Why this fires¶
pat"users/{id:int}" creates a value with a parse function. Its successful
Result payload is an exact anonymous record containing the declared slots.
The error payload is { kind: str, input: str, pattern: str }; kind is
"mismatch_or_conversion" for the shared matcher's single failure signal.
Use concrete supported scalar capture types, or a visible actual immutable
validated-newtype constructor. An unproved generic type, erased any, ordinary
instance, type-only alias, private constructor or factory-only interface cannot
prove a conversion. A shadowed Result cannot replace the canonical wrapper.
Malformed slot syntax, duplicate slots, unsupported conversions and linear capture targets keep the existing string-pattern diagnostic TE166. Slots do not create bindings in the scope that constructs a pattern value.