FESADev/phases/1-linear-static-mitc4/step12.md

Step 12: assembly-reaction-recovery

Sprint Contract

Objective

Implement assembly of element stiffness/load contributions into full and reduced system data while preserving full-space data for reactions.

Required Reading

• /AGENTS.md
• /PROGRESS.md
• /PLAN.md
• /docs/README.md
• /docs/HARNESS_ENGINEERING.md
• /docs/ARCHITECTURE.md
• /docs/ADR.md
• /docs/NUMERICAL_CONVENTIONS.md
• /docs/RESULTS_SCHEMA.md
• /phases/1-linear-static-mitc4/step6.md
• /phases/1-linear-static-mitc4/step7.md
• /phases/1-linear-static-mitc4/step11.md

Scope

• Assemble global stiffness and load data from active elements and nodal loads.
• Create reduced free-DOF systems using DofManager mappings.
• Preserve or reconstruct full-space K_full, F_full, and U_full data needed for RF = K_full * U_full - F_full.
• Add assembly diagnostics for missing contributions and singular-prone untouched DOFs where detectable.

Allowed Files

• include/**
• src/**
• tests/**
• PLAN.md
• PROGRESS.md
• phases/1-linear-static-mitc4/index.json

Explicit Non-Goals

• Do not implement the full LinearStaticAnalysis orchestration here.
• Do not compute reactions from reduced quantities only.
• Do not add pressure loads, nonzero prescribed displacement, or nonlinear residual assembly.

Tests To Write First

• Assembly tests for simple element/load contributions into full and reduced matrices/vectors.
• Constrained elimination tests using known DOF mappings.
• Full-vector reaction recovery tests using RF = K_full * U_full - F_full.
• Missing contribution or untouched free DOF diagnostic tests.

Reference Artifacts

• None required. RF reference CSV is not available; use internal equilibrium/reaction tests for this step.

Acceptance Commands

python scripts/validate_workspace.py

Evaluator Checklist

• Full-space reaction data is preserved.
• Reduced system assembly matches constrained/free DOF mapping.
• Reaction tests use full vectors and the documented sign convention.
• Unsupported loads and nonlinear behavior are not introduced.

Handoff Requirements

• Record assembly and RF recovery behavior in PROGRESS.md.
• Update PLAN.md if R-010 remains unresolved or becomes resolved.
• Update the matching phase index entry: use completed with a one-line summary, or blocked with blocked_reason, or error with error_message.

Verification

1. Run the acceptance command.
2. Inspect reaction tests for full-vector recovery.

Do Not

• Do not allow reduced-system convenience to overwrite the documented RF convention.