Memory impact analysis gathered candidate platforms from all test files
(including variant test-*.yaml) but the CI build runs
test_build_components.py with --base-only, which only compiles base
test.<platform>.yaml files. It could therefore select a platform that no
changed component has a base test for, leaving the merged build with
nothing to compile and failing memory extraction.
Detect platforms using the same base-test discovery as the runner via a
shared get_component_test_platforms helper, and keep only components that
have a base test on the selected platform, falling back to the platform
supported by the most components when a hint picks an unbuildable one.
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