From f59c7b25253e6203f6f30f3cd1036808516d25f0 Mon Sep 17 00:00:00 2001
From: Bohdan Triapitsyn <artmore@protonmail.com>
Date: Mon, 19 Jan 2026 14:04:23 +0200
Subject: [PATCH] fix: skip trimming for active sessions to preserve anchor

---
 packages/ui/src/stores/useSessionStore.ts | 5 +++++
 1 file changed, 5 insertions(+)

diff --git a/packages/ui/src/stores/useSessionStore.ts b/packages/ui/src/stores/useSessionStore.ts
index 7726a719..f6ffa46c 100644
--- a/packages/ui/src/stores/useSessionStore.ts
+++ b/packages/ui/src/stores/useSessionStore.ts
@@ -506,6 +506,11 @@ export const useSessionStore = create<SessionStore>()(
                 getActiveTurnAnchor: (sessionId: string) => useMessageStore.getState().getActiveTurnAnchor(sessionId),
                 trimToViewportWindow: (sessionId: string, targetSize?: number) => {
                     const currentSessionId = useSessionManagementStore.getState().currentSessionId;
+                    // Skip trimming for sessions in active phase (busy/cooldown) to preserve anchor/spacer
+                    const phase = get().sessionActivityPhase?.get(sessionId);
+                    if (phase === 'busy' || phase === 'cooldown') {
+                        return;
+                    }
                     return useMessageStore.getState().trimToViewportWindow(sessionId, targetSize, currentSessionId || undefined);
                 },
                 evictLeastRecentlyUsed: () => {