feat(pj_datastore): add ObjectStore::findTopic(dataset_id, name)

pj_datastore/include/pj_datastore/object_store.hpp

@@ -9,6 +9,7 @@
 #include <optional>
 #include <shared_mutex>
 #include <string>
+#include <string_view>
 #include <utility>
 #include <variant>
 #include <vector>
@@ -91,6 +92,11 @@ class ObjectStore {
 
   Expected<ObjectTopicId> registerTopic(const ObjectTopicDescriptor& descriptor);
 
+  // Resolve a topic id by (dataset_id, topic_name) without registering. Returns
+  // nullopt if no topic with that key exists. Used by hosts that need to bind a
+  // parser-side write surface to a topic the source already registered.
+  std::optional<ObjectTopicId> findTopic(DatasetId dataset_id, std::string_view topic_name) const;
+
   const ObjectTopicDescriptor& descriptor(ObjectTopicId id) const;
 
   std::vector<ObjectTopicId> listTopics() const;

pj_datastore/src/object_store.cpp

@@ -21,6 +21,17 @@ Expected<ObjectTopicId> ObjectStore::registerTopic(const ObjectTopicDescriptor&
   return id;
 }
 
+std::optional<ObjectTopicId> ObjectStore::findTopic(
+    DatasetId dataset_id, std::string_view topic_name) const {
+  std::shared_lock lock(store_mutex_);
+  for (const auto& [tid, series] : topics_) {
+    if (series->descriptor.dataset_id == dataset_id && series->descriptor.topic_name == topic_name) {
+      return tid;
+    }
+  }
+  return std::nullopt;
+}
+
 const ObjectTopicDescriptor& ObjectStore::descriptor(ObjectTopicId id) const {
   std::shared_lock lock(store_mutex_);
   const auto* s = findSeries(id);

pj_datastore/tests/object_store_test.cpp

@@ -48,6 +48,21 @@ TEST(ObjectStoreTest, SameNameDifferentDatasetOk) {
   EXPECT_NE(id1.id, id2_or->id);
 }
 
+TEST(ObjectStoreTest, FindTopicReturnsRegisteredId) {
+  ObjectStore store;
+  auto id = registerTestTopic(store, "cam/image");
+  auto found = store.findTopic(1, "cam/image");
+  ASSERT_TRUE(found.has_value());
+  EXPECT_EQ(found->id, id.id);
+}
+
+TEST(ObjectStoreTest, FindTopicMissingReturnsNullopt) {
+  ObjectStore store;
+  registerTestTopic(store, "cam/image");
+  EXPECT_FALSE(store.findTopic(1, "other/topic").has_value());
+  EXPECT_FALSE(store.findTopic(99, "cam/image").has_value());
+}
+
 TEST(ObjectStoreTest, ListTopics) {
   ObjectStore store;
   auto id1 = registerTestTopic(store, "topic_a");