Hi Kaigai-san,
Sorry for delayed response. I updated the patch, although I didn't change any about timing issue you and Fujita-san concern.
1) add some FDW options for cost estimation. Default behavior is not changed.
2) get rid of array of libpq option names, similary to recent change of dblink
3) enhance document, especially remote query optimization
4) rename to postgres_fdw, to avoid naming conflict with the validator which exists in core
5) cope with changes about error context handling