runtime size budget red on main since 2026-09-24: native runtime +4.8–7.7% over budget and still growing

The native runtime size budget (runtime_size_budget.py, the budget in budget.json) has failed on main's darwin nightly since 2026-09-24, and the overrun is growing:

run	async	cli	json	loop
budget	5,804,512	5,804,416	5,721,728	5,589,376
main `400ae8c` (09-24)	5,986,192 (+3.13%)	6,234,096 (+7.40%)	5,903,424 (+3.18%)	5,771,056 (+3.25%)
main `ebbc11f` (09-26)	6,035,840 (+3.99%)	6,201,264 (+6.84%)	5,969,648 (+4.33%)	5,820,752 (+4.14%)
main `e379a7a` (09-27)	6,085,408 (+4.84%)	6,250,816 (+7.69%)	6,019,200 (+5.20%)	5,870,320 (+5.03%)

The job only runs in the full tier, so PRs don't see it. Every full-tier PR run is therefore red for a reason on main (it was first noticed on #11413, which a linux A/B showed adds 0 bytes).

To fix it, bisect 09-23..09-27 for the growth (the dominator analysis from #11135 attributes exact bytes per cut). Then either cut the growth or, if it was a deliberate trade, raise budget.json with a written justification.