An entrypoint that links to the interpreter is the interpreter

bunx --version under a published bun runtime printed bun’s own executable header: wrapper smoke (bunx --version) failed: 1 | \x7fELF\x02\x01\x01\x02>…. Five of the eight platform legs of the bun factory’s roll answered the same line.

A runtime payload declares the commands it serves, and the wrapper chooses one of two forms for a declared name. The direct form is right when the entrypoint is the interpreter itself, because then the kernel should start the interpreter and the name is a convenience. The composed form is right for everything else, because the interpreter must run the program. The gate that chose between them compared the declared path with the interpreter’s path literally, and bunx is a symbolic link to bun, so the two spellings differed, the direct form was refused, and bun was handed its own binary as source.

The gate now asks the engine for identity instead of comparing spellings. Both paths resolve through the link resolution the engine already owns — the chain follows through the mount router and stops with ELOOP at 32 hops — and the direct form follows when the canonical paths agree. The neighbouring case that must not take it keeps its behaviour: bin/npm in a Node.js distribution is a link to a shebang script, so npm composes through the interpreter as before.

The wrapper’s suite gains the bunx shape beside the npm one, on a fixture whose bin/bunx is a real symbolic link to the interpreter, and asserts that the program is the interpreter’s bytes and that the entrypoint is never an argument in the vector.

The node factory’s macOS smoke answered npm smoke failed: tebako-runtime-launcher: cannot materialize the entrypoint '/tfs/bin/npm' for the preloaded interpreter: Is a directory.

The preload mechanism bridges an entry token to a host twin so that an interpreter’s exec heuristics see plain data at a plain path. That is right for a script and wrong for a link, because a twin carries the target’s bytes at a temporary host path: npm’s own `require('../lib/cli.js') then resolved outside the image, where the directory it needed does not exist.

A link entry now keeps its virtual spelling under preload. The armed shim serves that spelling, and realpath answers the canonical target, which is exactly the surface Node.js module resolution asks for. The suite gains the preload-plus-link shape beside the exec-cache case and the direct-form case.

The two composition paths that produced the failures are now the two the wrapper’s suite asserts: a declared command whose link resolves to the interpreter starts the interpreter, and a link entry under preload keeps the virtual spelling that the interpreter’s own module resolution asks for. That suite is the release’s proof, because both defects were reachable only through a real runtime’s entrypoint rather than through a test of ours.

The end-to-end proof is the next runtime publish on each line: the node factory’s npm --version smoke and the bun factory’s bunx --version smoke are the two legs that failed, and they answer first. A package pressed against an earlier release on this line picks the change up through the runtime pair — resolving a newer runtime inside the same range — so no payload needs to be rebuilt.

The workspace version is the only value that moves. The mounted filesystem model, the wire format and the driver contract are unchanged, so packages pressed against earlier releases on this line continue to load.

Both defects were reachable only after version 2.8.60 taught the reader about links and the interposed realpath made a canonical target answerable. The link reader, the canonicalizer and this composition are the three parts that a declared command needed, and a factory smoke found the last two of them.