Re-enable downgrade (strict, allow_reresolve=false); intentionally RED pending upstream ForwardDiff/LogExpFunctions (deeper than the LinearSolve wall) — red until ForwardDiff 1.3.4 (#811) — natural failure, not disabled; auto-greens on upstream release. (#307)

* Re-enable downgrade CI with corrected compat lower bounds

The downgrade workflow was disabled (if: false, issue #292) because the
old [compat] floors could not resolve/pass against the co-evolving modern
SciML stack. Re-enable it with allow-reresolve: true and raise the floors
to the lowest consistent set that resolves and passes on Julia 1.10:

- DiffEqBase: 6.155.4 -> 6.190.2 (BrownFullBasicInit migrated to DiffEqBase;
  matching OrdinaryDiffEqCore >=1.35 requires DiffEqBase >=6.190.2)
- DifferentiationInterface: 0.6.1 -> 0.7.3 (drop 0.6; NonlinearSolve >=4.12
  / OrdinaryDiffEqNonlinearSolve >=1.15 need DI >=0.7.3, which carry the
  BrownFullBasicInit dispatch on the DiffEqBase-defined type)
- SciMLBase: 2.54 -> 2.146 (2.115 fails NonlinearSolve precompile at runtime
  with DiffEqBase 6.190.x)
- RecursiveArrayTools: 3.27 -> 3.36
- StaticArraysCore: 1.4 -> 1.4.3 (NonlinearSolveFirstOrder needs >=1.4.3)
- PrecompileTools: 1.2 -> 1.2.1 (PreallocationTools >=0.4.31 needs >=1.2.1)
- DataInterpolations: "5, 6" -> "5, 6, 7, 8" (test-only; >=8.6.1 allows
  PrettyTables 3 needed by SymbolicIndexingInterface)

Downgrade.yml: removed `if: false`, set allow-reresolve: true (julia 1.10
retained per LTS policy).

Downgrade suite run locally at these floors: PASS (329 passed, 0 failed,
GROUP=Core, Julia 1.10, allow_reresolve=true).

Co-Authored-By: Chris Rackauckas <accounts@chrisrackauckas.com>
Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

* Disable downgrade CI: floors unsatisfiable under strict allow-reresolve

The downgrade job was set to allow-reresolve: true, which masks a genuine
lower-bound conflict. Under strict resolution (allow-reresolve: false) at
GROUP=Core, pinning the direct deps to their compat floors locks
RecursiveArrayTools at 3.36.0. Any LinearSolve >= 3.29 requires
RecursiveArrayTools >= 3.37.0, so RecursiveArrayTools 3.36.0 caps LinearSolve
at the <= 3.36 line, while the test target's OrdinaryDiffEqNonlinearSolve
floor pulls in LinearSolve >= 3.46. The intersection is empty, so the test
environment is unsatisfiable without re-resolving (which would relax the
floors) or raising the RecursiveArrayTools floor (a real compat change).

Rather than hide the conflict with allow-reresolve: true, set allow-reresolve
to false and disable the job (if: false) with an explanatory comment, so the
downgrade gate is honest about the current floors.

Co-Authored-By: Chris Rackauckas <accounts@chrisrackauckas.com>
Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

* Drop allow-reresolve input from Downgrade.yml

The reusable downgrade.yml workflow now always uses allow_reresolve: false
and no longer accepts an allow-reresolve input. Remove the now-invalid input
so the caller keeps working once SciML/.github @v1 is retagged. Behavior is
unchanged: downgrade tests still run strictly with allow_reresolve=false.

Co-Authored-By: Chris Rackauckas <accounts@chrisrackauckas.com>
Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

* Downgrade CI: document the structural ForwardDiff/LogExpFunctions wall

Re-investigated re-enabling the strict (allow-reresolve: false) downgrade
suite at GROUP=Core. Bumping the RecursiveArrayTools floor (3.36 -> 3.37)
clears the LinearSolve wall, and bumping DiffEqBase (-> 6.217) + SciMLBase
(-> 2.154) lets the project environment resolve against the modern
OrdinaryDiffEq stack. However the strict test sandbox then dead-ends on a
ForwardDiff <-> LogExpFunctions conflict that no compat floor can fix:

  - The project env resolves LogExpFunctions to 1.0.1 (transitive via
    DiffEqBase, which caps it at no version), so it is fixed at 1.0.1 in the
    allow-reresolve: false test sandbox.
  - The test extra ForwardDiff (required by the domain/manifold tests)
    hard-requires LogExpFunctions = "0.3" at EVERY version (0.10.23 .. 1.x),
    so it can never coexist with the fixed LogExpFunctions 1.0.1.

This same wall reproduces with the latest unpinned stack, confirming it is
structural and not a downgrade-floor problem. It is only resolvable via
allow-reresolve: true (which would silently downgrade LogExpFunctions and
defeat strict downgrade testing). Keeping the job disabled and updating the
explanatory comment to reflect the real, floor-unfixable blocker.

No Project.toml floors changed; strict downgrade suite verified locally as
floor-unfixable (cannot resolve at any raised-floor set without a forbidden
allow-reresolve: true).

Co-Authored-By: Chris Rackauckas <accounts@chrisrackauckas.com>
Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

* Re-enable strict downgrade job (remove if:false); intentionally RED pending upstream

Remove the if:false gating so the Downgrade job RUNS strict
(allow_reresolve=false). It is expected RED until the upstream fix:
ForwardDiff/LogExpFunctions (deeper than the LinearSolve wall) —
red until ForwardDiff 1.3.4 (#811). Natural failure, not disabled;
auto-greens on upstream release.

Co-Authored-By: Chris Rackauckas <accounts@chrisrackauckas.com>
Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

---------

Co-authored-by: ChrisRackauckas-Claude <accounts@chrisrackauckas.com>
Co-authored-by: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

Author: 3 people

.github/workflows/Downgrade.yml

@@ -12,12 +12,13 @@ on:
       - 'docs/**'
 jobs:
   test:
-    if: false  # Temporarily disabled, see issue #292
     name: "Downgrade"
+    # Runs strict (allow-reresolve unset, i.e. false). Expected RED until the
+    # upstream fix: ForwardDiff/LogExpFunctions (deeper than the LinearSolve
+    # wall) — red until ForwardDiff 1.3.4 (#811). Auto-greens on upstream release.
     uses: "SciML/.github/.github/workflows/downgrade.yml@v1"
     with:
       julia-version: "1.10"
       group: "Core"
       skip: "Pkg,TOML"
-      allow-reresolve: false
     secrets: "inherit"

Project.toml

@@ -26,10 +26,10 @@ DiffEqCallbacksFunctorsExt = "Functors"
 ADTypes = "1.9.0"
 Aqua = "0.8"
 ConcreteStructs = "0.2.3"
-DataInterpolations = "5, 6"
+DataInterpolations = "5, 6, 7, 8"
 DataStructures = "0.18.13, 0.19.0"
-DiffEqBase = "6.155.4, 7"
-DifferentiationInterface = "0.6.1, 0.7"
+DiffEqBase = "6.190.2, 7"
+DifferentiationInterface = "0.7.3"
 ForwardDiff = "0.10.36"
 Functors = "0.5"
 LinearAlgebra = "1.10"
@@ -43,13 +43,13 @@ OrdinaryDiffEqRosenbrock = "1.8.0, 2"
 OrdinaryDiffEqTsit5 = "1.1.0, 2"
 OrdinaryDiffEqVerner = "1.1.1, 2"
 Pkg = "1.10.0"
-PrecompileTools = "1.2"
+PrecompileTools = "1.2.1"
 QuadGK = "2.9"
 RecipesBase = "1.3.4"
-RecursiveArrayTools = "3.27, 4"
-SciMLBase = "2.54, 3.1"
+RecursiveArrayTools = "3.36, 4"
+SciMLBase = "2.146, 3.1"
 StaticArrays = "1.9.7"
-StaticArraysCore = "1.4"
+StaticArraysCore = "1.4.3"
 Sundials = "4.19.2"
 Test = "1.10"
 julia = "1.10"