-- `_` in a match-arm pattern binds the matched inner value (or the subject
-- itself for plain `_:body` wildcards). Bodies that don't reference `_` are
-- unaffected — discard remains free. SPEC.md line 1069's `~_:~_` example
-- relies on this: re-wrap unchanged composes at zero extra tokens.
-- Re-wrap unchanged: `~_:~_` reads the unwrapped value via `_` and rewraps
-- it in Ok. Same shape, no rename to `~v:~v`.
rewrap s:t>R n t;r=num s;?r{~_:~_;^_:^"e"}
-- Debug-log the discarded err without renaming `^_` to `^e`.
log-err s:t>t;r=num s;?r{~v:str v;^_:fmt "err: {}" _}
-- Plain wildcard catch-all: `_:_` echoes the subject.
echo x:n>n;?x{1:10;_:_}
-- TypeIs wildcard `n _:_` binds the typed-matched value too.
typed-echo x:n>n;?x{n _:+_ 1;_:0}
-- run: rewrap 3.14
-- out: 3.14
-- run: rewrap oops
-- err: ^e
-- run: log-err abc
-- out: err: abc
-- run: echo 42
-- out: 42
-- run: echo 1
-- out: 10
-- run: typed-echo 5
-- out: 6