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Annotations not showing

Good afternoon,

I have a reference trace from which I compute a new one (I simply extract all points in between the reference trace’s one).
I need this new trace not to be displayed, but to serve as an anchor for annotations to be displayed over : this way, I can display permanent anchors located in the middle of all the reference track’s points.

Everything seems to be working, except for the annotations rendering. Here is how I do it:

// this trace contains the mid points I talked about earlier
  const traceCartouche = [{
    x: traceCartoucheX, // computed above
    y: traceCartoucheY, // idem
    type: 'scatter',
    showlegend: false,
    mode: 'text', // make the tooltip persistent
  }]

  // these are the actual annotation representation
  const annotations = []
  for (let i = 0; i < traceCartoucheX.length; i++) {
    annotations.push({
      x: traceCartoucheX[i],
      y: traceCartoucheY[i],
      xref: 'x',
      yref: 'y',
      // [...] styling...
    })
  }

  Plotly.addTraces('myDiv', traceCartouche) // adding the ghost mid points trace
  Plotly.relayout('myDiv', {}, annotations)   // updates the graph layout with the annotations

Here are the annotations after creation:
deleteme

However, they never show up. What did I do wrong ?