feat(gateway): accurate status read for apps and components

[bburda]

Summary

Make GET /{apps|components}/{id}/status report ready / notReady from real signals instead of
coarse ones. Read-only; the PUT lifecycle transitions stay 501 (actuation is tracked separately).

• App status: for a managed lifecycle node (one exposing lifecycle_msgs get_state and
  change_state), the status is read from the actual lifecycle state via a GetState service call
  (active is ready; any other state, or an unreachable/timed-out read, is notReady). This
  subsumes liveness, since a dead node's service is gone. Plain (unmanaged) nodes keep using
  App::is_online (presence in the ROS 2 graph), which is the best signal available for an
  unmanaged node.
• Component status: the synthetic host component (carrying host_metadata) is ready while the
  gateway is serving the request. Any other local component derives readiness from its hosted apps:
  it is notReady when it hosts apps and every one of them is offline (the subsystem is down), and
  ready otherwise, including when it hosts no apps. A single down hosted app is that app's own
  notReady, not enough to mark the component down. Remote components are unchanged (reached
  through aggregation forwarding).

The lifecycle read goes through a small injected LifecycleStateReader seam: a pure interface in
gateway_core (keeps the handler unit-testable with a stub and preserves core purity) plus a
gateway_ros2 implementation that calls GetState on a private node and private single-threaded
executor spun inline (mirrors the existing ros2_fault_service_transport pattern, so it never
blocks or races the gateway executor). A managed_lifecycle rclcpp_lifecycle demo node and an
integration test prove the path end to end.

The third LifecycleHandlers constructor parameter is defaulted, so existing call sites and
non-lifecycle apps are unchanged. No API break.

Issue

• closes Accurate status read for apps and components #454

Type

• New feature or tests

Testing

Unit (GTest):

• Pure helpers: active to ready, other state or nullopt to notReady; the lifecycle-service
  detector requires both get_state and change_state.
• Ros2LifecycleStateReader against an in-process GetState service: reads active / inactive,
  returns nullopt for an unreachable service.
• Handler: a managed node whose state is inactive reports notReady even though it is online
  (the discriminator); an active managed node reports ready; a plain node still uses is_online.
  Component reads return ready for the host component and a zero-app component, and notReady for
  a component that hosts apps which are all offline.

Integration (launch_testing):

• A managed_lifecycle node is launched and left unconfigured. It is present in the ROS 2 graph
  (so is_online alone would say ready), but GET /apps/managed_lifecycle/status returns
  notReady, proving the status is read from the lifecycle state via GetState. Tagged
  @verifies REQ_INTEROP_076.

clang-tidy is clean on the changed files.

Checklist

• Breaking changes are clearly described (none - additive; the new constructor parameter is defaulted)
• Tests were added or updated if needed
• Docs were updated if behavior or public API changed (design doc + README)

[Copilot]

Pull request overview

This PR makes GET /api/v1/{apps|components}/{id}/status reflect more accurate readiness signals: lifecycle-managed apps report readiness from lifecycle_msgs/srv/GetState, and local components are always ready while the gateway is reachable (remote components still rely on aggregation forwarding).

Changes:

• App status now uses lifecycle state when the app exposes both GetState and ChangeState services (active → ready, otherwise/timeout → notReady), falling back to is_online for unmanaged nodes.
• Component status (no provider) is simplified: any reachable local component returns ready independent of hosted app presence.
• Adds a LifecycleStateReader seam (core interface + ROS2 implementation), plus unit/integration tests and a new lifecycle demo node.

Reviewed changes

Copilot reviewed 19 out of 19 changed files in this pull request and generated 1 comment.

Show a summary per file

File	Description
src/ros2_medkit_integration_tests/test/features/test_lifecycle.test.py	Adds an integration test proving lifecycle-based status for an unconfigured lifecycle node.
src/ros2_medkit_integration_tests/ros2_medkit_test_utils/launch_helpers.py	Registers the new managed_lifecycle demo node for launch tests.
src/ros2_medkit_integration_tests/package.xml	Adds rclcpp_lifecycle dependency for the new demo node.
src/ros2_medkit_integration_tests/demo_nodes/managed_lifecycle_node.cpp	New lifecycle demo node (defaults to unconfigured) used by integration tests.
src/ros2_medkit_integration_tests/CMakeLists.txt	Builds/installs the managed_lifecycle demo executable and finds rclcpp_lifecycle.
src/ros2_medkit_gateway/include/ros2_medkit_gateway/core/status/lifecycle_state_reader.hpp	Introduces core lifecycle reader interface + helper declarations (core-pure seam).
src/ros2_medkit_gateway/src/core/status/lifecycle_status_helpers.cpp	Implements lifecycle-state → SOVD-status mapping and lifecycle-service detection helper.
src/ros2_medkit_gateway/include/ros2_medkit_gateway/ros2/status/ros2_lifecycle_state_reader.hpp	Declares ROS2 GetState-backed lifecycle reader implementation.
src/ros2_medkit_gateway/src/ros2/status/ros2_lifecycle_state_reader.cpp	Implements lifecycle state reads via a private node/executor and bounded timeout.
src/ros2_medkit_gateway/src/http/rest_server.cpp	Wires Ros2LifecycleStateReader into LifecycleHandlers at server construction.
src/ros2_medkit_gateway/include/ros2_medkit_gateway/core/http/handlers/lifecycle_handlers.hpp	Extends LifecycleHandlers constructor to accept an optional lifecycle reader (defaulted).
src/ros2_medkit_gateway/src/http/handlers/lifecycle_handlers.cpp	Updates default status logic for apps/components (lifecycle-aware apps; local components always ready).
src/ros2_medkit_gateway/test/test_lifecycle_status_helpers.cpp	Adds unit coverage for the helper mapping and lifecycle-service detection behavior.
src/ros2_medkit_gateway/test/test_ros2_lifecycle_state_reader.cpp	Adds unit coverage for Ros2LifecycleStateReader against an in-process GetState service.
src/ros2_medkit_gateway/test/test_lifecycle_handlers.cpp	Updates handler tests for new component semantics and adds stubbed-reader tests for lifecycle apps.
src/ros2_medkit_gateway/CMakeLists.txt	Adds new tests/targets and lifecycle_msgs dependency; registers lifecycle reader source in gateway_ros2.
src/ros2_medkit_gateway/package.xml	Adds lifecycle_msgs dependency required for GetState usage.
src/ros2_medkit_gateway/README.md	Updates user-facing docs for the new status derivation rules.
src/ros2_medkit_gateway/design/lifecycle.rst	Updates design doc to reflect lifecycle-based app status and new component readiness rule.