prompts: fix the reference's own record/variant construction syntax

[alpibrupa]

Summary

• The canonical quick-start's own Shape example was invalid Lex:

  type Shape = Circle(Float) | Rect { w :: Float, h :: Float }
  match shape { Circle(r) => ..., Rect { w, h } => w * h }

  lex check on that exact snippet: parse error ... expected \import`, `type`, or `fn` at top level, got Some(LBrace). A record-shaped variant's payload needs parens like any other variant argument — Rect({ w :: Float, h :: Float }), constructed Rect({ w: 1.0, h: 2.0 }), matched Rect({ w, h }) => ...— there is no bareRect { ... }form. Everylex-code` invocation this session opened with this example as the FIRST thing shown for algebraic data types.
• Found live: a fresh lex-economy repo's identity module build (dogfooding impl_test_fix_loop_verified on a brand-new domain) stalled for close to an hour on a closely related mistake — writing KeyPair { secret: x, public: y } for a plain record type alias (not a sum type), which also doesn't parse. Records construct with a bare literal, { field: value, ... } — the type name is never written at construction, only in an annotation or return type; TypeName { ... } reads as an ADT variant lookup and fails with a confusing unknown_variant or expected RParen error that doesn't say what's actually wrong.
• Confirmed all of this with minimal repros against the real compiler before touching anything, including that the fixed forms type-check and the broken forms don't.
• Fixed the quick-start's Shape example, added a worked Company/incorporate example showing bare-literal construction, and added two new pitfalls-table rows ({ field = value } vs :; the TypeName-prefixed construction mistake, both for plain records and for record-shaped ADT variants).

Test plan

• lex check / lex fmt --check / lex doc-sync --check — clean
• lex test tests — 4/4 existing tests still pass
• Rendered pitfalls_topic() and reference()'s actual string output to confirm escaping and content are correct, not just that the outer .lex file parses
• Every new/changed example snippet verified against the real compiler in isolation (/tmp scratch repro) before being added here

🤖 Generated with Claude Code