[Chat] Fix duplicate messages when history fetch races firehose (#10839)

Co-authored-by: Claude Fable 5 <noreply@anthropic.com>

src/state/messages/convo/agent.ts

@@ -917,17 +917,27 @@ export class Convo {
             ChatBskyConvoDefs.isLogCreateMessage(ev) &&
             ChatBskyConvoDefs.isMessageView(ev.message)
           ) {
-            /**
+            /*
-             * If this message is already in new messages, it was added by our
+             * If this message is already in past messages, the initial
-             * sending logic, and is based on client-ordering. When we receive
+             * history fetch raced this log event and already returned it.
-             * the "committed" event from the log, we should replace this
+             * Update in place rather than inserting a duplicate into new
-             * reference and re-insert in order to respect the order we received
+             * messages.
-             * from the log.
              */
-            if (this.newMessages.has(ev.message.id)) {
+            if (this.pastMessages.has(ev.message.id)) {
-              this.newMessages.delete(ev.message.id)
+              this.pastMessages.set(ev.message.id, ev.message)
+            } else {
+              /**
+               * If this message is already in new messages, it was added by our
+               * sending logic, and is based on client-ordering. When we receive
+               * the "committed" event from the log, we should replace this
+               * reference and re-insert in order to respect the order we received
+               * from the log.
+               */
+              if (this.newMessages.has(ev.message.id)) {
+                this.newMessages.delete(ev.message.id)
+              }
+              this.newMessages.set(ev.message.id, ev.message)
             }
-            this.newMessages.set(ev.message.id, ev.message)
             needsCommit = true
           } else if (
             ChatBskyConvoDefs.isLogDeleteMessage(ev) &&
@@ -964,7 +974,12 @@ export class Convo {
           } else {
             const systemView = toSystemMessageView(ev)
             if (systemView) {
-              this.newMessages.set(systemView.id, systemView)
+              // same as above: avoid duplicating if history fetch won the race
+              if (this.pastMessages.has(systemView.id)) {
+                this.pastMessages.set(systemView.id, systemView)
+              } else {
+                this.newMessages.set(systemView.id, systemView)
+              }
               needsCommit = true
             }
           }