fix(test): wait for task completion before fetching documents

The testGetTaskDocumentsClient test was calling getTaskDocuments on a
task that hadn't completed yet, causing a JsonException when trying to
parse the NDJSON response. Wait for the task to finish first.

Also removes the redundant assertNotEmpty($documents) that phpstan
flagged as alreadyNarrowedType since the array is guaranteed non-empty
by the assertNotEmpty($lines) above.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

Author: mvanhorn

tests/Endpoints/TasksTest.php

@@ -55,6 +55,7 @@ public function testGetTaskDocumentsClient(): void
         $http->patch('/experimental-features', ['getTaskDocumentsRoute' => true]);
 
         $task = $this->index->updateDocuments(self::DOCUMENTS);
+        $task->wait();
 
         $stream = $this->client->getTaskDocuments($task->getTaskUid());
 
@@ -63,7 +64,6 @@ public function testGetTaskDocumentsClient(): void
         self::assertNotEmpty($lines, 'Stream should contain at least one NDJSON line');
 
         $documents = array_map(fn (string $line) => json_decode($line, true, 512, \JSON_THROW_ON_ERROR), $lines);
-        self::assertNotEmpty($documents);
         self::assertArrayHasKey('id', $documents[0], 'Each document should have an id field');
     }