Add explicit micronaut-jackson-databind dependency

pom.xml

@@ -248,6 +248,12 @@
       <scope>runtime</scope>
     </dependency>
 
+    <dependency>
+      <groupId>io.micronaut</groupId>
+      <artifactId>micronaut-jackson-databind</artifactId>
+      <version>4.4.6</version>
+    </dependency>
+
     <!-- required to fix transitive exclusion by google-cloud-bigtable -->
     <dependency>
       <groupId>org.apache.httpcomponents</groupId>

src/test/java/org/signal/registration/json/JsonMapperInjectionIntegrationTest.java

@@ -0,0 +1,36 @@
+package org.signal.registration.json;
+
+import static org.junit.jupiter.api.Assertions.assertNotNull;
+import static org.mockito.Mockito.mock;
+
+import com.google.i18n.phonenumbers.Phonenumber;
+import io.micronaut.json.JsonMapper;
+import io.micronaut.test.annotation.MockBean;
+import io.micronaut.test.extensions.junit5.annotation.MicronautTest;
+import jakarta.inject.Inject;
+import jakarta.inject.Named;
+import org.junit.jupiter.api.Test;
+import org.signal.registration.ratelimit.RateLimiter;
+import org.signal.registration.sender.SenderSelectionStrategy;
+
+@MicronautTest
+public class JsonMapperInjectionIntegrationTest {
+
+  @MockBean
+  SenderSelectionStrategy senderSelectionStrategy = mock(SenderSelectionStrategy.class);
+
+  @SuppressWarnings("unchecked")
+  @MockBean(named = "session-creation")
+  @Named("session-creation")
+  RateLimiter<Phonenumber.PhoneNumber> sessionCreationRateLimiter = mock(RateLimiter.class);
+
+  @Inject
+  JsonMapper jsonMapper;
+
+  @Test
+  void testJsonMapper() {
+    // This won't actually fail - the failure will happen in the beforeEach that looks for the bean
+    assertNotNull(jsonMapper, "a json mapper must be available for injection");
+  }
+
+}