Ignore this draft until reviewed by @ChrisRackauckas.

Depends on #4066. This branch intentionally contains only the test-harness and regression-test changes; it does not duplicate the compatibility-floor changes from #4066.

Summary

• Call SciMLTesting's public develop_sources! helper before root-package group dispatch so Julia 1.10 tests the monorepo's local sublibraries. The helper is a no-op on Julia 1.11 and later, where [sources] is native.
• Assert that the limiter integration test loads OrdinaryDiffEqCore, OrdinaryDiffEqLowOrderRK, and OrdinaryDiffEqSSPRK from this checkout.

Problem

Julia 1.10 ignores the root project's [sources] section when Pkg.test() creates its temporary environment. A clean GROUP=Integrators_I Pkg.test() at fd3f95bb99 therefore selected registered OrdinaryDiffEqCore 4.11.0, OrdinaryDiffEqLowOrderRK 2.2.1, and OrdinaryDiffEqSSPRK 2.2.0 instead of the local Core 4.12.0, LowOrderRK 2.2.2, and SSPRK 2.2.3. The Step Limiter test then reported 170 passes, 2 failures, and 1 error.

The hosted Julia 1.10 jobs for #3835 and #4003 passed because the reusable workflow separately developed in-repo sources before testing. The package's direct test harness should establish the same coherent source graph itself.

This is a test-environment issue, not a regression in the recent stage-limiter trait. The immediate parent of #4003 also fails with registered siblings. Older checkouts are not stable bisect endpoints against today's moving registry: the pre-#3835 checkout fails all 129 old constructor-level limiter assertions because newer registered siblings call those callbacks twice. Commit fe90a44dd8 is relevant only as the structural introduction of the root [sources] assumption that Julia 1.10 cannot honor natively.

Local verification

• Julia 1.10.11, GROUP=Integrators_I, on Restore SciMLBase 3.39 compatibility for owner imports #4066 plus this focused diff:
  • Step Limiter Tests: 254 passed / 254 total
  • Discontinuity Detection Tests: 28 passed / 28 total
  • Testing OrdinaryDiffEq tests passed
• Julia 1.12.6, GROUP=Integrators_I, on Restore SciMLBase 3.39 compatibility for owner imports #4066 plus this focused diff:
  • Step Limiter Tests: 254 passed / 254 total
  • Discontinuity Detection Tests: 28 passed / 28 total
  • Testing OrdinaryDiffEq tests passed
• Runic passes both changed files.
• git diff --check passes.

A repository-wide Runic check identifies only the pre-existing test/Integrators_I/disco_tests.jl formatting failure handled independently by #4064.