Overall the change looks good. We have JDT-LS (quick-fix) calling to the client with java.action.addAllMissingImports, which calls back to JDT-LS with java/addAllMissingImports, which may call back to the client with java.action.organizeImports.chooseImports before returning to the client with the chosen result.

Why can't we just return java.action.organizeImports.chooseImports as the command at https://github.com/eclipse/eclipse.jdt.ls/blob/5c326daac216bb73cc5f43fc9a068fa7e569a9dd/org.eclipse.jdt.ls.core/src/org/eclipse/jdt/ls/core/internal/corrections/proposals/UnresolvedElementsSubProcessor.java#L726 ?

You're right. It seems that we don't need these capability/request/response, and just return the code action/quick fix as proposal and lazy resolve them. I'll update this PR later.