refactor(jmle): rebase Rust optimizer ownership contract on current main

[seonghobae]

Controlled clean-lineage replacement for #738 / issue #626

Protected main at creation is 933ce6cdfedbbf92b30e73ed25f0ef0d926357f2. Old Draft #738 is now stale and its exact writer handoffs were explicitly bound to predecessor bases. This replacement preserves its only unique delta—the fail-first JMLE optimizer-ownership contract—without transferring predecessor checks, reviews, approvals or mergeability.

Intentional RED

The first commit adds only tests/test_jmle_rust_optimizer_ownership.py. It requires installed public JMLE fitting under backend="rust" to complete for adam, lbfgs, and adam_lbfgs while sentinels replace legacy Python _adam / _lbfgs loops.

Valid RED must build/import the actual Rust/PyO3 package and reach optimizer ownership. Setup/import/fixture/changelog failure is not evidence.

Minimum GREEN

Move result-affecting JMLE optimizer arithmetic/control into mlsirm-core: Adam state/update and gradient clipping; L-BFGS history/two-loop/curvature/line-search; and adam_lbfgs phase sequencing/convergence needed to preserve the public result. Expose thin PyO3 transport; Python keeps validation, deterministic marshalling and reporting only. Missing/incompatible Rust capability must fail closed. Preserve public optimizer/model/seed/restart/objective/trace semantics unless a separate test-first scientific defect proves otherwise.

Add direct Rust/public parity and realistic aligned bias/MAE/RMSE/convergence recovery, complete docs/rustdoc, APA-7 method traceability and changelog only after GREEN. Keep CPU execution unless profiling justifies GPU. Require one unchanged final head with focused/full Python 3.12/3.14, Rust/PyO3, package/reinstall, existing GPU/fuzz, Security/SAST, exact coverage/docstrings and current-head review/governance gates.

Do not widen into MMLE, providers, dependencies/workflows/version/release, hosted state, or canonical #604 documentation. Advances #626 and supersedes #738 once this replacement is established.

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[seonghobae]

@opencode-agent address

Exact bounded implementation handoff for issue #626 / Draft #744. Re-read source head 48d050d046362d011e2e85bf2b55c3a57d5e88f1 and independently resolve protected main; proceed only while live main remains 933ce6cdfedbbf92b30e73ed25f0ef0d926357f2 and no other source writer has moved or claimed this branch. Preserve the fail-first commit/history; no force-push, destructive rebase, temporary writer workflow, documentation side branch, or unrelated cleanup.

RED is exact and production-boundary-valid on CI run 31515549519: editable Rust/PyO3 build and Rust-primary backend verification succeeded; Rust workspace, package/reinstall/release acceptance, GPU smoke, fuzz, Security Scan and SAST succeeded; Python 3.12 reached the full suite and failed only the three new ownership cases (adam, lbfgs, adam_lbfgs) because public JMLE executes Python _adam / _lbfgs arithmetic. Do not weaken/delete/skip those tests.

Implement the narrowest GREEN that makes Rust the production optimizer owner while preserving current public behavior:

1. Move Adam update/state/gradient clipping and L-BFGS history/two-loop/curvature/line-search plus adam_lbfgs phase sequencing/convergence into mlsirm-core; prefer one explicit Rust optimizer entrypoint/interface over Python callbacks that retain result-affecting arithmetic.
2. Expose thin PyO3 marshalling. Python may validate inputs/config, initialize/marshal deterministic state, select declared optimizer mode, and construct/report results; it must not retain an independent production Adam/L-BFGS numerical implementation as a fallback. Missing/incompatible core capability fails closed.
3. Preserve current FitConfig optimizer names, model/objective semantics, restart/seed behavior, iteration accounting/status/trace fields and numeric tolerances unless a separate realistic RED proves a defect. Do not touch MMLE.
4. Add direct Rust/Python field parity and focused Rust tests for Adam, L-BFGS and combined sequencing, including non-finite/line-search/curvature/convergence edge behavior already encoded by current Python tests. Preserve existing JMLE recovery; add/strengthen aligned bias/MAE/RMSE/convergence evidence where ownership changes expose a gap. Correlation alone is insufficient.
5. CPU-f64 only for this slice unless profiling demonstrates material GPU benefit. Add complete rustdoc/public docs, APA-7 optimizer source traceability and a changelog fragment only after GREEN.
6. Before any Ready transition: focused GREEN, complete relevant Python 3.12/3.14, Rust/PyO3, package/reinstall, existing GPU/fuzz, Security/SAST, exact coverage/docstrings, current-head automated review and repository governance on one unchanged head.

Stop writing immediately if source/base/writer identity changes. Update the PR body with exact new evidence; keep Draft while any gate remains.

[seonghobae]

Superseded by clean current-main Draft #751. Fresh compare proved #744 head 48d050d046362d011e2e85bf2b55c3a57d5e88f1 is four protected-main commits behind and its only unique path is tests/test_jmle_rust_optimizer_ownership.py. The exact prior writer handoff was explicitly conditional on protected main remaining 933ce6...; that condition is false, so it is stale. #751 recreates the exact ownership RED from protected main 8a56d7b1b024e18a5a96a94db4ede1bf6648ead1 on head 386fe8ca52ba9def121e050993cdb5317f37c184. No predecessor checks/reviews/approval transfer.