Ignore until reviewed by @ChrisRackauckas.

Summary

• initialize disco_checkpoint with zero(t) instead of zero(tType)
• preserve runtime dimensions for time representations whose type alone does not encode them
• strengthen the existing DynamicQuantities + Measurements downstream regression to inspect the initialized checkpoint and complete through solve!

Root cause

The DISCO optimization added disco_checkpoint = zero(tType). DynamicQuantities deliberately rejects zero(::Type{<:Quantity}) when dimensions are runtime data, so ODE initialization failed before the first step. The initial time value already carries those dimensions, and zero(t) produces the correctly typed additive identity.

A controlled parent/child test with an otherwise identical dependency graph passed 4/4 at c538565b25 and failed during initialization at 408a7a30fe0; git bisect identifies 408a7a30fe0 (disco optimizations) as the first bad commit. The failure is present with DynamicQuantities 1.12.2 and 1.13.0, so it is not a 1.13-only behavior change.

CI prerequisite

#4066 is the current resolver prerequisite for testing this branch against registry SciMLBase 3.39.1. The code change itself is independent; the official Downstream validation below used a test-only stack of #4066 plus this commit.

Validation

• Julia 1.12, DynamicQuantities 1.12.2 + Measurements 2.14.1: focused test 6/6
• Julia 1.12, DynamicQuantities 1.13.0 + Measurements 2.14.1: focused test 6/6
• Julia 1.10 LTS, DynamicQuantities 1.13.0 + Measurements 2.14.1, local DiffEqBase/Core/Tsit5 stack: focused test 6/6
• Julia 1.12 official GROUP=Downstream on Restore SciMLBase 3.39 compatibility for owner imports #4066 + this commit: Time derivative 202/202, DynamicQuantities + Measurements 6/6, Pkg.test passed in 1879.4 seconds
• Runic check passes on both changed files
• whole-repository Runic reports only the three pre-existing DISCO formatting files addressed by Run Runic on the disco-optimizations files #4064; neither changed file appears in that diff
• git diff --check passes