diff --git a/src/i18n/locales/en/settings.json b/src/i18n/locales/en/settings.json
index 7f1aeaaf2..f31e9d511 100644
--- a/src/i18n/locales/en/settings.json
+++ b/src/i18n/locales/en/settings.json
@@ -794,6 +794,7 @@
       },
       "install": {
         "integrityFailed": "Plugin bundle failed its integrity check — install blocked.",
+        "alreadyInstalling": "This plugin is already being installed — check Settings › Plugins.",
         "failed": "Failed to install plugin.",
         "versionUnsupported": "This plugin requires app version {{version}} or later."
       },
diff --git a/src/i18n/locales/fr/settings.json b/src/i18n/locales/fr/settings.json
index bfae89cfb..ec1a66fbc 100644
--- a/src/i18n/locales/fr/settings.json
+++ b/src/i18n/locales/fr/settings.json
@@ -794,6 +794,7 @@
       },
       "install": {
         "integrityFailed": "L'intégrité du module a échoué — installation bloquée.",
+        "alreadyInstalling": "Ce module est déjà en cours d'installation — voir Paramètres › Modules.",
         "failed": "Échec de l'installation du module.",
         "versionUnsupported": "Ce module nécessite la version {{version}} ou supérieure de l'application."
       },
diff --git a/src/i18n/locales/ru/settings.json b/src/i18n/locales/ru/settings.json
index b9d961d76..22acb5808 100644
--- a/src/i18n/locales/ru/settings.json
+++ b/src/i18n/locales/ru/settings.json
@@ -895,6 +895,7 @@
       },
       "install": {
         "integrityFailed": "Пакет плагина не прошёл проверку целостности — установка заблокирована.",
+        "alreadyInstalling": "Этот плагин уже устанавливается — откройте «Настройки › Плагины».",
         "failed": "Не удалось установить плагин.",
         "versionUnsupported": "Этот плагин требует версию приложения {{version}} или новее."
       },
diff --git a/src/i18n/locales/zh/settings.json b/src/i18n/locales/zh/settings.json
index e06947402..4e5217cec 100644
--- a/src/i18n/locales/zh/settings.json
+++ b/src/i18n/locales/zh/settings.json
@@ -614,6 +614,7 @@
       },
       "install": {
         "integrityFailed": "插件包未通过完整性校验——已阻止安装。",
+        "alreadyInstalling": "该插件正在安装中——请查看“设置 › 插件”。",
         "failed": "安装插件失败。",
         "versionUnsupported": "此插件需要应用版本 {{version}} 或更高版本。"
       },
diff --git a/src/plugins/installErrors.ts b/src/plugins/installErrors.ts
index 3f54b82f3..052b9f54d 100644
--- a/src/plugins/installErrors.ts
+++ b/src/plugins/installErrors.ts
@@ -7,6 +7,17 @@ export interface TranslatableMessage {
   params?: Record<string, string>;
 }
 
+/** Raised when an install is requested for an id whose install is still running.
+ *  The second request is refused rather than joined: the two callers may have
+ *  reviewed different manifests for the same id, so the running install cannot
+ *  stand in for the one this caller consented to. */
+export class PluginInstallInProgressError extends Error {
+  constructor(public readonly id: string) {
+    super(`An install of "${id}" is already in progress.`);
+    this.name = "PluginInstallInProgressError";
+  }
+}
+
 /**
  * The user-facing message for a failed plugin install, matched on the error's
  * type rather than its text. A hash mismatch is the user's only tamper signal,
@@ -15,6 +26,7 @@ export interface TranslatableMessage {
  */
 export function pluginInstallErrorMessage(e: unknown, fallbackKey: string): TranslatableMessage {
   if (e instanceof PluginHashMismatchError) return { key: "settings.plugins.install.integrityFailed" };
+  if (e instanceof PluginInstallInProgressError) return { key: "settings.plugins.install.alreadyInstalling" };
   if (e instanceof MinAppVersionError)
     return { key: "settings.plugins.install.versionUnsupported", params: { version: e.required } };
   return { key: fallbackKey };
diff --git a/src/stores/marketplaceStore.installUpdate.test.ts b/src/stores/marketplaceStore.installUpdate.test.ts
index 31b1fe73c..ccb692f81 100644
--- a/src/stores/marketplaceStore.installUpdate.test.ts
+++ b/src/stores/marketplaceStore.installUpdate.test.ts
@@ -31,6 +31,7 @@ import { getExposedApi, getLoadedPlugins, unloadPlugin } from "@/plugins/runtime
 import * as runtimeModule from "@/plugins/runtime";
 import { injectPluginStyle } from "@/plugins/importPluginModule";
 import { PluginHashMismatchError } from "@/plugins/integrity";
+import { PluginInstallInProgressError } from "@/plugins/installErrors";
 import { sha256Hex } from "@/plugins/integrity";
 import type { PluginRegisterFn } from "@/plugins/api";
 
@@ -246,3 +247,59 @@ test("installing a plugin that was never loaded does not call unloadPlugin", asy
     spy.mockRestore();
   }
 });
+
+/** Parks installPlugin inside its first plugin_fetch_url until the returned
+ *  release() runs, so a second install can race a genuinely in-flight one. */
+function gatedFetch(): () => void {
+  let release!: () => void;
+  const gate = new Promise<void>((resolve) => { release = resolve; });
+  h.invoke.mockImplementation(async (cmd: string, args: { url?: string }) => {
+    if (cmd === "plugin_fetch_url") {
+      await gate;
+      return args.url!.endsWith("manifest.json") ? manifestFor("1.0.0") : "v1-js";
+    }
+    return undefined;
+  });
+  return release;
+}
+
+test("a second install of an id already installing is refused rather than resolving as a no-op", async () => {
+  mockBundle("v1");
+  const release = gatedFetch();
+
+  const first = useMarketplaceStore.getState().installPlugin(basePlugin());
+
+  // A caller that resolves here — the deep-link confirm sheet — would report a
+  // success for an install it never performed.
+  await expect(
+    useMarketplaceStore.getState().installPlugin(basePlugin()),
+  ).rejects.toBeInstanceOf(PluginInstallInProgressError);
+
+  release();
+  await first;
+  expect(getExposedApi("p1")).toBe("v1");
+});
+
+test("a refused concurrent install does not clear the running install's busy state", async () => {
+  mockBundle("v1");
+  const release = gatedFetch();
+
+  const first = useMarketplaceStore.getState().installPlugin(basePlugin());
+  await expect(useMarketplaceStore.getState().installPlugin(basePlugin())).rejects.toThrow();
+
+  expect(useMarketplaceStore.getState().installing.has("p1")).toBe(true);
+  release();
+  await first;
+  expect(useMarketplaceStore.getState().installing.has("p1")).toBe(false);
+});
+
+test("an id is installable again once its previous install has settled", async () => {
+  mockBundle("v1");
+  h.invoke.mockImplementation(async (cmd: string, args: { url?: string }) => {
+    if (cmd === "plugin_fetch_url") return args.url!.endsWith("manifest.json") ? manifestFor("1.0.0") : "v1-js";
+    return undefined;
+  });
+  await useMarketplaceStore.getState().installPlugin(basePlugin());
+
+  await expect(useMarketplaceStore.getState().installPlugin(basePlugin())).resolves.toBeUndefined();
+});
diff --git a/src/stores/marketplaceStore.ts b/src/stores/marketplaceStore.ts
index b51cff45e..599b0dc2e 100644
--- a/src/stores/marketplaceStore.ts
+++ b/src/stores/marketplaceStore.ts
@@ -9,6 +9,7 @@ import { usePluginRegistryStore } from "@/stores/pluginRegistryStore";
 import { appFetch } from "@/services/http";
 import { resolveVerifiedHash } from "@/plugins/integrity";
 import { assertValidPluginId } from "@/plugins/pluginId";
+import { PluginInstallInProgressError } from "@/plugins/installErrors";
 import { satisfiesMinAppVersion, MinAppVersionError, beatsSeededVersion, isParsableVersion } from "@/plugins/version";
 import { useSeededTombstoneStore, loadSeededEntries } from "@/stores/seededTombstoneStore";
 
@@ -349,7 +350,10 @@ export const useMarketplaceStore = create<MarketplaceState>((set, get) => ({
     // checked separately by loadPlugin, since the two are not required to match.
     assertValidPluginId(plugin.id);
     const { installing, installedMeta } = get();
-    if (installing.has(plugin.id)) return;
+    // Refused, not silently skipped: resolving here told every caller the install
+    // succeeded — a deep-link confirm sheet accepted while the Settings tab was
+    // installing the same id closed reporting success having written nothing.
+    if (installing.has(plugin.id)) throw new PluginInstallInProgressError(plugin.id);
 
     set((s) => ({ installing: new Set([...s.installing, plugin.id]) }));
     try {