[rogeriojorge]

Summary

• return the Newton convergence flag from the midpoint nonlinear solve
• promote Optimistix's standard nonlinear_max_steps_reached status through Diffrax when Newton exhausts max_iters
• add a forced-exhaustion regression test

This is stacked on #18. It does not change converged midpoint solutions, Newton updates, GMRES, tolerances, or physics. It only stops an unconverged step from being labeled successful.

Motivation

ImplicitMidpoint.step currently returns diffrax.RESULTS.successful unconditionally, even when its Newton loop exits because max_iters was reached. Diffrax can only reject, stop, or expose such a failure if the solver returns the correct status.

Validation

• pytest -q: 5 passed
• ruff check spectrax/midpoint_solver.py tests/test_simulation_runs.py: passed
• the regression test uses max_iters=0 and verifies the exact promoted nonlinear_max_steps_reached result

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.

Files with missing lines	Coverage Δ
spectrax/midpoint_solver.py	98.03% <100.00%> (+0.08%)	⬆️

🚀 New features to boost your workflow:

• ❄️ Test Analytics: Detect flaky tests, report on failures, and find test suite problems.

[rogeriojorge]

Squashed into #18.