fix(updates): drop redundant id guard in register seed path + CHANGELOG

Callers of UpdateManager::register_update (update_handlers.cpp:108)
already validate that metadata["id"] is a non-empty string before
invoking the manager, so the outer `if (metadata.contains("id") &&
metadata["id"].is_string())` check wrapping the seed block could never
hit its else branch with any in-tree caller. Replace it with a direct
metadata.at("id").get<std::string>() so the precondition is expressed
explicitly and .at() would throw clearly if the contract were ever
broken. The inner `!state_ptr` idempotency check is kept, matching the
pattern in start_prepare / run_prepare.

Add a CHANGELOG.rst entry under Unreleased documenting the observable
contract change: GET /api/v1/updates/{id}/status returns 200 pending
immediately after POST /api/v1/updates, whereas previously 404 was
returned for registered-but-idle packages. 404 is now reserved for
packages that are not registered.

Author: bburda

src/ros2_medkit_gateway/CHANGELOG.rst

@@ -5,6 +5,10 @@ Changelog for package ros2_medkit_gateway
 Unreleased
 ----------
 
+**Fixes:**
+
+* ``GET /api/v1/updates/{id}/status`` no longer returns ``404`` for a registered-but-idle package; ``POST /api/v1/updates`` now seeds a ``pending`` status, so the endpoint returns ``200 {"status": "pending"}`` immediately after registration. ``404`` is reserved for packages that are not registered. Clients that used ``404`` as a signal for "registered but nothing started yet" must adapt (`#378 <https://github.com/selfpatch/ros2_medkit/issues/378>`_)
+
 **Features:**
 
 * Plugin API version bumped to v7. Adds ``PluginContext::notify_entities_changed(EntityChangeScope)`` lifecycle hook for plugins that mutate the entity surface at runtime; default no-op keeps v6 source code compiling unchanged against v7 headers. Binary compatibility is not provided: the plugin loader uses a strict equality check on ``plugin_api_version()``, so out-of-tree plugins must be recompiled (`#376 <https://github.com/selfpatch/ros2_medkit/issues/376>`_)

src/ros2_medkit_gateway/src/updates/update_manager.cpp

@@ -104,18 +104,17 @@ tl::expected<void, UpdateError> UpdateManager::register_update(const nlohmann::j
   // consumers (UpdatesDashboard) gate action buttons on the status field
   // and won't render "Prepare" when the status query fails, so a newly-
   // registered update would otherwise be stuck from the frontend's view.
-  // Preserve an already-seeded state if a concurrent caller raced us
-  // through the backend (shouldn't happen with current backends, but the
-  // defensive check keeps the method idempotent).
-  if (metadata.contains("id") && metadata["id"].is_string()) {
-    const auto id = metadata["id"].get<std::string>();
-    std::lock_guard<std::mutex> lock(mutex_);
-    auto & state_ptr = states_[id];
-    if (!state_ptr) {
-      state_ptr = std::make_unique<PackageState>();
-      state_ptr->phase = UpdatePhase::None;
-      state_ptr->status = UpdateStatusInfo{UpdateStatus::Pending, std::nullopt, std::nullopt, std::nullopt};
-    }
+  // Callers (update_handlers.cpp) validate id presence + non-empty string
+  // before invoking register_update, so metadata.at("id") is guaranteed to
+  // hold a string at this point. The !state_ptr check matches the
+  // idempotent-seed pattern used in start_prepare / run_prepare.
+  const auto id = metadata.at("id").get<std::string>();
+  std::lock_guard<std::mutex> lock(mutex_);
+  auto & state_ptr = states_[id];
+  if (!state_ptr) {
+    state_ptr = std::make_unique<PackageState>();
+    state_ptr->phase = UpdatePhase::None;
+    state_ptr->status = UpdateStatusInfo{UpdateStatus::Pending, std::nullopt, std::nullopt, std::nullopt};
   }
   return {};
 }