fix(split pane): hide the close button when no split panes exist

apps/client/src/widgets/buttons/close_pane_button.tsx

@@ -1,17 +1,19 @@
 import { useEffect, useState } from "preact/hooks";
 import { t } from "../../services/i18n";
 import ActionButton from "../react/ActionButton";
-import { useNoteContext, useTriliumEvent } from "../react/hooks";
+import { useNoteContext, useTriliumEvents } from "../react/hooks";
+import appContext from "../../components/app_context";
 
 export default function ClosePaneButton() {
     const { noteContext, ntxId, parentComponent } = useNoteContext();
     const [isEnabled, setIsEnabled] = useState(false);
 
     function refresh() {
-        setIsEnabled(!!(noteContext && !!noteContext.mainNtxId));
+        const isMainOfSomeContext = appContext.tabManager.noteContexts.some(c => c.mainNtxId === ntxId);
+        setIsEnabled(!!(noteContext && (!!noteContext.mainNtxId || isMainOfSomeContext)));
     }
 
-    useTriliumEvent("noteContextReorder", refresh);
+    useTriliumEvents(["noteContextRemoved", "noteContextReorder", "newNoteContextCreated"], refresh);
     useEffect(refresh, [ntxId]);
 
     return (

apps/client/src/widgets/containers/split_note_container.ts

@@ -100,9 +100,23 @@ export default class SplitNoteContainer extends FlexContainer<SplitNoteWidget> {
     }
 
     async closeThisNoteSplitCommand({ ntxId }: CommandListenerData<"closeThisNoteSplit">) {
-        if (ntxId) {
-            await appContext.tabManager.removeNoteContext(ntxId);
+        if (!ntxId) return;
+        const contexts = appContext.tabManager.noteContexts;
+
+        const currentIndex = contexts.findIndex((c) => c.ntxId === ntxId);
+        if (currentIndex === -1) return;
+
+        const isRemoveMainContext = !contexts[currentIndex].mainNtxId;
+        if (isRemoveMainContext && currentIndex + 1 <= contexts.length) {
+            const ntxIds = contexts.map((c) => c.ntxId).filter((c) => !!c) as string[];
+            this.triggerCommand("noteContextReorder", {
+                ntxIdsInOrder: ntxIds,
+                oldMainNtxId: ntxId,
+                newMainNtxId: ntxIds[currentIndex + 1]
+            });
         }
+
+        await appContext.tabManager.removeNoteContext(ntxId);
     }
 
     async moveThisNoteSplitCommand({ ntxId, isMovingLeft }: CommandListenerData<"moveThisNoteSplit">) {