FESADev/phases/cpp-object-oriented-modular-refactoring/step16.md

Step 16: Generic SparseAssembler

과거 개발 계획이다. 아래 작업·상태·예시는 현재 실행 지시가 아니다. 현재 구현과 검증 한계는 기능 요약을 따른다.

읽어야 할 파일

• /AGENTS.md
• ../../docs/solver-core/README.md
• ../../docs/solver-core/README.md
• ../../docs/solver-core/README.md
• ../../docs/cpp-object-oriented-modular-refactoring/README.md
• Step 14 runtime Element contribution contract
• Step 15 DofManager and invariant contract
• /include/fesa/assembly/sparse_assembler.h, /src/fesa/assembly/sparse_assembler.cpp
• /include/fesa/assembly/parallel_for.h, /src/fesa/assembly/parallel_for.cpp
• /tests/unit/assembly/sparse_assembler_test.cpp
• /tests/unit/elements/euler_beam_3d_test.cpp
• /tests/unit/elements/mitc4_shell_test.cpp
• /phases/cpp-object-oriented-modular-refactoring/index.json
• /phases/cpp-object-oriented-modular-refactoring/step16.md

작업

Requirement R-PIPELINE-001의 assembly portion을 구현한다.

1. sparse_assembler_test.cpp에 C-ASSEMBLY-001을 먼저 추가한다. A fake runtime Element emits a known 2x2/3x3 local contribution with nonconsecutive full DOFs; tests verify exact CSR structure/values and repeated serial/TBB byte identity.
2. Current assembler's concrete storage branch fails to assemble the fake, providing RED.
3. Candidate API:

Result<SparseMatrix> SparseAssembler::Assemble(
    const ElementView& elements,
    const DofManager& dof_manager,
    ParallelFor& parallel_for) const;

4. Each stable element index owns one local COO buffer created from Element::ComputeStiffness() and DofManager scatter. Worker threads never mutate global CSR.
5. Concatenate and reduce in the existing stable tuple ordering. Do not replace exact fixed reduction with atomics, unordered containers or nondeterministic task completion order.
6. Remove B33/MITC4 concrete branches from SparseAssembler after both current elements flow through the interface.

Acceptance Criteria

과거 도구 실행·출력 지시는 정리했으며, 현재 검증 방법은 기능 요약을 따른다.

검증 및 상태 갱신

• RED fake contribution, exact CSR/repeated determinism, branch scan and full CTest를 summary에 기록한다.
• Any ordering/numeric regression is error; do not relax equality.
• 성공 시 현재 Step만 completed로 갱신한다.
• timestamp, retry, commit, advancement는 Executor 소유다.

금지사항

• Worker가 global CSR storage를 직접 수정하게 하지 마라.
• Floating-point reduction order or TBB policy를 변경하지 마라.
• Load assembly를 이 interface에 합치지 마라. 이유: separate responsibility.
• 직접 commit하거나 hook script를 수동 실행하지 마라.