Proposed resolution (approved by CWG 2023-06-13):

Change in 10.3 [module.import] paragraph 5 as follows:

[Note 2: A header unit is a separate translation unit with an independent set of defined macros. All declarations within a header unit are implicitly exported (10.2 [module.interface]), and are attached to the global module (10.1 [module.unit]). —end note]