The flat ChatMessagePart interface had 20+ optional fields, preventing
TypeScript from narrowing types on switch(part.type). Each consumer
needed runtime validation, type assertions, or defensive ?. chains.
Add `variants` struct tags to ChatMessagePart fields declaring which
union variants include each field. A codegen mutation in apitypings
reads these tags via reflect and generates per-variant sub-interfaces
(ChatTextPart, ChatReasoningPart, etc.) plus a union type alias.
A test validates every field has a variants tag or is explicitly
excluded, and every part type is covered.
Remove dead frontend code: normalizeBlockType, alias case branches
("thinking", "toolcall", "toolresult"), legacy field fallbacks
(line_number, typedBlock.name/id/input/output), and result_delta
handling. Add test coverage for args_delta streaming, provider_executed
skip logic, and source part parsing.
Mathias Fredriksson
66f809388e