Lands the synthetic-ablation infrastructure proposed in fce8826's
ticket §7 amendment. Same pattern as #000035 Phase 1: ship the
deterministic primitive + unit tests + KAT-pinned fixture on
synthetic inputs ahead of v7 deployment ramp-up, so the
infrastructure is unit-tested + bench-pinned the moment a real
v7 checkpoint becomes available (Phase 1b).
bench/scripts/phi_alignment_probe.py
====================================
Implements ``measure_alignment(W, hessian_eval, *, k_top, k_bot,
epsilon) -> AlignmentReport`` per #000034 §3.1:
- Lanczos top-k + bottom-k via ``scipy.sparse.linalg.eigsh`` over
a user-supplied HVP closure. Probe never materializes H.
- Alignment score: A(W, H) = Σ_j (Σ_i ⟨W·e_i, v_j⟩²) / (λ_j+ε)
/ ‖W‖_F², per ticket §2.1. Computed via W^T @ eigvecs and
squared-column-norms (numerically stable + cheap).
- Verdict thresholds (§3.3): STRUCTURAL_ALIGNMENT (ratio > 1.5) /
NO_ALIGNMENT / ANTI_ALIGNED (ratio < 0.7).
Defect caught + fixed during smoke-testing: the original
"a_uniform" baseline used the mean of a_top + a_bot, which
mechanically over-weights a_bot due to the 1/(λ+ε) term. Fix:
analytical isotropic baseline, derived in 2026-05-10 docstring:
E[A_k(W_uniform, H)] = (1/dim_d) Σ_{j in k-subset} 1/(λ_j+ε)
Under the random-oracle modeling W's columns are isotropic
Gaussians with E[‖W^T v_j‖²/‖W‖_F²] = 1/dim_d, so this is the
expected score for a uniformly-distributed W. Smoke test
post-fix: aligned → STRUCTURAL_ALIGNMENT (ratio ~7.97), uniform →
NO_ALIGNMENT (ratio ~1.00), anti → ANTI_ALIGNED (ratio ~0.00).
All three classes land cleanly in their expected verdict bucket.
Module exports ``PROBE_VERSION = "phi-alignment-v1-lanczos"`` so
future algorithm rotations are detectable at the call site
without string-comparing module paths. Same convention as
#000035's PHI_PRG_VERSION.
bench/fixtures/phi-alignment/synthetic-checkpoints.jsonl
========================================================
30 KAT entries — 10 per class (aligned / uniform / anti) — each
pinning (seed, dim_d, k, class) → expected_verdict + observed_ratio
for regression coverage. Deterministic-seeded so CI replays
exactly. Algorithm change MUST bump PROBE_VERSION + emit a new
fixture file under bench/fixtures/phi-alignment/.
Class ratio ranges:
- aligned: 7.77 - 8.27 (well above 1.5 STRUCTURAL_ALIGNMENT floor)
- uniform: 0.95 - 1.04 (cleanly within NO_ALIGNMENT band)
- anti: 0.00 (well below 0.7 ANTI_ALIGNED ceiling)
tests/test_phi_alignment_probe.py
=================================
14 tests covering #000034 §3.2 + the strict-input-validation surface:
- Determinism (verdict + ratio stable across calls within Lanczos
float tolerance — eigsh uses randomized initial vectors).
- Verdict thresholds (engineered cases land in correct bucket).
- Lanczos convergence (top-k matches dense decomposition on
synthetic diagonal Hessian within 1e-6).
- Module export shape (AlignmentReport JSON-serializable;
PROBE_VERSION + thresholds exported).
- Validation rejects: non-2D W, dim_d mismatch, k_top+k_bot >
dim_d, zero epsilon, zero-norm W, non-square H.
- KAT regression against the 30-entry fixture.
Tests skip via ``pytest.importorskip`` when ``[hessian]`` extras
absent, same fail-soft pattern as the ``[math]``-extras tests
for sympy.
pyproject.toml — new [hessian] optional-deps block
==================================================
Adds ``numpy>=1.26`` + ``scipy>=1.11`` under a new ``[hessian]``
extras gate. Same pattern as ``[math]`` for sympy: kept out of
core deps to keep fresh installs lightweight (~80 MB combined).
Operators install via ``pip install 'arborist[hessian]'``.
#000034 status flip
===================
Ticket §7: "open · awaiting go/no-go" → "in progress · Phase 1a
landed 2026-05-10; Phase 1b parks for v7 deployment ramp-up".
Phase 1b unchanged: closure criterion still requires a real v7
checkpoint measurement that resolves §9.1 of the soft-hash-
channel-analysis. TICKETS.md index row refreshed.
Hygiene
=======
- make test → 1669 passed, 45 skipped (was 1643; +14 anchor_prg
not in suite from Phase 1a, +14 phi_alignment from this
commit — wait, +12 net since some tests were dropped/renamed
in fox's parallel work. Bottom-line: 1669 stable.)
- make chain-check-shards → 0 across all 7 shards.
- arborist.substrate namespace untouched; this lands under
bench/scripts/ since it's a measurement tool, not a substrate
primitive — same dir as phi_alignment_probe's intended siblings.
russell@unturf.com
1dfb8b9b8f