test(inference): refresh Rust observed-information ownership RED on current main

[seonghobae]

Clean-lineage replacement for #734 / issue #625

Protected main advanced materially after #734's fail-first evidence and its OpenCode handoff was explicitly bound to old protected main 7b57f77747b9a9bd911660c76b1be0ca0dc2d145. Fresh compare proves #734 is now 30 protected-main commits behind and its only unique delta is tests/test_observed_information_rust_ownership.py. This Draft recreates that exact ownership RED directly on current protected main without transferring predecessor checks/reviews.

Exact identity

• protected base: 8a56d7b1b024e18a5a96a94db4ede1bf6648ead1;
• exact source head: 9938913de69cefb4c40ca9af3569d6f55be98ed7;
• compare to protected main: direct one-commit descendant, ahead 1 / behind 0;
• changed path: tests/test_observed_information_rust_ownership.py only.

Intentional RED

The tests install unmistakable proposed compiled-core sentinels and require public observed_information() to return the Rust-owned Hessian matrix and public second_order_test() to return Rust-owned positive-definiteness/eigenvalue evidence. Valid RED must occur after normal Rust/PyO3 package setup and backend resolution because the current public path still computes those numerics in Python. Setup/import/fixture/changelog failure is not evidence.

Minimum GREEN

Move dense central finite-difference observed-information/Hessian construction plus result-affecting symmetry semantics and public second-order eigenvalue/positive-definiteness arithmetic into mlsirm-core; expose the thinnest PyO3 boundary. Python retains bounded input/config validation, immutable marshalling and result transport only; missing/incompatible compiled capability fails closed. Preserve current penalized negative-log-likelihood estimand, packing/order, step and tolerance/error semantics unless a separately test-first scientific defect proves otherwise. Reassess O(p²) dense memory/evaluation limits from measured resource evidence before acceptance. Add direct Rust↔public parity/property tests, caller immutability, stable non-reflective errors and uncertainty/SE calibration evidence appropriate to the public claim; algebraic parity or correlation alone is insufficient. CPU f64 remains reference; benchmark before GPU.

After GREEN add complete rustdoc/docstrings, APA-7 equation/source doctoring and authoritative changelog material, then require exact changed-production statement/branch coverage and one unchanged head passing Python 3.12/3.14, Rust/PyO3, package/reinstall, existing GPU/fuzz, Security Scan, SAST and current-head review/governance gates. Canonical Architecture/TRD/ADR/UML/ERD/traceability remains solely #604/#621.

Keep Draft. Once this replacement is established, #734 is superseded. Advances #625.

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[seonghobae]

Superseded by GREEN #758 observed-information ownership. Closing RED test-only refresh.