ci(coverage): weekly cargo-llvm-cov workspace baseline (non-blocking)
Add the weekly line-coverage report (backlog#1153 infra-5):
- .github/workflows/coverage.yml — Sunday 07:00 UTC + workflow_dispatch;
runs `cargo llvm-cov nextest --workspace --exclude e2e_test` under
NEXTEST_PROFILE=ci (same scope and profile as the ci.yml test gate),
writes a per-crate line-coverage table to the job summary, uploads
lcov + JSON as a 90-day artifact, and routes scheduled failures
through the shared schedule-failure-issue action (ci-8). Runs only on
schedule/dispatch, so it can never become a required PR check.
- scripts/coverage_per_crate.py — stdlib-only aggregation of the
llvm-cov JSON export into the per-crate markdown table (worst-first,
TOTAL row), shared by the workflow and the local target.
- make coverage (.config/make/coverage.mak) — local equivalent with the
same command sequence; fails with install hints when cargo-llvm-cov
or cargo-nextest are missing. Listed in make help.
- docs/testing/README.md — Coverage section: cadence, where the table
and artifacts live, the trend-comparison method, and what is not
measured (doctests, e2e_test).
Zhengchao An