prompt: record PyAutoArray#449 merged for constant-zeroth-repair

active.md

@@ -11,18 +11,6 @@
   Disjoint from the registered mge-lane-death claim (research/mge-lane-death, never created).
   This is the canonical copy of the 2026-08-17 human-approved inference programme.
 
-## constant-zeroth-repair
-- issue: https://github.com/PyAutoLabs/PyAutoArray/issues/448
-- status: remote-handoff (prepared 2026-08-17 for a cloud/phone session; NO local worktree claim)
-- worktree: none (remote session clones PyAutoLabs/PyAutoArray and branches itself)
-- repos:
-  - PyAutoArray: feature/constant-zeroth-repair (to be created by the remote session)
-- prompt: active/constant_zeroth_broken_dead_code.md
-- note: Phase 8C of the inference programme (autolens_profiling#134). CPU-only, numpy-only
-  tests — deliberately chosen for a no-GPU remote session. PyAutoArray's other claim
-  (version-stamp-sync-guards) touches only `autoarray/__init__.py` + `files/release.sh`;
-  this task touches `autoarray/inversion/regularization/` — file-disjoint. Merge is human.
-
 ## positions-lh-penalty-accumulation
 - issue: https://github.com/PyAutoLabs/PyAutoLens/issues/699
 - status: pr-open (https://github.com/PyAutoLabs/PyAutoLens/pull/700)

complete/2026/08/constant-zeroth-repair.md

@@ -0,0 +1,124 @@
+- issue: https://github.com/PyAutoLabs/PyAutoArray/issues/448 (CLOSED completed)
+- pr: https://github.com/PyAutoLabs/PyAutoArray/pull/449 — MERGED 2026-08-18 as `74cf5a0`, 2 files, +99/-1
+- classification: library (PyAutoArray) — bug, Phase 8C of the inference programme (autolens_profiling#134)
+- branch: `feature/constant-zeroth-repair` (remote cloud session; the issue's suggested branch, not the session's `claude/…` default)
+- worktree: none — remote-handoff task by design (CPU-only, numpy-only tests); no local claim was ever made
+
+## What was wrong
+
+`al.reg.ConstantZeroth` was dead code presenting as a public feature — two
+independent defects in `autoarray/inversion/regularization/constant_zeroth.py`,
+both reproduced on clean main (`7d1906e`) before any fix (tracebacks on #448):
+
+1. **`eye(P)` shape bug** — the zeroth term was `xp.eye(P)` with
+   `P = neighbors.shape[1]` (neighbour-column count, e.g. 4), not `S` (mesh
+   pixel count), so `const + zeroth` raised a broadcast `ValueError` whenever
+   `S != P`.
+2. **Missing `neighbors_sizes` at the class API** —
+   `ConstantZeroth.regularization_matrix_from` omitted the required argument,
+   raising `TypeError` before the shape bug was even reached.
+
+## Fix
+
+Zeroth term is now the full `S x S` scaled identity
+(`xp.eye(S) * coefficient_zeroth**2`, matching `zeroth.py`'s `eye(pixels)`
+semantics); the class API threads `neighbors_sizes=linear_obj.neighbors.sizes`
+mirroring `Constant`. Siblings `adapt_split_zeroth.py` / `brightness_zeroth.py`
+checked clean — their zeroth terms are `xp.diag` over per-pixel weights, no
+copy-paste pattern. Four numpy-only tests added
+(`test_autoarray/inversion/regularizations/test_constant_zeroth.py`): shape
+`(S, S)` with `S != P`, no null mode (`min eigvalsh >= lambda_z^2`), reduction
+to Constant `+ lambda_z^2 * I`, class-API smoke. Constant/Adapt/AdaptSplit
+numerics and `autoarray/__init__.py` untouched.
+
+**Null-mode-lift verification** (9-pixel rectangular fixture,
+`lambda_n = lambda_z = 1`): Constant min eigenvalue `1e-8` (jitter-floor null
+mode, condition number `6e8`) → ConstantZeroth min eigenvalue `1.0 = lambda_z^2`
+(condition number `7.0`); element-wise residual against `Constant + lambda_z^2 I`
+exactly `0.0`. Recorded in the PR body for Phase 8C to cite. The fix makes the
+scheme WORK; it does not recommend it over AdaptSplit.
+
+## Traps and findings
+
+- **No numerics or unique-identifier impact.** The class API raised
+  unconditionally, so no fit anywhere ever produced a likelihood through it;
+  `__init__` and instance attributes are unchanged, so PyAutoFit identifiers
+  (built from model composition, not method bodies) are stable — no output
+  paths orphaned.
+- **One silent-wrongness edge existed in the old code:** with `P == 1` the
+  `(S,S) + (1,1)` broadcast *succeeded* and added `lambda_z^2` to every element
+  instead of the diagonal. Pathological mesh, unreachable via the class API,
+  now correct — but any hand-rolled direct util call on such a mesh would
+  (correctly) change value.
+- **`zeroth.py` observed but not touched:** its class API drops `xp`
+  (`zeroth_regularization_matrix_from(..., pixels=...)` without `xp=xp`) — a
+  latent JAX-backend drop, out of scope here, worth a hygiene glance.
+- **Remote-container environment traps:** `autonerves` requires Python >=3.12
+  while the container default is 3.11 (use `uv venv --python 3.12`); the full
+  suite needs the dev extras `numba` and `pynufft` or 4 tests fail on import;
+  the 3 `test__nufft_pynufft__*` transformer tests fail regardless on modern
+  scipy (`scipy.linalg.pinv2` removed, inside pynufft) — pre-existing on clean
+  main, unrelated. Final run: 988 passed, 59 skipped, those 3 env failures.
+  Repo CI (3.12/3.13) was fully green on the PR.
+
+## Original prompt
+
+# ConstantZeroth regularization is broken twice over — dead code presenting as a feature
+
+Type: bug
+Target: autoarray
+Repos:
+- @PyAutoArray
+Difficulty: small
+Autonomy: supervised
+Priority: normal
+Status: draft
+
+Found during the reg-logdet investigation (autolens_workspace_developer#104
+follow-up), and **independently confirmed by a second reviewer who actually ran
+it**. `al.reg.ConstantZeroth` has never worked through its class API — it raises
+before returning a matrix — yet it is a public, exported scheme
+(`autoarray/inversion/regularization/__init__.py`).
+
+Two distinct defects in `autoarray/inversion/regularization/constant_zeroth.py`:
+
+1. **Shape bug.** `constant_zeroth_regularization_matrix_from` builds the
+   neighbour term `const` as an `S x S` matrix (`S` = number of mesh pixels) but
+   then builds the zeroth term as `xp.eye(P)` where `P = neighbors.shape[1]` is
+   the **neighbour count** (e.g. 4), not `S`. `const + zeroth` therefore
+   broadcasts `900x900 + 4x4` and raises. `constant_zeroth.py:68-72`:
+   ```python
+   reg_coeff = coefficient_zeroth**2.0
+   zeroth = xp.eye(P) * reg_coeff        # P is the neighbour count, should be S
+   return const + zeroth
+   ```
+   The zeroth-order term is meant to be a full `S x S` scaled identity
+   (`+lam_z^2` on every pixel's diagonal), which is precisely the term that would
+   lift the graph-Laplacian null mode and make this scheme well-conditioned.
+
+2. **Missing-argument bug.** `ConstantZeroth.regularization_matrix_from` (the
+   class API path) does not pass `neighbors_sizes` to
+   `constant_zeroth_regularization_matrix_from`, so a correctly-shaped call raises
+   `TypeError` before reaching the shape bug. Verify the exact call site and
+   signature.
+
+**Why this matters beyond "a broken scheme":** in the reg-logdet investigation,
+`ConstantZeroth` was hypothesised to be the *already-correct* answer — a scheme
+that adds a genuine model-scaled zeroth-order term (`+lam_z^2 * I`) lifting the
+null mode, immune to the `1e-8`-below-the-noise-floor conditioning collapse that
+afflicts `Constant`/`Adapt`. That hypothesis is **dead on arrival** because the
+scheme itself is dead. Fixing it would resurrect a genuinely useful,
+well-conditioned regularization option — and is a prerequisite for "just point
+users at the zeroth-order variant" ever being a real answer.
+
+Task: reproduce both failures on clean main FIRST (a two-line call through the
+class API, then through the function with correct args). Then fix the `eye(P)` →
+`eye(S)`/`S x S` shape and thread `neighbors_sizes`. Check the sibling
+`adapt_split_zeroth.py` and `brightness_zeroth.py` for the same `eye(P)` / missing
+-arg pattern — they may share the copy-paste. Add a unit test that builds the
+matrix and asserts shape `(S, S)` and positive-definiteness (the whole point of a
+zeroth-order term is that the result has NO null mode). Numpy-only test per repo
+policy.
+
+Do NOT bundle this with the reg-logdet log-det change or the Adapt double-square
+probe — it is an independent, self-contained defect.

complete/index.md

@@ -6,7 +6,7 @@ Token-light navigation over the finished-work records (schema:
 only then grep a dated bucket. Curators: edit the band between the CURATED
 markers; everything below GENERATED is rebuilt.
 
-1001 records across 7 buckets.
+1002 records across 7 buckets.
 
 <!-- CURATED:START -->
 ## Highlights
@@ -38,6 +38,7 @@ _(curate hard-won records here — survives regeneration.)_
 - [compile-axis-triage-drift](2026/08/compile-axis-triage-drift.md)
 - [compile-warm-baseline-dashboard](2026/08/compile-warm-baseline-dashboard.md)
 - [conductor-discovery-lifecycle-split](2026/08/conductor-discovery-lifecycle-split.md) — closed on merge
+- [constant-zeroth-repair](2026/08/constant-zeroth-repair.md) — CLOSED completed
 - [correct-circular-sersic-hazard](2026/08/correct-circular-sersic-hazard.md) — Corrected the circular Sersic hazard in the actual fitted ell_comps coordinates. The q-angle structural findin…
 - [covariance-interpolator-rng-seed](2026/08/covariance-interpolator-rng-seed.md) — auto-closed by the merge
 - [crashed-run-poisons-resume](2026/08/crashed-run-poisons-resume.md) — A run interrupted while writing output left a half-written JSON file,

dashboard.md

@@ -8,7 +8,7 @@ Tasks only — the organism's health lives with the Heart (`/health`), not here.
 
 | Where | Count |
 |-------|------:|
-| [In flight](#in-flight) (`active/`) | 12 |
+| [In flight](#in-flight) (`active/`) | 11 |
 | [Parked](#parked) (`parked.md`) | 5 |
 | [Planned](#planned) (`planned.md`) | 7 |
 | [Backlog](#backlog) (`draft/`) | 139 |
@@ -48,7 +48,6 @@ Live on GitHub: [open issues](https://github.com/search?q=org%3APyAutoLabs+is%3A
 
 Issued — each has an open GitHub issue and usually a branch. The full record for each is in [`active.md`](active.md).
 
-- [ConstantZeroth regularization is broken twice over — dead code presenting](active/constant_zeroth_broken_dead_code.md) — [issue #448](https://github.com/PyAutoLabs/PyAutoArray/issues/448) — remote-handoff (prepared 2026-08-17 for a cloud/phone session; NO local worktree claim)
 - [Address ECEB editorial comments on ECLIPSE-C](active/euclid_eceb_editorial_revision.md)
 - [Commit the inference-methods programme plan + knowledge ledger into autolens_profiling](active/inference_programme_ledger.md) — [issue #134](https://github.com/PyAutoLabs/autolens_profiling/issues/134) — pr-open (https://github.com/PyAutoLabs/autolens_profiling/pull/135)
 - [JAX-native posterior sampler wave — ranked shortlist from the 2026-07-16](active/jax_native_posterior_sampler_wave.md) — [issue #113](https://github.com/PyAutoLabs/autolens_workspace_developer/issues/113) — PARKED 2026-07-24 — stage (a) POSITIVE: warm-started gradient SMC SAMPLES (acc 0.80->0.17 across tempering, einstein_radius…