weir v0.0.37

Fixed

• REPL Tab completes record fields through a pipe. A record piped
  into _. or a lambda param — x |> from yaml T |> _., r |> _.,
  x |> … |> (fun row -> row. — offered no fields (or, for the lambda,
  every declared record's fields, unioned). The completer only unwrapped
  a seq element and gave up on a scalar record, but from yaml T
  yields one document, not a sequence. It now types the value flowing
  into the position — a seq still unwraps to its element, a scalar
  record surfaces its own fields — so #infer's payoff (a typed record
  → field completion) lands in the pipe positions people actually use.
• Tab on an empty prompt no longer dumps the universe. A fresh Tab
  used to return over a thousand candidates — every PATH executable plus
  every module, keyword and constructor, sorted — because the empty
  prefix matched everything. It now offers the session directives,
  #help first, so a bare Tab teaches the REPL's affordances instead.
  A prefix (Fi, Wr) filters as before, and a Tab in argument
  position still lists the directory.
• Union-case constructors are no longer offered as statement heads.
  WriteFile, Some, Get, Bearer and the other constructors leaked
  into head completion, but a constructor as a statement head is a
  discarded value (a check error). They are subtracted from the head
  pool while staying available in expression and argument positions,
  where they are valid.