diff --git a/src/plugins/channel-plugin-ids.test.ts b/src/plugins/channel-plugin-ids.test.ts
index b126fab7217..afc705ff0d8 100644
--- a/src/plugins/channel-plugin-ids.test.ts
+++ b/src/plugins/channel-plugin-ids.test.ts
@@ -245,6 +245,28 @@ function createManifestRegistryFixture() {
         providers: [],
         cliBackends: [],
       },
+      {
+        id: "demo-global-startup-opt-out",
+        channels: [],
+        activation: {
+          onStartup: false,
+        },
+        origin: "global",
+        enabledByDefault: undefined,
+        providers: [],
+        cliBackends: [],
+      },
+      {
+        id: "demo-global-explicit-startup",
+        channels: [],
+        activation: {
+          onStartup: true,
+        },
+        origin: "global",
+        enabledByDefault: undefined,
+        providers: [],
+        cliBackends: [],
+      },
     ].map(withManifestLoadPaths),
     diagnostics: [],
   };
@@ -297,7 +319,12 @@ function createInstalledPluginRecordFixture(
     enabled: true,
     ...(record.enabledByDefault === true ? { enabledByDefault: true } : {}),
     startup: {
-      sidecar: record.channels.length === 0 && !hasRuntimeContractSurface(record) && !memory,
+      sidecar:
+        record.activation?.onStartup === true ||
+        (record.activation?.onStartup === undefined &&
+          record.channels.length === 0 &&
+          !hasRuntimeContractSurface(record) &&
+          !memory),
       memory,
       deferConfiguredChannelFullLoadUntilAfterListen:
         record.startupDeferConfiguredChannelFullLoadUntilAfterListen === true,
@@ -623,6 +650,42 @@ describe("resolveGatewayStartupPluginIds", () => {
     });
   });
 
+  it("keeps deprecated implicit startup sidecar fallback for legacy plugins", () => {
+    expectStartupPluginIdsCase({
+      config: createStartupConfig({
+        enabledPluginIds: ["demo-global-sidecar"],
+        allowPluginIds: ["demo-global-sidecar"],
+        noConfiguredChannels: true,
+        memorySlot: "none",
+      }),
+      expected: ["demo-global-sidecar"],
+    });
+  });
+
+  it("skips deprecated implicit startup sidecar fallback when activation.onStartup is false", () => {
+    expectStartupPluginIdsCase({
+      config: createStartupConfig({
+        enabledPluginIds: ["demo-global-startup-opt-out"],
+        allowPluginIds: ["demo-global-startup-opt-out"],
+        noConfiguredChannels: true,
+        memorySlot: "none",
+      }),
+      expected: [],
+    });
+  });
+
+  it("loads explicit startup plugins when activation.onStartup is true", () => {
+    expectStartupPluginIdsCase({
+      config: createStartupConfig({
+        enabledPluginIds: ["demo-global-explicit-startup"],
+        allowPluginIds: ["demo-global-explicit-startup"],
+        noConfiguredChannels: true,
+        memorySlot: "none",
+      }),
+      expected: ["demo-global-explicit-startup"],
+    });
+  });
+
   it("starts bundled sidecars selected by root config activation paths", () => {
     const rawConfig = {
       browser: {
diff --git a/src/plugins/gateway-startup-plugin-ids.ts b/src/plugins/gateway-startup-plugin-ids.ts
index c152735b83b..13890c3d6c8 100644
--- a/src/plugins/gateway-startup-plugin-ids.ts
+++ b/src/plugins/gateway-startup-plugin-ids.ts
@@ -65,8 +65,16 @@ function isGatewayStartupMemoryPlugin(plugin: InstalledPluginIndexRecord): boole
   return plugin.startup.memory;
 }
 
-function isGatewayStartupSidecar(plugin: InstalledPluginIndexRecord): boolean {
-  return plugin.startup.sidecar;
+/**
+ * @deprecated Compatibility fallback for plugins that do not declare
+ * `activation.onStartup`. Keep this path visible so we can remove it after
+ * plugin manifests migrate to explicit startup activation.
+ */
+function isDeprecatedLegacyImplicitStartupSidecar(params: {
+  plugin: InstalledPluginIndexRecord;
+  manifest: PluginManifestRecord | undefined;
+}): boolean {
+  return params.plugin.startup.sidecar && params.manifest?.activation?.onStartup === undefined;
 }
 
 function resolveGatewayStartupDreamingPluginIds(config: OpenClawConfig): Set<string> {
@@ -108,12 +116,26 @@ function resolveMemorySlotStartupPluginId(params: {
 
 function shouldConsiderForGatewayStartup(params: {
   plugin: InstalledPluginIndexRecord;
+  manifest: PluginManifestRecord | undefined;
   startupDreamingPluginIds: ReadonlySet<string>;
   memorySlotStartupPluginId?: string;
 }): boolean {
-  if (isGatewayStartupSidecar(params.plugin)) {
+  if (params.manifest?.activation?.onStartup === true) {
     return true;
   }
+  if (params.plugin.startup.sidecar) {
+    if (params.manifest?.activation?.onStartup === false) {
+      return false;
+    }
+    // Deprecated compatibility fallback: plugins without explicit startup
+    // activation metadata may still need startup import to register hooks or
+    // services. All plugins should declare activation.onStartup explicitly as
+    // we migrate away from implicit startup sidecar loading.
+    return isDeprecatedLegacyImplicitStartupSidecar({
+      plugin: params.plugin,
+      manifest: params.manifest,
+    });
+  }
   if (!isGatewayStartupMemoryPlugin(params.plugin)) {
     return false;
   }
@@ -399,15 +421,6 @@ export function resolveGatewayStartupPluginIdsFromRegistry(params: {
         });
         return activationState.enabled;
       }
-      if (
-        !shouldConsiderForGatewayStartup({
-          plugin,
-          startupDreamingPluginIds,
-          memorySlotStartupPluginId,
-        })
-      ) {
-        return false;
-      }
       if (
         canStartConfiguredRootPlugin({
           plugin,
@@ -419,6 +432,16 @@ export function resolveGatewayStartupPluginIdsFromRegistry(params: {
       ) {
         return true;
       }
+      if (
+        !shouldConsiderForGatewayStartup({
+          plugin,
+          manifest,
+          startupDreamingPluginIds,
+          memorySlotStartupPluginId,
+        })
+      ) {
+        return false;
+      }
       const activationState = resolveEffectivePluginActivationState({
         id: plugin.pluginId,
         origin: plugin.origin,