add fetch_event tool and backfill get_room_history beyond event cache

src/bin/mcp.rs

@@ -58,6 +58,13 @@ mod protocol_inline {
             room_id: String,
             limit: Option<usize>,
         },
+
+        #[serde(rename = "fetch_event")]
+        FetchEvent {
+            room_id: String,
+            event_id: String,
+            context_before: Option<u32>,
+        },
     }
 
     #[derive(Debug, Serialize, Deserialize)]
@@ -125,6 +132,24 @@ struct GetRoomHistoryParams {
     limit: Option<usize>,
 }
 
+#[derive(Debug, Deserialize, JsonSchema)]
+struct FetchEventParams {
+    /// The event ID to fetch. Can be the shortened form shown in the
+    /// timeline (e.g. $abc123de...) or a full ID. Use this to dereference
+    /// reply targets shown as [reply to $abc...] in the prompt, or to look
+    /// up any specific event by ID.
+    event_id: String,
+    /// Number of context messages BEFORE the target to include. Default 0.
+    /// Pass 5-10 for conversational context. The response also includes an
+    /// `earlier_handle` event_id you can pass to fetch_event to page further
+    /// back into history.
+    #[serde(default)]
+    context_before: Option<u32>,
+    /// Room ID to look in. Defaults to source room if omitted.
+    #[serde(default)]
+    room_id: Option<String>,
+}
+
 // ---------------------------------------------------------------------------
 // MCP server struct
 // ---------------------------------------------------------------------------
@@ -268,7 +293,7 @@ impl MatrixBridge {
         Self::response_to_result(resp)
     }
 
-    #[tool(description = "Get recent message history for any joined room. Returns JSON list of messages and reactions with timestamps.")]
+    #[tool(description = "Get recent message history for any joined room. Returns JSON list of messages and reactions with timestamps. Backfills via /messages if cache is short.")]
     async fn get_room_history(
         &self,
         Parameters(params): Parameters<GetRoomHistoryParams>,
@@ -281,6 +306,22 @@ impl MatrixBridge {
             .await?;
         Self::response_to_result(resp)
     }
+
+    #[tool(description = "Fetch a specific event by ID with optional context messages before it. Use to dereference [reply to $...] markers or arbitrary event IDs. Response includes earlier_handle for paging further back.")]
+    async fn fetch_event(
+        &self,
+        Parameters(params): Parameters<FetchEventParams>,
+    ) -> Result<CallToolResult, McpError> {
+        let room_id = params.room_id.unwrap_or_else(|| self.source_room.clone());
+        let resp = self
+            .call(&DaemonRequest::FetchEvent {
+                room_id,
+                event_id: params.event_id,
+                context_before: params.context_before,
+            })
+            .await?;
+        Self::response_to_result(resp)
+    }
 }
 
 // ---------------------------------------------------------------------------

src/claude.rs

@@ -58,7 +58,7 @@ pub async fn invoke_claude(
         "--add-dir",
         &identity_str,
         "--allowedTools",
-        "Read,Edit,Write,Glob,Grep,mcp__matrix__send_message,mcp__matrix__send_dm,mcp__matrix__send_reaction,mcp__matrix__send_reply,mcp__matrix__list_rooms,mcp__matrix__list_room_members,mcp__matrix__get_room_history",
+        "Read,Edit,Write,Glob,Grep,mcp__matrix__send_message,mcp__matrix__send_dm,mcp__matrix__send_reaction,mcp__matrix__send_reply,mcp__matrix__list_rooms,mcp__matrix__list_room_members,mcp__matrix__get_room_history,mcp__matrix__fetch_event",
         "--mcp-config",
         &mcp_config_str,
         "-p",

src/protocol.rs

@@ -35,6 +35,13 @@ pub enum DaemonRequest {
         room_id: String,
         limit: Option<usize>,
     },
+
+    #[serde(rename = "fetch_event")]
+    FetchEvent {
+        room_id: String,
+        event_id: String,
+        context_before: Option<u32>,
+    },
 }
 
 /// Response from daemon to MCP server.

src/socket.rs

@@ -77,6 +77,11 @@ async fn handle_request(request: DaemonRequest, client: &Client) -> DaemonRespon
         DaemonRequest::GetRoomHistory { room_id, limit } => {
             get_room_history(client, &room_id, limit).await
         }
+        DaemonRequest::FetchEvent {
+            room_id,
+            event_id,
+            context_before,
+        } => fetch_event(client, &room_id, &event_id, context_before).await,
     }
 }
 
@@ -251,45 +256,202 @@ async fn get_room_history(
     };
     let limit = limit.unwrap_or(20).min(100);
 
-    let tl = match timeline::load_timeline(&room, limit, &own_user).await {
-        Ok(t) => t,
-        Err(e) => return DaemonResponse::err(format!("failed to load timeline: {e}")),
+    // Backfill via /messages if cache is short
+    if let Ok((cache, _)) = room.event_cache().await {
+        let mut tl = match timeline::load_timeline(&room, limit, &own_user).await {
+            Ok(t) => t,
+            Err(e) => return DaemonResponse::err(format!("failed to load timeline: {e}")),
+        };
+        let mut tries = 0;
+        while tl.len() < limit && tries < 5 {
+            tries += 1;
+            match cache.pagination().run_backwards_once((limit - tl.len()) as u16).await {
+                Ok(outcome) => {
+                    if outcome.reached_start {
+                        break;
+                    }
+                }
+                Err(e) => {
+                    tracing::warn!("backfill failed: {e}");
+                    break;
+                }
+            }
+            tl = match timeline::load_timeline(&room, limit, &own_user).await {
+                Ok(t) => t,
+                Err(e) => return DaemonResponse::err(format!("reload after backfill failed: {e}")),
+            };
+        }
+
+        let items: Vec<_> = tl.iter().map(timeline_item_to_json).collect();
+        DaemonResponse::ok(items)
+    } else {
+        DaemonResponse::err("event cache not available".to_owned())
+    }
+}
+
+fn timeline_item_to_json(item: &crate::types::TimelineItem) -> serde_json::Value {
+    match item {
+        crate::types::TimelineItem::Message {
+            event_id,
+            sender,
+            body,
+            is_self,
+            ts,
+            in_reply_to,
+        } => json!({
+            "kind": "message",
+            "event_id": event_id.as_str(),
+            "sender": sender.as_str(),
+            "body": body,
+            "is_self": is_self,
+            "ts": ts,
+            "in_reply_to": in_reply_to.as_ref().map(|e| e.as_str()),
+        }),
+        crate::types::TimelineItem::Reaction {
+            sender,
+            target_event_id,
+            key,
+            is_self,
+            ts,
+        } => json!({
+            "kind": "reaction",
+            "sender": sender.as_str(),
+            "target_event_id": target_event_id.as_str(),
+            "key": key,
+            "is_self": is_self,
+            "ts": ts,
+        }),
+    }
+}
+
+/// Fetch a specific event by ID via the homeserver `/context` endpoint.
+/// Returns the event plus `context_before` events before it. Includes one
+/// extra event as `earlier_handle` so the shard can page further backward
+/// by calling fetch_event again with that id.
+async fn fetch_event(
+    client: &Client,
+    room_id: &str,
+    event_id: &str,
+    context_before: Option<u32>,
+) -> DaemonResponse {
+    use matrix_sdk::ruma::events::AnySyncTimelineEvent;
+    use matrix_sdk::ruma::events::room::message::MessageType;
+
+    let rid = match room_id.parse::<OwnedRoomId>() {
+        Ok(r) => r,
+        Err(e) => return DaemonResponse::err(format!("invalid room_id: {e}")),
+    };
+    let Some(room) = client.get_room(&rid) else {
+        return DaemonResponse::err(format!("room {rid} not found"));
+    };
+    let own_user = match client.user_id() {
+        Some(u) => u.to_owned(),
+        None => return DaemonResponse::err("not logged in".to_owned()),
     };
 
-    let items: Vec<_> = tl
-        .iter()
-        .map(|item| match item {
-            crate::types::TimelineItem::Message {
-                event_id,
-                sender,
-                body,
-                is_self,
-                ts,
-                in_reply_to,
-            } => json!({
-                "kind": "message",
-                "event_id": event_id.as_str(),
-                "sender": sender.as_str(),
-                "body": body,
-                "is_self": is_self,
-                "ts": ts,
-                "in_reply_to": in_reply_to.as_ref().map(|e| e.as_str()),
-            }),
-            crate::types::TimelineItem::Reaction {
-                sender,
-                target_event_id,
-                key,
-                is_self,
-                ts,
-            } => json!({
-                "kind": "reaction",
-                "sender": sender.as_str(),
-                "target_event_id": target_event_id.as_str(),
-                "key": key,
-                "is_self": is_self,
-                "ts": ts,
-            }),
-        })
-        .collect();
-    DaemonResponse::ok(items)
+    // Resolve possibly-shortened event id against recent timeline first;
+    // fall back to parsing as a full id.
+    let resolve_tl = timeline::load_timeline(&room, 50, &own_user)
+        .await
+        .unwrap_or_default();
+    let full_eid = match timeline::resolve_event_id(&resolve_tl, event_id) {
+        Some(eid) => eid,
+        None => match event_id.parse::<matrix_sdk::ruma::OwnedEventId>() {
+            Ok(eid) => eid,
+            Err(e) => {
+                return DaemonResponse::err(format!("invalid or unknown event_id: {e}"));
+            }
+        },
+    };
+
+    // Request one extra event so we can split it off as the paging handle
+    let context_before = context_before.unwrap_or(0).min(50);
+    let request_size = context_before + 1;
+
+    let response = match room
+        .event_with_context(
+            &full_eid,
+            false,
+            matrix_sdk::ruma::UInt::from(request_size),
+            None,
+        )
+        .await
+    {
+        Ok(r) => r,
+        Err(e) => return DaemonResponse::err(format!("event_with_context failed: {e}")),
+    };
+
+    let render = |raw: &matrix_sdk::deserialized_responses::TimelineEvent| -> Option<serde_json::Value> {
+        let deserialized = raw.raw().deserialize().ok()?;
+        let AnySyncTimelineEvent::MessageLike(msg) = deserialized else {
+            return None;
+        };
+        match msg {
+            matrix_sdk::ruma::events::AnySyncMessageLikeEvent::RoomMessage(
+                matrix_sdk::ruma::events::SyncMessageLikeEvent::Original(orig),
+            ) => {
+                let MessageType::Text(text) = &orig.content.msgtype else {
+                    return None;
+                };
+                let ms: u64 = orig.origin_server_ts.0.into();
+                let ts = (ms / 1000) as i64;
+                let in_reply_to = match &orig.content.relates_to {
+                    Some(matrix_sdk::ruma::events::room::message::Relation::Reply { in_reply_to }) => {
+                        Some(in_reply_to.event_id.as_str().to_owned())
+                    }
+                    _ => None,
+                };
+                Some(json!({
+                    "kind": "message",
+                    "event_id": orig.event_id.as_str(),
+                    "sender": orig.sender.as_str(),
+                    "body": text.body,
+                    "is_self": orig.sender == own_user,
+                    "ts": ts,
+                    "in_reply_to": in_reply_to,
+                }))
+            }
+            matrix_sdk::ruma::events::AnySyncMessageLikeEvent::Reaction(
+                matrix_sdk::ruma::events::SyncMessageLikeEvent::Original(orig),
+            ) => {
+                let ms: u64 = orig.origin_server_ts.0.into();
+                let ts = (ms / 1000) as i64;
+                Some(json!({
+                    "kind": "reaction",
+                    "sender": orig.sender.as_str(),
+                    "target_event_id": orig.content.relates_to.event_id.as_str(),
+                    "key": orig.content.relates_to.key,
+                    "is_self": orig.sender == own_user,
+                    "ts": ts,
+                }))
+            }
+            _ => None,
+        }
+    };
+
+    // events_before is newest-first per matrix /context spec - reverse for chronological
+    let mut before: Vec<_> = response.events_before.iter().filter_map(render).collect();
+    before.reverse();
+
+    // The "earlier handle" is the oldest event we got, if we asked for more than 0
+    // It's used by the shard to page further back via another fetch_event call
+    let earlier_handle = if context_before > 0 && before.len() > context_before as usize {
+        before.first().and_then(|e| e.get("event_id").and_then(|v| v.as_str()).map(String::from))
+    } else {
+        None
+    };
+    let context_events: Vec<_> = if earlier_handle.is_some() {
+        // First event is the handle - skip it from the main events list
+        before.into_iter().skip(1).collect()
+    } else {
+        before
+    };
+
+    let target = response.event.as_ref().and_then(render);
+
+    DaemonResponse::ok(json!({
+        "event": target,
+        "context_before": context_events,
+        "earlier_handle": earlier_handle,
+    }))
 }