feat(adapters): allow external plugins to override built-in adapters

Previously external adapters matching a built-in type were skipped with
a warning. Now they override the built-in, so plugin developers can ship
improved versions of existing adapters (e.g. hermes-paperclip-adapter)
without removing the built-in fallback for users who haven't installed
the plugin.

server/src/__tests__/adapter-registry.test.ts

@@ -55,4 +55,36 @@ describe("server adapter registry", () => {
       "Unknown adapter type: external_test",
     );
   });
+
+  it("allows external plugin to override a built-in adapter type", () => {
+    // claude_local is always built-in
+    const builtIn = findServerAdapter("claude_local");
+    expect(builtIn).not.toBeNull();
+
+    const plugin: ServerAdapterModule = {
+      type: "claude_local",
+      execute: async () => ({
+        exitCode: 0,
+        signal: null,
+        timedOut: false,
+      }),
+      testEnvironment: async () => ({
+        adapterType: "claude_local",
+        status: "pass",
+        checks: [],
+        testedAt: new Date(0).toISOString(),
+      }),
+      models: [{ id: "plugin-model", label: "Plugin Override" }],
+      supportsLocalAgentJwt: false,
+    };
+
+    registerServerAdapter(plugin);
+
+    // Plugin wins
+    const resolved = requireServerAdapter("claude_local");
+    expect(resolved).toBe(plugin);
+    expect(resolved.models).toEqual([
+      { id: "plugin-model", label: "Plugin Override" },
+    ]);
+  });
 });

server/src/adapters/registry.ts

@@ -234,11 +234,11 @@ const externalAdaptersReady: Promise<void> = (async () => {
   try {
     const externalAdapters = await buildExternalAdapters();
     for (const externalAdapter of externalAdapters) {
-      if (BUILTIN_ADAPTER_TYPES.has(externalAdapter.type)) {
-        console.warn(
-          `[paperclip] Skipping external adapter "${externalAdapter.type}" — conflicts with built-in adapter`,
+      const overriding = BUILTIN_ADAPTER_TYPES.has(externalAdapter.type);
+      if (overriding) {
+        console.log(
+          `[paperclip] External adapter \"${externalAdapter.type}\" overrides built-in adapter`,
         );
-        continue;
       }
       adaptersByType.set(
         externalAdapter.type,