multiply a variant's flattened choice into one closed object per combination, where the refusal stood

[eburgos]

A struct variant flattening a multi-branch source, or an Option-wrapped one,
was refused: the variant's members are written inside the union member that
carries them, and a single closed object cannot describe a member with more
than one key set. The other two surfaces never had the problem — TypeScript
distributes an intersection over a union, and the JSON document multiplies at
run time — so the refusal was a Zod limitation blamed on the variant.

Zod gets the multiplication now, written out at expansion: one closed object
per combination of the variant's own members with each key set its sources can
write, joined in a union. An Option-wrapped source contributes its keys and
their absence; a multi-branch source one combination per branch; several
sources multiply; a single-branch source collapses to the one object it always
was, byte-identical. The variant still contributes exactly one member to its
enclosing union, so nothing about how the four tagged forms assemble moves —
the internally tagged form drops to a plain union exactly as it already does
for any flattening variant.

The three runtime behaviours the design leans on were measured against zod
4.4.3 before anything was built, not assumed: a union nested in a union accepts
each inner branch and rejects the mixed and partial shapes; a discriminated
union still discriminates when a member's content is itself a union, failing an
unknown discriminator with the single issue at the tag's path; and two
separately written closed objects validate identically. The final schemas were
then re-emitted and run against real serde payloads: every branch of every
multiplied variant accepted, every stale, mixed and unknown-key shape rejected.

What stays refused is the different question it always was: a flattened plain
enum, and a union with a non-object member — sources with no members to merge.
The two refusals this replaces come off with their tests turned into
acceptance; every other flatten fixture is pinned byte-identical.

just check, just quick, just lint-all across all 68 toggles, and the test
powerset across all 68 in four partitions — all green.