Tapping a new-mail notification only brought the app to the foreground:
the content PendingIntent was a bare launch intent shared by every
notification, and nothing on the activity side handled a message target.
Per-message notifications now carry an explicit open-message intent —
action + id extra + a per-message data URI, so each message keeps its
own PendingIntent under filterEquals instead of all collapsing onto one
FLAG_UPDATE_CURRENT entry. MainActivity parses the id on fresh launch
and in onNewIntent and hands it to the NavHost as pending state (the
pendingCompose handoff pattern) to navigate to the reader. The group
summary keeps the plain open-the-app intent.
Fixes#56
Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>