[dweindl]

Fixes #3412.

Event assignments that reference expressions (w), e.g., targets of SBML assignment rules (y := 3 * x, E1: at time > 1: v = v + y), produced uncompilable code (deltax.cpp: 'y_' was not declared in this scope), since deltax is evaluated without access to w.

Event.get_state_update now takes a function that replaces expressions by their (recursively expanded) definitions, which is applied before substituting x by x_old. This reuses the substitution #3388 added for noise formulas, moved to DEModel._get_expression_substituter. Since the fix is in DEModel, it also applies to the JAX backend's _delta_x for expressions that only depend on states, parameters and conservation law totals. JAX's _delta_x doesn't get t and the Heaviside variables, so event assignments that depend on time or piecewise, directly or via expressions, still fail there, as on main (#3423).

Event assignments using expressions that contain splines still don't compile (deltax.cpp: 'spl_0_' was not declared in this scope), as on main, since only w and dwdx get the spline values (#3424).

The new test test_event_assignment_with_expressions uses a chain of assignment rules depending on a state and a parameter. It checks the simulated values against the analytical solution, and forward and adjoint sensitivities against finite differences. On main, model compilation fails.

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[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 80.11%. Comparing base (589bb74) to head (fff8213).
⚠️ Report is 2 commits behind head on main.

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #3416   +/-   ##
=======================================
  Coverage   80.10%   80.11%           
=======================================
  Files         320      320           
  Lines       22699    22705    +6     
  Branches     1536     1535    -1     
=======================================
+ Hits        18183    18189    +6     
  Misses       4508     4508           
  Partials        8        8           

Flag	Coverage Δ
cpp	74.22% <100.00%> (+<0.01%)	⬆️
cpp_python	35.09% <90.90%> (+0.01%)	⬆️
petab	48.47% <90.90%> (+0.01%)	⬆️
petab_sciml	16.96% <72.72%> (+0.01%)	⬆️
petab_sciml_benchmarks	15.54% <72.72%> (+0.01%)	⬆️
python	72.40% <100.00%> (+<0.01%)	⬆️
sbmlsuite	51.02% <ø> (ø)

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Files with missing lines	Coverage Δ
python/sdist/amici/_symbolic/de_model.py	93.88% <100.00%> (+0.02%)	⬆️
...ython/sdist/amici/_symbolic/de_model_components.py	96.62% <100.00%> (+0.03%)	⬆️

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