routes.email_helpers._decode_header joined the runs from
email.header.decode_header() with " ". Those runs carry their own
surrounding whitespace (e.g. (b"Re: ", None)), and RFC 2047 §6.2 requires
the whitespace between two adjacent encoded-words to be dropped, so the
join produced a double space after an ASCII prefix ("Re: Jóse"), a
spurious space in "Name <addr>" senders, and a stray space between two
adjacent encoded-words ("Café 日本"). _decode_header backs the inbox list,
message read, search, and the background pollers, so the corruption hit
essentially every non-ASCII subject/sender.
Use email.header.make_header(...) for RFC-correct concatenation, keeping
the existing lossy per-part fallback for malformed/unknown MIME charsets
(make_header raises LookupError there) so the unknown-charset contract in
tests/test_email_decode_header.py still holds.
The sibling mcp_servers.email_server._decode_header was already fixed the
same way (commit 46999de); this brings the routes.email_helpers copy in
line, with regression coverage.
Supported by Claude Opus 4.8
Co-authored-by: SurprisedDuck <288741682+SurprisedDuck@users.noreply.github.com>
SurprisedDuck