Brings in worktree-agent-a284432c (commit f62860ea8): per-branch SAXPY
sub-launches via correction-factor pattern. Trunk gets mean budget,
branch HEAD weights get branch[b]/trunk_mean correction multiplier.
Resolves Pearl 2 averaging from SP5 Layer B (compute_adaptive_budgets)
which collapsed 4 per-branch budgets into a single scalar.
Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>