diff --git a/src/lib/loadPlugin.js b/src/lib/loadPlugin.js
index 9c3d50a83..14aa18a50 100644
--- a/src/lib/loadPlugin.js
+++ b/src/lib/loadPlugin.js
@@ -8,6 +8,27 @@ export default async function loadPlugin(pluginId, justInstalled = false) {
 	const baseUrl = await helpers.toInternalUri(Url.join(PLUGIN_DIR, pluginId));
 	const cacheFile = Url.join(CACHE_STORAGE, pluginId);
 
+	// Unmount the old version before loading the new one.
+	// This MUST be done here by the framework, not by the new plugin code itself,
+	// because once the new script loads, it calls acode.setPluginUnmount(id, newDestroy)
+	// which overwrites the old version's destroy callback. At that point the old
+	// destroy — which holds references to the old sidebar app, commands, event
+	// listeners, etc. — is lost and can never be called. Letting the framework
+	// invoke unmountPlugin() first ensures the OLD destroy() runs while it still
+	// exists, so all old-version resources are properly cleaned up.
+	try {
+		acode.unmountPlugin(pluginId);
+	} catch (e) {
+		// unmountPlugin() itself is safe when no callback is registered (it no-ops),
+		// but a plugin's destroy() callback may throw. We catch here so a faulty
+		// cleanup in the old version does not block reloading the new one.
+		console.error(`Error while unmounting plugin "${pluginId}":`, e);
+	}
+
+	// Remove the old <script> tag so the browser fetches the new source.
+	const oldScript = document.getElementById(`${pluginId}-mainScript`);
+	if (oldScript) oldScript.remove();
+
 	const pluginJson = await fsOperation(
 		Url.join(PLUGIN_DIR, pluginId, "plugin.json"),
 	).readFile("json");