CI eqdata-fixture drift detection for trlib/eqlib/totlib equivalence tests

[k-yoshimi]

Context

PR #195 (#192) and PR #199 introduced committed eqdata binary fixtures under:

• python/trlib/tests/fixtures/eqdata.{ITER01,TST-2}
• python/eqlib/tests/fixtures/eqdata.{ITER01,TST-2}
• python/totlib/tests/fixtures/{eqdata-HT6M,eqdata.demo2014} (PR test(totlib): mirror trlib/eqlib eqdata fallback to fix silent SKIP #199)

These are exact copies of test_run/test_output/<case>/eqdata* produced by the standalone eq.x / tot/tot Fortran binaries at the time of commit. They act as the silent-SKIP safety net for Layer 1 (1e-10) equivalence tests in the three Phase L Python wrappers.

Risk

If the upstream eq.x / tot/tot binary's EQSAVE format or numerics drift (e.g. compiler upgrade, eq subroutine refactor), the committed fixtures could go stale silently: the test would PASS against the OLD baseline + OLD fixture, but the staging-path eqdata (which the test prefers when present) would differ. CI staging currently catches "fixture missing" via test -s, but not "fixture stale".

Surfaced as low-probability LOW by in-house code reviewer on PR #199; same risk applies symmetrically to all 3 libs.

Possible remediations (not yet decided)

• A. CI checksum gate: at the end of the CI staging step, cmp (or md5) the CI-generated eqdata against the committed fixture; fail loudly on mismatch.
• B. Periodic regen workflow: tie into PR ci+eq+tr: workflow_dispatch baseline regen + graphics-stubs (#197) #198's workflow_dispatch regen path (see .github/workflows/regen-baselines.yml) so fixtures can be refreshed on a cadence or on demand.
• C. Acceptance: declare the eq physics layer too stable for this to matter in practice. Reconsider only when a real drift is observed.

Out of scope

• The metrics.json baselines under test_run/baselines/ are NOT covered by this issue — they're regenerated more rigorously via PR ci+eq+tr: workflow_dispatch baseline regen + graphics-stubs (#197) #198's CI workflow.

Source

In-house code reviewer's LOW L2 finding on PR #199 (totlib eqdata fallback polish).