545e74d0 (post-0.21.2) made the Matrix YAML bridge seed its values into
PlatformConfig.extra so secondary multiplex profiles read their own config. The
"csv" bridge kind seeds any non-None value, so `free_response_rooms: ''` now
reaches extra as '' — and the readers' `if raw is None` fallback no longer fires,
so MATRIX_FREE_RESPONSE_ROOMS is ignored and require_mention drops every
un-mentioned message. Before that commit the bridge only wrote env and the key
was absent from extra, so the env value applied.
Route the three identity-check readers (_extra_csv_set, _extra_truthy,
_resolve_max_message_length — the last a three-tier chain where '' also
short-circuited the plugin-registry default) through the shared
gateway.platforms._shared.extra_or_secret, whose default already treats a blank
string as unset (the idiom mattermost/dingtalk/slack readers use). Explicit
scalars, bools and lists (including []) stay authoritative.
Two invariant tests replace the salvaged suite (moved to
tests/plugins/platforms/matrix/ to mirror the source path): blank falls through
for all three readers; explicit values still beat env.
Fixes#109358
Co-authored-by: KoNit-K <124019182+KoNit-K@users.noreply.github.com>
3ad65cc892