`SetLensWeights` refused an identical set by comparing raw maps, but a
lens a map does not name weighs zero. `{charter:3}` to
`{patina:0, charter:3}` therefore committed, and changing back committed
again, though both sets draw identically.
Equality is now `LensWeights::weighs_the_same_as`, owned in `lens.rs`: every
stock lens's effective weight is equal. The reducer's arm calls it; the
stored spelling is whatever the last committed set said.
Test, through the public mailbox in both directions:
`a_lens_set_spelled_with_or_without_its_zero_weights_commits_nothing`. A
sparse world set refuses a one-zero padded twin and an all-eight padded
twin; a padded world set refuses two sparse twins; each refusal is
`NoCanonicalChange` with revision, digests, operator log and stored
spelling unchanged; real changes commit.
Builds.
Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>
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