Mail · Writing: the composer, recipients that suggest, a signature, send later

MailComposer writes a message: To, and Cc and Bcc once asked for, as
tag fields that suggest contacts and mark what is not an address; the
subject and the words; the files, each with a way off; the signature
under the words. Send wakes once there is someone to send to and every
address is one; it hands over the draft now or at a time, and Discard
lets it go. A new start from the owner begins the draft over.

forms::TagInput now suggests: the rows that hold the typed words float
under it through the list Combobox uses; Up, Down and Enter pick, and
Escape sets them aside. RecipientInput points to it. ScheduleSend
offers tomorrow morning, tomorrow afternoon, Monday morning, or a day
and hour picked in a dialog. SignatureEditor writes the lines and shows
how they sit under a message; it tells the owner's echo from a new
signature, so the caret stays.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

tasks/ch21-30.md

@@ -375,10 +375,10 @@
 
 ## T29c Mail · Writing
 
-- [ ] MailComposer
-- [ ] RecipientInput
-- [ ] SignatureEditor
-- [ ] ScheduleSend
+- [x] MailComposer
+- [x] RecipientInput → `forms::TagInput`, its suggestions and an address check
+- [x] SignatureEditor
+- [x] ScheduleSend
 
 ## T29d Mail · Sorting