Step 7: fortran-implementation

Read First

/AGENTS.md
/docs/ABAQUS_SUBROUTINE_AGENT_DESIGN.md
/docs/ARCHITECTURE.md
/docs/ADR.md
/.codex/skills/abaqus-fortran-tdd/SKILL.md
/docs/requirements/uel-3d-euler-beam.md
/docs/research/uel-3d-euler-beam-research.md
/docs/formulations/uel-3d-euler-beam.md
/docs/numerical-reviews/uel-3d-euler-beam.md
/docs/io-definitions/uel-3d-euler-beam.md
/docs/reference-models/uel-3d-euler-beam.md
/docs/build-test-reports/uel-3d-euler-beam-red.md
/tests/fortran/manifest.json

Task

Implement the minimum Fortran production code needed to make the approved no-Abaqus tests pass.

Use the production source layout approved in /docs/reference-models/uel-3d-euler-beam.md. If the layout is missing, prefer:

/src/fortran/kernels/uel_3d_euler_beam_kernel.f90 for testable calculation logic.
/src/fortran/abaqus/UEL_3D_EULER_BEAM.for for the thin Abaqus UEL wrapper.

Implementation scope:

Build the 3D Euler-Bernoulli local stiffness matrix.
Build and validate the local-to-global transformation.
Compute static internal force/residual contribution according to the approved Abaqus UEL sign convention.
Fill AMATRX and RHS for the supported LFLAGS subset.
Validate element length, orientation, and material/section properties.
Keep SVARS and ENERGY behavior consistent with the approved interface contract.
Keep Abaqus ABI wrapper thin; testable logic belongs in the kernel or no-Abaqus driver layer.

Follow RED -> GREEN -> VERIFY. Do not change the approved tests unless the upstream contract is objectively wrong; in that case mark the step blocked and explain which upstream document must change.

After GREEN evidence, create /docs/build-test-reports/uel-3d-euler-beam-green.md with commands, compiler mode, and summarized results.

Tests To Write First

Tests were written in step 6 and must already exist.
Add only narrowly scoped additional no-Abaqus tests if implementation uncovers an untested requirement. If added, run RED for the new test before code changes.

Acceptance Criteria

python -m unittest discover -s scripts -p "test_*.py"
python scripts/validate_fortran.py
python scripts/validate_reference_artifacts.py
python scripts/validate_workspace.py

The step is complete only when the no-Abaqus Fortran validation passes, or the step is marked blocked with concrete environment evidence such as missing Intel Fortran compiler.

Validation Notes

Do not create or modify external reference CSVs in this implementation step.
Update /phases/uel-3d-euler-beam/index.json step 7 with completed, error, or blocked and a concrete summary or reason.

Forbidden

Do not add JavaScript/TypeScript/npm fallback.
Do not run Abaqus analyses from this project.
Do not generate reference CSVs.
Do not bypass or weaken TDD guard behavior.
Do not break existing tests.

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