feat(dqn-v2): C.1 quantile-based atom support (Plan 2 Task 1)
Replaces half = max(10*q_gap, 3*std_ema, floor) tuned constants with
quantile-based: half = max(|q_p95 - v_center|, |v_center - q_p5|)
clamped to [min_half_floor, abs_half]. Covers observed Q distribution
directly.
New GPU kernel q_quantile_reduce reads per-sample Q-values from q_out_buf,
sorts per branch (bitonic for power-of-2 N, quickselect otherwise), writes
ISV[Q_P05_*=47..51) and ISV[Q_P95_*=51..55). Cold-path per-epoch (4 blocks,
1 thread each). No atomicAdd.
ISV slots 47-54 added at tail (8 total). Fingerprint shifted to 55-56.
ISV_TOTAL_DIM grows 49 -> 57. Fingerprint seed updated; recomputes hash
at compile time (new value: 0xbf6c400c026d77e3).
Launch order: reduce_current_q_stats (populates q_out_buf) ->
q_quantile_reduce (writes ISV P5/P95) -> reduce_current_q_stats_per_branch
-> update_eval_v_range (reads ISV P5/P95 for half-width).
Bootstrap: q_p05 = v_min, q_p95 = v_max (matches current atom range at
cold start). FoldReset: isv_q_quantiles dispatch arm resets to bootstrap
values at fold boundary.
StateResetRegistry: isv_q_quantiles as FoldReset; dispatch arm added in
training_loop.rs::reset_named_state.
Docs: isv-slots.md rows [47..57) updated, fingerprint tail reference
corrected to [55..57). dqn-wire-up-audit.md: q_quantile_kernel.cu added.
Plan 2 Task 1. Spec §4.C.1.
Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>
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