MacroSelectors

Loose variant of extractSingleFieldName — strips Inlined / Typed wrappers around the lambda AND around its Select body, and does NOT require the Select receiver to be the bare lambda parameter. Used by the cursor macros' .field(_.x) sugar, whose selectors are always single-hop but may arrive wrapped. Kept distinct from extractSingleFieldName (which rejects nested chains by construction) so callers that need the strict form still have it.

Strips Inlined / Typed wrappers and peeks inside the lambda body for a single Select whose receiver is exactly the lambda parameter (an Ident). Receiver-is-Ident is load-bearing — nested paths like _.a.b parse as Select(Select(Ident(_), "a"), "b") and fall through to None so each macro can produce its own "nested paths" message.

The single element type of a Scala collection type A (via its Iterable base type), or abort with a who-tagged error. Shared by the cursor macros' .at / .each sugar.

Reject duplicate field names; aborts on the first duplicate. The who tag prefixes the message.