feat: consolidate units to Metric/Imperial with unit-aware dialogs

- core/units: two dominant systems (Metric m/kN, Imperial ft/kip) with
  display conversion helpers, legacy 4-system migration in ProjectMeta
- dialogs/docks: unit-aware material, section, case, load, grid and
  results labels; diagram renderer unit labels; render controls update
- docs: add consistent_units.md; regen examples/*.osmodel artifacts
- tests: update persistence/phase8/project/unit-labels for new systems

tests/gui/test_pushover_curve_units.py

@@ -42,7 +42,7 @@ def test_is_rotation_dof_ndf6() -> None:
 
 @pytest.mark.gui
 def test_si_translation_labels(qtbot) -> None:  # type: ignore[no-untyped-def]
-    v = PushoverCurveView(units=UnitSystem.SI_M_N, ndf=6)
+    v = PushoverCurveView(units=UnitSystem.METRIC, ndf=6)
     qtbot.addWidget(v)
     v.set_results(_pushover(control_dof=1))
     assert "m" in v._plot.getAxis("bottom").labelText
@@ -53,7 +53,7 @@ def test_si_translation_labels(qtbot) -> None:  # type: ignore[no-untyped-def]
 
 @pytest.mark.gui
 def test_si_rotation_labels_show_curvature_and_moment(qtbot) -> None:  # type: ignore[no-untyped-def]
-    v = PushoverCurveView(units=UnitSystem.SI_M_N, ndf=3)
+    v = PushoverCurveView(units=UnitSystem.METRIC, ndf=3)
     qtbot.addWidget(v)
     v.set_results(_pushover(control_dof=3))
     assert "1/m" in v._plot.getAxis("bottom").labelText
@@ -65,7 +65,7 @@ def test_si_rotation_labels_show_curvature_and_moment(qtbot) -> None:  # type: i
 @pytest.mark.gui
 def test_us_in_kip_rotation_labels(qtbot) -> None:  # type: ignore[no-untyped-def]
     """kip-in Moment-Curvature project must NOT show cm / kN anywhere."""
-    v = PushoverCurveView(units=UnitSystem.US_IN_KIP, ndf=3)
+    v = PushoverCurveView(units=UnitSystem.IMPERIAL, ndf=3)
     qtbot.addWidget(v)
     v.set_results(_pushover(control_dof=3))
     x_label = v._plot.getAxis("bottom").labelText
@@ -78,7 +78,7 @@ def test_us_in_kip_rotation_labels(qtbot) -> None:  # type: ignore[no-untyped-de
 
 @pytest.mark.gui
 def test_us_in_kip_translation_labels(qtbot) -> None:  # type: ignore[no-untyped-def]
-    v = PushoverCurveView(units=UnitSystem.US_IN_KIP, ndf=3)
+    v = PushoverCurveView(units=UnitSystem.IMPERIAL, ndf=3)
     qtbot.addWidget(v)
     v.set_results(_pushover(control_dof=1))
     assert "in" in v._plot.getAxis("bottom").labelText
@@ -90,7 +90,7 @@ def test_no_auto_scaling_applied_to_values(qtbot) -> None:  # type: ignore[no-un
     """Regression: earlier versions divided base_shear by 1000 to
     display kN. The values must now be drawn exactly as stored so
     kip-in users don't see nonsense scaling."""
-    v = PushoverCurveView(units=UnitSystem.US_IN_KIP, ndf=3)
+    v = PushoverCurveView(units=UnitSystem.IMPERIAL, ndf=3)
     qtbot.addWidget(v)
     r = _pushover(control_dof=3)
     v.set_results(r)

tests/gui/test_units_status_bar.py

@@ -12,6 +12,7 @@ from otko.core import UnitSystem  # noqa: E402
 @pytest.mark.gui
 def test_status_bar_combo_lists_all_unit_systems(qtbot) -> None:  # type: ignore[no-untyped-def]
     from otko.views.main_window import MainWindow
+
     mw = MainWindow()
     qtbot.addWidget(mw)
     assert mw._units_combo.count() == len(list(UnitSystem))
@@ -20,25 +21,27 @@ def test_status_bar_combo_lists_all_unit_systems(qtbot) -> None:  # type: ignore
 @pytest.mark.gui
 def test_status_bar_combo_reflects_project_units(qtbot) -> None:  # type: ignore[no-untyped-def]
     from otko.views.main_window import MainWindow
+
     mw = MainWindow()
     qtbot.addWidget(mw)
     mw._vm.new_project()
-    mw._vm.project.meta.units = UnitSystem.US_IN_KIP
+    mw._vm.project.meta.units = UnitSystem.IMPERIAL
     mw._sync_units_combo()
-    assert mw._units_combo.currentData() == UnitSystem.US_IN_KIP
+    assert mw._units_combo.currentData() == UnitSystem.IMPERIAL
 
 
 @pytest.mark.gui
 def test_status_bar_combo_write_updates_project(qtbot) -> None:  # type: ignore[no-untyped-def]
     """Changing the combo writes through to project.meta.units."""
     from otko.views.main_window import MainWindow
+
     mw = MainWindow()
     qtbot.addWidget(mw)
     mw._vm.new_project()
-    # Default is SI_M_N — switch to US_IN_KIP via the combo.
-    target_idx = mw._units_combo.findData(UnitSystem.US_IN_KIP)
+    # Default is Metric — switch to Imperial via the combo.
+    target_idx = mw._units_combo.findData(UnitSystem.IMPERIAL)
     mw._units_combo.setCurrentIndex(target_idx)
-    assert mw._vm.project.meta.units == UnitSystem.US_IN_KIP
+    assert mw._vm.project.meta.units == UnitSystem.IMPERIAL
     assert mw._vm.is_dirty
 
 
@@ -46,6 +49,7 @@ def test_status_bar_combo_write_updates_project(qtbot) -> None:  # type: ignore[
 def test_status_bar_combo_no_project_noop(qtbot) -> None:  # type: ignore[no-untyped-def]
     """Before a project is loaded, changing the combo is a no-op."""
     from otko.views.main_window import MainWindow
+
     mw = MainWindow()
     qtbot.addWidget(mw)
     # No crash even with no project.

tests/integration/test_concrete04_runner.py

@@ -56,7 +56,7 @@ def _build_project() -> Project:
     return Project(
         meta=ProjectMeta(
             name="Concrete04 fiber-section cantilever",
-            units=UnitSystem.SI_M_N,
+            units=UnitSystem.METRIC,
         ),
         ndm=2,
         ndf=3,

tests/integration/test_material_tester.py

@@ -40,7 +40,7 @@ from otko.services.material_tester import (
 def _simple_cantilever() -> Project:
     """Minimal 2-node elastic cantilever for the interleave test."""
     return Project(
-        meta=ProjectMeta(name="interleave-ref", units=UnitSystem.SI_M_N),
+        meta=ProjectMeta(name="interleave-ref", units=UnitSystem.METRIC),
         ndm=2,
         ndf=3,
         nodes=[

tests/unit/test_persistence.py

@@ -26,7 +26,7 @@ from otko.services import PROJECT_FILE_SUFFIX, load_project, save_project
 
 def _sample_project() -> Project:
     return Project(
-        meta=ProjectMeta(name="Sample", author="Ozan", units=UnitSystem.SI_M_N),
+        meta=ProjectMeta(name="Sample", author="Ozan", units=UnitSystem.METRIC),
         ndm=3, ndf=6,
         nodes=[
             Node(id=1, coords=(0, 0, 0), restraint=(True,) * 6),

tests/unit/test_phase8b.py

@@ -89,7 +89,7 @@ def test_pushover_case_schema() -> None:
 
 def test_pushover_case_round_trip(tmp_path) -> None:  # type: ignore[no-untyped-def]
     p = Project(
-        meta=ProjectMeta(name="PO test", units=UnitSystem.SI_M_N),
+        meta=ProjectMeta(name="PO test", units=UnitSystem.METRIC),
         ndm=3, ndf=6,
         nodes=[
             Node(id=1, coords=(0, 0, 0), restraint=(True,) * 6),
@@ -144,7 +144,7 @@ def test_pushover_case_round_trip(tmp_path) -> None:  # type: ignore[no-untyped-
 
 def test_beam_with_hinges_round_trip(tmp_path) -> None:  # type: ignore[no-untyped-def]
     p = Project(
-        meta=ProjectMeta(name="BWH", units=UnitSystem.SI_M_N),
+        meta=ProjectMeta(name="BWH", units=UnitSystem.METRIC),
         ndm=3, ndf=6,
         nodes=[
             Node(id=1, coords=(0, 0, 0), restraint=(True,) * 6),

tests/unit/test_phase8c.py

@@ -87,7 +87,7 @@ def _two_dof_modal(masses: list[float]) -> tuple[Project, ModalResults]:
     φ = (1, -1). Eigenvalues set to ω² = 100 and 400 (T = 0.628 s, 0.314 s).
     """
     p = Project(
-        meta=ProjectMeta(name="2dof", units=UnitSystem.SI_M_N),
+        meta=ProjectMeta(name="2dof", units=UnitSystem.METRIC),
         ndm=3, ndf=6,
         nodes=[
             Node(id=1, coords=(0, 0, 0), restraint=(True,) * 6),
@@ -170,7 +170,7 @@ def test_cqc_equals_srss_for_well_separated_modes() -> None:
 # ── ResponseSpectrumCase persistence ─────────────────────────────────
 def test_response_spectrum_case_round_trip(tmp_path) -> None:  # type: ignore[no-untyped-def]
     p = Project(
-        meta=ProjectMeta(name="rs", units=UnitSystem.SI_M_N),
+        meta=ProjectMeta(name="rs", units=UnitSystem.METRIC),
         ndm=3, ndf=6,
         nodes=[Node(id=1, coords=(0, 0, 0), restraint=(True,) * 6),
                Node(id=2, coords=(0, 0, 3))],

tests/unit/test_project.py

@@ -31,7 +31,7 @@ def test_empty_project_is_valid() -> None:
     assert p.schema_version == 1
     assert p.ndm == 3 and p.ndf == 6
     assert p.nodes == []
-    assert p.meta.units == UnitSystem.SI_M_N
+    assert p.meta.units == UnitSystem.METRIC
 
 
 def test_invalid_ndm_ndf_pair_rejected() -> None:
@@ -42,9 +42,9 @@ def test_invalid_ndm_ndf_pair_rejected() -> None:
 
 
 def test_meta_round_trip() -> None:
-    p = Project(meta=ProjectMeta(name="Bridge", author="Ozan", units=UnitSystem.SI_MM_N))
+    p = Project(meta=ProjectMeta(name="Bridge", author="Ozan", units=UnitSystem.IMPERIAL))
     assert p.meta.name == "Bridge"
-    assert p.meta.units == UnitSystem.SI_MM_N
+    assert p.meta.units == UnitSystem.IMPERIAL
 
 
 # ────────────────────────── id allocation ──────────────────────────
@@ -126,7 +126,8 @@ def test_validate_references_catches_missing_time_series_in_pattern() -> None:
         nodes=[Node(id=1, coords=(0, 0, 0))],
         load_patterns=[
             PlainLoadPattern(
-                id=1, time_series_id=99,
+                id=1,
+                time_series_id=99,
                 nodal_loads=[NodalLoad(node_id=1, forces=(0, 0, -10, 0, 0, 0))],
             )
         ],
@@ -143,8 +144,13 @@ def test_validate_references_catches_missing_material_in_fiber_patch() -> None:
                 id=1,
                 patches=[
                     RectangularPatch(
-                        material_id=99, n_fib_y=2, n_fib_z=2,
-                        y_i=-0.1, z_i=-0.1, y_j=0.1, z_j=0.1,
+                        material_id=99,
+                        n_fib_y=2,
+                        n_fib_z=2,
+                        y_i=-0.1,
+                        z_i=-0.1,
+                        y_j=0.1,
+                        z_j=0.1,
                     )
                 ],
             )
@@ -162,8 +168,13 @@ def test_validate_references_catches_missing_material_in_fiber_layer() -> None:
                 id=1,
                 layers=[
                     StraightLayer(
-                        material_id=99, n_bars=3, bar_area=1e-4,
-                        y_start=-0.1, z_start=-0.1, y_end=0.1, z_end=-0.1,
+                        material_id=99,
+                        n_bars=3,
+                        bar_area=1e-4,
+                        y_start=-0.1,
+                        z_start=-0.1,
+                        y_end=0.1,
+                        z_end=-0.1,
                     )
                 ],
             )
@@ -179,7 +190,8 @@ def test_validate_references_catches_missing_material_in_aggregator_pairing() ->
         sections=[
             ElasticSection(id=1, E=200e9, A=0.01, Iz=8.33e-6),
             SectionAggregator(
-                id=2, section_id=1,
+                id=2,
+                section_id=1,
                 pairings=[AggregatorDOF(material_id=99, dof="T")],
             ),
         ],
@@ -194,7 +206,8 @@ def test_validate_references_catches_missing_base_section_in_aggregator() -> Non
         materials=[Steel01(id=1, Fy=420e6, E0=200e9, b=0.01)],
         sections=[
             SectionAggregator(
-                id=2, section_id=42,
+                id=2,
+                section_id=42,
                 pairings=[AggregatorDOF(material_id=1, dof="T")],
             ),
         ],
@@ -214,19 +227,30 @@ def test_validate_references_passes_on_valid_fiber_and_aggregator() -> None:
                 id=1,
                 patches=[
                     RectangularPatch(
-                        material_id=1, n_fib_y=2, n_fib_z=2,
-                        y_i=-0.1, z_i=-0.1, y_j=0.1, z_j=0.1,
+                        material_id=1,
+                        n_fib_y=2,
+                        n_fib_z=2,
+                        y_i=-0.1,
+                        z_i=-0.1,
+                        y_j=0.1,
+                        z_j=0.1,
                     )
                 ],
                 layers=[
                     StraightLayer(
-                        material_id=2, n_bars=3, bar_area=1e-4,
-                        y_start=-0.1, z_start=-0.1, y_end=0.1, z_end=-0.1,
+                        material_id=2,
+                        n_bars=3,
+                        bar_area=1e-4,
+                        y_start=-0.1,
+                        z_start=-0.1,
+                        y_end=0.1,
+                        z_end=-0.1,
                     )
                 ],
             ),
             SectionAggregator(
-                id=2, section_id=1,
+                id=2,
+                section_id=1,
                 pairings=[AggregatorDOF(material_id=1, dof="T")],
             ),
         ],
@@ -237,7 +261,8 @@ def test_validate_references_passes_on_valid_fiber_and_aggregator() -> None:
 # ────────────────────────── small smoke build ──────────────────────────
 def test_full_truss_project_builds_and_validates() -> None:
     p = Project(
-        ndm=2, ndf=2,
+        ndm=2,
+        ndf=2,
         nodes=[
             Node(id=1, coords=(0, 0, 0), restraint=(True, True, False, False, False, False)),
             Node(id=2, coords=(4, 0, 0), restraint=(False, True, False, False, False, False)),
@@ -253,7 +278,8 @@ def test_full_truss_project_builds_and_validates() -> None:
         time_series=[LinearTimeSeries(id=1)],
         load_patterns=[
             PlainLoadPattern(
-                id=1, time_series_id=1,
+                id=1,
+                time_series_id=1,
                 nodal_loads=[NodalLoad(node_id=3, forces=(0, -1000, 0, 0, 0, 0))],
             )
         ],

tests/unit/test_unit_labels.py

@@ -5,10 +5,21 @@ from __future__ import annotations
 import pytest
 
 from otko.core import UnitSystem, labels_for
+from otko.core.units import (
+    QUANTITIES,
+    display_factor,
+    display_for,
+    display_label,
+    display_with_alias,
+    format_display,
+    format_rotation,
+    native_label,
+    to_display,
+)
 
 
-def test_si_m_n_labels() -> None:
-    lab = labels_for(UnitSystem.SI_M_N)
+def test_metric_labels() -> None:
+    lab = labels_for(UnitSystem.METRIC)
     assert lab.length == "m"
     assert lab.force == "N"
     assert lab.moment == "N·m"
@@ -16,8 +27,8 @@ def test_si_m_n_labels() -> None:
     assert lab.curvature == "1/m"
 
 
-def test_us_in_kip_labels() -> None:
-    lab = labels_for(UnitSystem.US_IN_KIP)
+def test_imperial_labels() -> None:
+    lab = labels_for(UnitSystem.IMPERIAL)
     assert lab.length == "in"
     assert lab.force == "kip"
     assert lab.moment == "kip·in"
@@ -25,20 +36,25 @@ def test_us_in_kip_labels() -> None:
     assert lab.curvature == "1/in"
 
 
-def test_us_ft_kip_labels() -> None:
-    lab = labels_for(UnitSystem.US_FT_KIP)
-    assert lab.length == "ft"
-    assert lab.force == "kip"
-    assert lab.moment == "kip·ft"
-    assert lab.stress == "ksf"
-    assert lab.curvature == "1/ft"
+def test_only_two_unit_systems_remain() -> None:
+    """The status-bar dropdown offers Metric and Imperial only."""
+    assert {u.name for u in UnitSystem} == {"METRIC", "IMPERIAL"}
 
 
-def test_si_mm_n_labels() -> None:
-    lab = labels_for(UnitSystem.SI_MM_N)
-    assert lab.length == "mm"
-    assert lab.force == "N"
-    assert lab.stress == "MPa"
+def test_legacy_unit_strings_migrate_on_load() -> None:
+    """Old .osmodel files (4-system era) load onto Metric/Imperial."""
+    from otko.core import ProjectMeta
+
+    assert ProjectMeta.model_validate({"units": "SI (m, N, kg, s, Pa)"}).units is UnitSystem.METRIC
+    assert ProjectMeta.model_validate({"units": "SI (mm, N, t, s, MPa)"}).units is UnitSystem.METRIC
+    assert (
+        ProjectMeta.model_validate({"units": "US (ft, kip, slug, s, ksf)"}).units
+        is UnitSystem.IMPERIAL
+    )
+    assert (
+        ProjectMeta.model_validate({"units": "US (in, kip, kip·s²/in, s, ksi)"}).units
+        is UnitSystem.IMPERIAL
+    )
 
 
 def test_labels_for_covers_every_unit_system() -> None:
@@ -47,3 +63,80 @@ def test_labels_for_covers_every_unit_system() -> None:
         lab = labels_for(us)
         # sanity: at least length / force populated.
         assert lab.length and lab.force
+
+
+def test_display_table_covers_taxonomy_per_system() -> None:
+    """Every system exposes every taxonomy quantity (§5 key set)."""
+    for us in UnitSystem:
+        for q in QUANTITIES:
+            label, factor = display_for(us, q)
+            assert label
+            assert factor > 0
+
+
+def test_display_identity_for_imperial() -> None:
+    """Imperial stores = displays (no factors)."""
+    for q in QUANTITIES:
+        assert display_factor(UnitSystem.IMPERIAL, q) == 1.0
+
+
+def test_display_spot_factors() -> None:
+    """Spot-check Metric factors: N→kN, Pa→MPa, m→mm."""
+    assert display_for(UnitSystem.METRIC, "force") == ("kN", 1e-3)
+    assert display_for(UnitSystem.METRIC, "stress") == ("MPa", 1e-6)
+    assert display_for(UnitSystem.METRIC, "displacement") == ("mm", 1000.0)
+    assert display_for(UnitSystem.METRIC, "section_dim") == ("mm", 1000.0)
+    assert display_for(UnitSystem.METRIC, "area") == ("mm²", 1e6)
+    assert display_for(UnitSystem.METRIC, "inertia") == ("mm⁴", 1e12)
+    assert display_for(UnitSystem.IMPERIAL, "stress") == ("ksi", 1.0)
+
+
+def test_rotation_always_factor_one() -> None:
+    """Rotation stays rad everywhere; ° is formatting only."""
+    for us in UnitSystem:
+        assert display_for(us, "rotation") == ("rad", 1.0)
+    assert format_rotation(3.14159265).startswith("3.142")
+    assert "°" in format_rotation(3.14159265, use_deg=True)
+
+
+def test_dimensionless_absent_from_table() -> None:
+    """Strain/drift/damping never take factors — KeyError by design."""
+    for us in UnitSystem:
+        for q in ("strain", "drift", "damping_ratio", "mass_participation"):
+            with pytest.raises(KeyError):
+                display_for(us, q)
+
+
+def test_to_display_applies_factor_on_read() -> None:
+    """1 m → 1000 mm; Imperial identity; values never written back."""
+    assert to_display(1.0, UnitSystem.METRIC, "displacement") == pytest.approx(1000.0)
+    assert to_display(1.0, UnitSystem.IMPERIAL, "displacement") == pytest.approx(1.0)
+    assert to_display(2.0, UnitSystem.METRIC, "force") == pytest.approx(0.002)
+    assert format_display(1.0, UnitSystem.METRIC, "displacement") == "1000 mm"
+    assert display_label(UnitSystem.IMPERIAL, "moment") == "kip·in"
+
+
+def test_native_labels_match_stored_units() -> None:
+    """Labels next to native values must be native units, not prefixes."""
+    assert native_label(UnitSystem.METRIC, "force") == "N"
+    assert native_label(UnitSystem.METRIC, "stress") == "Pa"
+    assert native_label(UnitSystem.METRIC, "displacement") == "m"
+    assert native_label(UnitSystem.METRIC, "distributed_load") == "N/m"
+    assert native_label(UnitSystem.METRIC, "area") == "m²"
+    assert native_label(UnitSystem.METRIC, "inertia") == "m⁴"
+    assert native_label(UnitSystem.IMPERIAL, "force") == "kip"
+    assert native_label(UnitSystem.IMPERIAL, "stress") == "ksi"
+    assert native_label(UnitSystem.IMPERIAL, "length") == "in"
+    for us in UnitSystem:
+        for q in QUANTITIES:
+            assert native_label(us, q)
+
+
+def test_small_value_lbf_alias() -> None:
+    """0.004 kip renders as 4.0 lbf; large values stay in kip."""
+    val, label = display_with_alias(0.004, UnitSystem.IMPERIAL, "force")
+    assert label == "lbf"
+    assert val == pytest.approx(4.0)
+    val_big, label_big = display_with_alias(2.0, UnitSystem.IMPERIAL, "force")
+    assert label_big == "kip"
+    assert val_big == pytest.approx(2.0)