fix: pass harness prompts through stdin

CMakeLists.txt

@@ -0,0 +1,12 @@
+cmake_minimum_required(VERSION 3.20)
+
+project(FESA LANGUAGES CXX)
+
+file(GLOB_RECURSE FESA_CORE_SOURCES CONFIGURE_DEPENDS src/fesa/*.cpp)
+
+add_library(fesa_core STATIC ${FESA_CORE_SOURCES})
+target_compile_features(fesa_core PUBLIC cxx_std_17)
+target_include_directories(fesa_core PUBLIC ${CMAKE_CURRENT_SOURCE_DIR}/src)
+
+enable_testing()
+add_subdirectory(tests)

docs/build-test-reports/solver-core-skeleton.md

@@ -0,0 +1,80 @@
+# Solver Core Skeleton Build/Test Report
+
+## Metadata
+- phase: solver-core-skeleton
+- scope: C++ skeleton classes only
+- status: passed
+
+## Commands Run
+
+```powershell
+python -m unittest scripts.test_header_declaration_only
+```
+
+- exit_code: 0
+- summary: Solver headers contain declarations only; function bodies are implemented in `.cpp` files.
+
+```powershell
+python -m unittest discover -s scripts -p "test_*.py"
+```
+
+- exit_code: 0
+- summary: 99 Python Harness tests passed.
+
+```powershell
+python scripts/validate_workspace.py
+```
+
+- exit_code: 0
+- summary: CMake configure, MSVC Debug build, and full CTest suite passed.
+
+```powershell
+ctest --test-dir build/msvc-debug --output-on-failure -C Debug -R solver_core_skeleton_integration_test
+```
+
+- exit_code: 0
+- summary: `solver_core_skeleton_integration_test` passed.
+
+## CTest Tests Added
+
+- `harness_smoke_test`
+- `core_diagnostic_test`
+- `core_ids_test`
+- `core_primitives_test`
+- `core_status_test`
+- `model_analysis_step_test`
+- `model_boundary_condition_test`
+- `model_domain_test`
+- `model_element_test`
+- `model_load_test`
+- `model_material_test`
+- `model_node_test`
+- `model_property_test`
+- `analysis_model_view_test`
+- `dof_manager_dof_key_test`
+- `dof_manager_numbering_test`
+- `analysis_state_vectors_test`
+- `analysis_flow_linear_static_analysis_test`
+- `analysis_flow_template_test`
+- `results_containers_test`
+- `solver_core_skeleton_integration_test`
+
+## Structural Tests Added
+
+- `scripts.test_header_declaration_only`
+
+## Build Structure
+
+- `fesa_core` now builds as a static library from `src/fesa/**/*.cpp`.
+- Solver headers under `src/fesa/**/*.hpp` declare functions only; method bodies live in matching `.cpp` translation units.
+
+## Known Limitations
+
+- No element stiffness, residual, tangent, or stress recovery calculation is implemented.
+- No material law evaluation is implemented.
+- No sparse assembly implementation is implemented beyond `DofManager` sparse pattern ownership.
+- No linear solver backend is implemented.
+- No HDF5 writer or reader is implemented.
+- No Abaqus `.inp` parser is implemented.
+- No reference comparison against Abaqus CSV artifacts is implemented.
+- `LinearStaticAnalysis` currently prepares the analysis model, DOF map, and zero-valued state only.

phases/euler-beam-3d/index.json

@@ -0,0 +1,99 @@
+{
+  "project": "FESA Structural Solver",
+  "phase": "euler-beam-3d",
+  "steps": [
+    {
+      "step": 0,
+      "name": "requirements-baseline",
+      "status": "pending",
+      "allowed_paths": [
+        "docs/requirements/euler-beam-3d.md"
+      ]
+    },
+    {
+      "step": 1,
+      "name": "research-evidence",
+      "status": "pending",
+      "allowed_paths": [
+        "docs/research/euler-beam-3d-research.md"
+      ]
+    },
+    {
+      "step": 2,
+      "name": "formulation-spec",
+      "status": "pending",
+      "allowed_paths": [
+        "docs/formulations/euler-beam-3d-formulation.md"
+      ]
+    },
+    {
+      "step": 3,
+      "name": "numerical-review",
+      "status": "pending",
+      "allowed_paths": [
+        "docs/numerical-reviews/euler-beam-3d-review.md"
+      ]
+    },
+    {
+      "step": 4,
+      "name": "io-reference-contract",
+      "status": "pending",
+      "allowed_paths": [
+        "docs/io-definitions/euler-beam-3d-io.md",
+        "docs/reference-models/euler-beam-3d-reference-models.md"
+      ]
+    },
+    {
+      "step": 5,
+      "name": "implementation-plan",
+      "status": "pending",
+      "allowed_paths": [
+        "docs/implementation-plans/euler-beam-3d-implementation-plan.md"
+      ]
+    },
+    {
+      "step": 6,
+      "name": "model-beam-topology",
+      "status": "pending",
+      "allowed_paths": [
+        "src/fesa/model/element.hpp",
+        "src/fesa/model/element.cpp",
+        "tests/unit/model_element_test.cpp"
+      ]
+    },
+    {
+      "step": 7,
+      "name": "local-stiffness-kernel",
+      "status": "pending",
+      "allowed_paths": [
+        "src/fesa/elements/",
+        "tests/unit/euler_beam_3d_*_test.cpp"
+      ]
+    },
+    {
+      "step": 8,
+      "name": "global-transform-recovery",
+      "status": "pending",
+      "allowed_paths": [
+        "src/fesa/elements/",
+        "tests/unit/euler_beam_3d_*_test.cpp"
+      ]
+    },
+    {
+      "step": 9,
+      "name": "build-test-report",
+      "status": "pending",
+      "allowed_paths": [
+        "docs/build-test-reports/euler-beam-3d-build-test.md"
+      ]
+    },
+    {
+      "step": 10,
+      "name": "release-readiness-note",
+      "status": "pending",
+      "allowed_paths": [
+        "docs/releases/euler-beam-3d-release.md"
+      ]
+    }
+  ]
+}

phases/euler-beam-3d/step0.md

@@ -0,0 +1,63 @@
+# Step 0: requirements-baseline
+
+## Read These Files First
+
+Read the following files before editing:
+
+- `/AGENTS.md`
+- `/docs/PRD.md`
+- `/docs/ARCHITECTURE.md`
+- `/docs/ADR.md`
+- `/docs/requirements/README.md`
+
+## Task
+
+Create `/docs/requirements/euler-beam-3d.md` for a kernel-first 3D Euler-Bernoulli beam feature.
+
+Scope the first implementable increment narrowly:
+
+- two-node, straight, prismatic, small-displacement 3D Euler-Bernoulli beam element
+- six mechanical DOFs per node in this order: `ux, uy, uz, rx, ry, rz`
+- linear elastic section constants: `E`, `G`, `A`, `J`, `Iy`, `Iz`
+- local and global 12x12 stiffness matrix support
+- local and global element end-force recovery from nodal displacement vectors
+- no shear deformation, warping, end releases, offsets, distributed loads, mass matrix, geometric stiffness, nonlinear kinematics, dynamics, or thermal coupling in this increment
+- no Abaqus reference CSV generation in this increment
+- no full Abaqus compatibility claim
+
+The document must contain:
+
+- metadata: `feature_id: euler-beam-3d`, owner agent, status
+- explicit assumptions and non-goals
+- `must` requirements with stable IDs such as `EB3D-REQ-001`
+- verification quantities: displacement DOFs, reactions/end forces, stiffness symmetry, rigid body modes, local/global transformation consistency
+- acceptance criteria that distinguish kernel completion from full solver release readiness
+- open issues for parser integration, reference artifact availability, and full end-to-end assembly
+
+Do not create C++ files in this step.
+
+## Tests To Write First
+
+- No C++ test is required in this documentation-only step.
+- Still run the harness validation commands in the acceptance criteria.
+
+## Acceptance Criteria
+
+```powershell
+python -m unittest discover -s scripts -p "test_*.py"
+python scripts/validate_workspace.py
+```
+
+## Verification Notes
+
+1. Confirm the requirements do not claim full Abaqus compatibility.
+2. Confirm each `must` requirement has an acceptance criterion or a downstream verification hook.
+3. Update `phases/euler-beam-3d/index.json` step 0:
+   - success: `"status": "completed"`, `"summary": "3D Euler beam kernel requirements baseline added"`
+   - failure after retries: `"status": "error"`, `"error_message": "<specific error>"`
+   - blocked: `"status": "blocked"`, `"blocked_reason": "<specific reason>"`
+
+## Forbidden
+
+- Do not create or modify reference CSV files.
+- Do not modify source or test files.

phases/euler-beam-3d/step1.md

@@ -0,0 +1,60 @@
+# Step 1: research-evidence
+
+## Read These Files First
+
+Read the following files before editing:
+
+- `/AGENTS.md`
+- `/docs/PRD.md`
+- `/docs/ARCHITECTURE.md`
+- `/docs/ADR.md`
+- `/docs/requirements/euler-beam-3d.md`
+- `/docs/research/README.md`
+
+## Task
+
+Create `/docs/research/euler-beam-3d-research.md`.
+
+Summarize the evidence needed to implement the approved kernel-first 3D Euler-Bernoulli beam increment. The document must be implementation-oriented and must include:
+
+- supported theory: straight prismatic Euler-Bernoulli beam, axial, torsion, and two uncoupled bending planes
+- assumptions and applicability limits
+- local DOF ordering and sign convention used by the planned matrix
+- source reliability classification
+- benchmark-style checks that do not require external reference solver execution:
+  - local stiffness symmetry
+  - axial-only response
+  - torsion-only response
+  - bending about local `y`
+  - bending about local `z`
+  - rigid body translation/rotation zero internal forces in local coordinates
+  - global transform identity for an axis-aligned beam
+- risks: orientation vector parallel to element axis, near-zero length, nonpositive section constants, ill-conditioning for very slender elements
+
+If internet access or a FEM wiki is used, cite sources briefly. Do not include long copyrighted excerpts.
+
+Do not create C++ files in this step.
+
+## Tests To Write First
+
+- No C++ test is required in this documentation-only step.
+
+## Acceptance Criteria
+
+```powershell
+python -m unittest discover -s scripts -p "test_*.py"
+python scripts/validate_workspace.py
+```
+
+## Verification Notes
+
+1. Confirm the research document ties each source or theory point to a planned implementation check.
+2. Confirm unresolved items are listed as risks or open issues instead of silently assumed.
+3. Update `phases/euler-beam-3d/index.json` step 1:
+   - success: `"status": "completed"`, `"summary": "3D Euler beam research evidence added"`
+   - failure after retries: `"status": "error"`, `"error_message": "<specific error>"`
+   - blocked: `"status": "blocked"`, `"blocked_reason": "<specific reason>"`
+
+## Forbidden
+
+- Do not modify source, test, reference, or I/O contract files.

phases/euler-beam-3d/step10.md

@@ -0,0 +1,60 @@
+# Step 10: release-readiness-note
+
+## Read These Files First
+
+Read the following files before editing:
+
+- `/AGENTS.md`
+- `/docs/PRD.md`
+- `/docs/ADR.md`
+- `/docs/releases/README.md`
+- `/docs/requirements/euler-beam-3d.md`
+- `/docs/io-definitions/euler-beam-3d-io.md`
+- `/docs/reference-models/euler-beam-3d-reference-models.md`
+- `/docs/build-test-reports/euler-beam-3d-build-test.md`
+
+## Task
+
+Create `/docs/releases/euler-beam-3d-release.md`.
+
+This is a readiness note, not a release approval. It must state:
+
+- status: `not-release-ready-kernel-increment-complete` unless all upstream gates and reference artifacts somehow exist
+- completed scope: local/global stiffness and end-force kernel for two-node 3D Euler-Bernoulli beam
+- missing for full feature release:
+  - parser implementation for the approved Abaqus subset
+  - section/property semantic model integration
+  - assembler/static solver integration
+  - HDF5 result emission for beam quantities
+  - stored Abaqus reference artifacts
+  - reference comparison report
+  - physics sanity report
+- known limitations from requirements
+- next recommended phase or phase dependencies
+
+Do not change source or tests in this step.
+
+## Tests To Write First
+
+- No C++ test is required in this documentation-only step.
+
+## Acceptance Criteria
+
+```powershell
+python -m unittest discover -s scripts -p "test_*.py"
+python scripts/validate_workspace.py
+```
+
+## Verification Notes
+
+1. Confirm the note does not claim full release readiness.
+2. Confirm all missing gates are explicit.
+3. Update `phases/euler-beam-3d/index.json` step 10:
+   - success: `"status": "completed"`, `"summary": "3D Euler beam release readiness note added"`
+   - failure after retries: `"status": "error"`, `"error_message": "<specific error>"`
+   - blocked: `"status": "blocked"`, `"blocked_reason": "<specific reason>"`
+
+## Forbidden
+
+- Do not create or modify reference artifacts.
+- Do not modify source, tests, requirements, formulations, or I/O contracts.

phases/euler-beam-3d/step2.md

@@ -0,0 +1,63 @@
+# Step 2: formulation-spec
+
+## Read These Files First
+
+Read the following files before editing:
+
+- `/AGENTS.md`
+- `/docs/PRD.md`
+- `/docs/ARCHITECTURE.md`
+- `/docs/ADR.md`
+- `/docs/requirements/euler-beam-3d.md`
+- `/docs/research/euler-beam-3d-research.md`
+- `/docs/formulations/README.md`
+
+## Task
+
+Create `/docs/formulations/euler-beam-3d-formulation.md`.
+
+The formulation must define the implementation contract for the C++ kernel. Include:
+
+- local coordinate system: local `x` from node 1 to node 2; local `y` from the user orientation vector projected normal to local `x`; local `z = x cross y`
+- local DOF order: `[u1, v1, w1, rx1, ry1, rz1, u2, v2, w2, rx2, ry2, rz2]`
+- section constants: `E`, `G`, `A`, `J`, `Iy`, `Iz`
+- local 12x12 stiffness matrix terms for:
+  - axial: `EA/L`
+  - torsion: `GJ/L`
+  - bending in local `x-y` using `EIz`
+  - bending in local `x-z` using `EIy`
+- transformation matrix convention and global stiffness equation `K_global = T^T K_local T`
+- end-force recovery equation `f_local = K_local u_local`
+- validation tolerances for unit tests, using deterministic double comparisons
+- singular and invalid input handling:
+  - zero or near-zero length throws `std::invalid_argument`
+  - nonpositive `E`, `G`, `A`, `J`, `Iy`, or `Iz` throws `std::invalid_argument`
+  - orientation vector parallel to beam axis throws `std::invalid_argument`
+
+Use compact matrices and named scalar coefficients so the implementation step can transcribe directly.
+
+Do not create C++ files in this step.
+
+## Tests To Write First
+
+- No C++ test is required in this documentation-only step.
+
+## Acceptance Criteria
+
+```powershell
+python -m unittest discover -s scripts -p "test_*.py"
+python scripts/validate_workspace.py
+```
+
+## Verification Notes
+
+1. Confirm the matrix is symmetric by construction.
+2. Confirm local/global transformation convention is unambiguous.
+3. Update `phases/euler-beam-3d/index.json` step 2:
+   - success: `"status": "completed"`, `"summary": "3D Euler beam formulation contract added"`
+   - failure after retries: `"status": "error"`, `"error_message": "<specific error>"`
+   - blocked: `"status": "blocked"`, `"blocked_reason": "<specific reason>"`
+
+## Forbidden
+
+- Do not modify requirements, source, tests, or reference artifacts.

phases/euler-beam-3d/step3.md

@@ -0,0 +1,56 @@
+# Step 3: numerical-review
+
+## Read These Files First
+
+Read the following files before editing:
+
+- `/AGENTS.md`
+- `/docs/PRD.md`
+- `/docs/ARCHITECTURE.md`
+- `/docs/ADR.md`
+- `/docs/requirements/euler-beam-3d.md`
+- `/docs/research/euler-beam-3d-research.md`
+- `/docs/formulations/euler-beam-3d-formulation.md`
+- `/docs/numerical-reviews/README.md`
+
+## Task
+
+Create `/docs/numerical-reviews/euler-beam-3d-review.md`.
+
+Review the formulation for implementation readiness. The review must include:
+
+- dimension and units check for each stiffness coefficient
+- symmetry and rigid body mode expectations
+- local axis construction risks
+- positive semi-definite local stiffness expectation before constraints
+- test obligations before production code
+- known numerical limits for slender beams and very small section constants
+- pass/fail verdict for kernel implementation planning
+
+If the formulation is not ready, mark the document status as `needs-upstream-decision` and update this phase step as blocked with a concrete reason.
+
+Do not create C++ files in this step.
+
+## Tests To Write First
+
+- No C++ test is required in this documentation-only step.
+
+## Acceptance Criteria
+
+```powershell
+python -m unittest discover -s scripts -p "test_*.py"
+python scripts/validate_workspace.py
+```
+
+## Verification Notes
+
+1. Confirm the review does not change requirements or formulation.
+2. Confirm implementation-owned risks are turned into concrete tests.
+3. Update `phases/euler-beam-3d/index.json` step 3:
+   - success: `"status": "completed"`, `"summary": "3D Euler beam numerical review added"`
+   - failure after retries: `"status": "error"`, `"error_message": "<specific error>"`
+   - blocked: `"status": "blocked"`, `"blocked_reason": "<specific reason>"`
+
+## Forbidden
+
+- Do not modify requirements, formulation, source, tests, or reference artifacts.

phases/euler-beam-3d/step4.md

@@ -0,0 +1,68 @@
+# Step 4: io-reference-contract
+
+## Read These Files First
+
+Read the following files before editing:
+
+- `/AGENTS.md`
+- `/docs/PRD.md`
+- `/docs/ARCHITECTURE.md`
+- `/docs/ADR.md`
+- `/docs/requirements/euler-beam-3d.md`
+- `/docs/formulations/euler-beam-3d-formulation.md`
+- `/docs/numerical-reviews/euler-beam-3d-review.md`
+- `/docs/io-definitions/README.md`
+- `/docs/reference-models/README.md`
+
+## Task
+
+Create two documents:
+
+- `/docs/io-definitions/euler-beam-3d-io.md`
+- `/docs/reference-models/euler-beam-3d-reference-models.md`
+
+The I/O contract must describe the planned Abaqus subset without claiming it is implemented in this kernel increment:
+
+- element keyword mapping candidate: two-node beam topology equivalent to Abaqus `B31`
+- section keyword candidate: beam section constants sufficient for `A`, `J`, `Iy`, `Iz`, `E`, and `G`
+- orientation data requirement for constructing local axes
+- boundary/load DOFs: `1..6` map to `ux, uy, uz, rx, ry, rz`
+- HDF5 output quantities expected after solver integration: nodal displacement, reaction, element internal force, stress placeholders if stress recovery is later approved
+- unsupported input cases and diagnostics
+
+The reference model contract must list required future models without generating artifacts:
+
+- axial cantilever bar-as-beam
+- torsion cantilever
+- bending cantilever about local `y`
+- bending cantilever about local `z`
+- skew-oriented beam transform check
+
+For each future model, specify expected files under `reference/<model-id>/` and which CSV quantities are required. State that Abaqus reference CSVs must not be generated or modified in this phase.
+
+Do not create C++ files in this step.
+
+## Tests To Write First
+
+- No C++ test is required in this documentation-only step.
+
+## Acceptance Criteria
+
+```powershell
+python -m unittest discover -s scripts -p "test_*.py"
+python scripts/validate_workspace.py
+```
+
+## Verification Notes
+
+1. Confirm reference artifacts are specified, not created.
+2. Confirm unsupported parser or solver paths are explicit open issues.
+3. Update `phases/euler-beam-3d/index.json` step 4:
+   - success: `"status": "completed"`, `"summary": "3D Euler beam I/O and reference model contracts added"`
+   - failure after retries: `"status": "error"`, `"error_message": "<specific error>"`
+   - blocked: `"status": "blocked"`, `"blocked_reason": "<specific reason>"`
+
+## Forbidden
+
+- Do not create or modify files under `/reference/`.
+- Do not modify source or tests.

phases/euler-beam-3d/step5.md

@@ -0,0 +1,75 @@
+# Step 5: implementation-plan
+
+## Read These Files First
+
+Read the following files before editing:
+
+- `/AGENTS.md`
+- `/docs/PRD.md`
+- `/docs/ARCHITECTURE.md`
+- `/docs/ADR.md`
+- `/docs/SOLVER_AGENT_DESIGN.md`
+- `/docs/implementation-plans/README.md`
+- `/docs/requirements/euler-beam-3d.md`
+- `/docs/research/euler-beam-3d-research.md`
+- `/docs/formulations/euler-beam-3d-formulation.md`
+- `/docs/numerical-reviews/euler-beam-3d-review.md`
+- `/docs/io-definitions/euler-beam-3d-io.md`
+- `/docs/reference-models/euler-beam-3d-reference-models.md`
+- `/src/fesa/model/element.hpp`
+- `/tests/unit/model_element_test.cpp`
+
+## Task
+
+Create `/docs/implementation-plans/euler-beam-3d-implementation-plan.md`.
+
+The implementation plan must be ready for C++ TDD work and must include:
+
+- readiness check for requirements, research, formulation, numerical review, I/O, reference model contract
+- explicit kernel-first implementation scope
+- tasks matching the remaining phase steps:
+  - model beam topology
+  - local stiffness kernel
+  - global transform and end-force recovery
+  - build/test report
+  - release readiness note
+- test IDs and RED/GREEN conditions for each production change
+- candidate files:
+  - `src/fesa/model/element.hpp`
+  - `src/fesa/model/element.cpp`
+  - `tests/unit/model_element_test.cpp`
+  - `src/fesa/elements/euler_beam_3d.hpp`
+  - `src/fesa/elements/euler_beam_3d.cpp`
+  - `tests/unit/euler_beam_3d_local_stiffness_test.cpp`
+  - `tests/unit/euler_beam_3d_transform_recovery_test.cpp`
+- CTest commands:
+  - `ctest --test-dir build/msvc-debug --output-on-failure -C Debug -R model_element_test`
+  - `ctest --test-dir build/msvc-debug --output-on-failure -C Debug -R euler_beam_3d_local_stiffness_test`
+  - `ctest --test-dir build/msvc-debug --output-on-failure -C Debug -R euler_beam_3d_transform_recovery_test`
+- acceptance traceability from requirements to tests
+
+Do not create C++ files in this step.
+
+## Tests To Write First
+
+- No C++ test is required in this documentation-only step.
+
+## Acceptance Criteria
+
+```powershell
+python -m unittest discover -s scripts -p "test_*.py"
+python scripts/validate_workspace.py
+```
+
+## Verification Notes
+
+1. Confirm every production file named in the plan has a related test.
+2. Confirm the plan does not ask Implementation Agent to change requirements, formulation, I/O contracts, reference artifacts, or tolerance policies.
+3. Update `phases/euler-beam-3d/index.json` step 5:
+   - success: `"status": "completed"`, `"summary": "3D Euler beam implementation plan added"`
+   - failure after retries: `"status": "error"`, `"error_message": "<specific error>"`
+   - blocked: `"status": "blocked"`, `"blocked_reason": "<specific reason>"`
+
+## Forbidden
+
+- Do not modify source, tests, reference artifacts, or CMake files.

phases/euler-beam-3d/step6.md

@@ -0,0 +1,79 @@
+# Step 6: model-beam-topology
+
+## Read These Files First
+
+Read the following files before editing:
+
+- `/AGENTS.md`
+- `/docs/ARCHITECTURE.md`
+- `/docs/ADR.md`
+- `/docs/implementation-plans/euler-beam-3d-implementation-plan.md`
+- `/src/fesa/model/element.hpp`
+- `/src/fesa/model/element.cpp`
+- `/tests/unit/model_element_test.cpp`
+
+## Task
+
+Use TDD to add a semantic model topology for a two-node 3D beam.
+
+Required production behavior:
+
+- Add `beam2` to `fesa::model::ElementTopology`.
+- Preserve existing `truss2`, `bar2`, and `unknown` behavior.
+- Do not store equation IDs on `Element`.
+- Do not add section constants to `Element` in this step.
+
+## Tests To Write First
+
+Modify `/tests/unit/model_element_test.cpp` first.
+
+Add a failing assertion that constructs an element with:
+
+- id `ElementId{10}`
+- topology `ElementTopology::beam2`
+- node ids `{NodeId{1}, NodeId{2}}`
+- property id `PropertyId{7}`
+
+The test must verify:
+
+- `element.topology() == ElementTopology::beam2`
+- `element.node_ids().size() == 2`
+- existing `bar2` behavior still works or the test still covers it
+
+RED command:
+
+```powershell
+ctest --test-dir build/msvc-debug --output-on-failure -C Debug -R model_element_test
+```
+
+Expected RED: compile failure because `ElementTopology::beam2` is not defined.
+
+Then implement the minimal enum addition.
+
+GREEN command:
+
+```powershell
+ctest --test-dir build/msvc-debug --output-on-failure -C Debug -R model_element_test
+```
+
+## Acceptance Criteria
+
+```powershell
+ctest --test-dir build/msvc-debug --output-on-failure -C Debug -R model_element_test
+python -m unittest discover -s scripts -p "test_*.py"
+python scripts/validate_workspace.py
+```
+
+## Verification Notes
+
+1. Confirm the test failed before editing production code.
+2. Confirm no unrelated model refactor was made.
+3. Update `phases/euler-beam-3d/index.json` step 6:
+   - success: `"status": "completed"`, `"summary": "beam2 model topology added with unit test"`
+   - failure after retries: `"status": "error"`, `"error_message": "<specific error>"`
+   - blocked: `"status": "blocked"`, `"blocked_reason": "<specific reason>"`
+
+## Forbidden
+
+- Do not create parser code.
+- Do not add beam stiffness code in this step.

phases/euler-beam-3d/step7.md

@@ -0,0 +1,110 @@
+# Step 7: local-stiffness-kernel
+
+## Read These Files First
+
+Read the following files before editing:
+
+- `/AGENTS.md`
+- `/docs/ARCHITECTURE.md`
+- `/docs/ADR.md`
+- `/docs/formulations/euler-beam-3d-formulation.md`
+- `/docs/numerical-reviews/euler-beam-3d-review.md`
+- `/docs/implementation-plans/euler-beam-3d-implementation-plan.md`
+
+Also read any files created by previous steps in this phase.
+
+## Task
+
+Use TDD to create the local 12x12 stiffness kernel for the 3D Euler-Bernoulli beam.
+
+Create:
+
+- `/src/fesa/elements/euler_beam_3d.hpp`
+- `/src/fesa/elements/euler_beam_3d.cpp`
+- `/tests/unit/euler_beam_3d_local_stiffness_test.cpp`
+
+Required API:
+
+```cpp
+namespace fesa::elements {
+
+using Vector12 = std::array<double, 12>;
+using Matrix12 = std::array<double, 144>;
+
+struct EulerBeam3DSection {
+    double young_modulus;
+    double shear_modulus;
+    double area;
+    double torsion_constant;
+    double second_moment_y;
+    double second_moment_z;
+};
+
+Matrix12 euler_beam_3d_local_stiffness(double length, const EulerBeam3DSection& section);
+Vector12 euler_beam_3d_local_end_forces(double length,
+                                        const EulerBeam3DSection& section,
+                                        const Vector12& local_displacements);
+
+} // namespace fesa::elements
+```
+
+Implementation rules:
+
+- Matrix storage is row-major: index `(row, col)` is `row * 12 + col`.
+- Validate `length > 0` and all section constants are positive; throw `std::invalid_argument` otherwise.
+- Use only C++17 standard library.
+- Do not introduce an external linear algebra dependency.
+- Do not edit CMake files; source and test globs should pick up new files.
+
+## Tests To Write First
+
+Create `/tests/unit/euler_beam_3d_local_stiffness_test.cpp` before production code.
+
+Test behavior:
+
+- For `L = 2.0`, `E = 210.0`, `G = 80.0`, `A = 3.0`, `J = 4.0`, `Iy = 5.0`, `Iz = 6.0`, verify representative matrix entries:
+  - axial: `K(0,0) = EA/L`, `K(0,6) = -EA/L`, `K(6,6) = EA/L`
+  - torsion: `K(3,3) = GJ/L`, `K(3,9) = -GJ/L`, `K(9,9) = GJ/L`
+  - local `x-y` bending uses `EIz`: `K(1,1) = 12*E*Iz/L^3`, `K(1,5) = 6*E*Iz/L^2`, `K(5,5) = 4*E*Iz/L`
+  - local `x-z` bending uses `EIy`: `K(2,2) = 12*E*Iy/L^3`, `K(2,4) = -6*E*Iy/L^2`, `K(4,4) = 4*E*Iy/L`
+- Verify all entries are symmetric within `1.0e-10`.
+- Verify `euler_beam_3d_local_end_forces` returns `K * u` for a displacement vector with at least three nonzero components.
+- Verify invalid length and nonpositive section constants throw `std::invalid_argument`.
+
+RED command:
+
+```powershell
+ctest --test-dir build/msvc-debug --output-on-failure -C Debug -R euler_beam_3d_local_stiffness_test
+```
+
+Expected RED: test executable missing or compile failure because the header/API does not exist.
+
+Then implement the minimal API.
+
+GREEN command:
+
+```powershell
+ctest --test-dir build/msvc-debug --output-on-failure -C Debug -R euler_beam_3d_local_stiffness_test
+```
+
+## Acceptance Criteria
+
+```powershell
+ctest --test-dir build/msvc-debug --output-on-failure -C Debug -R euler_beam_3d_local_stiffness_test
+python -m unittest discover -s scripts -p "test_*.py"
+python scripts/validate_workspace.py
+```
+
+## Verification Notes
+
+1. Confirm RED failed before production code was added.
+2. Confirm no parser, assembly, or results writer code was changed.
+3. Update `phases/euler-beam-3d/index.json` step 7:
+   - success: `"status": "completed"`, `"summary": "local 3D Euler beam stiffness and local end-force kernel added"`
+   - failure after retries: `"status": "error"`, `"error_message": "<specific error>"`
+   - blocked: `"status": "blocked"`, `"blocked_reason": "<specific reason>"`
+
+## Forbidden
+
+- Do not add shear deformation or Timoshenko terms.
+- Do not modify reference artifacts.

phases/euler-beam-3d/step8.md

@@ -0,0 +1,97 @@
+# Step 8: global-transform-recovery
+
+## Read These Files First
+
+Read the following files before editing:
+
+- `/AGENTS.md`
+- `/docs/ARCHITECTURE.md`
+- `/docs/ADR.md`
+- `/docs/formulations/euler-beam-3d-formulation.md`
+- `/docs/numerical-reviews/euler-beam-3d-review.md`
+- `/docs/implementation-plans/euler-beam-3d-implementation-plan.md`
+- `/src/fesa/elements/euler_beam_3d.hpp`
+- `/src/fesa/elements/euler_beam_3d.cpp`
+- `/tests/unit/euler_beam_3d_local_stiffness_test.cpp`
+
+## Task
+
+Use TDD to add local/global transformation and global end-force recovery to the 3D Euler-Bernoulli beam kernel.
+
+Extend the API in `/src/fesa/elements/euler_beam_3d.hpp`:
+
+```cpp
+using Vector3 = std::array<double, 3>;
+
+struct EulerBeam3DGeometry {
+    Vector3 node1;
+    Vector3 node2;
+    Vector3 orientation;
+};
+
+Matrix12 euler_beam_3d_global_stiffness(const EulerBeam3DGeometry& geometry,
+                                        const EulerBeam3DSection& section);
+Vector12 euler_beam_3d_global_end_forces(const EulerBeam3DGeometry& geometry,
+                                         const EulerBeam3DSection& section,
+                                         const Vector12& global_displacements);
+```
+
+Implementation rules:
+
+- local `x` is normalized `node2 - node1`
+- local `y` is the normalized projection of `orientation` onto the plane normal to local `x`
+- local `z = x cross y`
+- use the same 3x3 rotation block for translational and rotational DOFs
+- compute `K_global = T^T K_local T`
+- compute global end forces by transforming global displacements to local, recovering local forces, then transforming forces back to global
+- throw `std::invalid_argument` for zero-length element, zero orientation vector, or orientation parallel to the beam axis
+
+## Tests To Write First
+
+Create `/tests/unit/euler_beam_3d_transform_recovery_test.cpp` before production code.
+
+Test behavior:
+
+- Axis-aligned beam from `(0,0,0)` to `(2,0,0)` with orientation `(0,1,0)` gives global stiffness equal to local stiffness.
+- A rotated beam preserves stiffness symmetry.
+- A rigid global translation vector produces near-zero global end forces.
+- A simple global axial extension on the axis-aligned beam produces equal and opposite axial end forces.
+- Parallel orientation vector throws `std::invalid_argument`.
+
+RED command:
+
+```powershell
+ctest --test-dir build/msvc-debug --output-on-failure -C Debug -R euler_beam_3d_transform_recovery_test
+```
+
+Expected RED: test executable missing or compile failure because the transform API does not exist.
+
+Then implement the minimal API.
+
+GREEN command:
+
+```powershell
+ctest --test-dir build/msvc-debug --output-on-failure -C Debug -R euler_beam_3d_transform_recovery_test
+```
+
+## Acceptance Criteria
+
+```powershell
+ctest --test-dir build/msvc-debug --output-on-failure -C Debug -R "euler_beam_3d_(local_stiffness|transform_recovery)_test"
+python -m unittest discover -s scripts -p "test_*.py"
+python scripts/validate_workspace.py
+```
+
+## Verification Notes
+
+1. Confirm RED failed before production code was added.
+2. Confirm local stiffness tests still pass.
+3. Update `phases/euler-beam-3d/index.json` step 8:
+   - success: `"status": "completed"`, `"summary": "global transform and global end-force recovery added for 3D Euler beam"`
+   - failure after retries: `"status": "error"`, `"error_message": "<specific error>"`
+   - blocked: `"status": "blocked"`, `"blocked_reason": "<specific reason>"`
+
+## Forbidden
+
+- Do not add assembly or solver integration in this step.
+- Do not modify reference artifacts.

phases/euler-beam-3d/step9.md

@@ -0,0 +1,57 @@
+# Step 9: build-test-report
+
+## Read These Files First
+
+Read the following files before editing:
+
+- `/AGENTS.md`
+- `/docs/build-test-reports/README.md`
+- `/docs/implementation-plans/euler-beam-3d-implementation-plan.md`
+- `/src/fesa/elements/euler_beam_3d.hpp`
+- `/src/fesa/elements/euler_beam_3d.cpp`
+- `/tests/unit/euler_beam_3d_local_stiffness_test.cpp`
+- `/tests/unit/euler_beam_3d_transform_recovery_test.cpp`
+
+## Task
+
+Create `/docs/build-test-reports/euler-beam-3d-build-test.md`.
+
+The report must record:
+
+- feature id
+- changed files observed for this phase
+- command log summary with exit codes and short evidence tails
+- validation results for:
+  - harness self-test
+  - CMake configure/build
+  - CTest
+  - feature-specific tests
+- failure classification if anything failed
+- explicit statement that this report does not approve reference verification or release readiness
+
+Do not change source or tests in this step.
+
+## Tests To Write First
+
+- No C++ test is required in this documentation-only step.
+
+## Acceptance Criteria
+
+```powershell
+ctest --test-dir build/msvc-debug --output-on-failure -C Debug -R "model_element_test|euler_beam_3d_(local_stiffness|transform_recovery)_test"
+python -m unittest discover -s scripts -p "test_*.py"
+python scripts/validate_workspace.py
+```
+
+## Verification Notes
+
+1. Record actual command exit codes and concise output evidence.
+2. If validation fails for an environment reason, mark the report `needs-environment-fix` and update this phase step as blocked.
+3. Update `phases/euler-beam-3d/index.json` step 9:
+   - success: `"status": "completed"`, `"summary": "3D Euler beam build/test report added"`
+   - failure after retries: `"status": "error"`, `"error_message": "<specific error>"`
+   - blocked: `"status": "blocked"`, `"blocked_reason": "<specific reason>"`
+
+## Forbidden
+
+- Do not modify source, tests, requirements, formulations, I/O contracts, or reference artifacts.

phases/index.json

@@ -2,6 +2,10 @@
   "phases": [
     {
       "dir": "solver-core-skeleton",
+      "status": "completed"
+    },
+    {
+      "dir": "euler-beam-3d",
       "status": "pending"
     }
   ]

phases/solver-core-skeleton/index.json

@@ -9,79 +9,92 @@
       "allowed_paths": [
         "CMakeLists.txt",
         "tests/"
-      ]
+      ],
+      "started_at": "2026-06-12T02:09:10+0900",
+      "summary": "CMake/CTest bootstrap with fesa_core interface target and smoke test",
+      "status": "completed"
     },
     {
       "step": 1,
       "name": "core-primitives",
-      "status": "pending",
+      "status": "completed",
       "allowed_paths": [
         "src/fesa/core/",
         "tests/unit/core_*_test.cpp"
-      ]
+      ],
+      "summary": "Core ID, diagnostic, and status primitives added with tests"
     },
     {
       "step": 2,
       "name": "domain-model-entities",
-      "status": "pending",
+      "status": "completed",
       "allowed_paths": [
         "src/fesa/model/",
         "tests/unit/model_*_test.cpp"
-      ]
+      ],
+      "summary": "Model entities and Domain ownership API added with tests"
     },
     {
       "step": 3,
       "name": "analysis-model-view",
-      "status": "pending",
+      "status": "completed",
       "allowed_paths": [
         "src/fesa/analysis/",
         "tests/unit/analysis_model_*_test.cpp"
-      ]
+      ],
+      "summary": "AnalysisModel step view added without Domain copies"
     },
     {
       "step": 4,
       "name": "dof-manager",
-      "status": "pending",
+      "status": "completed",
       "allowed_paths": [
         "src/fesa/fem/",
         "tests/unit/dof_manager_*_test.cpp"
-      ]
+      ],
+      "summary": "DofManager deterministic numbering and constrained/free mapping added"
     },
     {
       "step": 5,
       "name": "analysis-state",
-      "status": "pending",
+      "status": "completed",
       "allowed_paths": [
         "src/fesa/analysis/",
         "tests/unit/analysis_state_*_test.cpp"
-      ]
+      ],
+      "summary": "AnalysisState vector ownership and residual update added"
     },
     {
       "step": 6,
       "name": "analysis-template-flow",
-      "status": "pending",
+      "status": "completed",
       "allowed_paths": [
         "src/fesa/analysis/",
         "tests/unit/analysis_flow_*_test.cpp"
-      ]
+      ],
+      "summary": "Analysis template method and LinearStaticAnalysis skeleton added"
     },
     {
       "step": 7,
       "name": "results-containers",
-      "status": "pending",
+      "status": "completed",
       "allowed_paths": [
         "src/fesa/results/",
         "tests/unit/results_*_test.cpp"
-      ]
+      ],
+      "summary": "ResultStep, ResultFrame, FieldOutput, and HistoryOutput containers added"
     },
     {
       "step": 8,
       "name": "solver-skeleton-integration-report",
-      "status": "pending",
+      "status": "completed",
       "allowed_paths": [
         "tests/integration/",
         "docs/build-test-reports/"
-      ]
+      ],
+      "summary": "Solver skeleton integration test and build/test report added"
     }
-  ]
+  ],
+  "created_at": "2026-06-12T02:09:10+0900",
+  "completed_at": "2026-06-12T02:42:00+0900"
 }

scripts/execute.py

@@ -373,8 +373,8 @@ class StepExecutor:
 
         prompt = preamble + step_file.read_text(encoding="utf-8")
         result = subprocess.run(
-            ["codex", "exec", "--dangerously-bypass-approvals-and-sandbox", "--json", prompt],
-            cwd=self._root, capture_output=True, text=True, timeout=1800,
+            ["codex", "exec", "--dangerously-bypass-approvals-and-sandbox", "--json", "-"],
+            cwd=self._root, capture_output=True, text=True, input=prompt, timeout=1800,
         )
 
         if result.returncode != 0:

scripts/test_execute.py

@@ -281,6 +281,30 @@ class ExecuteRunnerSafetyTests(unittest.TestCase):
 
             self.assertEqual(cm.exception.code, 1)
 
+    def test_invoke_codex_passes_prompt_through_stdin(self):
+        execute = load_execute()
+        with tempfile.TemporaryDirectory() as tmp:
+            root = Path(tmp)
+            write_phase(root)
+            executor = make_executor(execute, root)
+            step = {"step": 1, "name": "Docs"}
+            long_preamble = "x" * 40000
+
+            def fake_run(cmd, **kwargs):
+                return subprocess.CompletedProcess(cmd, 0, '{"event":"done"}\n', "")
+
+            with patch.object(execute.subprocess, "run", side_effect=fake_run) as run_mock:
+                executor._invoke_codex(step, long_preamble)
+
+            cmd = run_mock.call_args.args[0]
+            kwargs = run_mock.call_args.kwargs
+            self.assertEqual(
+                cmd,
+                ["codex", "exec", "--dangerously-bypass-approvals-and-sandbox", "--json", "-"],
+            )
+            self.assertEqual(kwargs["input"], long_preamble + "# Step 1\n")
+            self.assertEqual(kwargs["cwd"], str(root))
+
 
 if __name__ == "__main__":
     unittest.main()

scripts/test_header_declaration_only.py

@@ -0,0 +1,45 @@
+import re
+import unittest
+from pathlib import Path
+
+
+ROOT = Path(__file__).resolve().parents[1]
+HEADER_ROOT = ROOT / "src" / "fesa"
+
+
+def _looks_like_function_definition(prefix):
+    if "(" not in prefix or ")" not in prefix:
+        return False
+
+    stripped = prefix.strip()
+    control_prefixes = ("if ", "for ", "while ", "switch ", "catch ")
+    declaration_prefixes = ("namespace ", "class ", "struct ", "enum ")
+    return not stripped.startswith(control_prefixes + declaration_prefixes)
+
+
+class HeaderDeclarationOnlyTests(unittest.TestCase):
+    def test_solver_headers_do_not_contain_function_bodies(self):
+        violations = []
+
+        for header in sorted(HEADER_ROOT.rglob("*.hpp")):
+            candidate = ""
+            for line_number, line in enumerate(header.read_text(encoding="utf-8").splitlines(), start=1):
+                stripped = line.strip()
+                if not stripped:
+                    continue
+
+                candidate = f"{candidate} {stripped}".strip()
+                if "{" in stripped and _looks_like_function_definition(candidate.split("{", 1)[0]):
+                    violations.append(f"{header.relative_to(ROOT)}:{line_number}: function body in header")
+
+                if re.search(r"\([^;{}]*\)\s*=\s*(default|delete)\s*;", stripped):
+                    violations.append(f"{header.relative_to(ROOT)}:{line_number}: function definition in header")
+
+                if stripped.endswith(";") or stripped.endswith("}") or stripped.endswith(":"):
+                    candidate = ""
+
+        self.assertEqual([], violations)
+
+
+if __name__ == "__main__":
+    unittest.main()

src/fesa/analysis/analysis.cpp

@@ -0,0 +1,30 @@
+#include <fesa/analysis/analysis.hpp>
+
+namespace fesa::analysis {
+
+Analysis::~Analysis() = default;
+
+void Analysis::run()
+{
+    initialize();
+    build_analysis_model();
+    build_dof_map();
+    build_sparse_pattern();
+    assemble();
+    apply_boundary_conditions();
+    solve();
+    update_state();
+    write_results();
+}
+
+void Analysis::initialize() {}
+void Analysis::build_analysis_model() {}
+void Analysis::build_dof_map() {}
+void Analysis::build_sparse_pattern() {}
+void Analysis::assemble() {}
+void Analysis::apply_boundary_conditions() {}
+void Analysis::solve() {}
+void Analysis::update_state() {}
+void Analysis::write_results() {}
+
+} // namespace fesa::analysis

src/fesa/analysis/analysis.hpp

@@ -0,0 +1,23 @@
+#pragma once
+
+namespace fesa::analysis {
+
+class Analysis {
+public:
+    virtual ~Analysis();
+
+    void run();
+
+protected:
+    virtual void initialize();
+    virtual void build_analysis_model();
+    virtual void build_dof_map();
+    virtual void build_sparse_pattern();
+    virtual void assemble();
+    virtual void apply_boundary_conditions();
+    virtual void solve();
+    virtual void update_state();
+    virtual void write_results();
+};
+
+} // namespace fesa::analysis

src/fesa/analysis/analysis_model.cpp

@@ -0,0 +1,60 @@
+#include <fesa/analysis/analysis_model.hpp>
+
+#include <stdexcept>
+
+namespace fesa::analysis {
+
+AnalysisModel::AnalysisModel(const model::Domain& domain, core::StepId step_id)
+    : domain_(domain), step_(domain.find_step(step_id))
+{
+    if (step_ == nullptr) {
+        throw std::invalid_argument("analysis step not found");
+    }
+
+    for (const auto& element : domain_.elements()) {
+        active_elements_.push_back(&element);
+    }
+    for (const auto& boundary_condition : step_->boundary_conditions()) {
+        active_boundary_conditions_.push_back(&boundary_condition);
+    }
+    for (const auto& load : step_->loads()) {
+        active_loads_.push_back(&load);
+    }
+}
+
+const model::Domain& AnalysisModel::domain() const
+{
+    return domain_;
+}
+
+const model::AnalysisStep& AnalysisModel::step() const
+{
+    return *step_;
+}
+
+const std::vector<const model::Element*>& AnalysisModel::active_elements() const
+{
+    return active_elements_;
+}
+
+const std::vector<const model::BoundaryCondition*>& AnalysisModel::active_boundary_conditions() const
+{
+    return active_boundary_conditions_;
+}
+
+const std::vector<const model::Load*>& AnalysisModel::active_loads() const
+{
+    return active_loads_;
+}
+
+const model::Property* AnalysisModel::property_for(const model::Element& element) const
+{
+    return domain_.find_property(element.property_id());
+}
+
+const model::Material* AnalysisModel::material_for(const model::Property& property) const
+{
+    return domain_.find_material(property.material_id());
+}
+
+} // namespace fesa::analysis

src/fesa/analysis/analysis_model.hpp

@@ -0,0 +1,29 @@
+#pragma once
+
+#include <fesa/model/domain.hpp>
+
+#include <vector>
+
+namespace fesa::analysis {
+
+class AnalysisModel {
+public:
+    AnalysisModel(const model::Domain& domain, core::StepId step_id);
+
+    const model::Domain& domain() const;
+    const model::AnalysisStep& step() const;
+    const std::vector<const model::Element*>& active_elements() const;
+    const std::vector<const model::BoundaryCondition*>& active_boundary_conditions() const;
+    const std::vector<const model::Load*>& active_loads() const;
+    const model::Property* property_for(const model::Element& element) const;
+    const model::Material* material_for(const model::Property& property) const;
+
+private:
+    const model::Domain& domain_;
+    const model::AnalysisStep* step_;
+    std::vector<const model::Element*> active_elements_;
+    std::vector<const model::BoundaryCondition*> active_boundary_conditions_;
+    std::vector<const model::Load*> active_loads_;
+};
+
+} // namespace fesa::analysis

src/fesa/analysis/analysis_state.cpp

@@ -0,0 +1,124 @@
+#include <fesa/analysis/analysis_state.hpp>
+
+#include <cstddef>
+#include <stdexcept>
+#include <utility>
+
+namespace fesa::analysis {
+
+AnalysisState::AnalysisState(int total_dof_count)
+    : displacement_(vector_of(total_dof_count)),
+      velocity_(vector_of(total_dof_count)),
+      acceleration_(vector_of(total_dof_count)),
+      temperature_(vector_of(total_dof_count)),
+      external_force_(vector_of(total_dof_count)),
+      internal_force_(vector_of(total_dof_count)),
+      residual_(vector_of(total_dof_count))
+{
+}
+
+const std::vector<double>& AnalysisState::displacement() const
+{
+    return displacement_;
+}
+
+const std::vector<double>& AnalysisState::velocity() const
+{
+    return velocity_;
+}
+
+const std::vector<double>& AnalysisState::acceleration() const
+{
+    return acceleration_;
+}
+
+const std::vector<double>& AnalysisState::temperature() const
+{
+    return temperature_;
+}
+
+const std::vector<double>& AnalysisState::external_force() const
+{
+    return external_force_;
+}
+
+const std::vector<double>& AnalysisState::internal_force() const
+{
+    return internal_force_;
+}
+
+const std::vector<double>& AnalysisState::residual() const
+{
+    return residual_;
+}
+
+void AnalysisState::set_displacement(std::vector<double> values)
+{
+    assign_same_size(displacement_, std::move(values));
+}
+
+void AnalysisState::set_external_force(std::vector<double> values)
+{
+    assign_same_size(external_force_, std::move(values));
+}
+
+void AnalysisState::set_internal_force(std::vector<double> values)
+{
+    assign_same_size(internal_force_, std::move(values));
+}
+
+void AnalysisState::update_residual()
+{
+    for (std::size_t index = 0; index < residual_.size(); ++index) {
+        residual_[index] = external_force_[index] - internal_force_[index];
+    }
+}
+
+IterationState& AnalysisState::iteration_state()
+{
+    return iteration_state_;
+}
+
+const IterationState& AnalysisState::iteration_state() const
+{
+    return iteration_state_;
+}
+
+void AnalysisState::set_element_state(core::ElementId element_id, std::vector<double> state)
+{
+    for (auto& entry : element_states_) {
+        if (entry.first.value == element_id.value) {
+            entry.second = std::move(state);
+            return;
+        }
+    }
+    element_states_.push_back({element_id, std::move(state)});
+}
+
+const std::vector<double>* AnalysisState::element_state(core::ElementId element_id) const
+{
+    for (const auto& entry : element_states_) {
+        if (entry.first.value == element_id.value) {
+            return &entry.second;
+        }
+    }
+    return nullptr;
+}
+
+std::vector<double> AnalysisState::vector_of(int size)
+{
+    if (size < 0) {
+        throw std::invalid_argument("negative dof count");
+    }
+    return std::vector<double>(static_cast<std::size_t>(size), 0.0);
+}
+
+void AnalysisState::assign_same_size(std::vector<double>& target, std::vector<double> values)
+{
+    if (target.size() != values.size()) {
+        throw std::invalid_argument("vector size mismatch");
+    }
+    target = std::move(values);
+}
+
+} // namespace fesa::analysis

src/fesa/analysis/analysis_state.hpp

@@ -0,0 +1,53 @@
+#pragma once
+
+#include <fesa/core/ids.hpp>
+
+#include <vector>
+
+namespace fesa::analysis {
+
+struct IterationState {
+    double time = 0.0;
+    int increment = 0;
+    int iteration = 0;
+};
+
+class AnalysisState {
+public:
+    explicit AnalysisState(int total_dof_count);
+
+    const std::vector<double>& displacement() const;
+    const std::vector<double>& velocity() const;
+    const std::vector<double>& acceleration() const;
+    const std::vector<double>& temperature() const;
+    const std::vector<double>& external_force() const;
+    const std::vector<double>& internal_force() const;
+    const std::vector<double>& residual() const;
+
+    void set_displacement(std::vector<double> values);
+    void set_external_force(std::vector<double> values);
+    void set_internal_force(std::vector<double> values);
+    void update_residual();
+
+    IterationState& iteration_state();
+    const IterationState& iteration_state() const;
+
+    void set_element_state(core::ElementId element_id, std::vector<double> state);
+    const std::vector<double>* element_state(core::ElementId element_id) const;
+
+private:
+    static std::vector<double> vector_of(int size);
+    static void assign_same_size(std::vector<double>& target, std::vector<double> values);
+
+    std::vector<double> displacement_;
+    std::vector<double> velocity_;
+    std::vector<double> acceleration_;
+    std::vector<double> temperature_;
+    std::vector<double> external_force_;
+    std::vector<double> internal_force_;
+    std::vector<double> residual_;
+    IterationState iteration_state_;
+    std::vector<std::pair<core::ElementId, std::vector<double>>> element_states_;
+};
+
+} // namespace fesa::analysis

src/fesa/analysis/linear_static_analysis.cpp

@@ -0,0 +1,48 @@
+#include <fesa/analysis/linear_static_analysis.hpp>
+
+namespace fesa::analysis {
+
+LinearStaticAnalysis::LinearStaticAnalysis(const model::Domain& domain, core::StepId step_id)
+    : domain_(domain), step_id_(step_id)
+{
+}
+
+const AnalysisModel* LinearStaticAnalysis::analysis_model() const
+{
+    return analysis_model_.get();
+}
+
+const AnalysisState* LinearStaticAnalysis::state() const
+{
+    return state_.get();
+}
+
+void LinearStaticAnalysis::build_analysis_model()
+{
+    analysis_model_ = std::make_unique<AnalysisModel>(domain_, step_id_);
+}
+
+void LinearStaticAnalysis::build_dof_map()
+{
+    dof_manager_ = std::make_unique<fem::DofManager>();
+    for (const auto* element : analysis_model_->active_elements()) {
+        for (const auto node_id : element->node_ids()) {
+            dof_manager_->define_node_dofs(node_id, {
+                model::DofComponent::ux,
+                model::DofComponent::uy,
+                model::DofComponent::uz
+            });
+        }
+    }
+    for (const auto* boundary_condition : analysis_model_->active_boundary_conditions()) {
+        dof_manager_->apply_boundary_condition(*boundary_condition);
+    }
+    dof_manager_->number_equations();
+}
+
+void LinearStaticAnalysis::update_state()
+{
+    state_ = std::make_unique<AnalysisState>(dof_manager_->total_dof_count());
+}
+
+} // namespace fesa::analysis

src/fesa/analysis/linear_static_analysis.hpp

@@ -0,0 +1,32 @@
+#pragma once
+
+#include <fesa/analysis/analysis.hpp>
+#include <fesa/analysis/analysis_model.hpp>
+#include <fesa/analysis/analysis_state.hpp>
+#include <fesa/fem/dof_manager.hpp>
+
+#include <memory>
+
+namespace fesa::analysis {
+
+class LinearStaticAnalysis : public Analysis {
+public:
+    LinearStaticAnalysis(const model::Domain& domain, core::StepId step_id);
+
+    const AnalysisModel* analysis_model() const;
+    const AnalysisState* state() const;
+
+protected:
+    void build_analysis_model() override;
+    void build_dof_map() override;
+    void update_state() override;
+
+private:
+    const model::Domain& domain_;
+    core::StepId step_id_;
+    std::unique_ptr<AnalysisModel> analysis_model_;
+    std::unique_ptr<fem::DofManager> dof_manager_;
+    std::unique_ptr<AnalysisState> state_;
+};
+
+} // namespace fesa::analysis

src/fesa/core/diagnostic.hpp

@@ -0,0 +1,19 @@
+#pragma once
+
+#include <string>
+
+namespace fesa::core {
+
+enum class Severity {
+    info,
+    warning,
+    error
+};
+
+struct Diagnostic {
+    Severity severity;
+    std::string code;
+    std::string message;
+};
+
+} // namespace fesa::core

src/fesa/core/ids.hpp

@@ -0,0 +1,25 @@
+#pragma once
+
+namespace fesa::core {
+
+struct NodeId {
+    int value;
+};
+
+struct ElementId {
+    int value;
+};
+
+struct MaterialId {
+    int value;
+};
+
+struct PropertyId {
+    int value;
+};
+
+struct StepId {
+    int value;
+};
+
+} // namespace fesa::core

src/fesa/core/status.cpp

@@ -0,0 +1,34 @@
+#include <fesa/core/status.hpp>
+
+#include <utility>
+
+namespace fesa::core {
+
+Status Status::ok()
+{
+    return Status{};
+}
+
+Status Status::failure(Diagnostic diagnostic)
+{
+    Status status;
+    status.add(std::move(diagnostic));
+    return status;
+}
+
+bool Status::is_ok() const
+{
+    return diagnostics_.empty();
+}
+
+const std::vector<Diagnostic>& Status::diagnostics() const
+{
+    return diagnostics_;
+}
+
+void Status::add(Diagnostic diagnostic)
+{
+    diagnostics_.push_back(std::move(diagnostic));
+}
+
+} // namespace fesa::core

src/fesa/core/status.hpp

@@ -0,0 +1,22 @@
+#pragma once
+
+#include <fesa/core/diagnostic.hpp>
+
+#include <vector>
+
+namespace fesa::core {
+
+class Status {
+public:
+    static Status ok();
+    static Status failure(Diagnostic diagnostic);
+
+    bool is_ok() const;
+    const std::vector<Diagnostic>& diagnostics() const;
+    void add(Diagnostic diagnostic);
+
+private:
+    std::vector<Diagnostic> diagnostics_;
+};
+
+} // namespace fesa::core

src/fesa/fem/dof_key.cpp

@@ -0,0 +1,10 @@
+#include <fesa/fem/dof_key.hpp>
+
+namespace fesa::fem {
+
+bool operator==(const DofKey& lhs, const DofKey& rhs)
+{
+    return lhs.node_id.value == rhs.node_id.value && lhs.component == rhs.component;
+}
+
+} // namespace fesa::fem

src/fesa/fem/dof_key.hpp

@@ -0,0 +1,15 @@
+#pragma once
+
+#include <fesa/core/ids.hpp>
+#include <fesa/model/boundary_condition.hpp>
+
+namespace fesa::fem {
+
+struct DofKey {
+    core::NodeId node_id;
+    model::DofComponent component;
+};
+
+bool operator==(const DofKey& lhs, const DofKey& rhs);
+
+} // namespace fesa::fem

src/fesa/fem/dof_manager.cpp

@@ -0,0 +1,133 @@
+#include <fesa/fem/dof_manager.hpp>
+
+#include <algorithm>
+#include <cstddef>
+#include <stdexcept>
+
+namespace fesa::fem {
+
+void DofManager::define_node_dofs(core::NodeId node_id, std::vector<model::DofComponent> components)
+{
+    for (const auto component : components) {
+        DofKey key{node_id, component};
+        if (find_record(key) == records_.end()) {
+            records_.push_back({key});
+        }
+    }
+}
+
+void DofManager::apply_boundary_condition(const model::BoundaryCondition& bc)
+{
+    auto record = find_record({bc.node_id(), bc.component()});
+    if (record == records_.end()) {
+        throw std::invalid_argument("boundary condition references undefined dof");
+    }
+    record->constrained = true;
+}
+
+void DofManager::number_equations()
+{
+    std::sort(records_.begin(), records_.end(), [](const Record& lhs, const Record& rhs) {
+        if (lhs.key.node_id.value != rhs.key.node_id.value) {
+            return lhs.key.node_id.value < rhs.key.node_id.value;
+        }
+        return static_cast<int>(lhs.key.component) < static_cast<int>(rhs.key.component);
+    });
+
+    int free_id = 0;
+    for (int equation_id = 0; equation_id < static_cast<int>(records_.size()); ++equation_id) {
+        records_[equation_id].equation_id = equation_id;
+        if (records_[equation_id].constrained) {
+            records_[equation_id].free_equation_id = std::nullopt;
+        } else {
+            records_[equation_id].free_equation_id = free_id++;
+        }
+    }
+
+    sparse_pattern_.clear();
+    for (int row = 0; row < free_id; ++row) {
+        for (int column = 0; column < free_id; ++column) {
+            sparse_pattern_.push_back({row, column});
+        }
+    }
+}
+
+int DofManager::total_dof_count() const
+{
+    return static_cast<int>(records_.size());
+}
+
+int DofManager::free_dof_count() const
+{
+    return static_cast<int>(
+        std::count_if(records_.begin(), records_.end(), [](const Record& record) {
+            return !record.constrained;
+        })
+    );
+}
+
+int DofManager::constrained_dof_count() const
+{
+    return total_dof_count() - free_dof_count();
+}
+
+bool DofManager::is_constrained(DofKey key) const
+{
+    return require_record(key).constrained;
+}
+
+int DofManager::equation_id(DofKey key) const
+{
+    return require_record(key).equation_id;
+}
+
+std::optional<int> DofManager::free_equation_id(DofKey key) const
+{
+    return require_record(key).free_equation_id;
+}
+
+std::vector<double> DofManager::expand_free_vector(const std::vector<double>& free_values) const
+{
+    if (free_values.size() != static_cast<std::size_t>(free_dof_count())) {
+        throw std::invalid_argument("free vector size does not match dof manager");
+    }
+
+    std::vector<double> full(records_.size(), 0.0);
+    for (const auto& record : records_) {
+        if (record.free_equation_id.has_value()) {
+            full[static_cast<std::size_t>(record.equation_id)] =
+                free_values[static_cast<std::size_t>(*record.free_equation_id)];
+        }
+    }
+    return full;
+}
+
+const std::vector<std::pair<int, int>>& DofManager::sparse_pattern() const
+{
+    return sparse_pattern_;
+}
+
+std::vector<DofManager::Record>::iterator DofManager::find_record(DofKey key)
+{
+    return std::find_if(records_.begin(), records_.end(), [key](const Record& record) {
+        return record.key == key;
+    });
+}
+
+std::vector<DofManager::Record>::const_iterator DofManager::find_record(DofKey key) const
+{
+    return std::find_if(records_.begin(), records_.end(), [key](const Record& record) {
+        return record.key == key;
+    });
+}
+
+const DofManager::Record& DofManager::require_record(DofKey key) const
+{
+    const auto record = find_record(key);
+    if (record == records_.end()) {
+        throw std::invalid_argument("dof is not defined");
+    }
+    return *record;
+}
+
+} // namespace fesa::fem

src/fesa/fem/dof_manager.hpp

@@ -0,0 +1,42 @@
+#pragma once
+
+#include <fesa/fem/dof_key.hpp>
+
+#include <optional>
+#include <utility>
+#include <vector>
+
+namespace fesa::fem {
+
+class DofManager {
+public:
+    void define_node_dofs(core::NodeId node_id, std::vector<model::DofComponent> components);
+    void apply_boundary_condition(const model::BoundaryCondition& bc);
+    void number_equations();
+
+    int total_dof_count() const;
+    int free_dof_count() const;
+    int constrained_dof_count() const;
+    bool is_constrained(DofKey key) const;
+    int equation_id(DofKey key) const;
+    std::optional<int> free_equation_id(DofKey key) const;
+    std::vector<double> expand_free_vector(const std::vector<double>& free_values) const;
+    const std::vector<std::pair<int, int>>& sparse_pattern() const;
+
+private:
+    struct Record {
+        DofKey key;
+        bool constrained = false;
+        int equation_id = -1;
+        std::optional<int> free_equation_id;
+    };
+
+    std::vector<Record>::iterator find_record(DofKey key);
+    std::vector<Record>::const_iterator find_record(DofKey key) const;
+    const Record& require_record(DofKey key) const;
+
+    std::vector<Record> records_;
+    std::vector<std::pair<int, int>> sparse_pattern_;
+};
+
+} // namespace fesa::fem

src/fesa/model/analysis_step.cpp

@@ -0,0 +1,42 @@
+#include <fesa/model/analysis_step.hpp>
+
+#include <utility>
+
+namespace fesa::model {
+
+AnalysisStep::AnalysisStep(core::StepId id, std::string name)
+    : id_(id), name_(std::move(name))
+{
+}
+
+core::StepId AnalysisStep::id() const
+{
+    return id_;
+}
+
+const std::string& AnalysisStep::name() const
+{
+    return name_;
+}
+
+void AnalysisStep::add_boundary_condition(BoundaryCondition bc)
+{
+    boundary_conditions_.push_back(std::move(bc));
+}
+
+void AnalysisStep::add_load(Load load)
+{
+    loads_.push_back(std::move(load));
+}
+
+const std::vector<BoundaryCondition>& AnalysisStep::boundary_conditions() const
+{
+    return boundary_conditions_;
+}
+
+const std::vector<Load>& AnalysisStep::loads() const
+{
+    return loads_;
+}
+
+} // namespace fesa::model

src/fesa/model/analysis_step.hpp

@@ -0,0 +1,29 @@
+#pragma once
+
+#include <fesa/model/boundary_condition.hpp>
+#include <fesa/model/load.hpp>
+
+#include <string>
+#include <vector>
+
+namespace fesa::model {
+
+class AnalysisStep {
+public:
+    AnalysisStep(core::StepId id, std::string name);
+
+    core::StepId id() const;
+    const std::string& name() const;
+    void add_boundary_condition(BoundaryCondition bc);
+    void add_load(Load load);
+    const std::vector<BoundaryCondition>& boundary_conditions() const;
+    const std::vector<Load>& loads() const;
+
+private:
+    core::StepId id_;
+    std::string name_;
+    std::vector<BoundaryCondition> boundary_conditions_;
+    std::vector<Load> loads_;
+};
+
+} // namespace fesa::model

src/fesa/model/boundary_condition.cpp

@@ -0,0 +1,25 @@
+#include <fesa/model/boundary_condition.hpp>
+
+namespace fesa::model {
+
+BoundaryCondition::BoundaryCondition(core::NodeId node_id, DofComponent component, double value)
+    : node_id_(node_id), component_(component), value_(value)
+{
+}
+
+core::NodeId BoundaryCondition::node_id() const
+{
+    return node_id_;
+}
+
+DofComponent BoundaryCondition::component() const
+{
+    return component_;
+}
+
+double BoundaryCondition::value() const
+{
+    return value_;
+}
+
+} // namespace fesa::model

src/fesa/model/boundary_condition.hpp

@@ -0,0 +1,31 @@
+#pragma once
+
+#include <fesa/core/ids.hpp>
+
+namespace fesa::model {
+
+enum class DofComponent {
+    ux,
+    uy,
+    uz,
+    rx,
+    ry,
+    rz,
+    temperature
+};
+
+class BoundaryCondition {
+public:
+    BoundaryCondition(core::NodeId node_id, DofComponent component, double value);
+
+    core::NodeId node_id() const;
+    DofComponent component() const;
+    double value() const;
+
+private:
+    core::NodeId node_id_;
+    DofComponent component_;
+    double value_;
+};
+
+} // namespace fesa::model

src/fesa/model/domain.cpp

@@ -0,0 +1,107 @@
+#include <fesa/model/domain.hpp>
+
+#include <utility>
+
+namespace fesa::model {
+
+void Domain::add_node(Node node)
+{
+    nodes_.push_back(std::move(node));
+}
+
+void Domain::add_element(Element element)
+{
+    elements_.push_back(std::move(element));
+}
+
+void Domain::add_material(Material material)
+{
+    materials_.push_back(std::move(material));
+}
+
+void Domain::add_property(Property property)
+{
+    properties_.push_back(std::move(property));
+}
+
+void Domain::add_step(AnalysisStep step)
+{
+    steps_.push_back(std::move(step));
+}
+
+const std::vector<Node>& Domain::nodes() const
+{
+    return nodes_;
+}
+
+const std::vector<Element>& Domain::elements() const
+{
+    return elements_;
+}
+
+const std::vector<Material>& Domain::materials() const
+{
+    return materials_;
+}
+
+const std::vector<Property>& Domain::properties() const
+{
+    return properties_;
+}
+
+const std::vector<AnalysisStep>& Domain::steps() const
+{
+    return steps_;
+}
+
+const Node* Domain::find_node(core::NodeId id) const
+{
+    for (const auto& node : nodes_) {
+        if (node.id().value == id.value) {
+            return &node;
+        }
+    }
+    return nullptr;
+}
+
+const Element* Domain::find_element(core::ElementId id) const
+{
+    for (const auto& element : elements_) {
+        if (element.id().value == id.value) {
+            return &element;
+        }
+    }
+    return nullptr;
+}
+
+const Material* Domain::find_material(core::MaterialId id) const
+{
+    for (const auto& material : materials_) {
+        if (material.id().value == id.value) {
+            return &material;
+        }
+    }
+    return nullptr;
+}
+
+const Property* Domain::find_property(core::PropertyId id) const
+{
+    for (const auto& property : properties_) {
+        if (property.id().value == id.value) {
+            return &property;
+        }
+    }
+    return nullptr;
+}
+
+const AnalysisStep* Domain::find_step(core::StepId id) const
+{
+    for (const auto& step : steps_) {
+        if (step.id().value == id.value) {
+            return &step;
+        }
+    }
+    return nullptr;
+}
+
+} // namespace fesa::model

src/fesa/model/domain.hpp

@@ -0,0 +1,41 @@
+#pragma once
+
+#include <fesa/model/analysis_step.hpp>
+#include <fesa/model/element.hpp>
+#include <fesa/model/material.hpp>
+#include <fesa/model/node.hpp>
+#include <fesa/model/property.hpp>
+
+#include <vector>
+
+namespace fesa::model {
+
+class Domain {
+public:
+    void add_node(Node node);
+    void add_element(Element element);
+    void add_material(Material material);
+    void add_property(Property property);
+    void add_step(AnalysisStep step);
+
+    const std::vector<Node>& nodes() const;
+    const std::vector<Element>& elements() const;
+    const std::vector<Material>& materials() const;
+    const std::vector<Property>& properties() const;
+    const std::vector<AnalysisStep>& steps() const;
+
+    const Node* find_node(core::NodeId id) const;
+    const Element* find_element(core::ElementId id) const;
+    const Material* find_material(core::MaterialId id) const;
+    const Property* find_property(core::PropertyId id) const;
+    const AnalysisStep* find_step(core::StepId id) const;
+
+private:
+    std::vector<Node> nodes_;
+    std::vector<Element> elements_;
+    std::vector<Material> materials_;
+    std::vector<Property> properties_;
+    std::vector<AnalysisStep> steps_;
+};
+
+} // namespace fesa::model

src/fesa/model/element.cpp

@@ -0,0 +1,38 @@
+#include <fesa/model/element.hpp>
+
+#include <utility>
+
+namespace fesa::model {
+
+Element::Element(core::ElementId id,
+                 ElementTopology topology,
+                 std::vector<core::NodeId> node_ids,
+                 core::PropertyId property_id)
+    : id_(id),
+      topology_(topology),
+      node_ids_(std::move(node_ids)),
+      property_id_(property_id)
+{
+}
+
+core::ElementId Element::id() const
+{
+    return id_;
+}
+
+ElementTopology Element::topology() const
+{
+    return topology_;
+}
+
+const std::vector<core::NodeId>& Element::node_ids() const
+{
+    return node_ids_;
+}
+
+core::PropertyId Element::property_id() const
+{
+    return property_id_;
+}
+
+} // namespace fesa::model

src/fesa/model/element.hpp

@@ -0,0 +1,34 @@
+#pragma once
+
+#include <fesa/core/ids.hpp>
+
+#include <vector>
+
+namespace fesa::model {
+
+enum class ElementTopology {
+    truss2,
+    bar2,
+    unknown
+};
+
+class Element {
+public:
+    Element(core::ElementId id,
+            ElementTopology topology,
+            std::vector<core::NodeId> node_ids,
+            core::PropertyId property_id);
+
+    core::ElementId id() const;
+    ElementTopology topology() const;
+    const std::vector<core::NodeId>& node_ids() const;
+    core::PropertyId property_id() const;
+
+private:
+    core::ElementId id_;
+    ElementTopology topology_;
+    std::vector<core::NodeId> node_ids_;
+    core::PropertyId property_id_;
+};
+
+} // namespace fesa::model

src/fesa/model/load.cpp

@@ -0,0 +1,25 @@
+#include <fesa/model/load.hpp>
+
+namespace fesa::model {
+
+Load::Load(core::NodeId node_id, DofComponent component, double value)
+    : node_id_(node_id), component_(component), value_(value)
+{
+}
+
+core::NodeId Load::node_id() const
+{
+    return node_id_;
+}
+
+DofComponent Load::component() const
+{
+    return component_;
+}
+
+double Load::value() const
+{
+    return value_;
+}
+
+} // namespace fesa::model

src/fesa/model/load.hpp

@@ -0,0 +1,21 @@
+#pragma once
+
+#include <fesa/model/boundary_condition.hpp>
+
+namespace fesa::model {
+
+class Load {
+public:
+    Load(core::NodeId node_id, DofComponent component, double value);
+
+    core::NodeId node_id() const;
+    DofComponent component() const;
+    double value() const;
+
+private:
+    core::NodeId node_id_;
+    DofComponent component_;
+    double value_;
+};
+
+} // namespace fesa::model

src/fesa/model/material.cpp

@@ -0,0 +1,22 @@
+#include <fesa/model/material.hpp>
+
+#include <utility>
+
+namespace fesa::model {
+
+Material::Material(core::MaterialId id, std::string name)
+    : id_(id), name_(std::move(name))
+{
+}
+
+core::MaterialId Material::id() const
+{
+    return id_;
+}
+
+const std::string& Material::name() const
+{
+    return name_;
+}
+
+} // namespace fesa::model

src/fesa/model/material.hpp

@@ -0,0 +1,21 @@
+#pragma once
+
+#include <fesa/core/ids.hpp>
+
+#include <string>
+
+namespace fesa::model {
+
+class Material {
+public:
+    Material(core::MaterialId id, std::string name);
+
+    core::MaterialId id() const;
+    const std::string& name() const;
+
+private:
+    core::MaterialId id_;
+    std::string name_;
+};
+
+} // namespace fesa::model

src/fesa/model/node.cpp

@@ -0,0 +1,20 @@
+#include <fesa/model/node.hpp>
+
+namespace fesa::model {
+
+Node::Node(core::NodeId id, std::array<double, 3> coordinates)
+    : id_(id), coordinates_(coordinates)
+{
+}
+
+core::NodeId Node::id() const
+{
+    return id_;
+}
+
+const std::array<double, 3>& Node::coordinates() const
+{
+    return coordinates_;
+}
+
+} // namespace fesa::model

src/fesa/model/node.hpp

@@ -0,0 +1,21 @@
+#pragma once
+
+#include <fesa/core/ids.hpp>
+
+#include <array>
+
+namespace fesa::model {
+
+class Node {
+public:
+    Node(core::NodeId id, std::array<double, 3> coordinates);
+
+    core::NodeId id() const;
+    const std::array<double, 3>& coordinates() const;
+
+private:
+    core::NodeId id_;
+    std::array<double, 3> coordinates_;
+};
+
+} // namespace fesa::model

src/fesa/model/property.cpp

@@ -0,0 +1,27 @@
+#include <fesa/model/property.hpp>
+
+#include <utility>
+
+namespace fesa::model {
+
+Property::Property(core::PropertyId id, std::string name, core::MaterialId material_id)
+    : id_(id), name_(std::move(name)), material_id_(material_id)
+{
+}
+
+core::PropertyId Property::id() const
+{
+    return id_;
+}
+
+const std::string& Property::name() const
+{
+    return name_;
+}
+
+core::MaterialId Property::material_id() const
+{
+    return material_id_;
+}
+
+} // namespace fesa::model

src/fesa/model/property.hpp

@@ -0,0 +1,23 @@
+#pragma once
+
+#include <fesa/core/ids.hpp>
+
+#include <string>
+
+namespace fesa::model {
+
+class Property {
+public:
+    Property(core::PropertyId id, std::string name, core::MaterialId material_id);
+
+    core::PropertyId id() const;
+    const std::string& name() const;
+    core::MaterialId material_id() const;
+
+private:
+    core::PropertyId id_;
+    std::string name_;
+    core::MaterialId material_id_;
+};
+
+} // namespace fesa::model

src/fesa/results/results.cpp

@@ -0,0 +1,70 @@
+#include <fesa/results/results.hpp>
+
+#include <stdexcept>
+#include <utility>
+
+namespace fesa::results {
+
+ResultFrame::ResultFrame(int frame_id, double time)
+    : frame_id_(frame_id), time_(time)
+{
+}
+
+int ResultFrame::frame_id() const
+{
+    return frame_id_;
+}
+
+double ResultFrame::time() const
+{
+    return time_;
+}
+
+void ResultFrame::add_field_output(FieldOutput output)
+{
+    if (output.components.empty()) {
+        throw std::invalid_argument("field output must have components");
+    }
+    if (output.entity_ids.size() * output.components.size() != output.values.size()) {
+        throw std::invalid_argument("field output values do not match row shape");
+    }
+    field_outputs_.push_back(std::move(output));
+}
+
+void ResultFrame::add_history_output(HistoryOutput output)
+{
+    history_outputs_.push_back(std::move(output));
+}
+
+const std::vector<FieldOutput>& ResultFrame::field_outputs() const
+{
+    return field_outputs_;
+}
+
+const std::vector<HistoryOutput>& ResultFrame::history_outputs() const
+{
+    return history_outputs_;
+}
+
+ResultStep::ResultStep(std::string name)
+    : name_(std::move(name))
+{
+}
+
+const std::string& ResultStep::name() const
+{
+    return name_;
+}
+
+ResultFrame& ResultStep::add_frame(int frame_id, double time)
+{
+    frames_.push_back(ResultFrame{frame_id, time});
+    return frames_.back();
+}
+
+const std::vector<ResultFrame>& ResultStep::frames() const
+{
+    return frames_;
+}
+
+} // namespace fesa::results

src/fesa/results/results.hpp

@@ -0,0 +1,59 @@
+#pragma once
+
+#include <string>
+#include <vector>
+
+namespace fesa::results {
+
+enum class FieldLocation {
+    nodal,
+    element,
+    integration_point
+};
+
+struct FieldOutput {
+    std::string name;
+    FieldLocation location;
+    std::vector<std::string> components;
+    std::vector<int> entity_ids;
+    std::vector<double> values;
+};
+
+struct HistoryOutput {
+    std::string name;
+    std::vector<double> time;
+    std::vector<double> values;
+};
+
+class ResultFrame {
+public:
+    ResultFrame(int frame_id, double time);
+
+    int frame_id() const;
+    double time() const;
+    void add_field_output(FieldOutput output);
+    void add_history_output(HistoryOutput output);
+    const std::vector<FieldOutput>& field_outputs() const;
+    const std::vector<HistoryOutput>& history_outputs() const;
+
+private:
+    int frame_id_;
+    double time_;
+    std::vector<FieldOutput> field_outputs_;
+    std::vector<HistoryOutput> history_outputs_;
+};
+
+class ResultStep {
+public:
+    explicit ResultStep(std::string name);
+
+    const std::string& name() const;
+    ResultFrame& add_frame(int frame_id, double time);
+    const std::vector<ResultFrame>& frames() const;
+
+private:
+    std::string name_;
+    std::vector<ResultFrame> frames_;
+};
+
+} // namespace fesa::results

tests/CMakeLists.txt

@@ -0,0 +1,2 @@
+add_subdirectory(unit)
+add_subdirectory(integration)

tests/integration/CMakeLists.txt

@@ -0,0 +1,8 @@
+file(GLOB FESA_INTEGRATION_TEST_SOURCES CONFIGURE_DEPENDS "${CMAKE_CURRENT_SOURCE_DIR}/*_test.cpp")
+
+foreach(test_source IN LISTS FESA_INTEGRATION_TEST_SOURCES)
+    get_filename_component(test_name "${test_source}" NAME_WE)
+    add_executable("${test_name}" "${test_source}")
+    target_link_libraries("${test_name}" PRIVATE fesa_core)
+    add_test(NAME "${test_name}" COMMAND "${test_name}")
+endforeach()

tests/integration/solver_core_skeleton_integration_test.cpp

@@ -0,0 +1,64 @@
+#include <fesa/analysis/linear_static_analysis.hpp>
+#include <fesa/results/results.hpp>
+
+namespace {
+
+int fail()
+{
+    return 1;
+}
+
+fesa::model::Domain make_domain()
+{
+    fesa::model::Domain domain;
+    domain.add_node({fesa::core::NodeId{1}, {0.0, 0.0, 0.0}});
+    domain.add_node({fesa::core::NodeId{2}, {1.0, 0.0, 0.0}});
+    domain.add_material({fesa::core::MaterialId{3}, "steel"});
+    domain.add_property({fesa::core::PropertyId{4}, "bar", fesa::core::MaterialId{3}});
+    domain.add_element({
+        fesa::core::ElementId{5},
+        fesa::model::ElementTopology::truss2,
+        {fesa::core::NodeId{1}, fesa::core::NodeId{2}},
+        fesa::core::PropertyId{4}
+    });
+    fesa::model::AnalysisStep step{fesa::core::StepId{6}, "static-step"};
+    step.add_boundary_condition({fesa::core::NodeId{1}, fesa::model::DofComponent::ux, 0.0});
+    step.add_load({fesa::core::NodeId{2}, fesa::model::DofComponent::ux, 10.0});
+    domain.add_step(step);
+    return domain;
+}
+
+} // namespace
+
+int main()
+{
+    const auto domain = make_domain();
+    fesa::analysis::LinearStaticAnalysis analysis{domain, fesa::core::StepId{6}};
+    analysis.run();
+
+    if (analysis.analysis_model() == nullptr || analysis.state() == nullptr) {
+        return fail();
+    }
+    if (analysis.analysis_model()->active_elements().size() != 1 ||
+        analysis.analysis_model()->active_boundary_conditions().size() != 1 ||
+        analysis.analysis_model()->active_loads().size() != 1) {
+        return fail();
+    }
+
+    fesa::results::ResultStep result_step{"static-step"};
+    auto& frame = result_step.add_frame(0, 0.0);
+    frame.add_field_output({
+        "U",
+        fesa::results::FieldLocation::nodal,
+        {"ux", "uy", "uz"},
+        {1, 2},
+        {0.0, 0.0, 0.0, 0.0, 0.0, 0.0}
+    });
+
+    if (result_step.frames().size() != 1 ||
+        result_step.frames()[0].field_outputs().size() != 1) {
+        return fail();
+    }
+
+    return 0;
+}

tests/unit/CMakeLists.txt

@@ -0,0 +1,8 @@
+file(GLOB FESA_UNIT_TEST_SOURCES CONFIGURE_DEPENDS "${CMAKE_CURRENT_SOURCE_DIR}/*_test.cpp")
+
+foreach(test_source IN LISTS FESA_UNIT_TEST_SOURCES)
+    get_filename_component(test_name "${test_source}" NAME_WE)
+    add_executable("${test_name}" "${test_source}")
+    target_link_libraries("${test_name}" PRIVATE fesa_core)
+    add_test(NAME "${test_name}" COMMAND "${test_name}")
+endforeach()

tests/unit/analysis_flow_linear_static_analysis_test.cpp

@@ -0,0 +1,37 @@
+#include <fesa/analysis/linear_static_analysis.hpp>
+
+namespace {
+
+fesa::model::Domain make_domain()
+{
+    fesa::model::Domain domain;
+    domain.add_node({fesa::core::NodeId{1}, {0.0, 0.0, 0.0}});
+    domain.add_node({fesa::core::NodeId{2}, {1.0, 0.0, 0.0}});
+    domain.add_material({fesa::core::MaterialId{3}, "steel"});
+    domain.add_property({fesa::core::PropertyId{4}, "bar", fesa::core::MaterialId{3}});
+    domain.add_element({
+        fesa::core::ElementId{5},
+        fesa::model::ElementTopology::truss2,
+        {fesa::core::NodeId{1}, fesa::core::NodeId{2}},
+        fesa::core::PropertyId{4}
+    });
+    fesa::model::AnalysisStep step{fesa::core::StepId{6}, "static"};
+    step.add_boundary_condition({fesa::core::NodeId{1}, fesa::model::DofComponent::ux, 0.0});
+    step.add_load({fesa::core::NodeId{2}, fesa::model::DofComponent::ux, 10.0});
+    domain.add_step(step);
+    return domain;
+}
+
+} // namespace
+
+int main()
+{
+    const auto domain = make_domain();
+    fesa::analysis::LinearStaticAnalysis analysis{domain, fesa::core::StepId{6}};
+    analysis.run();
+
+    if (analysis.analysis_model() == nullptr || analysis.state() == nullptr) {
+        return 1;
+    }
+    return analysis.state()->displacement().size() == 6 ? 0 : 1;
+}

tests/unit/analysis_flow_template_test.cpp

@@ -0,0 +1,44 @@
+#include <fesa/analysis/analysis.hpp>
+
+#include <string>
+#include <vector>
+
+class RecordingAnalysis : public fesa::analysis::Analysis {
+public:
+    const std::vector<std::string>& calls() const
+    {
+        return calls_;
+    }
+
+protected:
+    void initialize() override { calls_.push_back("initialize"); }
+    void build_analysis_model() override { calls_.push_back("build_analysis_model"); }
+    void build_dof_map() override { calls_.push_back("build_dof_map"); }
+    void build_sparse_pattern() override { calls_.push_back("build_sparse_pattern"); }
+    void assemble() override { calls_.push_back("assemble"); }
+    void apply_boundary_conditions() override { calls_.push_back("apply_boundary_conditions"); }
+    void solve() override { calls_.push_back("solve"); }
+    void update_state() override { calls_.push_back("update_state"); }
+    void write_results() override { calls_.push_back("write_results"); }
+
+private:
+    std::vector<std::string> calls_;
+};
+
+int main()
+{
+    RecordingAnalysis analysis;
+    analysis.run();
+    const std::vector<std::string> expected{
+        "initialize",
+        "build_analysis_model",
+        "build_dof_map",
+        "build_sparse_pattern",
+        "assemble",
+        "apply_boundary_conditions",
+        "solve",
+        "update_state",
+        "write_results"
+    };
+    return analysis.calls() == expected ? 0 : 1;
+}

tests/unit/analysis_model_view_test.cpp

@@ -0,0 +1,73 @@
+#include <fesa/analysis/analysis_model.hpp>
+
+#include <stdexcept>
+
+namespace {
+
+fesa::model::Domain make_domain()
+{
+    fesa::model::Domain domain;
+    domain.add_node({fesa::core::NodeId{1}, {0.0, 0.0, 0.0}});
+    domain.add_node({fesa::core::NodeId{2}, {1.0, 0.0, 0.0}});
+    domain.add_material({fesa::core::MaterialId{3}, "steel"});
+    domain.add_property({fesa::core::PropertyId{4}, "bar", fesa::core::MaterialId{3}});
+    domain.add_element({
+        fesa::core::ElementId{5},
+        fesa::model::ElementTopology::truss2,
+        {fesa::core::NodeId{1}, fesa::core::NodeId{2}},
+        fesa::core::PropertyId{4}
+    });
+
+    fesa::model::AnalysisStep step{fesa::core::StepId{6}, "static"};
+    step.add_boundary_condition({fesa::core::NodeId{1}, fesa::model::DofComponent::ux, 0.0});
+    step.add_load({fesa::core::NodeId{2}, fesa::model::DofComponent::ux, 10.0});
+    domain.add_step(step);
+    return domain;
+}
+
+int fail()
+{
+    return 1;
+}
+
+} // namespace
+
+int main()
+{
+    const auto domain = make_domain();
+    const fesa::analysis::AnalysisModel model{domain, fesa::core::StepId{6}};
+
+    if (&model.domain() != &domain) {
+        return fail();
+    }
+    if (&model.step() != domain.find_step(fesa::core::StepId{6})) {
+        return fail();
+    }
+    if (model.active_elements().size() != 1 ||
+        model.active_elements()[0] != domain.find_element(fesa::core::ElementId{5})) {
+        return fail();
+    }
+    if (model.active_boundary_conditions().size() != 1 ||
+        model.active_loads().size() != 1) {
+        return fail();
+    }
+
+    const auto* property = model.property_for(*model.active_elements()[0]);
+    if (property == nullptr || property != domain.find_property(fesa::core::PropertyId{4})) {
+        return fail();
+    }
+
+    const auto* material = model.material_for(*property);
+    if (material == nullptr || material != domain.find_material(fesa::core::MaterialId{3})) {
+        return fail();
+    }
+
+    try {
+        const fesa::analysis::AnalysisModel missing{domain, fesa::core::StepId{99}};
+        (void)missing;
+        return fail();
+    } catch (const std::invalid_argument&) {
+    }
+
+    return 0;
+}

tests/unit/analysis_state_vectors_test.cpp

@@ -0,0 +1,80 @@
+#include <fesa/analysis/analysis_state.hpp>
+
+#include <stdexcept>
+#include <vector>
+
+namespace {
+
+int fail()
+{
+    return 1;
+}
+
+bool all_zero(const std::vector<double>& values)
+{
+    for (const double value : values) {
+        if (value != 0.0) {
+            return false;
+        }
+    }
+    return true;
+}
+
+} // namespace
+
+int main()
+{
+    fesa::analysis::AnalysisState state{3};
+    if (state.displacement().size() != 3 ||
+        state.velocity().size() != 3 ||
+        state.acceleration().size() != 3 ||
+        state.temperature().size() != 3 ||
+        state.external_force().size() != 3 ||
+        state.internal_force().size() != 3 ||
+        state.residual().size() != 3) {
+        return fail();
+    }
+    if (!all_zero(state.displacement()) || !all_zero(state.residual())) {
+        return fail();
+    }
+
+    state.set_displacement({1.0, 2.0, 3.0});
+    if (state.displacement()[2] != 3.0) {
+        return fail();
+    }
+
+    state.set_external_force({10.0, 20.0, 30.0});
+    state.set_internal_force({1.0, 2.0, 3.0});
+    state.update_residual();
+    if (state.residual()[0] != 9.0 ||
+        state.residual()[1] != 18.0 ||
+        state.residual()[2] != 27.0) {
+        return fail();
+    }
+
+    try {
+        state.set_displacement({1.0});
+        return fail();
+    } catch (const std::invalid_argument&) {
+    }
+
+    state.iteration_state().time = 1.25;
+    state.iteration_state().increment = 2;
+    state.iteration_state().iteration = 3;
+    if (state.iteration_state().time != 1.25 ||
+        state.iteration_state().increment != 2 ||
+        state.iteration_state().iteration != 3) {
+        return fail();
+    }
+
+    state.set_element_state(fesa::core::ElementId{7}, {4.0, 5.0});
+    const auto* element_state = state.element_state(fesa::core::ElementId{7});
+    if (element_state == nullptr || element_state->size() != 2 || (*element_state)[1] != 5.0) {
+        return fail();
+    }
+    if (state.element_state(fesa::core::ElementId{8}) != nullptr) {
+        return fail();
+    }
+
+    return 0;
+}

tests/unit/core_diagnostic_test.cpp

@@ -0,0 +1,11 @@
+#include <fesa/core/diagnostic.hpp>
+
+int main()
+{
+    const fesa::core::Diagnostic diagnostic{
+        fesa::core::Severity::info,
+        "core.info",
+        "diagnostic"
+    };
+    return diagnostic.code == "core.info" ? 0 : 1;
+}

tests/unit/core_ids_test.cpp

@@ -0,0 +1,9 @@
+#include <fesa/core/ids.hpp>
+
+#include <type_traits>
+
+int main()
+{
+    static_assert(!std::is_same_v<fesa::core::NodeId, fesa::core::ElementId>);
+    return fesa::core::NodeId{7}.value == 7 ? 0 : 1;
+}

tests/unit/core_primitives_test.cpp

@@ -0,0 +1,50 @@
+#include <fesa/core/diagnostic.hpp>
+#include <fesa/core/ids.hpp>
+#include <fesa/core/status.hpp>
+
+#include <string>
+#include <type_traits>
+
+namespace {
+
+int fail()
+{
+    return 1;
+}
+
+} // namespace
+
+int main()
+{
+    static_assert(!std::is_same_v<fesa::core::NodeId, fesa::core::ElementId>);
+
+    const auto ok = fesa::core::Status::ok();
+    if (!ok.is_ok() || !ok.diagnostics().empty()) {
+        return fail();
+    }
+
+    fesa::core::Diagnostic error{
+        fesa::core::Severity::error,
+        "core.error",
+        "core failure"
+    };
+    auto failed = fesa::core::Status::failure(error);
+    if (failed.is_ok() || failed.diagnostics().size() != 1) {
+        return fail();
+    }
+    if (failed.diagnostics()[0].code != "core.error" ||
+        failed.diagnostics()[0].message != "core failure") {
+        return fail();
+    }
+
+    failed.add({fesa::core::Severity::warning, "core.warning", "check warning"});
+    if (failed.diagnostics().size() != 2) {
+        return fail();
+    }
+    if (failed.diagnostics()[0].code != "core.error" ||
+        failed.diagnostics()[1].code != "core.warning") {
+        return fail();
+    }
+
+    return 0;
+}

tests/unit/core_status_test.cpp

@@ -0,0 +1,7 @@
+#include <fesa/core/status.hpp>
+
+int main()
+{
+    const auto status = fesa::core::Status::ok();
+    return status.is_ok() ? 0 : 1;
+}

tests/unit/dof_manager_dof_key_test.cpp

@@ -0,0 +1,8 @@
+#include <fesa/fem/dof_key.hpp>
+
+int main()
+{
+    const fesa::fem::DofKey lhs{fesa::core::NodeId{1}, fesa::model::DofComponent::ux};
+    const fesa::fem::DofKey rhs{fesa::core::NodeId{1}, fesa::model::DofComponent::ux};
+    return lhs == rhs ? 0 : 1;
+}

tests/unit/dof_manager_numbering_test.cpp

@@ -0,0 +1,83 @@
+#include <fesa/fem/dof_manager.hpp>
+
+#include <stdexcept>
+#include <vector>
+
+namespace {
+
+int fail()
+{
+    return 1;
+}
+
+} // namespace
+
+int main()
+{
+    fesa::fem::DofManager dofs;
+    dofs.define_node_dofs(fesa::core::NodeId{2}, {
+        fesa::model::DofComponent::ux,
+        fesa::model::DofComponent::uy
+    });
+    dofs.define_node_dofs(fesa::core::NodeId{1}, {
+        fesa::model::DofComponent::uy,
+        fesa::model::DofComponent::ux
+    });
+    dofs.apply_boundary_condition({
+        fesa::core::NodeId{1},
+        fesa::model::DofComponent::ux,
+        0.0
+    });
+    dofs.number_equations();
+
+    const fesa::fem::DofKey n1ux{fesa::core::NodeId{1}, fesa::model::DofComponent::ux};
+    const fesa::fem::DofKey n1uy{fesa::core::NodeId{1}, fesa::model::DofComponent::uy};
+    const fesa::fem::DofKey n2ux{fesa::core::NodeId{2}, fesa::model::DofComponent::ux};
+    const fesa::fem::DofKey n2uy{fesa::core::NodeId{2}, fesa::model::DofComponent::uy};
+
+    if (dofs.total_dof_count() != 4 ||
+        dofs.constrained_dof_count() != 1 ||
+        dofs.free_dof_count() != 3) {
+        return fail();
+    }
+    if (dofs.equation_id(n1ux) != 0 ||
+        dofs.equation_id(n1uy) != 1 ||
+        dofs.equation_id(n2ux) != 2 ||
+        dofs.equation_id(n2uy) != 3) {
+        return fail();
+    }
+    if (!dofs.is_constrained(n1ux) ||
+        dofs.free_equation_id(n1ux).has_value()) {
+        return fail();
+    }
+    if (!dofs.free_equation_id(n1uy).has_value() ||
+        *dofs.free_equation_id(n1uy) != 0 ||
+        *dofs.free_equation_id(n2ux) != 1 ||
+        *dofs.free_equation_id(n2uy) != 2) {
+        return fail();
+    }
+
+    const auto full = dofs.expand_free_vector({11.0, 22.0, 33.0});
+    if (full.size() != 4 ||
+        full[0] != 0.0 ||
+        full[1] != 11.0 ||
+        full[2] != 22.0 ||
+        full[3] != 33.0) {
+        return fail();
+    }
+
+    const auto& pattern = dofs.sparse_pattern();
+    if (pattern.size() != 9 ||
+        pattern.front() != std::pair<int, int>{0, 0} ||
+        pattern.back() != std::pair<int, int>{2, 2}) {
+        return fail();
+    }
+
+    try {
+        (void)dofs.equation_id({fesa::core::NodeId{99}, fesa::model::DofComponent::ux});
+        return fail();
+    } catch (const std::invalid_argument&) {
+    }
+
+    return 0;
+}

tests/unit/harness_smoke_test.cpp

@@ -0,0 +1,7 @@
+#include <string>
+
+int main()
+{
+    const std::string project = "fesa";
+    return project.size() == 4 ? 0 : 1;
+}

tests/unit/model_analysis_step_test.cpp

@@ -0,0 +1,7 @@
+#include <fesa/model/analysis_step.hpp>
+
+int main()
+{
+    const fesa::model::AnalysisStep step{fesa::core::StepId{1}, "static"};
+    return step.name() == "static" ? 0 : 1;
+}

tests/unit/model_boundary_condition_test.cpp

@@ -0,0 +1,11 @@
+#include <fesa/model/boundary_condition.hpp>
+
+int main()
+{
+    const fesa::model::BoundaryCondition bc{
+        fesa::core::NodeId{1},
+        fesa::model::DofComponent::ux,
+        0.0
+    };
+    return bc.node_id().value == 1 ? 0 : 1;
+}

tests/unit/model_domain_test.cpp

@@ -0,0 +1,79 @@
+#include <fesa/model/domain.hpp>
+
+#include <array>
+#include <vector>
+
+namespace {
+
+int fail()
+{
+    return 1;
+}
+
+} // namespace
+
+int main()
+{
+    fesa::model::Domain domain;
+
+    domain.add_node(fesa::model::Node{fesa::core::NodeId{1}, {1.0, 2.0, 3.0}});
+    domain.add_element(fesa::model::Element{
+        fesa::core::ElementId{10},
+        fesa::model::ElementTopology::truss2,
+        {fesa::core::NodeId{1}, fesa::core::NodeId{2}},
+        fesa::core::PropertyId{20}
+    });
+    domain.add_material(fesa::model::Material{fesa::core::MaterialId{30}, "steel"});
+    domain.add_property(fesa::model::Property{
+        fesa::core::PropertyId{20},
+        "bar",
+        fesa::core::MaterialId{30}
+    });
+
+    fesa::model::AnalysisStep step{fesa::core::StepId{40}, "load"};
+    step.add_boundary_condition({fesa::core::NodeId{1}, fesa::model::DofComponent::ux, 0.0});
+    step.add_load({fesa::core::NodeId{2}, fesa::model::DofComponent::ux, 10.0});
+    domain.add_step(step);
+
+    const auto* node = domain.find_node(fesa::core::NodeId{1});
+    if (node == nullptr || node->coordinates()[2] != 3.0) {
+        return fail();
+    }
+
+    const auto* element = domain.find_element(fesa::core::ElementId{10});
+    if (element == nullptr ||
+        element->topology() != fesa::model::ElementTopology::truss2 ||
+        element->node_ids().size() != 2 ||
+        element->property_id().value != 20) {
+        return fail();
+    }
+
+    const auto* material = domain.find_material(fesa::core::MaterialId{30});
+    if (material == nullptr || material->name() != "steel") {
+        return fail();
+    }
+
+    const auto* property = domain.find_property(fesa::core::PropertyId{20});
+    if (property == nullptr ||
+        property->name() != "bar" ||
+        property->material_id().value != 30) {
+        return fail();
+    }
+
+    const auto* analysis_step = domain.find_step(fesa::core::StepId{40});
+    if (analysis_step == nullptr ||
+        analysis_step->boundary_conditions().size() != 1 ||
+        analysis_step->loads().size() != 1) {
+        return fail();
+    }
+
+    if (domain.find_node(fesa::core::NodeId{999}) != nullptr ||
+        domain.find_element(fesa::core::ElementId{999}) != nullptr ||
+        domain.find_material(fesa::core::MaterialId{999}) != nullptr ||
+        domain.find_property(fesa::core::PropertyId{999}) != nullptr ||
+        domain.find_step(fesa::core::StepId{999}) != nullptr) {
+        return fail();
+    }
+
+    return 0;
+}

tests/unit/model_element_test.cpp

@@ -0,0 +1,12 @@
+#include <fesa/model/element.hpp>
+
+int main()
+{
+    const fesa::model::Element element{
+        fesa::core::ElementId{1},
+        fesa::model::ElementTopology::bar2,
+        {fesa::core::NodeId{1}, fesa::core::NodeId{2}},
+        fesa::core::PropertyId{3}
+    };
+    return element.node_ids().size() == 2 ? 0 : 1;
+}

tests/unit/model_load_test.cpp

@@ -0,0 +1,11 @@
+#include <fesa/model/load.hpp>
+
+int main()
+{
+    const fesa::model::Load load{
+        fesa::core::NodeId{2},
+        fesa::model::DofComponent::ux,
+        5.0
+    };
+    return load.value() == 5.0 ? 0 : 1;
+}

tests/unit/model_material_test.cpp

@@ -0,0 +1,7 @@
+#include <fesa/model/material.hpp>
+
+int main()
+{
+    const fesa::model::Material material{fesa::core::MaterialId{1}, "steel"};
+    return material.name() == "steel" ? 0 : 1;
+}

tests/unit/model_node_test.cpp

@@ -0,0 +1,7 @@
+#include <fesa/model/node.hpp>
+
+int main()
+{
+    const fesa::model::Node node{fesa::core::NodeId{1}, {0.0, 1.0, 2.0}};
+    return node.coordinates()[1] == 1.0 ? 0 : 1;
+}

tests/unit/model_property_test.cpp

@@ -0,0 +1,11 @@
+#include <fesa/model/property.hpp>
+
+int main()
+{
+    const fesa::model::Property property{
+        fesa::core::PropertyId{2},
+        "section",
+        fesa::core::MaterialId{3}
+    };
+    return property.material_id().value == 3 ? 0 : 1;
+}

tests/unit/results_containers_test.cpp

@@ -0,0 +1,69 @@
+#include <fesa/results/results.hpp>
+
+#include <stdexcept>
+
+namespace {
+
+int fail()
+{
+    return 1;
+}
+
+} // namespace
+
+int main()
+{
+    fesa::results::ResultStep step{"static"};
+    auto& frame = step.add_frame(1, 0.0);
+    if (step.name() != "static" ||
+        step.frames().size() != 1 ||
+        frame.frame_id() != 1 ||
+        frame.time() != 0.0) {
+        return fail();
+    }
+
+    frame.add_field_output({
+        "U",
+        fesa::results::FieldLocation::nodal,
+        {"ux", "uy"},
+        {1, 2},
+        {0.0, 0.1, 1.0, 1.1}
+    });
+    if (frame.field_outputs().size() != 1 ||
+        frame.field_outputs()[0].entity_ids[1] != 2 ||
+        frame.field_outputs()[0].values[3] != 1.1) {
+        return fail();
+    }
+
+    frame.add_history_output({"load-factor", {0.0, 1.0}, {0.0, 10.0}});
+    if (frame.history_outputs().size() != 1 ||
+        frame.history_outputs()[0].values[1] != 10.0) {
+        return fail();
+    }
+
+    try {
+        frame.add_field_output({
+            "bad",
+            fesa::results::FieldLocation::nodal,
+            {},
+            {1},
+            {0.0}
+        });
+        return fail();
+    } catch (const std::invalid_argument&) {
+    }
+
+    try {
+        frame.add_field_output({
+            "bad-shape",
+            fesa::results::FieldLocation::nodal,
+            {"ux", "uy"},
+            {1},
+            {0.0}
+        });
+        return fail();
+    } catch (const std::invalid_argument&) {
+    }
+
+    return 0;
+}