Tests: mock channel registry bundled fallback

Keep the registry fallback unit test on a minimal bundled fixture instead of loading the real Google Chat plugin. Doctor capability metadata remains covered by the doctor channel capability tests.

src/channels/plugins/registry.test.ts

@@ -1,9 +1,19 @@
-import { afterEach, describe, expect, it } from "vitest";
+import { afterEach, describe, expect, it, vi } from "vitest";
 import { createEmptyPluginRegistry } from "../../plugins/registry-empty.js";
 import type { PluginRegistry } from "../../plugins/registry.js";
 import { resetPluginRuntimeStateForTest, setActivePluginRegistry } from "../../plugins/runtime.js";
 import { getChannelPlugin, listChannelPlugins } from "./registry.js";
 
+vi.mock("./bundled.js", () => ({
+  getBundledChannelPlugin: (id: string) =>
+    id === "fallback"
+      ? {
+          id: "fallback",
+          meta: { label: "fallback" },
+        }
+      : undefined,
+}));
+
 function withMalformedChannels(registry: PluginRegistry): PluginRegistry {
   const malformed = { ...registry } as PluginRegistry;
   (malformed as { channels?: unknown }).channels = undefined;
@@ -25,11 +35,7 @@ describe("listChannelPlugins", () => {
   it("falls back to bundled channel plugins for direct lookups before registry bootstrap", () => {
     setActivePluginRegistry(createEmptyPluginRegistry());
 
-    expect(getChannelPlugin("googlechat")?.doctor).toMatchObject({
-      dmAllowFromMode: "nestedOnly",
-      groupAllowFromFallbackToAllowFrom: false,
-      warnOnEmptyGroupSenderAllowlist: false,
-    });
+    expect(getChannelPlugin("fallback")?.meta.label).toBe("fallback");
   });
 
   it("rebuilds channel lookups when the active registry object changes without a version bump", () => {