So, the ultimate answer proved to be totally different. After agonizing amounts of diagnosing, trying new configurations, I finally realized that there are two error messages up there: Reason: no suitable image found.  Did find:  file system relative paths not allowed in hardened programs The first one turned out to be correct; there was, in fact, a dylib missing from my build. (One for x86_64 arch) The second message is completely wrong, and led me down a long irrelevant path.

After posting, I realized an obvious difference: I'm now building the Apple Silicon version, not the Intel one, so the "existing binary" is running under Rosetta, but the compiled one is running apple silicon.