thanks for looking into this!

this area of protocol.ts is indeed kind of broken. in the event Stockfish emits multiple info lines at the same pv and depth within a single search, i think the most recent should be authoritative.

so i recommend something like:

      } else if (this.currentEval) {
        if (this.currentEval.pvs.length < multiPv) this.currentEval.pvs.push(pvData);
        else this.currentEval.pvs[multiPv - 1] = pvData;
        this.currentEval.depth = Math.min(this.currentEval.depth, depth);
      }

so i recommend something like:

      } else if (this.currentEval) {
        if (this.currentEval.pvs.length < multiPv) this.currentEval.pvs.push(pvData);
        else this.currentEval.pvs[multiPv - 1] = pvData;
        this.currentEval.depth = Math.min(this.currentEval.depth, depth);
      }

I would prefer to avoid using multiPv - 1 as an index, your recommendation is similar to my first commit, and I got a different kind of duplication during local testing: pv1 and pv2 (or another pv other than pv1 ) sometimes had the same first move, but slightly different subsequent moves in those pvs. It looks like pv1 should also have changed when overwritten by another worker, but pv1 itself remained old, and pv2 and subsequent ones are overwritten by the index and no longer duplicate each other.

Although I was unable to reproduce such duplication with your recommendation, perhaps this is the fix or duplication of the kind I described above is extremely rare.

multiPv - 1 is always the correct index.