Downgrade CI: SBMLImporter 4 needs Catalyst 16, but old-era compat floors (Catalyst 14.4.1 etc.) are pinned — cascade, needs a minimum-version decision

[ChrisRackauckas-Claude]

Summary

The Downgrade (Core) job fails at the Pkg re-resolve (before tests run) with Unsatisfiable requirements detected for package SBMLImporter. This is not fixable by a single compat floor bump — it is a structural mismatch between the test dependency SBMLImporter (pinned to major 4, which is Catalyst-16-only) and the package's still-declared Catalyst-14-era lower compat options. Resolving it requires a real dependency decision (drop the old-era support), so filing for triage rather than silently force-bumping.

Latest failing run: https://github.com/SciML/CatalystNetworkAnalysis.jl/actions/runs/27305595781 (job Downgrade (Core) / Downgrade Tests - Core).

The surface error (and a stale-registry caveat)

The CI log shows:

ERROR: Unsatisfiable requirements detected for package SBMLImporter [210efffb]:
 ├─restricted to versions 4 by project, leaving only versions: 4.0.0-4.1.0
 └─restricted by compatibility requirements with Catalyst to versions: [0.1.0-0.2.0, 2.0.0-2.8.1] — no versions left
    └─Catalyst ... restricted to versions 14.4.1 by an explicit requirement

The Catalyst [0.1.0-0.2.0, 2.0.0-2.8.1] figure in that log is from a stale registry snapshot on the runner. Against the live General registry, SBMLImporter's Catalyst compat is the opposite:

SBMLImporter	requires Catalyst
2.x	14
3.x	15
4.x	16

So the true constraint is: SBMLImporter 4 (the pinned test floor) requires Catalyst 16, but the downgrade pins Catalyst to its lowest declared option 14.4.1 → empty intersection.

Verified locally (Julia 1.10 LTS, live registry):

# Catalyst 14.4.1 + SBMLImporter 4.0.0  -> Unsatisfiable
#   "SBMLImporter restricted to 4.0.0 by explicit requirement;
#    Catalyst restricted by SBMLImporter to 16.0.0-16.2.0 — no versions left"
# Catalyst 16.0.0 + SBMLImporter 4.0.0  -> resolves (Catalyst 16.0.0, SBMLImporter 4.0.0)

Why a single floor bump does not fix it (cascade)

Project.toml declares many disjoint "old, new" compat ranges — the old (Catalyst-14-era) option plus a newer (Catalyst-16 / Oscar-1.7-era) option added in 32df9a3 "Upgrade to Catalyst 16 / Oscar 1.7 stack":

Catalyst                 = "14.4.1, 16"
SymbolicUtils            = "3.7.2, 4"
ModelingToolkit          = "9.46.1, 11"
Oscar                    = "1.1.1, 1.7"
Hecke                    = "0.34, 0.39"
Nemo                     = "0.47, 0.54, 0.56"
Polyhedra                = "0.7.8, 0.8"
ReactionNetworkImporters = "0.15.1, 1.3"
CDDLib                   = "0.9.4, 0.10"

The downgrade pins each to its lowest option. Because SBMLImporter 4 forces Catalyst 16, the entire old-era floor set is dead, and bumping only Catalyst exposes a chain of further old-era floor conflicts (all verified locally against the live registry at the 1.10 LTS floor):

1. Catalyst 14.4.1 vs SBMLImporter 4 (needs Catalyst 16) — the reported failure.
2. SymbolicUtils 3.7.2 vs Catalyst 16.0.0 (needs SymbolicUtils ≥ 4.9.1).
3. Nemo 0.47.0 vs Hecke 0.34.0 (Hecke 0.34.x needs Nemo 0.47.1-0.47).
4. Hecke 0.39.0 vs Nemo 0.54.0 (the Oscar/Hecke/Nemo trio is version-locked; the floor pair does not co-resolve).

No single bump resolves this; the old-era lower options are collectively incompatible with the SBMLImporter-4 test requirement.

Recommended fix (a real dep decision — hence this issue)

The latest-versions CI already resolves and the Core tests pass on the new-era stack (green job https://github.com/SciML/CatalystNetworkAnalysis.jl/actions/runs/27305595949 installed: Catalyst 16.2.0, Oscar 1.7.3, Nemo 0.54.2, Hecke 0.39.15, SymbolicUtils 4.35.0). The old-era lower options are leftovers and are not co-installable with the pinned SBMLImporter 4.

If CatalystNetworkAnalysis no longer needs to support the Catalyst-14 era (which seems to be the case given SBMLImporter is pinned to 4), the clean fix is to drop the dead old-era lower options and pin the disjoint compats to a coherent Catalyst-16-stack minimum, e.g.:

Catalyst                 = "16"
SymbolicUtils            = "4"          # (Catalyst 16 needs ≥ 4.9.1)
ModelingToolkit          = "11"
Oscar                    = "1.7"
Hecke                    = "0.39"
Nemo                     = "0.54, 0.56"
Polyhedra                = "0.8"
ReactionNetworkImporters = "1.3"
CDDLib                   = "0.10"

The exact minimal floor for the Oscar/Hecke/Nemo trio must be co-selected (they are lockstep-versioned; the green build used Hecke 0.39.15 / Nemo 0.54.2). This is a deliberate "minimum supported version" decision, which is why I'm filing it for maintainer sign-off rather than mechanically force-bumping every floor.

Alternatively, if Catalyst-14-era support is intended to be retained, the SBMLImporter test-dep floor would need to be widened down (e.g. SBMLImporter = "2, 4") so a Catalyst-14-compatible SBMLImporter exists at the floor — but that likely loses SBMLImporter 4 features and is also a real decision.

(Note: the latest-versions QA (julia 1) and Documentation jobs are also red on main, but for unrelated reasons — not this downgrade resolution wall.)