New answers tagged mergeshapes
Rather than thinking about merging A/B and trying to avoid merging A/E, merge them all together into a single lake polygon (I'm hoping here your data model does at least include a unique code for the lakes) with ST_Union. Then, use ST_DumpRings() to get just the rings. Then add the skeleton lines for just that lake to the collection. Then use ST_Polygonize() ...
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