Some rules that were good ideas before but become crucial with Plotly.react so that we recognize a non-change correctly:

• Never create new arrays in the supplyDefaults step - for example reshaping 1D to 2D arrays. That should be done in a calc step and NOT pushed back into _fullData.
• Don't modify attributes after finishing supplyDefaults, unless you're going to push the results back to the input (data/layout) as well, like autorange/range.
• When you're stashing things on _full*, always make _private attributes.

Most of the instances of this are taken care of in #2341, but a few are open:

• tick0, dtick -> default filled in late (After SD) - also for tickmode=array, not needed at all
• camera doesn’t push back into _fullLlayout after drag, only layout?
• tests for scatter3d with uneven or missing x/y/z
• tests for surface with uneven, missing, or ragged x/y/z
• autocolorscale: first time it gets set on, second time off - is that intentional? cauto sometimes shows a similar effect… see gl3d_scatter-color-mono-and-palette resolved in: Don't mutate colorscale, cmin/cmax and zmin/zmax into user traces #3341
• contourcarpet: zmin/zmax get filled in (after supplyDefaults) but they aren't actually attributes of contourcarpet. They should be!
• autorange: 'reversed' should get replaced in layout once it has been acted on. There's a polar mock where this doesn't happen until the second draw.