Add Enzyme extension to make AbstractSensitivityAlgorithm inactive

Fixes SciMLSensitivity.jl#1225: When `sensealg` is passed to ODEProblem
constructor, Enzyme would fail trying to differentiate through the sensitivity
algorithm object. This adds an inactive_type rule for AbstractSensitivityAlgorithm
to treat it as constant during Enzyme differentiation.

This is the correct place for this fix since AbstractSensitivityAlgorithm is
defined in SciMLBase, avoiding type piracy that would occur if the rule were
defined in SciMLSensitivity.

🤖 Generated with [Claude Code](https://claude.ai/code)

Co-Authored-By: Claude <[email protected]>

Author: ChrisRackauckas

Project.toml

@@ -37,6 +37,7 @@ SymbolicIndexingInterface = "2efcf032-c050-4f8e-a9bb-153293bab1f5"
 ChainRules = "082447d4-558c-5d27-93f4-14fc19e9eca2"
 ChainRulesCore = "d360d2e6-b24c-11e9-a2a3-2a2ae2dbcce4"
 Distributions = "31c24e10-a181-5473-b8eb-7969acd0382f"
+Enzyme = "7da242da-08ed-463a-9acd-ee780be4f1d9"
 ForwardDiff = "f6369f11-7733-5829-9624-2563aa707210"
 MLStyle = "d8e11817-5142-5d16-987a-aa16d5891078"
 Makie = "ee78f7c6-11fb-53f2-987a-cfe4a2b5a57a"
@@ -54,6 +55,7 @@ Zygote = "e88e6eb3-aa80-5325-afca-941959d7151f"
 [extensions]
 SciMLBaseChainRulesCoreExt = "ChainRulesCore"
 SciMLBaseDistributionsExt = "Distributions"
+SciMLBaseEnzymeExt = "Enzyme"
 SciMLBaseForwardDiffExt = "ForwardDiff"
 SciMLBaseMLStyleExt = "MLStyle"
 SciMLBaseMakieExt = "Makie"
@@ -80,6 +82,7 @@ ConstructionBase = "1.5"
 Distributed = "1.10"
 Distributions = "0.25"
 DocStringExtensions = "0.9"
+Enzyme = "0.13"
 EnumX = "1"
 ForwardDiff = "0.10.36, 1"
 FunctionWrappersWrappers = "0.1.3"

ext/SciMLBaseEnzymeExt.jl

@@ -0,0 +1,18 @@
+module SciMLBaseEnzymeExt
+
+using SciMLBase
+import Enzyme: EnzymeRules
+
+# Enzyme rules for SciMLBase abstract types
+#
+# Sensitivity algorithms define HOW to compute derivatives, not WHAT to differentiate.
+# They should be treated as inactive (constant) during Enzyme differentiation to prevent
+# errors when they are stored in problem structures that Enzyme differentiates through.
+#
+# This fixes issues like SciMLSensitivity.jl#1225 where passing `sensealg` to ODEProblem 
+# constructor would fail with Enzyme.
+
+# All sensitivity algorithm types should be inactive for Enzyme differentiation
+EnzymeRules.inactive_type(::Type{<:AbstractSensitivityAlgorithm}) = true
+
+end