Documents six cadcodec reader/writer gaps with source references, canary
tests and suggested fixes (nothing filed). Verifying them showed the Spline
DXF weight loss was an OCS bug: the writer emits weights only for a rational
spline, so the host now sets flags.rational from the weights. Spline passes
every gate.
Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>
