Unifies the Q-support range source across atom grid / warm-start quantile
clamp consumers via the ISV signal bus. One broadcast written at epoch
boundary from per-branch Q-stats EMAs, read by the two consumers that
previously held disagreeing ranges. Target observation: atom utilisation
≥40% (up from 11-15% on train-fpxnw).
Phase 0 — per-branch Q-stats kernel Rust plumbing:
* Load q_stats_per_branch_reduce alongside legacy q_stats_reduce
* Add per_branch_q_stats_pinned (28 f32 = 4 × 7, device-mapped)
* PerBranchQValueStats struct: [QValueStatsResult; 4]
* reduce_current_q_stats_per_branch launches the new kernel with the
four branch (off, size) pairs derived from config.branch_N_size
Phase 1 — ISV v-range plumbing (zero behavioural change at epoch 1):
* ISV_NETWORK_DIM=23 preserved for w_isv_fc1 sizing; ISV_TOTAL_DIM=31
allocates 8 additional slots for per-branch (centre, half-width)
* Slot constants V_CENTER_DIR..V_HALF_URG covering slots 23..30
* eval_q_mean_ema / eval_q_std_ema / eval_ema_initialized promoted
to [f32; 4] / [bool; 4]; scalar setters preserved for trajectory
backtracking (broadcast same value to all branches)
* Bootstrap at construction: centre=0, half=(v_max-v_min)/2 → the
byte-identical [config.v_min, config.v_max] span per branch before
any Q observations arrive
* reset_eval_v_range_state resets the 4 per-branch EMAs AND the 8 ISV
slots to bootstrap values; legacy eval_v_range_pinned[2] still reset
(deferred removal — spec Phase 3)
* update_eval_v_range reworked: signature takes PerBranchQValueStats and
per_branch_q_gaps. Maintains 4 independent adaptive-rate EMAs,
computes (centre, half) per branch with min_half_floor=0.1×(v_max-v_min)
and clamps to config bounds, writes 8 ISV slots. Branch-0 (direction)
centre±half is also mirrored into the legacy eval_v_range_pinned for
consumers that have not yet migrated to the per-branch bus.
Phase 2a/2b — atom grid per-branch v-range:
* adaptive_atom_positions kernel signature changed from
(v_min: float, v_max: float) to (branch_idx: int, isv_signals: float*);
reads centre/half from ISV slots 23+2·b, 24+2·b. Eliminates the f64→f32
ABI trap (spec Phase 2 side-effect) since the only per-branch range
path is now pointer-based.
* recompute_atom_positions passes branch_idx + isv_signals_dev_ptr per
branch; no scalar v_min/v_max arg remains.
Phase 2c — warm-start quantile clamp per-branch from ISV:
* warm_start_atom_positions reads per-branch (centre, half) from pinned
ISV host memory, clamps shared reward-quantile vector into each
branch's adaptive range before tiling into atom_positions_buf.
Bootstrap makes this equivalent to the pre-spec config.v_{min,max}
clamp until the first Q observation lands.
Deviations from spec:
* Phase 2d (per_sample_support_buf → [N, 4, 3]) NOT implemented. The
spec's premise was that per_sample_support is host-tiled from
eval_v_range, but the active path in this codebase has it filled by
iql_compute_per_sample_support (V(s)-centered, per-sample, already
adaptive) — orthogonal to the ISV bus. Migrating that kernel to
per-branch output would require rewriting iql_value_kernel +
iql_support_floor + C51/MSE loss kernel indexing in lockstep, which
the "no unrelated refactoring" constraint disallows. The loss-kernel
Bellman projection today uses V-centered bounds that are themselves
adaptive; the ISV v-range fix still lands the primary win (atom grid
+ warm-start agreement) without touching IQL.
Compile verified: cargo check -p ml + --workspace pass (SQLX_OFFLINE,
CARGO_INCREMENTAL=0, sccache). No TODO/FIXME/XXX introduced.
Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>
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