docs: specify item 63, sent mail, in its own design file

The backlog entry could not be planned because it turned on a fact about the
user's mail rather than a design choice. Measured against the real database: no
`sent` tag exists at all, so the XS branch is dead. Every account keeps sent
mail in a folder, and the folders disagree across three shapes, with one
account having no sent folder whatsoever. That rules out a `<maildir>/Sent`
convention and forces a per-account key.

Decisions recorded: a per-account `sent` key composed at run time rather than a
shipped [queries] entry, which cannot narrow to the selected account and goes
stale when an account is added; an account without the key omitted silently, as
`drafts` already is; all-accounts combines and one account scopes through the
existing wrap; and recipients on the card in a Sent view, since the sender is
the user on every row.

Three constraints came from probing rather than memory. A bracketed provider
path contains `[` and `]`, which are Xapian syntax, so quoting is load-bearing
and the composed query returns its real count only because each path is quoted.
notmuch has get_authors and no recipients call at any level, so the To summary
must be folded per message in the worker, under the same thread-ownership rule
as walkReplies. And GMime's internet_address_list_parse returns NULL for an
empty string, which is a crash if unguarded; it also parses a comma inside a
quoted display name correctly, so comma-splitting is out.

Size revised M, up from S: the recipients half is a new ThreadSummary field, a
worker-side per-message walk, the first GMime address parsing in this codebase,
and a card that has to know which view it is in.

The spec lives in its own file rather than inline. The backlog is past four
thousand lines and its job is to say what is open and how big, which a hundred
lines of design buries. The entry keeps the finding and the size and points at
the spec, following item 53. "Adding to this document" now states the split
rule so the next specified item does not land inline again.

Account keys and folder names in the spec are placeholders. The counts and the
folder shapes are the real measurement and are what the design turns on.

Backlog item 63.

0 files changed, 0 insertions, 0 deletions