fix(provider-webdriver): load the diagnostics emitter on demand so the eager closure holds

The static import of @agent-device/host-kit/diagnostics in the transport
added two modules to provider-webdriver's eager import closure (51 vs 49
at the merge-base). The unsupported-route diagnostic is a rare path, so
reportRouteUnsupported now imports the emitter inside the function; the
classifier stays synchronous. The closure walker counts only static and
top-level dynamic imports, so the budget holds. The host-kit dependency
stays declared because the dynamic import still resolves the package.

The diagnostic assertions wait for the event with vi.waitFor.

Mutations checked:
- remove the reportRouteUnsupported call: 6 tests fail (5 classifier
  rows and the terminate-app fallback test).

Author: thymikee

packages/provider-webdriver/src/webdriver-mutation-resend.test.ts

@@ -1,7 +1,7 @@
 import assert from 'node:assert/strict';
 import fs from 'node:fs';
 import path from 'node:path';
-import { afterEach, test } from 'vitest';
+import { afterEach, test, vi } from 'vitest';
 import {
   countDiagnosticEventsByPhase,
   withDiagnosticsScope,
@@ -252,7 +252,9 @@ test('an unsupported app-termination route falls back to the sibling route once'
 
   await withDiagnosticsScope({ command: 'close' }, async () => {
     await client.terminateApp('com.example.app');
-    assert.equal(countDiagnosticEventsByPhase(['webdriver_route_unsupported']), 1);
+    await vi.waitFor(() =>
+      assert.equal(countDiagnosticEventsByPhase(['webdriver_route_unsupported']), 1),
+    );
   });
 
   assert.equal(sendsTo('POST /session/:id/appium/device/terminate_app'), 1);

packages/provider-webdriver/src/webdriver-transport.test.ts

@@ -1,7 +1,7 @@
 import assert from 'node:assert/strict';
 import http from 'node:http';
 import net, { type AddressInfo } from 'node:net';
-import { afterEach, test } from 'vitest';
+import { afterEach, test, vi } from 'vitest';
 import {
   countDiagnosticEventsByPhase,
   withDiagnosticsScope,
@@ -298,9 +298,11 @@ for (const { status, body, unsupported } of ROUTE_ANSWERS) {
           return true;
         },
       );
-      assert.equal(
-        countDiagnosticEventsByPhase(['webdriver_route_unsupported']),
-        unsupported ? 1 : 0,
+      await vi.waitFor(() =>
+        assert.equal(
+          countDiagnosticEventsByPhase(['webdriver_route_unsupported']),
+          unsupported ? 1 : 0,
+        ),
       );
     });
   });

packages/provider-webdriver/src/webdriver-transport.ts

@@ -1,5 +1,4 @@
 import { setTimeout as sleep } from 'node:timers/promises';
-import { emitDiagnostic } from '@agent-device/host-kit/diagnostics';
 import { AppError } from '@agent-device/kernel/errors';
 import { agentDeviceRequestHeaders } from './request-headers.ts';
 import { basicAuthHeader, trimLeadingSlash, withTrailingSlash } from './webdriver-utils.ts';
@@ -203,9 +202,7 @@ export class WebDriverTransport {
     const payload = text ? parseJsonResponse(text) : {};
     if (ok) return readWebDriverValue(payload);
     const error = webdriverError(status, payload);
-    if (isWebDriverRouteUnsupported(error)) {
-      emitDiagnostic({ phase: WEBDRIVER_ROUTE_UNSUPPORTED_REASON, data: { method, path, status } });
-    }
+    if (isWebDriverRouteUnsupported(error)) reportRouteUnsupported({ method, path, status });
     throw error;
   }
 
@@ -371,6 +368,18 @@ function isUnsupportedRouteAnswer(status: number, payload: unknown): boolean {
   return UNSUPPORTED_ROUTE_STATUSES.has(status);
 }
 
+/**
+ * Records the answer in the request diagnostics. The emitter loads on demand because this path is
+ * rare and the transport sits in the provider's eager import closure.
+ */
+function reportRouteUnsupported(data: { method: string; path: string; status: number }): void {
+  void import('@agent-device/host-kit/diagnostics')
+    .then(({ emitDiagnostic }) =>
+      emitDiagnostic({ phase: WEBDRIVER_ROUTE_UNSUPPORTED_REASON, data }),
+    )
+    .catch(() => undefined);
+}
+
 /**
  * The driver answered that it does not implement the route, so nothing was dispatched and a
  * sibling route for the same action may be tried. A timeout or 5xx is not this answer: the first