Brings in worktree-agent-a4d8a879 (commit ed3fa066b): per-branch σ via
[4]-element mapped-pinned device buffer. add_advantage_noise kernel
indexes σ by branch derived from action_idx % total_actions; Q-value
layout is branch-major contiguous so per-branch σ derivation requires
no forward-pass restructuring.
3 ExperienceCollectorConfig constructors updated.
Resolves Pearl 3 averaging from SP5 Layer B which collapsed 4 per-branch
σ values into a single scalar via training_loop.rs:1747.
Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>