4c27c197

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

WIP: contour chart agreement rule for vanishing Gram determinants (unfinished)

Unfinished work of the final-fix agent on claude/olm-final f2adce4, stopped
for quota. It replaces the zero_external corner reflection's orientation
choice by a chart-agreement rule in tfun (expression and hand-written
kernel), adds tests/data/contour_gram_rounding.txt, and changes the 256-bit
two-mass shell test to the bits-56 input-cancellation floor. Generated code
in this commit is from an intermediate regeneration. Open at the stop: the
new negligibility check makes the interpreted route worse on about ten rows
(e.g. 5e-13 -> 7e-9); the agent was testing a real-part-only variant. Not
validated; see HANDOFF.md in the NinjaRS repository.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>