Spread values from make-spread were crashing the wire format serializer:
- serialize() had no "spread" case, fell through to (str val) producing
Python repr "<shared.sx.ref.sx_ref._Spread...>" which was treated as
an undefined symbol
- aser-call/async-aser-call didn't handle spread children — now merges
spread attrs as keyword args into the parent element
- aser-fragment/async-aser-fragment didn't filter spreads — now filters
them (fragments have no parent element to merge into)
- serialize() now handles spread type: (make-spread {:key "val"})
Added 3 aser-spreads tests. All 562 tests pass.
Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>