1df7aa38

By: ValentinHirschi <valentin.hirschi@gmail.com>

validate physical two-loop amplitude sampling and reference estimates

Register explicit full-rank amplitude surface charts from the generated
E-surface catalogue, warmed masses and external momenta. Preserve distinct
physical targets in their common parent output frame. Diagnose unsupported
spectator frames, ambiguous equations, unknown targets and invalid centers.
Add the UV-finite massive kite with real six-dimensional threshold tests.

Share reference and physical graph traversal and LMB routing. Accumulate
reference moments at each mapped point before statistical squaring, account
for graph/orientation selection and grid weights exactly once, and reject
invalid acceptance draws. Fix native-precision finite checks, exact radial
map capability, inverse-coordinate clipping and false root certification.

Validation: all 146 library sampling tests covered by passing isolated runs;
both API regressions pass, including saved/reloaded shifted Gaussian moments,
fully subtracted kite summed/MC agreement and independent default-LMB routing.
Core/API test checking, formatting, clippy and diff checks pass. Existing
unrelated clippy warnings remain. Saved state reload requires warmup; no
state format migration. No physical variance improvement claimed yet.

Record remaining two-sided radial focusing and warmup-cache work before
physical amplitude or GL638 variance comparisons.

User request:
Continue as planned, but also add that the advanced sampling implementation should also be tested for amplitude multiloop graphs (not just the cross-section ones), where it is of course simpler as there are no cuksosky cuts. Spawn a subagent to propose good candidates, but the 6-photons 2-loop graphs in the presence of thresholds is an idea, but it may be slow to generate, I would then rather consider some UV finite scalar 2-loop amplitude topologies. Let a subagent what would be best.
This allows to not only test the implementation of advanced sampling on amplitude, but also test the new advanced surface maps in a simpler context with not cutkosky cut rescaling, and also monitor the impact on the variance for these cases.

Timeline