fix(ui): eliminate N+1 reactive subscriptions in SessionTurn (#18924)

packages/app/src/pages/session/message-timeline.tsx

@@ -923,7 +923,15 @@ export function MessageTimeline(props: {
                 {(messageID) => {
                   const active = createMemo(() => activeMessageID() === messageID)
                   const comments = createMemo(() => messageComments(sync.data.part[messageID] ?? []), [], {
-                    equals: (a, b) => JSON.stringify(a) === JSON.stringify(b),
+                    equals: (a, b) =>
+                      a.length === b.length &&
+                      a.every(
+                        (c, i) =>
+                          c.path === b[i].path &&
+                          c.comment === b[i].comment &&
+                          c.selection?.startLine === b[i].selection?.startLine &&
+                          c.selection?.endLine === b[i].selection?.endLine,
+                      ),
                   })
                   const commentCount = createMemo(() => comments().length)
                   return (
@@ -979,6 +987,7 @@ export function MessageTimeline(props: {
                       <SessionTurn
                         sessionID={sessionID() ?? ""}
                         messageID={messageID}
+                        messages={sessionMessages()}
                         actions={props.actions}
                         active={active()}
                         status={active() ? sessionStatus() : undefined}