It looks to me as though the "c" inserted by line 135 of 147.scm
has the same meaning as the "c" in the test (because neither is
bound in the context where they are inserted) so free-identifier=?
recognizes them as equivalent.

The "c" inserted by line 135 of 147.scm is a pattern variable bound to this syntax rule. Wouldn't this have to be renamed to preserve hygiene?

I tried the following code at the repl:

(define-syntax foo

(syntax-rules ()

((foo bar x)

(define-syntax bar

(syntax-rules (x)

((bar c) 'matched)

((bar z) 'unmatched))))))

(foo bar c)

(bar q)

Chez, Chibi, Racket (R6RS), Larceny (R7R6, version from yesterday) all evaluate the last expression to matched.

This seems to indicate that all systems hygienically rename the pattern variable c in the output of the foo macro.

This seems to contradict your recent experiments (e.g. (define c #f)) with the 147.scm code. Did Larceny change its behaviour between yesterday and today with respect to the code snippet above?

From R6RS 11.19:

A literal identifier matches an input subform if and only
if the input subform is an identifier and either both its
occurrence in the input expression and its occurrence in
the list of literals have the same lexical binding, or the
two identifiers have the same name and both have no lexical
binding.

R7RS 4.3.2:

An element in the input matches a literal identifier if and
only if it is an identifier and either both its occurrence
in the macro expression and its occurrence in the macro
definition have the same lexical binding, or the two
identifiers are the same and both have no lexical binding.

The R6RS is more precise here, with the "have the same name"
explaining what the R7RS leaves open to more imaginative
interpretations by saying "are the same".

Renamed identifiers are certainly not the same (e.g. are not free-identifier=?); by the very meaning of "rename", they also do not have the same name.

(My test from above confirm that the implementations I tested agree on this.)

Your diagnosis is confirmed by adding the following definition
to 147.scm:

(define c #f) ; right-hand side is arbitrary

With that one-line change, all of your tests pass.

I still do not understand why the apparent renaming of "c" in the 147.scm does not work. (Or rather, why Chibi and Sagittarius work, but Larceny doesn't, while Larceny passes the above test.)

Of course it may be that I miss the forest for the trees and that I don't see the obvious.

You had already added a definition for :continuation, which was
necessary because it's used as a literal and you didn't want it
to match if that name happens to appear within a use. It's less
obvious that you need to do the same for other names that occur
free within your macro-defining macros, so they can't clash with
pattern literals originating in a use, but you do need to do
that.

":continuation" is introduced at the top-level, so it will never be renamed by the macro expander. That's why I bound :continuation.

Marc