初版：实现 AMESim 机械因果化与事件求解

初步支持 MECMAS21 刚性质量状态归并、端止事件、恢复系数，以及 LSTP 接触和压力流量显式因果化。

已知问题：显式传播仍会重复扫描全网方程，长时刚性仿真性能待优化；自适应积分器遇到越出物理域的试探状态时，尚未实现恢复并缩步重试。

app/simulation/systems/generic.py

@@ -8,6 +8,7 @@ from typing import Literal
 from app.simulation.core.base import DynamicComponent
 from app.simulation.core.metadata import ResultVariableMetadata
 from app.simulation.solvers.algebraic import PressureFlowSolver
+from app.simulation.solvers.mechanical import MechanicalStateReducer
 from app.simulation.solvers.pneumatic_volume import PneumaticVolumeResolver
 from app.simulation.solvers.solver import ODESolution, SolveIVPConfig, integrate_ode
 from app.simulation.solvers.signal import SignalResolver
@@ -233,6 +234,10 @@ class GenericFluidSystem:
             raise SimulationPreparationError(issues)
         self.network = network
         self.dynamic_components = network.dynamic_components()
+        self.mechanical_state_reducer = MechanicalStateReducer(
+            network,
+            self.dynamic_components,
+        )
         self.pressure_flow_solver = PressureFlowSolver(network)
         self.pneumatic_volume_resolver = PneumaticVolumeResolver(network)
         self.signal_resolver = SignalResolver(network)
@@ -245,10 +250,10 @@ class GenericFluidSystem:
         self.pneumatic_volume_propagation_count = 0
 
     def initial_state_vector(self) -> list[float]:
-        return self.network.initial_state_vector()
+        return self.mechanical_state_reducer.initial_state_vector()
 
     def apply_state_vector(self, values: list[float]) -> None:
-        self.network.apply_state_vector(values)
+        self.mechanical_state_reducer.apply_state_vector(values)
 
     def _close_current_state(self, time: float) -> dict[str, dict[str, float]]:
         signal = self.signal_resolver.solve(time)
@@ -263,6 +268,7 @@ class GenericFluidSystem:
                 component.refresh_thermodynamic_ports()
             algebraic = self.pressure_flow_solver.solve()
         stream, connected_h = self.stream_resolver.solve()
+        self.mechanical_state_reducer.update_constraint_accelerations()
         self.algebraic_solve_count += 1 + int(bool(pneumatic_volume.propagated))
         self.max_algebraic_residual = max(
             self.max_algebraic_residual,
@@ -278,21 +284,16 @@ class GenericFluidSystem:
         )
         return connected_h
 
-    def consistent_initial_state_vector(self) -> list[float]:
+    def consistent_initial_state_vector(self, time: float = 0.0) -> list[float]:
         state = self.initial_state_vector()
         self.apply_state_vector(state)
-        self._close_current_state(0.0)
+        self._close_current_state(time)
         return state
 
     def rhs(self, _time: float, state_vector: list[float]) -> list[float]:
         self.apply_state_vector(state_vector)
         connected_h = self._close_current_state(_time)
-        derivatives: list[float] = []
-        for component in self.dynamic_components:
-            derivatives.extend(
-                component.state_derivative_from_ports(connected_h[component.name])
-            )
-        return derivatives
+        return self.mechanical_state_reducer.state_derivatives(connected_h)
 
     def _append_current_state(self, series: dict[str, list[float]]) -> None:
         for component in self.network.components.values():
@@ -340,7 +341,7 @@ class GenericFluidSystem:
             config.t_start,
             config.t_stop,
         )
-        initial_state = self.consistent_initial_state_vector()
+        initial_state = self.consistent_initial_state_vector(config.t_start)
         report_progress(0.0, "integrating", force=True)
         duration = config.t_stop - config.t_start
         furthest_solver_time = config.t_start
@@ -370,6 +371,11 @@ class GenericFluidSystem:
                 report_solver_time if cancel_check is not None else None
             ),
             breakpoints=signal_event_times,
+            state_transition_handler=(
+                self.mechanical_state_reducer.state_transition
+                if self.mechanical_state_reducer.has_state_events
+                else None
+            ),
         )
         if isinstance(solution, ODESolution):
             run_status: SimulationRunStatus = solution.status
@@ -387,6 +393,7 @@ class GenericFluidSystem:
         times = [float(value) for value in solution.t]
         series: dict[str, list[float]] = {"time": []}
         postprocessing_error: Exception | None = None
+        self.mechanical_state_reducer.reset_constraint_modes()
         for time_index in range(len(times)):
             if (
                 run_status == "completed"