style: resolve the remaining ruff findings

Auto-fixes (UP037, UP038, F401, I001, SIM105, RUF100) plus hand-fixes:
drop the now-unused `Union` imports, annotate mutable class attributes
with ClassVar, raise ValidationError instead of blind Exception in the
zero-length test, delete two dead locals, and bind the per-iteration
grid-builder closures to their loop variables (B023).

tests/integration/test_basic_truss.py

@@ -11,7 +11,7 @@ import pytest
 
 pytest.importorskip("openseespy")
 
-from otko.services.opensees_runner import OpenSeesRunner  # noqa: E402
+from otko.services.opensees_runner import OpenSeesRunner
 
 pytestmark = pytest.mark.slow
 
@@ -25,7 +25,7 @@ def test_basic_truss_matches_opensees_tcl_reference() -> None:
     a linear rescale of the Tcl model — any deviation would flag a
     real solver/translation issue.
     """
-    from examples.basic_truss import build_basic_truss, IN_TO_M
+    from examples.basic_truss import IN_TO_M, build_basic_truss
 
     proj = build_basic_truss()
     runner = OpenSeesRunner(proj)
@@ -45,6 +45,7 @@ def test_basic_truss_matches_opensees_tcl_reference() -> None:
 def test_basic_truss_round_trips(tmp_path) -> None:  # type: ignore[no-untyped-def]
     """The example project must survive save/load without any information loss."""
     from examples.basic_truss import build_basic_truss
+
     from otko.services import load_project, save_project
 
     p = build_basic_truss()

tests/integration/test_beam_quad_2d.py

@@ -9,8 +9,8 @@ import pytest
 
 pytest.importorskip("openseespy")
 
-from otko.services import load_project, save_project  # noqa: E402
-from otko.services.opensees_runner import OpenSeesRunner  # noqa: E402
+from otko.services import load_project, save_project
+from otko.services.opensees_runner import OpenSeesRunner
 
 pytestmark = pytest.mark.slow
 

tests/integration/test_combinations.py

@@ -8,7 +8,7 @@ import pytest
 
 ops = pytest.importorskip("openseespy.opensees")  # skip if OpenSeesPy not installed
 
-from otko.core import (  # noqa: E402
+from otko.core import (
     ElasticBeamColumn,
     ElasticSection,
     LinearTimeSeries,
@@ -20,8 +20,8 @@ from otko.core import (  # noqa: E402
     Project,
     StaticCase,
 )
-from otko.services import OpenSeesRunner, evaluate_combination  # noqa: E402
-from otko.services.results import StaticResults  # noqa: E402
+from otko.services import OpenSeesRunner, evaluate_combination
+from otko.services.results import StaticResults
 
 pytestmark = pytest.mark.slow
 

tests/integration/test_concrete04_runner.py

@@ -18,7 +18,7 @@ import pytest
 
 pytest.importorskip("openseespy")
 
-from otko.core import (  # noqa: E402
+from otko.core import (
     Concrete04,
     FiberSection,
     ForceBeamColumn,
@@ -32,7 +32,7 @@ from otko.core import (  # noqa: E402
     StaticCase,
     UnitSystem,
 )
-from otko.services.opensees_runner import OpenSeesRunner  # noqa: E402
+from otko.services.opensees_runner import OpenSeesRunner
 
 pytestmark = pytest.mark.slow
 

tests/integration/test_dof_coverage.py

@@ -11,7 +11,7 @@ import pytest
 
 pytest.importorskip("openseespy")
 
-from otko.core import (  # noqa: E402
+from otko.core import (
     ElasticUniaxial,
     LinearTimeSeries,
     NodalLoad,
@@ -21,7 +21,7 @@ from otko.core import (  # noqa: E402
     StaticCase,
     TrussElement,
 )
-from otko.services.opensees_runner import OpenSeesRunner  # noqa: E402
+from otko.services.opensees_runner import OpenSeesRunner
 
 pytestmark = pytest.mark.slow
 

tests/integration/test_eigen_two_storey_one_bay_frame.py

@@ -8,9 +8,9 @@ import pytest
 
 pytest.importorskip("openseespy")
 
-from otko.core import ModalCase  # noqa: E402
-from otko.services import load_project, save_project  # noqa: E402
-from otko.services.opensees_runner import OpenSeesRunner  # noqa: E402
+from otko.core import ModalCase
+from otko.services import load_project, save_project
+from otko.services.opensees_runner import OpenSeesRunner
 
 pytestmark = pytest.mark.slow
 

tests/integration/test_eigen_two_storey_shear_frame.py

@@ -8,9 +8,9 @@ import pytest
 
 pytest.importorskip("openseespy")
 
-from otko.core import ModalCase  # noqa: E402
-from otko.services import load_project, save_project  # noqa: E402
-from otko.services.opensees_runner import OpenSeesRunner  # noqa: E402
+from otko.core import ModalCase
+from otko.services import load_project, save_project
+from otko.services.opensees_runner import OpenSeesRunner
 
 pytestmark = pytest.mark.slow
 

tests/integration/test_elastic_frame.py

@@ -8,9 +8,9 @@ import pytest
 
 pytest.importorskip("openseespy")
 
-from otko.core import ModalCase, StaticCase  # noqa: E402
-from otko.services import load_project, save_project  # noqa: E402
-from otko.services.opensees_runner import OpenSeesRunner  # noqa: E402
+from otko.core import ModalCase, StaticCase
+from otko.services import load_project, save_project
+from otko.services.opensees_runner import OpenSeesRunner
 
 pytestmark = pytest.mark.slow
 
@@ -29,7 +29,6 @@ def _reload(proj, tmp_path):  # type: ignore[no-untyped-def]
 def test_elastic_frame_gravity_reactions(tmp_path) -> None:  # type: ignore[no-untyped-def]
     """ΣFy at base = total applied gravity (distributed w × beam × floors)."""
     from examples.elastic_frame import (
-        BAY,
         LOAD_F1,
         LOAD_F2,
         LOAD_F3,
@@ -70,7 +69,6 @@ def test_elastic_frame_gravity_reactions(tmp_path) -> None:  # type: ignore[no-u
 def test_elastic_frame_gravity_plus_lateral_reactions(tmp_path) -> None:  # type: ignore[no-untyped-def]
     """ΣFx at base must equal -(lateral applied) within PDelta tolerance."""
     from examples.elastic_frame import (
-        BAY,
         LOAD_F1,
         LOAD_F2,
         LOAD_F3,
@@ -120,5 +118,5 @@ def test_elastic_frame_modal_periods(tmp_path) -> None:  # type: ignore[no-untyp
     # 0.1930, 0.1562, 0.130 s. Our solve nails these within 1.5%.
     expected = [1.040, 0.3526, 0.1930, 0.1562, 0.130]
     periods = [2.0 * math.pi / math.sqrt(v) for v in r.eigenvalues]
-    for i, (T, T_ref) in enumerate(zip(periods, expected), start=1):
-        assert T == pytest.approx(T_ref, rel=0.02), f"T{i} = {T:.4f} s, reference {T_ref:.4f} s"
+    for i, (T, T_ref) in enumerate(zip(periods, expected, strict=False), start=1):
+        assert pytest.approx(T_ref, rel=0.02) == T, f"T{i} = {T:.4f} s, reference {T_ref:.4f} s"

tests/integration/test_ex1a_canti2d.py

@@ -9,9 +9,9 @@ import pytest
 
 pytest.importorskip("openseespy")
 
-from otko.core import PushoverCase, TransientCase  # noqa: E402
-from otko.services import load_project, save_project  # noqa: E402
-from otko.services.opensees_runner import OpenSeesRunner  # noqa: E402
+from otko.core import PushoverCase, TransientCase
+from otko.services import load_project, save_project
+from otko.services.opensees_runner import OpenSeesRunner
 
 pytestmark = pytest.mark.slow
 

tests/integration/test_ex1a_canti2d_eq.py

@@ -9,8 +9,8 @@ import pytest
 
 pytest.importorskip("openseespy")
 
-from otko.services import load_project, save_project  # noqa: E402
-from otko.services.opensees_runner import OpenSeesRunner  # noqa: E402
+from otko.services import load_project, save_project
+from otko.services.opensees_runner import OpenSeesRunner
 
 pytestmark = pytest.mark.slow
 

tests/integration/test_ex1b_portal2d.py

@@ -9,9 +9,9 @@ import pytest
 
 pytest.importorskip("openseespy")
 
-from otko.core import PushoverCase, TransientCase  # noqa: E402
-from otko.services import load_project, save_project  # noqa: E402
-from otko.services.opensees_runner import OpenSeesRunner  # noqa: E402
+from otko.core import PushoverCase, TransientCase
+from otko.services import load_project, save_project
+from otko.services.opensees_runner import OpenSeesRunner
 
 pytestmark = pytest.mark.slow
 

tests/integration/test_ex2a_canti2d_elastic_element.py

@@ -9,9 +9,9 @@ import pytest
 
 pytest.importorskip("openseespy")
 
-from otko.core import PushoverCase, TransientCase  # noqa: E402
-from otko.services import load_project, save_project  # noqa: E402
-from otko.services.opensees_runner import OpenSeesRunner  # noqa: E402
+from otko.core import PushoverCase, TransientCase
+from otko.services import load_project, save_project
+from otko.services.opensees_runner import OpenSeesRunner
 
 pytestmark = pytest.mark.slow
 

tests/integration/test_ex2b_canti2d_inelastic_section.py

@@ -9,9 +9,9 @@ import pytest
 
 pytest.importorskip("openseespy")
 
-from otko.core import PushoverCase, TransientCase  # noqa: E402
-from otko.services import load_project, save_project  # noqa: E402
-from otko.services.opensees_runner import OpenSeesRunner  # noqa: E402
+from otko.core import PushoverCase, TransientCase
+from otko.services import load_project, save_project
+from otko.services.opensees_runner import OpenSeesRunner
 
 pytestmark = pytest.mark.slow
 

tests/integration/test_ex2c_canti2d_inelastic_fiber_section.py

@@ -9,9 +9,9 @@ import pytest
 
 pytest.importorskip("openseespy")
 
-from otko.core import PushoverCase, TransientCase  # noqa: E402
-from otko.services import load_project, save_project  # noqa: E402
-from otko.services.opensees_runner import OpenSeesRunner  # noqa: E402
+from otko.core import PushoverCase, TransientCase
+from otko.services import load_project, save_project
+from otko.services.opensees_runner import OpenSeesRunner
 
 pytestmark = pytest.mark.slow
 

tests/integration/test_ex3_canti2d_variants.py

@@ -9,9 +9,9 @@ import pytest
 
 pytest.importorskip("openseespy")
 
-from otko.core import PushoverCase, TransientCase  # noqa: E402
-from otko.services import load_project, save_project  # noqa: E402
-from otko.services.opensees_runner import OpenSeesRunner  # noqa: E402
+from otko.core import PushoverCase, TransientCase
+from otko.services import load_project, save_project
+from otko.services.opensees_runner import OpenSeesRunner
 
 pytestmark = pytest.mark.slow
 

tests/integration/test_ex4_portal2d_variants.py

@@ -9,9 +9,9 @@ import pytest
 
 pytest.importorskip("openseespy")
 
-from otko.core import PushoverCase, TransientCase  # noqa: E402
-from otko.services import load_project, save_project  # noqa: E402
-from otko.services.opensees_runner import OpenSeesRunner  # noqa: E402
+from otko.core import PushoverCase, TransientCase
+from otko.services import load_project, save_project
+from otko.services.opensees_runner import OpenSeesRunner
 
 pytestmark = pytest.mark.slow
 

tests/integration/test_moment_curvature.py

@@ -8,13 +8,11 @@ behaviour is exercised by the Phase 9 pushover tests.
 
 from __future__ import annotations
 
-import math
-
 import pytest
 
 pytest.importorskip("openseespy")
 
-from otko.core import (  # noqa: E402
+from otko.core import (
     ElasticUniaxial,
     FiberSection,
     LinearTimeSeries,
@@ -26,7 +24,7 @@ from otko.core import (  # noqa: E402
     StaticCase,
     ZeroLengthSectionElement,
 )
-from otko.services.opensees_runner import OpenSeesRunner  # noqa: E402
+from otko.services.opensees_runner import OpenSeesRunner
 
 pytestmark = pytest.mark.slow
 
@@ -134,7 +132,7 @@ def test_pushover_drives_rotation_for_moment_curvature() -> None:
 
     # Every (κ, M) point must satisfy M = E·I·κ (1 % tolerance allows
     # for the ~20-fibre discretisation of the rectangular section).
-    for kappa, moment in zip(result.control_disp, result.base_shear):
+    for kappa, moment in zip(result.control_disp, result.base_shear, strict=False):
         if abs(kappa) < 1e-12:
             continue
         expected_M = E * I * kappa

tests/integration/test_moment_curvature_example.py

@@ -6,8 +6,8 @@ import pytest
 
 pytest.importorskip("openseespy")
 
-from otko.services import load_project  # noqa: E402
-from otko.services.opensees_runner import OpenSeesRunner  # noqa: E402
+from otko.services import load_project
+from otko.services.opensees_runner import OpenSeesRunner
 
 pytestmark = pytest.mark.slow
 
@@ -15,13 +15,13 @@ pytestmark = pytest.mark.slow
 def test_moment_curvature_example_round_trips_and_converges(tmp_path) -> None:  # type: ignore[no-untyped-def]
     """build_moment_curvature() → save → load → run → expected shape."""
     from examples.moment_curvature import (
-        build_moment_curvature,
         COL_DEPTH,
         COVER,
         E_STEEL,
         FY,
         MU,
         NUM_INCR,
+        build_moment_curvature,
     )
 
     proj = build_moment_curvature()

tests/integration/test_pattern_factors.py

@@ -8,7 +8,7 @@ import pytest
 
 ops = pytest.importorskip("openseespy.opensees")  # skip if OpenSeesPy not installed
 
-from otko.core import (  # noqa: E402
+from otko.core import (
     ElasticBeamColumn,
     ElasticSection,
     LinearTimeSeries,
@@ -18,7 +18,7 @@ from otko.core import (  # noqa: E402
     Project,
     StaticCase,
 )
-from otko.services import OpenSeesRunner  # noqa: E402
+from otko.services import OpenSeesRunner
 
 pytestmark = pytest.mark.slow
 

tests/integration/test_rc_frame_earthquake.py

@@ -9,8 +9,8 @@ import pytest
 
 pytest.importorskip("openseespy")
 
-from otko.services import load_project, save_project  # noqa: E402
-from otko.services.opensees_runner import OpenSeesRunner  # noqa: E402
+from otko.services import load_project, save_project
+from otko.services.opensees_runner import OpenSeesRunner
 
 pytestmark = pytest.mark.slow
 
@@ -18,9 +18,8 @@ pytestmark = pytest.mark.slow
 def test_rc_frame_earthquake_runs_and_has_oscillatory_response(tmp_path) -> None:  # type: ignore[no-untyped-def]
     """Synthetic ground motion produces bounded, oscillatory response."""
     from examples.rc_frame_earthquake import (
-        build_rc_frame_earthquake,
-        DT,
         N_PTS,
+        build_rc_frame_earthquake,
     )
 
     proj = build_rc_frame_earthquake()

tests/integration/test_rc_frame_gravity.py

@@ -6,8 +6,8 @@ import pytest
 
 pytest.importorskip("openseespy")
 
-from otko.services import load_project, save_project  # noqa: E402
-from otko.services.opensees_runner import OpenSeesRunner  # noqa: E402
+from otko.services import load_project, save_project
+from otko.services.opensees_runner import OpenSeesRunner
 
 pytestmark = pytest.mark.slow
 
@@ -22,7 +22,7 @@ def test_rc_frame_gravity_matches_opensees_reference(tmp_path) -> None:  # type:
     The column axial force is 180 kip compression (from the 180 kip
     load stepped onto each top node).
     """
-    from examples.rc_frame_gravity import build_rc_frame_gravity, P_LOAD
+    from examples.rc_frame_gravity import P_LOAD, build_rc_frame_gravity
 
     proj = build_rc_frame_gravity()
     proj.validate_references()

tests/integration/test_rc_frame_pushover.py

@@ -6,8 +6,8 @@ import pytest
 
 pytest.importorskip("openseespy")
 
-from otko.services import load_project, save_project  # noqa: E402
-from otko.services.opensees_runner import OpenSeesRunner  # noqa: E402
+from otko.services import load_project, save_project
+from otko.services.opensees_runner import OpenSeesRunner
 
 pytestmark = pytest.mark.slow
 
@@ -19,10 +19,11 @@ def test_rc_frame_pushover_reaches_target_with_fallback(tmp_path) -> None:  # ty
     AND shows expected nonlinear shape.
     """
     from examples.rc_frame_pushover import (
-        build_rc_frame_pushover,
         D_STEP,
         D_TARGET,
+        build_rc_frame_pushover,
     )
+
     from otko.core import PushoverCase
 
     proj = build_rc_frame_pushover()

tests/integration/test_runner_imposed_motion.py

@@ -23,7 +23,7 @@ import pytest
 ops = pytest.importorskip("openseespy.opensees")
 h5py = pytest.importorskip("h5py")
 
-from otko.core import (  # noqa: E402
+from otko.core import (
     ElasticUniaxial,
     ImposedSupportMotionPattern,
     Node,
@@ -33,7 +33,7 @@ from otko.core import (  # noqa: E402
     UniformExcitationPattern,
     ZeroLengthElement,
 )
-from otko.services import OpenSeesRunner  # noqa: E402
+from otko.services import OpenSeesRunner
 
 pytestmark = pytest.mark.slow
 

tests/integration/test_runner_modal.py

@@ -15,16 +15,16 @@ import math
 
 import pytest
 
-ops = pytest.importorskip("openseespy.opensees")  # noqa: F401
+ops = pytest.importorskip("openseespy.opensees")
 
-from otko.core import (  # noqa: E402
+from otko.core import (
     ElasticBeamColumn,
     ElasticSection,
     ModalCase,
     Node,
     Project,
 )
-from otko.services import OpenSeesRunner  # noqa: E402
+from otko.services import OpenSeesRunner
 
 pytestmark = pytest.mark.slow
 

tests/integration/test_runner_static.py

@@ -12,7 +12,7 @@ import pytest
 
 ops = pytest.importorskip("openseespy.opensees")  # skip if OpenSeesPy not installed
 
-from otko.core import (  # noqa: E402
+from otko.core import (
     ElasticBeamColumn,
     ElasticSection,
     LinearTimeSeries,
@@ -22,7 +22,7 @@ from otko.core import (  # noqa: E402
     Project,
     StaticCase,
 )
-from otko.services import OpenSeesRunner  # noqa: E402
+from otko.services import OpenSeesRunner
 
 pytestmark = pytest.mark.slow
 

tests/integration/test_runner_transient.py

@@ -12,10 +12,10 @@ import math
 import numpy as np
 import pytest
 
-ops = pytest.importorskip("openseespy.opensees")  # noqa: F401
-h5py = pytest.importorskip("h5py")  # noqa: F401
+ops = pytest.importorskip("openseespy.opensees")
+h5py = pytest.importorskip("h5py")
 
-from otko.core import (  # noqa: E402
+from otko.core import (
     ConstantTimeSeries,
     ElasticBeamColumn,
     ElasticSection,
@@ -27,7 +27,7 @@ from otko.core import (  # noqa: E402
     StaticCase,
     TransientCase,
 )
-from otko.services import OpenSeesRunner  # noqa: E402
+from otko.services import OpenSeesRunner
 
 pytestmark = pytest.mark.slow
 
@@ -51,7 +51,6 @@ def test_sdof_free_vibration_matches_cosine(tmp_path) -> None:  # type: ignore[n
     # (already done), then verify dt-step Newmark integration of free
     # vibration starting from a static IC.
     F0 = 100.0
-    u0 = F0 / k
 
     project = Project(
         ndm=2,