Bootstrap value model

Type	Runtime value	Current representation
Int	Integer	Rust i64; checked addition
Float	Finite double-precision number	Rust f64; non-finite results are overflow
Bool	true or false	Rust bool

The AST contains literal and addition nodes with zero-based, half-open UTF-8 byte ranges. Public diagnostics distinguish syntax, type, and evaluation (overflow) failures. Types and values are distinct enums. There are no implicit conversions: neither Boolean-to-integer, nor integer-to-float widening, so addition takes two Int or two Float operands and returns that same type.

Signed 64-bit integers and binary double-precision floats are bootstrap implementation choices, not a permanent numeric design. Decimal semantics, rounding, and a unified numeric tower remain open. The eventual typed Card/document model is described as a boundary in architecture, not declared as a working value type here.