Widen Symbolics compat to include v7 (blocked by SymbolicTracingUtils)

[hmzh-khn]

Summary

Widens the Symbolics compat bound from "6.51.0" to "6.51.0, 7" in Project.toml to prepare for Symbolics.jl v7. This addresses CompatHelper PR #51.

Status: Blocked — Symbolics v7 cannot actually be installed yet. See investigation below.

Changes

• Project.toml: Updated Symbolics compat from "6.51.0" to "6.51.0, 7"

Investigation Findings

Blocker: SymbolicTracingUtils v0.1.3

The Pkg resolver cannot install Symbolics v7 because SymbolicTracingUtils v0.1.3 declares:

Symbolics = "4,5,6"

This is the only released version of SymbolicTracingUtils, and it has no v7 compat. The dependency chain is:

MixedHierarchyGames → SymbolicTracingUtils v0.1.3 → Symbolics "4,5,6" (BLOCKER)
MixedHierarchyGames → ParametricMCPs v0.1.17 → SymbolicTracingUtils v0.1.3 → Symbolics "4,5,6"

Upstream PR exists: JuliaGameTheoreticPlanning/SymbolicTracingUtils.jl#5 — a CompatHelper PR to bump compat to "4,5,6,7". It is open but untested (no CI checks, auto-generated).

Transitive version pins

With Symbolics held at v6, these are also held back:

• SymbolicUtils v3.32.0 (v7 requires SymbolicUtils v4)
• SymbolicLimits v0.2.3 (held by SymbolicUtils constraint)
• SciMLOperators v0.3.13 (held by SciMLBase and SymbolicTracingUtils)

Symbolics v7 Breaking Changes Analysis

When SymbolicTracingUtils is eventually updated, these are the key v7 changes relevant to our codebase:

1. New Const variant: Num now always wraps BasicSymbolic — constants become Const{T}(val). Code using Symbolics.Num.(...) for broadcasting conversion (our nonlinear_kkt.jl:318,328) may need adjustment.

2. symtype moved from type parameter to field: BasicSymbolic{T} where T is now vartype (not symtype). Our code uses Num type annotations (Dict{Int, Vector{Symbolics.Num}}) which should still work since Num remains.

3. SymbolicUtils v3 → v4: Internal representation uses Moshi.jl instead of Unityper. arguments() now returns read-only arrays.

4. Add/Mul merged into AddMul: Pattern matching internals changed, but we don't access these directly.

5. Expression simplification changes: (a/b)^c auto-rewrites to a^c/b^c in SymReal mode, which could affect numerical results in KKT condition simplification.

6. APIs we use that are UNCHANGED: @variables, Symbolics.gradient, Symbolics.jacobian, Symbolics.get_variables, build_function (via SymbolicTracingUtils).

Our Symbolics API Usage (for future reference)

API	Files	Impact
@variables	test/test_kkt_verification.jl	Unchanged surface API
Symbolics.gradient	src/qp_kkt.jl, src/nonlinear_kkt.jl	Unchanged
Symbolics.jacobian	src/qp_kkt.jl, src/nonlinear_kkt.jl	Unchanged
Symbolics.get_variables	src/problem_setup.jl	Unchanged
Symbolics.Num type annotations	src/problem_setup.jl, src/nonlinear_kkt.jl	Num still exists, likely safe
Symbolics.Num.(x) broadcasting	src/nonlinear_kkt.jl:318,328	May need adjustment — constants now wrap in Const
eltype() with symbolic vectors	Multiple src/ files	Should work, but Num internals differ
SymbolicTracingUtils.build_function	src/utils.jl, src/nonlinear_kkt.jl	Depends on upstream compat

Testing

• All 450 tests pass with the widened compat bound (Symbolics remains at v6.58.0 since the resolver cannot upgrade)
• No functional changes to the package

Recommendation

Do NOT merge this PR yet. The compat bound widening is harmless but premature — Symbolics v7 cannot be installed. The recommended path forward:

1. Wait for SymbolicTracingUtils.jl#5 to be tested and merged upstream
2. Wait for a new SymbolicTracingUtils release (≥0.1.4) with Symbolics = "4,5,6,7"
3. Then: update our SymbolicTracingUtils compat, run Pkg.update(), and test with actual Symbolics v7
4. Expected work: Minor adjustments to Symbolics.Num.(...) broadcasting in nonlinear_kkt.jl, possible test tolerance adjustments due to expression simplification changes

Alternatively, if urgency is high, consider forking SymbolicTracingUtils temporarily or using Pkg.develop() with the compat PR branch.

Changelog

• 2026-02-09: Initial PR with investigation results. Compat bound widened. Documented blocker and v7 breaking changes analysis.