fix(frontend): preserve chronological order of thread history after context compression (#3354)

* fix(frontend): preserve chronological order of thread history after context compression

Iterate runs from newest to match backend `list_by_thread` (newest-first) and the prepend semantics of the history loader, so refreshed history renders in A→B→C→D→E→F order.

Fixes #3352

* fix(frontend): auto-continue loading runs with no visible messages after context compression

frontend/src/core/threads/hooks.ts

@@ -106,11 +106,11 @@ function dedupeMessagesByIdentity(messages: Message[]): Message[] {
   });
 }
 
-function findLatestUnloadedRunIndex(
+export function findLatestUnloadedRunIndex(
   runs: Run[],
   loadedRunIds: ReadonlySet<string>,
 ): number {
-  for (let i = runs.length - 1; i >= 0; i--) {
+  for (let i = 0; i < runs.length; i++) {
     const run = runs[i];
     if (run && !loadedRunIds.has(run.run_id)) {
       return i;
@@ -119,6 +119,19 @@ function findLatestUnloadedRunIndex(
   return -1;
 }
 
+export const MAX_CONSECUTIVE_EMPTY_RUN_LOADS = 5;
+
+export function shouldAutoContinueOnEmptyRun(
+  fetchedMessageCount: number,
+  consecutiveEmptyLoads: number,
+  maxConsecutiveEmptyLoads: number = MAX_CONSECUTIVE_EMPTY_RUN_LOADS,
+): boolean {
+  return (
+    fetchedMessageCount === 0 &&
+    consecutiveEmptyLoads < maxConsecutiveEmptyLoads
+  );
+}
+
 type RunMessagesPageResponse = {
   data: RunMessage[];
   has_more?: boolean;
@@ -874,6 +887,7 @@ export function useThreadHistory(threadId: string) {
     setLoading(true);
 
     try {
+      let consecutiveEmptyLoads = 0;
       do {
         pendingLoadRef.current = false;
 
@@ -927,6 +941,17 @@ export function useThreadHistory(threadId: string) {
         } else {
           runBeforeSeqRef.current.delete(run.run_id);
           loadedRunIdsRef.current.add(run.run_id);
+          if (
+            shouldAutoContinueOnEmptyRun(
+              _messages.length,
+              consecutiveEmptyLoads,
+            )
+          ) {
+            consecutiveEmptyLoads += 1;
+            pendingLoadRef.current = true;
+          } else {
+            consecutiveEmptyLoads = 0;
+          }
         }
         indexRef.current = findLatestUnloadedRunIndex(
           runsRef.current,