A value with rules of its own — a URL, a path, a closed set, an identifier —
gets a type of its own. Passing it as a bare string discards those rules at the
first function boundary and leaves every consumer re-deriving them.
Added as a subsection of Architecture Preferences, with a table mapping the
common cases to the type to reach for in any language, the reasoning, and the
boundary rule: parse once at the edge, keep the type inward, serialize back only
where the wire actually demands a string. Notes the counter-case, so this is not
read as a mandate to wrap every string.
python.md gains the concrete choices: yarl.URL (already present wherever aiohttp
is), pathlib, StrEnum, and NewType for non-interchangeable identifiers.