PROBE-NXG-HIST-1: nested-mask histogram reproduces the partition-point rank on 94 572 real rows

.claude/board/AGENT_LOG.md

@@ -1,3 +1,12 @@
+## 2026-09-05 — PROBE-NXG-HIST-1: orchestrator-only, no worker spawned
+
+- **Why:** operator: "merge 1176 and start PROBE-NXG-HIST-1". #1176 merged (`a7520a15`). Plan §5 step 2 is a ~200-line probe with three pre-registered claims; briefing a worker costs more than writing it.
+- **Column:** `data/tts-cascade/tts_real_output.wav` `|sample|` — real, in-tree, 94 572 rows. No facet fixture exists in-tree; noted in the probe header and E-NXG-17.
+- **Result:** C1 PASS · C2 PASS · C3 PASS first run. Disable runs red-then-green: `AND3` for the bucket immediate (C1/C2/C3 all fail, exit 101); `partition_point(b <= v)` (C2 192 mismatches, exit 101); restored → green.
+- **Correction found:** histogram-midpoint σ over-reads by 12 % on quantile buckets (heavy top bucket). Plan §3 room 3 regraded in E-NXG-17; entropy-on-requantiled-buckets is flat by construction (D-NXG-9 caveat).
+- **Gates:** clippy `-D warnings` on the example clean (one `is_multiple_of` fix), fmt clean, append-only + citation-decay + plan-dids gates run locally, supersession index regenerated last.
+- **Board:** E-NXG-17; STATUS_BOARD D-NXG-1/2/4 rows updated; plan §5 step 2 marked GREEN.
+
 ## 2026-09-05 — Sonnet harvest fleet (4 readers + 7 PR sweepers), orchestrator-consolidated → `.claude/nexgen/`
 
 - **Why:** operator asked how HDR popcount-stacking, rolling floor, Prozentrang buckets, Mexican hat, Shannon, proprioception, EWA sandwich and sigker could combine with ternlog mask algebra for better thresholds; then asked for the last 50 lance-graph PRs + 25 OGAR + 25 ndarray swept for synergies, epiphanies written to the board, the raw agent output kept, and an expansion plan in the T0..T3 shape "27 rooms ahead".

.claude/board/EPIPHANIES.md

@@ -1,3 +1,44 @@
+## 2026-09-05 — E-NXG-17 — PROBE-NXG-HIST-1 GREEN: the nested-mask histogram reproduces the partition-point rank on 94 572 real rows
+
+**Status:** FINDING (measured; `crates/lance-graph-planner/examples/probe_nxg_hist_1.rs`).
+**Confidence:** High on C1–C3; the σ observation is a real correction to plan §3 room 3.
+
+The first gate of `nexgen-mask-histogram-thresholds-v1` §5 ran on a REAL
+column — `|sample|` of `data/tts-cascade/tts_real_output.wav`, 94 572 rows of
+16-bit speech, 1 478 mask words, B = 16 quantile bands. Three pre-registered
+claims, all PASS on the first run: **C1** the 16 band masks are nested, the 16
+bucket masks are pairwise disjoint, and their popcounts sum to exactly N;
+**C2** for every one of the 94 572 rows the bucket index read off the masks
+equals `boundaries.partition_point(|b| b < v)` (0 mismatches; anti-vacuity
+16/16 buckets non-empty, largest 5 925 ≈ N/16); **C3**
+`mask_ternlog::<AND_ANDNOT2>(M_i, M_{i-1}, M_{i-1})` is bit-identical to
+`mask_andnot(M_i, M_{i-1})` and `AND3` on the same operands differs at every i
+with a non-empty lower band. Two disable runs, red-then-green: bucket via
+`AND3` → C1 disjoint=false, sum=715 262, C2 88 659 mismatches, C3 false;
+partition point `b <= v` → C2 192 mismatches (the rows sitting exactly on a
+boundary — the off-by-one is real, not vacuous). E-NXG-1/2/3 are promoted from
+PROPOSAL to FINDING for the structure; the cost claims stay unmeasured.
+
+**What the probe corrected.** Plan §3 room 3 said σ is "recoverable from the
+histogram for free" via popcount-weighted bucket midpoints. Measured: σ_hist =
+4 244.9 vs σ_direct = 3 785.8, ratio 1.121. Quantile buckets are equal-mass,
+not equal-width, so the top bucket (9 299..20 634) is a heavy tail whose
+midpoint over-weights it. Room 3 is regraded: σ from the histogram needs
+per-bucket means (one more accumulator per bucket), not midpoints, and stays an
+observation until that variant is measured. The entropy preview
+(`thought_atoms::normalized_entropy` over the 16 popcounts) reads 0.99999964 —
+the expected ceiling for equal-mass buckets, which is why D-NXG-9's rollover
+timer must be read on FIXED boundaries after the distribution moves, never on
+freshly re-quantiled ones (a re-quantiled histogram is flat by construction and
+carries no signal).
+
+**Honest scope.** The column is audio, not a facet column — no facet fixture
+exists in-tree (harvest 2026-09-05). The mechanism is value-type-agnostic; the
+facet rerun is the next arm. `popcount_batch_u64` exists as a named T1 primitive
+(D-NXG-2's audit half-closed: present, scalar `count_ones` sum, not yet the
+POPCNT lane its comment promises). Mask bytes hot at this N: 189 184 B for 16
+bands — the plan's "16 × 8 KB" was at 65 536 rows; this column is 1.44× that.
+
 ## 2026-09-05 — E-NXG-1 — the exposure meter is a nested mask set
 
 **Status:** PROPOSAL (design reading of measured code; no code changed).
@@ -327,7 +368,7 @@ mechanisms disagreed by **58.2%**:
 
 | site | reading on `main` |
 |---|---|
-| `.claude/board/AGENT_LOG.md:481` | 58.2% **disagreement** |
+| `.claude/board/AGENT_LOG.md` under "2026-08-19 — oracle-boundary reassessment sweep" (the **58.2%** findings paragraph) | 58.2% **disagreement** |
 | `.claude/board/INTEGRATION_PLANS.md:910` | 58.2% **disagreement** |
 
 The source says the opposite. `MedCare-rs/crates/medcare-server/src/views/atlas.rs:465`

.claude/board/STATUS_BOARD.md

@@ -5,10 +5,10 @@ every row is Queued until PROBE-NXG-HIST-1 / ROLL-1 / FLOOR-1 (plan §5) run.
 
 | D-id | deliverable | status |
 |---|---|---|
-| D-NXG-1 | `NestedBands` sealed shape (T2), version-keyed, one owner | Queued |
-| D-NXG-2 | T1 name audit: `popcount_words` present or minted; bucket = `mask_ternlog::<0x10>` by name | Queued |
+| D-NXG-1 | `NestedBands` sealed shape (T2), version-keyed, one owner | **In progress** — structure measured by PROBE-NXG-HIST-1 (E-NXG-17, 2026-09-05); seal/ownership shape not yet built |
+| D-NXG-2 | T1 name audit: `popcount_words` present or minted; bucket = `mask_ternlog::<0x10>` by name | **Half-closed 2026-09-05** — `ndarray::simd::popcount_batch_u64` exists (scalar); bucket-by-name proven bit-identical to `mask_andnot` (C3) |
 | D-NXG-3 | T1 `bisect_column_by_mask` partial-popcount bisection | Queued |
-| D-NXG-4 | Prozentrang = bucket index; `shape × rank` computed from the slab | Queued |
+| D-NXG-4 | Prozentrang = bucket index; `shape × rank` computed from the slab | **Measured 2026-09-05** — rank == partition point on 94 572/94 572 real rows (C2); not yet wired to any consumer |
 | D-NXG-5 | rollover: split on budget or entropy, merge on collapse, never rewrite | Queued |
 | D-NXG-6 | rank-derived reject floor; σ demoted to diagnostic | Queued |
 | D-NXG-7 | preheat by mask inheritance | Queued |

.claude/board/TECH_DEBT.md

@@ -1,3 +1,34 @@
+## TD-SIGMA-PROBE-MASK-ALIGNMENT-AND-WORK-METRIC-1 (2026-09-05) — OPEN
+
+**`crates/lance-graph/examples/sigma_probe_masked_traverse.rs` (shipped in
+#1176 as an inherited commit, `a11fd64b`, "measurement only") carries two
+Codex P2 findings posted after the merge; neither is fixed here.** The example
+was not authored in the #1176 session; it rode the designated branch. The
+findings are recorded so the probe's numbers are not cited as evidence until
+they are addressed.
+
+1. **Block mask is not aligned to the generated communities.** With the
+   defaults `n=96`, `blocks=8` each community spans 12 ids, but `mask_blocks`
+   is called with counts 1, 9 and 38, so `(0..count)` cuts through a community
+   in every row. The random-vs-block delta therefore does not isolate block
+   alignment, which is the one thing the row claims to measure. Fix shape:
+   pass the community size in and select whole communities, or choose
+   densities whose counts are multiples of 12.
+2. **`sigma_result` measures output cardinality, not multiplication work.**
+   `GrBMatrix::mxm` visits every `(i, j)` and probes every entry of `a.row(i)`;
+   all successful products for one `(i, j)` collapse into at most one stored
+   nonzero. Two workloads with the same `nnz_masked / nnz_full` can have very
+   different masked-multiply costs, so the probe's stop/speedup conclusions
+   about mask pushdown are not supported by the ratio it prints. Fix shape:
+   count column probes / successful semiring ops, or time an inward-mask
+   implementation.
+
+**Why not fixed in #1178:** the example is not this session's work and #1176
+is merged; the honest move is a ledger row plus a pointer, not a drive-by
+rewrite of someone else's measurement. Owner: the sigma-probe author.
+Cross-ref: E-NXG-16 (independence assumption in popcount selectivity) — the
+same "cardinality is not work" caveat, one probe over.
+
 ## TD-SIGKER-CLIPPY-RED-ON-BASE-1 (2026-09-04) — RESOLVED 2026-09-04
 
 **`crates/sigker` does not pass `cargo clippy --all-targets -- -D warnings`, and

.claude/nexgen/plans/nexgen-mask-histogram-thresholds-v1.md

@@ -156,6 +156,10 @@ falsifier that would kill it. Ordered by how many rooms ahead it sits.
 2. PROBE-NXG-HIST-1: build one `NestedBands` from a real facet column; assert
    bucket masks are disjoint, nested, and sum to N; assert rank = partition
    point (rooms 0, 16).
+   **GREEN 2026-09-05** on a real audio column (94 572 rows), not a facet
+   column — `crates/lance-graph-planner/examples/probe_nxg_hist_1.rs`,
+   E-NXG-17. Room 3 regraded there (midpoint σ over-reads 12 % on quantile
+   buckets).
 3. PROBE-NXG-ROLL-1: rollover on a bimodal column; entropy-triggered vs
    budget-triggered split order (room 2, D-NXG-5).
 4. PROBE-NXG-FLOOR-1: rank-derived floor vs `mu + 3σ` on the HHTL tiers
@@ -166,7 +170,7 @@ falsifier that would kill it. Ordered by how many rooms ahead it sits.
 
 | D-id | deliverable | status |
 |---|---|---|
-| D-NXG-1 | `NestedBands` sealed shape (T2), version-keyed, one owner | Queued |
+| D-NXG-1 | `NestedBands` sealed shape (T2), version-keyed, one owner | In progress (structure measured, E-NXG-17) |
 | D-NXG-2 | T1 name audit: `popcount_words` present or minted; bucket = `mask_ternlog::<0x10>` by name | Queued |
 | D-NXG-3 | T1 `bisect_column_by_mask` partial-popcount bisection | Queued |
 | D-NXG-4 | Prozentrang = bucket index; `shape × rank` computed from the slab | Queued |