diff --git a/extensions/matrix/src/matrix/monitor/room-history.test.ts b/extensions/matrix/src/matrix/monitor/room-history.test.ts
index cb0f0243021..edf493ba0f1 100644
--- a/extensions/matrix/src/matrix/monitor/room-history.test.ts
+++ b/extensions/matrix/src/matrix/monitor/room-history.test.ts
@@ -64,6 +64,33 @@ describe("createRoomHistoryTracker — watermark monotonicity", () => {
     expect(retried.history.map((entry) => entry.body)).toEqual(["msg1"]);
     expect(retried.snapshotIdx).toBe(first.snapshotIdx);
   });
+
+  it("refreshes watermark recency before capped-map eviction", () => {
+    const tracker = createRoomHistoryTracker(200, 10, 2);
+    const room1 = "!room1:test";
+    const room2 = "!room2:test";
+    const room3 = "!room3:test";
+
+    tracker.recordPending(room1, entry("old msg in room1"));
+    const snap1 = tracker.recordTrigger(room1, entry("trigger in room1"));
+    tracker.consumeHistory(AGENT, room1, snap1);
+
+    tracker.recordPending(room2, entry("old msg in room2"));
+    const snap2 = tracker.recordTrigger(room2, entry("trigger in room2"));
+    tracker.consumeHistory(AGENT, room2, snap2);
+
+    // Refresh room1 so room2 becomes the stalest watermark entry.
+    tracker.consumeHistory(AGENT, room1, snap1);
+
+    tracker.recordPending(room3, entry("old msg in room3"));
+    const snap3 = tracker.recordTrigger(room3, entry("trigger in room3"));
+    tracker.consumeHistory(AGENT, room3, snap3);
+
+    tracker.recordPending(room1, entry("new msg in room1"));
+    const room1History = tracker.getPendingHistory(AGENT, room1, 100);
+    expect(room1History).toHaveLength(1);
+    expect(room1History[0]?.body).toBe("new msg in room1");
+  });
 });
 
 describe("createRoomHistoryTracker — roomQueues eviction", () => {
diff --git a/extensions/matrix/src/matrix/monitor/room-history.ts b/extensions/matrix/src/matrix/monitor/room-history.ts
index 80c77a3a116..aabc535e422 100644
--- a/extensions/matrix/src/matrix/monitor/room-history.ts
+++ b/extensions/matrix/src/matrix/monitor/room-history.ts
@@ -85,6 +85,7 @@ type RoomQueue = {
 export function createRoomHistoryTracker(
   maxQueueSize = DEFAULT_MAX_QUEUE_SIZE,
   maxRoomQueues = DEFAULT_MAX_ROOM_QUEUES,
+  maxWatermarkEntries = MAX_WATERMARK_ENTRIES,
 ): RoomHistoryTracker {
   const roomQueues = new Map<string, RoomQueue>();
   /** Maps `${agentId}:${roomId}` → absolute consumed-up-to index */
@@ -137,6 +138,21 @@ export function createRoomHistoryTracker(
     return `${agentId}:${messageId.trim()}`;
   }
 
+  function rememberWatermark(key: string, snapshotIdx: number): void {
+    const nextSnapshotIdx = Math.max(agentWatermarks.get(key) ?? 0, snapshotIdx);
+    if (agentWatermarks.has(key)) {
+      // Refresh insertion order so capped-map eviction removes the stalest pair, not an active one.
+      agentWatermarks.delete(key);
+    }
+    agentWatermarks.set(key, nextSnapshotIdx);
+    if (agentWatermarks.size > maxWatermarkEntries) {
+      const oldest = agentWatermarks.keys().next().value;
+      if (oldest !== undefined) {
+        agentWatermarks.delete(oldest);
+      }
+    }
+  }
+
   function computePendingHistory(
     queue: RoomQueue,
     agentId: string,
@@ -208,18 +224,11 @@ export function createRoomHistoryTracker(
       // Monotone write: never regress an already-advanced watermark.
       // Guards against out-of-order completion when two triggers for the same
       // (agentId, roomId) are in-flight concurrently.
-      agentWatermarks.set(key, Math.max(agentWatermarks.get(key) ?? 0, snapshotIdx));
+      rememberWatermark(key, snapshotIdx);
       const retryKey = preparedTriggerKey(agentId, messageId);
       if (queue && retryKey) {
         queue.preparedTriggers.delete(retryKey);
       }
-      // LRU-style eviction to prevent unbounded growth
-      if (agentWatermarks.size > MAX_WATERMARK_ENTRIES) {
-        const oldest = agentWatermarks.keys().next().value;
-        if (oldest !== undefined) {
-          agentWatermarks.delete(oldest);
-        }
-      }
     },
   };
 }