fix(gateway): plugin-provided entities own their bulk data and logs

[mfaferek93]

Closes #558.

Fault scoping and bulk-data scoping disagreed about what source an entity owns,
so a plugin-provided entity could not download the rosbag its own fault detail
advertised.

• The per-app rule (external -> bare entity id, checked before effective_fqn())
  moves out of the anonymous namespace into faults::resolve_app_source_fqn, and
  both collect_app_fqn and HandlerContext::resolve_app_host_fqns use it, so
  there is one definition of the rule rather than two that drift.
• compute_bulkdata_source_filters gains the two branches it was missing: an APP
  entity resolves through the same helper instead of falling through to an empty
  fqn, and an external COMPONENT owns its own id alongside its hosted apps -
  the same rule collect_component_app_fqns already applies for faults.

Logs go through the same resolver, so LogManager::get_logs is fixed with it.

Tests: ExternalAppResolvesToItsBareEntityId,
ExternalAppWithStrayBindingStillResolvesToItsId,
ComponentWithExternalAppsReturnsBareEntityIds, ExternalComponentAlsoOwnsItsOwnId.
Each fails on the pre-fix resolver. Full gateway suite: 4289 tests, 0 failures,
484 skipped; clang-format clean.

One behaviour change worth naming: a component that hosts external apps no longer
falls through to the fqn / namespace_path prefix filter, because that
fall-through only fires on an empty source set. That affects a manifest component
whose bags are sourced from a ROS namespace and which also hosts external apps.

[Copilot]

Pull request overview

This PR fixes inconsistent “entity -> reporting source” resolution between fault scoping and the HTTP-side bulk-data/log scoping so that plugin-provided (external) entities correctly “own” their rosbags and logs under their bare entity IDs.

Changes:

• Extracted the external-app source resolution rule into faults::resolve_app_source_fqn() and reused it from HandlerContext and bulk-data scoping.
• Extended bulk-data source filter computation to handle APP entities via the shared resolver, and to include an external component’s own ID alongside its hosted apps.
• Added targeted unit tests covering external apps/components and their expected source filters.

Reviewed changes

Copilot reviewed 7 out of 7 changed files in this pull request and generated 1 comment.

Show a summary per file

File	Description
src/ros2_medkit_gateway/test/test_handler_context.cpp	Adds tests ensuring external apps resolve to bare entity IDs in resolve_app_host_fqns.
src/ros2_medkit_gateway/test/test_bulkdata_handlers.cpp	Adds tests validating bulk-data source filters for external apps/components.
src/ros2_medkit_gateway/src/http/handlers/handler_context.cpp	Updates app-host source resolution to use faults::resolve_app_source_fqn().
src/ros2_medkit_gateway/src/http/handlers/bulkdata_handlers.cpp	Updates bulk-data source filter computation for APP and external COMPONENT cases.
src/ros2_medkit_gateway/src/core/faults/fault_scope.cpp	Introduces resolve_app_source_fqn() and reuses it in fault scoping.
src/ros2_medkit_gateway/include/ros2_medkit_gateway/http/handlers/handler_context.hpp	Updates documentation to describe source resolution semantics (external apps -> bare ID).
src/ros2_medkit_gateway/include/ros2_medkit_gateway/core/faults/fault_scope.hpp	Declares resolve_app_source_fqn() (note: header doc needs a small terminology update per review comment).

Comments suppressed due to low confidence (1)

src/ros2_medkit_gateway/include/ros2_medkit_gateway/core/faults/fault_scope.hpp:40

• The doc comment for resolve_entity_source_fqns still says it resolves “App effective-FQNs”, but APP resolution now goes through resolve_app_source_fqn() (external apps resolve to their bare entity id, and unbound non-external apps resolve to nothing). The header comment should match the actual semantics so callers don’t accidentally rely on “effective FQN only” behavior.

/// Resolve the set of App effective-FQNs that fall within an entity's scope by
/// walking the entity cache:
///   - APP: the app's own effective FQN
///   - COMPONENT: every hosted app's FQN
///   - AREA: every app under the area and its (recursive) subareas

[bburda]

Additional findings outside the diff:

• Could you also look at the APP branch in log_handlers.cpp (the last else)? It queries {entity.fqn}, which is "" for an external app, so GET /apps/<external_app>/logs returns nothing even though the entries are stored under the entity id. The logs claim in the description holds for functions, areas and components only.
• Could you add the external component's own id in the COMPONENT branch there as well? Right now such a component owns its rosbags but not its logs.
• Please check the cyclic subscription samplers in gateway_node.cpp. They still resolve with a raw effective_fqn() and use a private filter_faults_by_fqns, so a subscription on an external app returns "Entity no longer available" every cycle, and an external component gets an empty fault list.
• Could you update the docs in this PR? docs/api/rest.rst says component logs query child apps "by exact FQN", and bulkdata_handlers.hpp still documents the old APP and COMPONENT behaviour of the function you changed.
• Would you mind adding an integration test for the reported 404? test_external_app_fault_rollup.test.py and external_app_fault_manifest.yaml already set up an external app, so reporting a fault there and downloading the advertised bulk_data_uri would cover it.

[mfaferek93]

The outside-diff findings, all on the branch now:

• App logs resolve through the shared rule (bare id for external apps), with the exact-fqn fallback kept when the resolver yields nothing - 7669b29.
• The external component's own id is in the log scope, and component/area logs merge the namespace query instead of losing it.
• Both cyclic samplers use the shared resolvers plus faults::filter_faults_by_sources; the private filter_faults_by_fqns copy is deleted. A cyclic subscription on an external app now returns the fault list instead of 'Entity no longer available'.
• rest.rst, bulkdata_handlers.hpp and fault_scope.hpp describe the one rule.
• test_external_app_fault_rollup.test.py now captures a real bag and downloads every advertised URI (app, area, function) - the area assert fails on the pre-fix binary.

Agreed on the last note: the namespace filter never matched an app source in the listing, so the visible change is only the stricter download check.