Unsupported when-condition operator

**Describe the bug 🐞**

When transforming parsed Base Modelica to MTK when-conditions that are not a simple comparison fail.

**Expected behavior**

Handle boolean conditions (single boolean variable, boolean operations from multiple boolean variables).

**Minimal Reproducible Example 👇**

In this example the when-condition is a boolean which becomes true at time 0.5:

*BrokenWhenCondition.bmo*
```modelica
//! base 0.1.0
package 'BrokenWhenCondition'
  model 'BrokenWhenCondition'
    Boolean 'u' "Boolean input signal";
    discrete Real 'entryTime'(unit = "s", quantity = "Time") "Time instant when u became true";
    Real 'y' "Timer output";
  initial equation
    pre('entryTime') = 0.0;
  equation
    when 'u' then
      'entryTime' = time;
    end when;
    'y' = if 'u' then time - 'entryTime' else 0.0;
    'u' = time > 0.5;
  end 'BrokenWhenCondition';
end 'BrokenWhenCondition';
```

```julia
using BaseModelica
bmo_file = "BrokenWhenCondition.bmo"
package = BaseModelica.parse_file_antlr(bmo_file)
sys = BaseModelica.baseModelica_to_ModelingToolkit(package)
```

**Error & Stacktrace ⚠️**

```julia
ERROR: Unsupported when-condition operator: u. Only simple comparisons (>=, >, <=, <, ==) are supported.
Stacktrace:
 [1] error(s::String)
   @ Base ./error.jl:44
 [2] to_zero_crossing(cond::Symbolics.Num)
   @ BaseModelica ~/workdir/julia/SciML/BaseModelica.jl/src/evaluator.jl:231
 [3] eval_AST(when_eq::BaseModelica.BaseModelicaWhenEquation)
   @ BaseModelica ~/workdir/julia/SciML/BaseModelica.jl/src/evaluator.jl:377
 [4] eval_AST(model::BaseModelica.BaseModelicaModel)
   @ BaseModelica ~/workdir/julia/SciML/BaseModelica.jl/src/evaluator.jl:680
 [5] eval_AST(package::BaseModelica.BaseModelicaPackage)
   @ BaseModelica ~/workdir/julia/SciML/BaseModelica.jl/src/evaluator.jl:833
 [6] baseModelica_to_ModelingToolkit(package::BaseModelica.BaseModelicaPackage)
   @ BaseModelica ~/workdir/julia/SciML/BaseModelica.jl/src/evaluator.jl:883
 [7] top-level scope
   @ REPL[4]:1
```

**Environment (please complete the following information):**

  - Output of `using Pkg; Pkg.status()`

```julia
Project BaseModelica v1.6.0
Status `~/workdir/julia/SciML/BaseModelica.jl/Project.toml`
  [992eb4ea] CondaPkg v0.2.34
  [2b5f629d] DiffEqBase v6.211.0
  [d8e11817] MLStyle v0.4.17
  [961ee093] ModelingToolkit v11.17.0
  [7771a370] ModelingToolkitBase v1.24.0
  [fae87a5f] ParserCombinator v2.2.1
  [6099a3de] PythonCall v0.9.31
```

  - Output of `using Pkg; Pkg.status(; mode = PKGMODE_MANIFEST)`

```julia
Project BaseModelica v1.6.0
Status `~/workdir/julia/SciML/BaseModelica.jl/Manifest.toml`
  [47edcb42] ADTypes v1.21.0
  [6e696c72] AbstractPlutoDingetjes v1.3.2
  [1520ce14] AbstractTrees v0.4.5
  [7d9f7c33] Accessors v0.1.44
  [79e6a3ab] Adapt v4.5.0
  [ec485272] ArnoldiMethod v0.4.0
  [4fba245c] ArrayInterface v7.23.0
  [4c555306] ArrayLayouts v1.12.2
  [15f4f7f2] AutoHashEquals v2.2.0
  [aae01518] BandedMatrices v1.11.0
  [e2ed5e7c] Bijections v0.2.2
  [caf10ac8] BipartiteGraphs v0.1.7
  [62783981] BitTwiddlingConvenienceFunctions v0.1.6
  [8e7c35d0] BlockArrays v1.9.3
  [70df07ce] BracketingNonlinearSolve v1.11.0
  [2a0fbf3d] CPUSummary v0.2.7
  [d360d2e6] ChainRulesCore v1.26.0
  [fb6a15b2] CloseOpenIntervals v0.1.13
⌅ [861a8166] Combinatorics v1.0.2
  [38540f10] CommonSolve v0.2.6
  [bbf7d656] CommonSubexpressions v0.3.1
  [f70d9fcc] CommonWorldInvalidations v1.0.0
  [34da2185] Compat v4.18.1
  [b152e2b5] CompositeTypes v0.1.4
  [a33af91c] CompositionsBase v0.1.2
  [2569d6c7] ConcreteStructs v0.2.3
  [992eb4ea] CondaPkg v0.2.34
  [187b0558] ConstructionBase v1.6.0
  [adafc99b] CpuId v0.3.1
  [9a962f9c] DataAPI v1.16.0
  [864edb3b] DataStructures v0.19.3
  [e2d170a0] DataValueInterfaces v1.0.0
  [2b5f629d] DiffEqBase v6.211.0
  [459566f4] DiffEqCallbacks v4.12.0
  [163ba53b] DiffResults v1.1.0
  [b552c78f] DiffRules v1.15.1
  [a0c0ee7d] DifferentiationInterface v0.7.16
  [ffbed154] DocStringExtensions v0.9.5
  [5b8099bc] DomainSets v0.7.16
  [7c1d4256] DynamicPolynomials v0.6.4
  [4e289a0a] EnumX v1.0.7
  [f151be2c] EnzymeCore v0.8.18
  [e2ba6199] ExprTools v0.1.10
  [55351af7] ExproniconLite v0.10.14
  [7034ab61] FastBroadcast v0.3.5
  [9aa1b823] FastClosures v0.3.2
  [a4df4552] FastPower v1.3.1
  [1a297f60] FillArrays v1.16.0
  [64ca27bc] FindFirstFunctions v1.8.0
  [6a86dc24] FiniteDiff v2.29.0
  [f6369f11] ForwardDiff v1.3.3
  [069b7b12] FunctionWrappers v1.1.3
  [77dc65aa] FunctionWrappersWrappers v0.1.3
  [46192b85] GPUArraysCore v0.2.0
  [86223c79] Graphs v1.14.0
  [615f187c] IfElse v0.1.1
  [3263718b] ImplicitDiscreteSolve v1.8.0
  [d25df0c9] Inflate v0.1.5
  [18e54dd8] IntegerMathUtils v0.1.3
  [8197267c] IntervalSets v0.7.13
  [3587e190] InverseFunctions v0.1.17
  [92d709cd] IrrationalConstants v0.2.6
  [82899510] IteratorInterfaceExtensions v1.0.0
  [692b3bcd] JLLWrappers v1.7.1
  [682c06a0] JSON v1.4.0
  [ae98c720] Jieko v0.2.1
  [ccbc3e58] JumpProcesses v9.23.2
  [ba0b0d4f] Krylov v0.10.6
  [10f19ff3] LayoutPointers v0.1.17
  [87fe0de2] LineSearch v0.1.6
  [7ed4a6bd] LinearSolve v3.68.0
  [2ab3a3ac] LogExpFunctions v0.3.29
  [e6f89c97] LoggingExtras v1.2.0
  [d8e11817] MLStyle v0.4.17
  [1914dd2f] MacroTools v0.5.16
  [d125e4d3] ManualMemory v0.1.8
  [bb5d69b7] MaybeInplace v0.1.4
  [0b3b1443] MicroMamba v0.1.15
  [961ee093] ModelingToolkit v11.17.0
  [7771a370] ModelingToolkitBase v1.24.0
  [6bb917b9] ModelingToolkitTearing v1.10.2
  [2e0e35c7] Moshi v0.3.7
  [46d2c3a1] MuladdMacro v0.2.4
  [102ac46a] MultivariatePolynomials v0.5.14
  [d8a4904e] MutableArithmetics v1.6.7
  [77ba4419] NaNMath v1.1.3
  [be0214bd] NonlinearSolveBase v2.16.0
  [5959db7a] NonlinearSolveFirstOrder v2.0.0
  [6fe1bfb0] OffsetArrays v1.17.0
  [bac558e1] OrderedCollections v1.8.1
  [bbf590c4] OrdinaryDiffEqCore v3.22.0
  [fae87a5f] ParserCombinator v2.2.1
  [69de0a69] Parsers v2.8.3
  [fa939f87] Pidfile v1.3.0
  [e409e4f3] PoissonRandom v0.4.7
  [f517fe37] Polyester v0.7.19
  [1d0040c9] PolyesterWeave v0.2.2
  [d236fae5] PreallocationTools v1.1.2
  [aea7be01] PrecompileTools v1.3.3
  [21216c6a] Preferences v1.5.2
  [27ebfcd6] Primes v0.5.7
  [6099a3de] PythonCall v0.9.31
  [988b38a3] ReadOnlyArrays v0.2.0
  [795d4caa] ReadOnlyDicts v1.0.1
  [3cdcf5f2] RecipesBase v1.3.4
  [731186ca] RecursiveArrayTools v3.48.0
  [189a3867] Reexport v1.2.2
  [ae029012] Requires v1.3.1
  [7e49a35a] RuntimeGeneratedFunctions v0.5.17
  [9dfe8606] SCCNonlinearSolve v1.11.0
  [94e857df] SIMDTypes v0.1.0
  [0bca4576] SciMLBase v2.152.1
  [19f34311] SciMLJacobianOperators v0.1.12
  [a6db7da4] SciMLLogging v1.9.1
  [c0aeaf25] SciMLOperators v1.15.1
  [431bcebd] SciMLPublic v1.0.1
  [53ae85a6] SciMLStructures v1.10.0
  [6c6a2e73] Scratch v1.3.0
  [efcf1570] Setfield v1.1.2
  [727e6d20] SimpleNonlinearSolve v2.11.0
  [699a6c99] SimpleTraits v0.9.5
  [276daf66] SpecialFunctions v2.7.1
  [64909d44] StateSelection v1.6.0
  [aedffcd0] Static v1.3.1
  [0d7ed370] StaticArrayInterface v1.9.0
  [90137ffa] StaticArrays v1.9.18
  [1e83bf80] StaticArraysCore v1.4.4
  [10745b16] Statistics v1.11.1
  [7792a7ef] StrideArraysCore v0.5.8
  [ec057cc2] StructUtils v2.7.1
  [2efcf032] SymbolicIndexingInterface v0.3.46
  [19f23fe9] SymbolicLimits v1.1.0
  [d1185830] SymbolicUtils v4.20.2
  [0c5d862f] Symbolics v7.16.1
  [3783bdb8] TableTraits v1.0.1
  [bd369af6] Tables v1.12.1
  [ed4db957] TaskLocalValues v0.1.3
  [8ea1fca8] TermInterface v2.0.0
  [8290d209] ThreadingUtilities v0.5.5
  [a759f4b9] TimerOutputs v0.5.29
  [781d530d] TruncatedStacktraces v1.4.0
  [3a884ed6] UnPack v1.0.2
  [e17b2a0c] UnsafePointers v1.0.0
  [d30d5f5c] WeakCacheSets v0.1.0
  [1d5cc7b8] IntelOpenMP_jll v2025.2.0+0
  [856f044c] MKL_jll v2025.2.0+0
  [efe28fd5] OpenSpecFun_jll v0.5.6+0
  [f8abcde7] micromamba_jll v2.3.1+0
  [1317d2d5] oneTBB_jll v2022.0.0+1
  [4d7b5844] pixi_jll v0.41.3+0
  [0dad84c5] ArgTools v1.1.2
  [56f22d72] Artifacts v1.11.0
  [2a0f44e3] Base64 v1.11.0
  [ade2ca70] Dates v1.11.0
  [8ba89e20] Distributed v1.11.0
  [f43a241f] Downloads v1.7.0
  [7b1f6079] FileWatching v1.11.0
  [9fa8497b] Future v1.11.0
  [b77e0a4c] InteractiveUtils v1.11.0
  [ac6e5ff7] JuliaSyntaxHighlighting v1.12.0
  [4af54fe1] LazyArtifacts v1.11.0
  [b27032c2] LibCURL v0.6.4
  [76f85450] LibGit2 v1.11.0
  [8f399da3] Libdl v1.11.0
  [37e2e46d] LinearAlgebra v1.12.0
  [56ddb016] Logging v1.11.0
  [d6f4376e] Markdown v1.11.0
  [ca575930] NetworkOptions v1.3.0
  [44cfe95a] Pkg v1.12.1
  [de0858da] Printf v1.11.0
  [3fa0cd96] REPL v1.11.0
  [9a3f8284] Random v1.11.0
  [ea8e919c] SHA v0.7.0
  [9e88b42a] Serialization v1.11.0
  [6462fe0b] Sockets v1.11.0
  [2f01184e] SparseArrays v1.12.0
  [f489334b] StyledStrings v1.11.0
  [fa267f1f] TOML v1.0.3
  [a4e569a6] Tar v1.10.0
  [8dfed614] Test v1.11.0
  [cf7118a7] UUIDs v1.11.0
  [4ec0a83e] Unicode v1.11.0
  [e66e0078] CompilerSupportLibraries_jll v1.3.0+1
  [deac9b47] LibCURL_jll v8.15.0+0
  [e37daf67] LibGit2_jll v1.9.0+0
  [29816b5a] LibSSH2_jll v1.11.3+1
  [14a3606d] MozillaCACerts_jll v2025.11.4
  [4536629a] OpenBLAS_jll v0.3.29+0
  [05823500] OpenLibm_jll v0.8.7+0
  [458c3c95] OpenSSL_jll v3.5.4+0
  [bea87d4a] SuiteSparse_jll v7.8.3+2
  [83775a58] Zlib_jll v1.3.1+2
  [8e850b90] libblastrampoline_jll v5.15.0+0
  [8e850ede] nghttp2_jll v1.64.0+1
  [3f19e933] p7zip_jll v17.7.0+0
Info Packages marked with ⌅ have new versions available but compatibility constraints restrict them from upgrading. To see why use `status --outdated -m`
```

  - Output of `versioninfo()`

```julia
Julia Version 1.12.5
Commit 5fe89b8ddc1 (2026-02-09 16:05 UTC)
Build Info:
  Official https://julialang.org release
Platform Info:
  OS: Linux (x86_64-linux-gnu)
  CPU: 28 × 13th Gen Intel(R) Core(TM) i7-13850HX
  WORD_SIZE: 64
  LLVM: libLLVM-18.1.7 (ORCJIT, alderlake)
  GC: Built with stock GC
Threads: 1 default, 1 interactive, 1 GC (on 28 virtual cores)
```

**Additional context**

The following 26 models from MSL seem to encounter this or a very similar issue:

* `Modelica.Electrical.PowerConverters.Examples.ACDC.Rectifier1Pulse.Thyristor1Pulse_R`
* `Modelica.Electrical.PowerConverters.Examples.ACDC.Rectifier1Pulse.Thyristor1Pulse_R_Characteristic`
* `Modelica.Electrical.PowerConverters.Examples.ACDC.RectifierBridge2Pulse.HalfControlledBridge2Pulse`
* `Modelica.Electrical.PowerConverters.Examples.ACDC.RectifierBridge2Pulse.ThyristorBridge2Pulse_DC_Drive`
* `Modelica.Electrical.PowerConverters.Examples.ACDC.RectifierBridge2Pulse.ThyristorBridge2Pulse_R`
* `Modelica.Electrical.PowerConverters.Examples.ACDC.RectifierBridge2Pulse.ThyristorBridge2Pulse_RL`
* `Modelica.Electrical.PowerConverters.Examples.ACDC.RectifierBridge2Pulse.ThyristorBridge2Pulse_RLV`
* `Modelica.Electrical.PowerConverters.Examples.ACDC.RectifierBridge2Pulse.ThyristorBridge2Pulse_RLV_Characteristic`
* `Modelica.Electrical.PowerConverters.Examples.ACDC.RectifierBridge2mPulse.HalfControlledBridge2mPulse`
* `Modelica.Electrical.PowerConverters.Examples.ACDC.RectifierBridge2mPulse.ThyristorBridge2mPulse_DC_Drive`
* `Modelica.Electrical.PowerConverters.Examples.ACDC.RectifierBridge2mPulse.ThyristorBridge2mPulse_R`
* `Modelica.Electrical.PowerConverters.Examples.ACDC.RectifierBridge2mPulse.ThyristorBridge2mPulse_RL`
* `Modelica.Electrical.PowerConverters.Examples.ACDC.RectifierBridge2mPulse.ThyristorBridge2mPulse_RLV`
* `Modelica.Electrical.PowerConverters.Examples.ACDC.RectifierBridge2mPulse.ThyristorBridge2mPulse_RLV_Characteristic`
* `Modelica.Electrical.PowerConverters.Examples.ACDC.RectifierCenterTap2Pulse.ThyristorCenterTap2Pulse_R`
* `Modelica.Electrical.PowerConverters.Examples.ACDC.RectifierCenterTap2Pulse.ThyristorCenterTap2Pulse_RL`
* `Modelica.Electrical.PowerConverters.Examples.ACDC.RectifierCenterTap2Pulse.ThyristorCenterTap2Pulse_RLV`
* `Modelica.Electrical.PowerConverters.Examples.ACDC.RectifierCenterTap2Pulse.ThyristorCenterTap2Pulse_RLV_Characteristic`
* `Modelica.Electrical.PowerConverters.Examples.ACDC.RectifierCenterTap2mPulse.ThyristorCenterTap2mPulse_R`
* `Modelica.Electrical.PowerConverters.Examples.ACDC.RectifierCenterTap2mPulse.ThyristorCenterTap2mPulse_RL`
* `Modelica.Electrical.PowerConverters.Examples.ACDC.RectifierCenterTap2mPulse.ThyristorCenterTap2mPulse_RLV`
* `Modelica.Electrical.PowerConverters.Examples.ACDC.RectifierCenterTap2mPulse.ThyristorCenterTap2mPulse_RLV_Characteristic`
* `Modelica.Electrical.PowerConverters.Examples.ACDC.RectifierCenterTapmPulse.ThyristorCenterTapmPulse_R`
* `Modelica.Electrical.PowerConverters.Examples.ACDC.RectifierCenterTapmPulse.ThyristorCenterTapmPulse_RL`
* `Modelica.Electrical.PowerConverters.Examples.ACDC.RectifierCenterTapmPulse.ThyristorCenterTapmPulse_RLV`
* `Modelica.Electrical.PowerConverters.Examples.ACDC.RectifierCenterTapmPulse.ThyristorCenterTapmPulse_RLV_Characteristic`



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Unsupported when-condition operator #114

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Unsupported when-condition operator #114

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