/10-android-app.md b/docs/10-android-app.md
index a3ba7d2..14d845f 100644
--- a/docs/10-android-app.md
+++ b/docs/10-android-app.md
@@ -126,6 +126,20 @@ app/shared/src/
 ### Intermediate messages
 - `commentary` frames → dimmed/smaller bubble, distinct from final answers.
 
+### Message selection + delete
+- **Long-press** a message bubble (touch) or **right-click** it (desktop mouse)
+  enters selection mode: the tapped message is selected (a circular check appears
+  beside each bubble) and the composer is replaced by a selection toolbar
+  (count + **Delete** + cancel ✕).
+- While selecting, **tap** a bubble to toggle it; the ✕ (or deselecting the last
+  message) exits selection mode. Only finalized messages are selectable — a
+  streaming bubble has no final id yet and a pending echo isn't on the server.
+- **Delete** → confirm dialog → `message.delete {message_ids:[…]}` for the
+  current lane. The server removes the message(s) from the outbox (so
+  `history`/`sync` no longer return them) and broadcasts `message.deleted` to
+  every device; each device drops them from its cache (the requesting device
+  also drops them locally for snappy UX). Deleting is idempotent.
+
 ### Agent busy / stop / steer
 - `agent.busy` → show "thinking…" indicator in chat header (animated dots).
 - `agent.idle` → clear indicator.
diff --git a/docs/protocol/frames.schema.json b/docs/protocol/frames.schema.json
index 5214d72..7162d4f 100644
--- a/docs/protocol/frames.schema.json
+++ b/docs/protocol/frames.schema.json
@@ -42,6 +42,7 @@
       "message.start": { "payload": { "message_id": { "type": "string" }, "role": { "type": "string" } } },
       "message.update": { "payload": { "message_id": { "type": "string" }, "text": { "type": "string", "description": "Full current text (app replaces)." } } },
       "message.stop": { "payload": { "message_id": { "type": "string" }, "final_text": { "type": "string" }, "reasoning": { "type": "string" }, "model": { "type": "string" }, "tokens": { "type": "integer" }, "ts": { "type": "integer" } } },
+      "message.deleted": { "description": "The given message(s) were deleted from a chat/thread. Response to a message.delete request (id set) and broadcast to every device so all drop them from their cache; also outboxed so an offline device learns of the deletion on its next sync.", "payload": { "message_ids": { "type": "array", "items": { "type": "string" } } } },
       "commentary": { "description": "Intermediate assistant beat.", "payload": { "message_id": { "type": "string" }, "text": { "type": "string" } } },
       "tool.start": { "payload": { "index": { "type": "integer" }, "name": { "type": "string" }, "preview": { "type": "string" }, "args": { "type": "object" } } },
       "tool.progress": { "payload": { "index": { "type": "integer" }, "name": { "type": "string" }, "note": { "type": "string" } } },
@@ -77,6 +78,7 @@
       "search": { "payload": { "query": { "type": "string" }, "scope": { "type": "string", "enum": ["all", "chat"] }, "chat_id": { "type": "string" }, "thread_id": { "type": "string" }, "limit": { "type": "integer", "description": "Optional; server default 20." } } },
       "sync": { "description": "Reconnect catch-up; replays undelivered outbox frames only (not full history).", "payload": { "cursor": { "type": "integer" } } },
       "history": { "description": "Load a page of full message history for a chat/thread (initial open, scroll-up pagination).", "payload": { "before_message_id": { "type": "string", "description": "Return messages older than this (omit for newest page)." }, "limit": { "type": "integer", "description": "Max messages (default 50, max 200)." } } },
+      "message.delete": { "description": "Delete the given message(s) from a chat/thread. The server removes them from the outbox (so history/sync no longer return them) and broadcasts message.deleted to every device. Idempotent: a message already gone (pruned) still yields a message.deleted broadcast.", "payload": { "message_ids": { "type": "array", "items": { "type": "string" }, "description": "One or more message_id values to delete." } } },
       "fcm.register": { "payload": { "fcm_token": { "type": "string" }, "ntfy_topic": { "type": "string" } } },
       "ping": { "payload": { "ts": { "type": "integer" } } }
     }
@@ -105,7 +107,7 @@
   ],
   "reliability": {
     "ordering": "Per-connection (TCP/WS). message.update for a message_id is monotonic; app may coalesce to latest.",
-    "never_dropped": ["message", "message.stop", "tool.end", "notification", "channel.*", "search.results", "error"],
+    "never_dropped": ["message", "message.stop", "message.deleted", "tool.end", "notification", "channel.*", "search.results", "error"],
     "coalescable_under_backpressure": ["message.update", "tool.progress"],
     "offline": "Undelivered frames go to the outbox; replayed by sync. Terminal frames always outboxed."
   }
diff --git a/gateway-plugin/adapter.py b/gateway-plugin/adapter.py
index 7cc0232..4a77a0c 100644
--- a/gateway-plugin/adapter.py
+++ b/gateway-plugin/adapter.py
@@ -2216,6 +2216,52 @@ class AndroidAdapter(BasePlatformAdapter):
         )
         await self._ws_server.send_to(device_id, resp)
 
+    # ── Message deletion (app -> agent) ───────────────────────────────────
+
+    async def on_message_delete(self, frame: protocol.Frame, device_id: str) -> None:
+        """Handle an inbound ``message.delete`` request.
+
+        Removes the requested message(s) from the outbox (so ``history`` and
+        ``sync`` no longer return them) and broadcasts ``message.deleted`` to
+        every device (outboxed too, so an offline device learns of the
+        deletion on its next ``sync``). Deleting is idempotent: a message that
+        is already gone (pruned by retention) simply yields 0 removed rows,
+        and the ``message.deleted`` broadcast is still emitted so live caches
+        drop it.
+        """
+        payload = frame.payload
+        chat_id = frame.chat_id or payload.get("chat_id")
+        if not isinstance(chat_id, str) or not chat_id.strip():
+            await self._ws_server.send_to(
+                device_id,
+                protocol.error(protocol.ERR_NOT_FOUND, "message.delete requires chat_id", id=frame.id),
+            )
+            return
+        chat_id = chat_id.strip()
+        thread_id = frame.thread_id or payload.get("thread_id")
+        if not isinstance(thread_id, str) or not thread_id.strip():
+            thread_id = None
+        message_ids = payload.get("message_ids")
+        if not isinstance(message_ids, list):
+            message_ids = [payload.get("message_id")] if payload.get("message_id") else []
+        message_ids = [m for m in message_ids if isinstance(m, str) and m.strip()]
+        if not message_ids:
+            await self._ws_server.send_to(
+                device_id,
+                protocol.error(protocol.ERR_UNSUPPORTED, "message.delete requires message_ids", id=frame.id),
+            )
+            return
+        removed = 0
+        for mid in message_ids:
+            removed += self._outbox.delete_message(chat_id, mid, thread_id=thread_id)
+        logger.info(
+            "android: message.delete from %s chat_id=%r thread_id=%r ids=%s removed=%s",
+            device_id, chat_id, thread_id, message_ids, removed,
+        )
+        resp = protocol.message_deleted(chat_id, message_ids, thread_id=thread_id)
+        resp.id = frame.id
+        await self._broadcast_or_log(chat_id, resp)
+
     # ── M5: push token registration ───────────────────────────────────────
 
     async def on_fcm_register(self, frame: protocol.Frame, device_id: str) -> None:
diff --git a/gateway-plugin/outbox.py b/gateway-plugin/outbox.py
index 0770b29..e9a7eec 100644
--- a/gateway-plugin/outbox.py
+++ b/gateway-plugin/outbox.py
@@ -277,6 +277,55 @@ class Outbox:
             "oldest_message_id": oldest_message_id,
         }
 
+    # ── message deletion ──────────────────────────────────────────────────
+
+    def delete_message(
+        self,
+        chat_id: str,
+        message_id: str,
+        thread_id: Optional[str] = None,
+    ) -> int:
+        """Remove every outbox frame belonging to *message_id* in *chat_id*.
+
+        A message can span several frames (``message`` / ``message.start`` /
+        ``message.update`` / ``message.stop`` / ``media.offer`` /
+        ``commentary``); all of them are removed so neither ``history`` nor a
+        ``sync`` replay can resurrect the message. The delete is scoped to the
+        exact lane: a flat-lane delete (``thread_id=None``) matches only frames
+        with no ``thread_id``, and a thread delete matches only that thread's
+        frames (a ``message_id`` is unique to one lane, so this is a safety
+        net, not a filter that drops real frames). Returns the number of rows
+        removed (0 when the message is not in the outbox — e.g. already pruned
+        by retention).
+        """
+        if not message_id:
+            return 0
+        with self._lock:
+            rows = self._conn.execute(
+                "SELECT cursor, frame FROM outbox WHERE chat_id = ?", (chat_id,)
+            ).fetchall()
+            cursors: List[int] = []
+            for r in rows:
+                try:
+                    frame = json.loads(r["frame"])
+                except (json.JSONDecodeError, TypeError):
+                    continue
+                if not isinstance(frame, dict):
+                    continue
+                if frame.get("thread_id") != thread_id:
+                    continue
+                payload = frame.get("payload")
+                if isinstance(payload, dict) and payload.get("message_id") == message_id:
+                    cursors.append(int(r["cursor"]))
+            if not cursors:
+                return 0
+            placeholders = ",".join("?" * len(cursors))
+            self._conn.execute(
+                f"DELETE FROM outbox WHERE cursor IN ({placeholders})", cursors
+            )
+            self._conn.commit()
+            return len(cursors)
+
     # ── retention ─────────────────────────────────────────────────────────
 
     def _maybe_prune(self) -> None:
diff --git a/gateway-plugin/protocol.py b/gateway-plugin/protocol.py
index 5093fac..2e79c9b 100644
--- a/gateway-plugin/protocol.py
+++ b/gateway-plugin/protocol.py
@@ -42,6 +42,10 @@ TYPE_MESSAGE_START = "message.start"
 TYPE_MESSAGE_UPDATE = "message.update"
 TYPE_MESSAGE_STOP = "message.stop"
 
+# Message deletion (app requests; broadcast to all devices)
+TYPE_MESSAGE_DELETE = "message.delete"
+TYPE_MESSAGE_DELETED = "message.deleted"
+
 # Tool activity (M2)
 TYPE_TOOL_START = "tool.start"
 TYPE_TOOL_PROGRESS = "tool.progress"
@@ -528,6 +532,33 @@ def history(
     )
 
 
+# ---------------------------------------------------------------------------
+# Message deletion frames
+# ---------------------------------------------------------------------------
+
+def message_deleted(
+    chat_id: str,
+    message_ids: List[str],
+    *,
+    thread_id: Optional[str] = None,
+    id: Optional[int] = None,
+) -> Frame:
+    """Broadcast: the given message(s) were deleted from a chat/thread.
+
+    Carried by the response to a ``message.delete`` request (``id`` set) and
+    broadcast to every device so all of them drop the message(s) from their
+    cache. Also outboxed, so a device that was offline learns of the deletion
+    on its next ``sync``.
+    """
+    return Frame(
+        type=TYPE_MESSAGE_DELETED,
+        id=id,
+        chat_id=chat_id,
+        thread_id=thread_id,
+        payload={"message_ids": list(message_ids)},
+    )
+
+
 # ---------------------------------------------------------------------------
 # Push / notification frames (M5)
 # ---------------------------------------------------------------------------
diff --git a/gateway-plugin/ws_server.py b/gateway-plugin/ws_server.py
index 88485a2..4e5347a 100644
--- a/gateway-plugin/ws_server.py
+++ b/gateway-plugin/ws_server.py
@@ -380,6 +380,8 @@ class WsServer:
             await self._adapter.on_sync(frame, device_id)
         elif frame.type == protocol.TYPE_HISTORY:
             await self._adapter.on_history(frame, device_id)
+        elif frame.type == protocol.TYPE_MESSAGE_DELETE:
+            await self._adapter.on_message_delete(frame, device_id)
         elif frame.type == protocol.TYPE_MEDIA_UPLOAD_START:
             await self._adapter.on_media_upload_start(frame, device_id)
         elif frame.type == protocol.TYPE_MEDIA_UPLOAD_END: