diff --git a/server/shell.ts b/server/shell.ts
index 6913892..d75b91a 100644
--- a/server/shell.ts
+++ b/server/shell.ts
@@ -419,10 +419,15 @@ export function renderShell(opts: ShellOptions): string {
       window.__rspaceTabBar = tabBar;
 
       // ── CommunitySync: merge with Automerge once connected ──
+      // NOTE: The TAB LIST is shared via Automerge (which modules are open),
+      // but the ACTIVE TAB is always local (determined by the URL / currentModuleId).
+      // This prevents windows from fighting over which tab is highlighted.
       document.addEventListener('community-sync-ready', (e) => {
         const sync = e.detail?.sync;
         if (!sync) return;
 
+        const localActiveId = 'layer-' + currentModuleId;
+
         // Merge: Automerge layers win if they exist, otherwise seed from localStorage
         const remoteLayers = sync.getLayers();
         if (remoteLayers.length > 0) {
@@ -433,24 +438,21 @@ export function renderShell(opts: ShellOptions): string {
           }
           layers = sync.getLayers();
           tabBar.setLayers(layers);
-          const activeId = sync.doc.activeLayerId;
-          if (activeId) tabBar.setAttribute('active', activeId);
           tabBar.setFlows(sync.getFlows());
         } else {
           // First connection: push all localStorage tabs into Automerge
           for (const l of layers) {
             sync.addLayer(l);
           }
-          sync.setActiveLayer('layer-' + currentModuleId);
         }
 
+        // Active tab stays local — always matches the URL
+        tabBar.setAttribute('active', localActiveId);
+
         // Keep localStorage in sync
         saveTabs();
 
-        // Sync layer changes back to Automerge
-        tabBar.addEventListener('layer-switch', (e) => {
-          sync.setActiveLayer(e.detail.layerId);
-        });
+        // Sync layer list changes to Automerge (not active tab)
         tabBar.addEventListener('layer-add', (e) => {
           const { moduleId } = e.detail;
           const newLayer = makeLayer(moduleId, sync.getLayers().length);
@@ -469,13 +471,13 @@ export function renderShell(opts: ShellOptions): string {
         tabBar.addEventListener('flow-remove', (e) => { sync.removeFlow(e.detail.flowId); });
         tabBar.addEventListener('view-toggle', (e) => { sync.setLayerViewMode(e.detail.mode); });
 
-        // Listen for remote changes
+        // Listen for remote changes — sync tab list and flows only.
+        // Never touch the active tab: it's managed locally by TabCache
+        // and the tab-bar component via layer-switch events.
         sync.addEventListener('change', () => {
           layers = sync.getLayers();
           tabBar.setLayers(layers);
           tabBar.setFlows(sync.getFlows());
-          const activeId = sync.doc.activeLayerId;
-          if (activeId) tabBar.setAttribute('active', activeId);
           const viewMode = sync.doc.layerViewMode;
           if (viewMode) tabBar.setAttribute('view-mode', viewMode);
           saveTabs(); // keep localStorage in sync