feat: named case-result load combinations with full GUI support

Snapshots the current development tree, headlined by proper load
combinations (user request): a reusable LoadCombination entity of
weighted completed static-case results (e.g. 1.2xDead + 1.6xLive).

- core: LoadCombination/LoadCombinationItem entities, Project
  integration (lookup, unique ids, reference validation)
- services: combinations.py (linear superposition + envelope),
  exported via services __init__
- commands: undoable Add/Delete/Update for combinations
- GUI: Load Combinations manager dialog, Run-dialog evaluation,
  envelope display in Results panel, Combinations tab in Table dock
- tests: unit coverage (validation, math, error paths) + integration
  superposition check vs a single factored run

tests/gui/test_analysis_commands.py

@@ -0,0 +1,151 @@
+"""Unit tests for analysis case commands."""
+
+from __future__ import annotations
+
+import pytest
+
+pytest.importorskip("PySide6")
+
+from otko.commands import (  # noqa: E402
+    AddAnalysisCasesCommand,
+    DeleteAnalysisCasesCommand,
+    UpdateAnalysisCaseCommand,
+)
+from otko.core import (  # noqa: E402
+    LinearTimeSeries,
+    ModalCase,
+    NodalLoad,
+    Node,
+    PlainLoadPattern,
+    StaticCase,
+    TransientCase,
+)
+from otko.viewmodels import ProjectViewModel  # noqa: E402
+
+
+def _vm_with_pattern() -> ProjectViewModel:
+    vm = ProjectViewModel()
+    vm.new_project()
+    vm.project.nodes.append(Node(id=1, coords=(0, 0, 0)))
+    vm.project.time_series.append(LinearTimeSeries(id=1))
+    vm.project.load_patterns.append(
+        PlainLoadPattern(
+            id=1, time_series_id=1, nodal_loads=[NodalLoad(node_id=1, forces=(100, 0, 0, 0, 0, 0))]
+        )
+    )
+    return vm
+
+
+# ──────────────────────── Add ────────────────────────
+@pytest.mark.gui
+def test_add_static_case(qtbot) -> None:  # type: ignore[no-untyped-def]
+    vm = _vm_with_pattern()
+    case = StaticCase(id=1, name="LS", pattern_ids=[1])
+    vm.apply_command(AddAnalysisCasesCommand(vm, [case]))
+    assert len(vm.project.analyses) == 1
+    assert isinstance(vm.project.analyses[0], StaticCase)
+
+
+@pytest.mark.gui
+def test_add_modal_case_no_pattern_needed(qtbot) -> None:  # type: ignore[no-untyped-def]
+    vm = ProjectViewModel()
+    vm.new_project()
+    vm.apply_command(AddAnalysisCasesCommand(vm, [ModalCase(id=1, n_modes=3)]))
+    assert isinstance(vm.project.analyses[0], ModalCase)
+
+
+@pytest.mark.gui
+def test_add_emits_modelMutated(qtbot) -> None:  # type: ignore[no-untyped-def]
+    vm = _vm_with_pattern()
+    with qtbot.waitSignal(vm.modelMutated, timeout=500):
+        vm.apply_command(
+            AddAnalysisCasesCommand(
+                vm,
+                [
+                    StaticCase(id=1, pattern_ids=[1]),
+                ],
+            )
+        )
+
+
+@pytest.mark.gui
+def test_add_duplicate_id_raises(qtbot) -> None:  # type: ignore[no-untyped-def]
+    vm = _vm_with_pattern()
+    vm.apply_command(AddAnalysisCasesCommand(vm, [StaticCase(id=1, pattern_ids=[1])]))
+    with pytest.raises(ValueError, match="already exists"):
+        vm.apply_command(AddAnalysisCasesCommand(vm, [StaticCase(id=1, pattern_ids=[1])]))
+
+
+# ──────────────────────── Update ────────────────────────
+@pytest.mark.gui
+def test_update_static_changes_n_steps(qtbot) -> None:  # type: ignore[no-untyped-def]
+    vm = _vm_with_pattern()
+    vm.apply_command(
+        AddAnalysisCasesCommand(
+            vm,
+            [
+                StaticCase(id=1, name="A", pattern_ids=[1], n_steps=1),
+            ],
+        )
+    )
+    new = StaticCase(id=1, name="A", pattern_ids=[1], n_steps=10)
+    vm.apply_command(UpdateAnalysisCaseCommand(vm, new))
+    assert vm.project.analyses[0].n_steps == 10
+    vm.undo_stack.undo()
+    assert vm.project.analyses[0].n_steps == 1
+
+
+@pytest.mark.gui
+def test_update_changes_case_type(qtbot) -> None:  # type: ignore[no-untyped-def]
+    vm = _vm_with_pattern()
+    vm.apply_command(
+        AddAnalysisCasesCommand(
+            vm,
+            [
+                StaticCase(id=1, pattern_ids=[1]),
+            ],
+        )
+    )
+    swapped = ModalCase(id=1, name="Mode swap", n_modes=5)
+    vm.apply_command(UpdateAnalysisCaseCommand(vm, swapped))
+    assert isinstance(vm.project.analyses[0], ModalCase)
+    vm.undo_stack.undo()
+    assert isinstance(vm.project.analyses[0], StaticCase)
+
+
+@pytest.mark.gui
+def test_update_unknown_id_raises(qtbot) -> None:  # type: ignore[no-untyped-def]
+    vm = _vm_with_pattern()
+    bogus = ModalCase(id=99)
+    with pytest.raises(KeyError):
+        vm.apply_command(UpdateAnalysisCaseCommand(vm, bogus))
+
+
+# ──────────────────────── Delete ────────────────────────
+@pytest.mark.gui
+def test_delete_round_trip(qtbot) -> None:  # type: ignore[no-untyped-def]
+    vm = _vm_with_pattern()
+    vm.apply_command(
+        AddAnalysisCasesCommand(
+            vm,
+            [
+                StaticCase(id=1, pattern_ids=[1]),
+                ModalCase(id=2),
+            ],
+        )
+    )
+    vm.apply_command(DeleteAnalysisCasesCommand(vm, {1}))
+    assert {c.id for c in vm.project.analyses} == {2}
+    vm.undo_stack.undo()
+    assert {c.id for c in vm.project.analyses} == {1, 2}
+
+
+# ──────────────────────── Transient defaults ────────────────────────
+@pytest.mark.gui
+def test_transient_case_default_integrator_params(qtbot) -> None:  # type: ignore[no-untyped-def]
+    """Newmark γ=0.5, β=0.25 (average acceleration) — unconditionally stable."""
+    vm = _vm_with_pattern()
+    case = TransientCase(id=1, pattern_ids=[1], dt=0.01, n_steps=100)
+    vm.apply_command(AddAnalysisCasesCommand(vm, [case]))
+    assert vm.project.analyses[0].integrator == "Newmark"
+    assert vm.project.analyses[0].integrator_params == (0.5, 0.25)