Tier 1 tests

Tier 1 is the fast subsystem sentinel layer. Each target should answer one coarse question: is this subsystem basically alive?

Rules:

• Prefer one kitchen-sink case over a broad corpus.
• Prefer dedicated fixtures under test/tier1/kitchen/ over sampling old corpora. KIT_CORPUS_LIST remains available for focused Tier 2 probes.
• Keep output in build/test/tier1/logs/.
• Keep heavy platform, ecosystem, selfhost, and full corpus sweeps in Tier 2/3.
• If a Tier 1 sentinel fails, run the matching focused suite from test/TESTMAP.md.

The cross sentinel is build/link-only. It covers the supported cross matrix and reports missing provisioned sysroots or SDKs as SKIP, which fails Tier 1 by default because it means the requested coverage did not run. Narrow it with T1_CROSS_TARGETS=<selector> when needed; use KIT_TEST_ALLOW_SKIP=1 only for an explicitly permissive local probe.

make test runs Tier 1 in parallel. The previous broad default is available as make test-full.