Someone opened a pull request against my Safari MCP server last week. Three functions, same treatment each, clean write-up, all CI green. It fixed a real bug — his repro was solid, mine reproduced it too.
Then I sat down to write it up, built a 40-line model of the thing to make sure I understood it, and discovered that half of his patch does nothing at all. Not "does something subtle." Nothing. The two hunks he described as the fix are behaviorally identical to the code they replace.
The half he didn't emphasize is the one that closes the bug. And the reason neither of us could tell — the reason I couldn't tell about my own code — turns out to be the actual story here.
The protocol: positional, ID-free, and one mistake from disaster
My server talks to a small Swift helper for the things JavaScript can't do on a Mac: focus an app, hide a window, synthesize a real OS-level click. Newline-delimited JSON over stdin/stdout. Request and response are correlated positionally — there are no request IDs:
