Return Mail search pages when the scope count times out (#8)

* Return Mail search pages when the scope count times out

* Keep Mail scope counts consistent with searchable messages

Read messages that Mail stores only as partial files (#7)

Mail writes <rowid>.partial.emlx when it stores some parts of a
message, such as attachments and inline images, in separate files.
The partial file keeps the headers and the text parts, and leaves the
body of each separate part empty, with an X-Apple-Content-Length field.
Envelope threw MailError.partialMessage for these messages.

The reader now reads the partial file when no complete .emlx file
exists, with the same containment and size checks. Content.attachments
lists the parts that have a filename or that Mail stores separately,
and isStoredSeparately marks the parts whose content the file leaves
out. A part that Mail stores separately cannot supply the body; when no
other part can, Content throws EmlxError.partialMessage.
MailError.partialMessage is deprecated, and its text no longer says
that opening the message in Mail downloads it.

Read account addresses that Mail records as the account URL authority (…

…#5)

Current stores record an IMAP account's address as the whole authority
of its AccountURL, such as imap://user%40example.com/, so URLComponents
reports the address as the host and no user. Read the address from the
host when the URL has no user, and keep reading the user form.

Log why the account map gives no address: a missing, unreadable, or
unrecognized map, an entry without an address, or an account that
mailboxes refer to but the map does not list.

Merge everything into one Envelope module, and adopt iMCP's API sugge…

…stions (#4)

* Merge Mail, Emlx, and MIME into one Envelope module

Clients qualify Envelope's types with a distinctive module name, such as Envelope.MailError, and the package no longer adds generic module names like Mail and MIME to a dependency graph. The sources keep their Mail, Emlx, and MIME folders.

* Find the store location without waiting for other calls

location() reads only directory entries and links, so a status check no longer waits behind a running search or read.

* Validate Configuration when it is created, so Store.init does not throw

Configuration.init throws for a limit that is not positive, and Configuration.default holds the default limits. Callers no longer handle an error that the default configuration cannot produce.

* Add Mailbox.ID with a string form that includes the store

Mailbox row identifiers belong to one store, so a stale identifier now fails with storeChanged instead of naming a different mailbox. Mailbox.ID, Message.Identifier, and FetchRequest.Cursor encode as their string forms, so clients that send them as JSON strings no longer parse them by hand.

* Document a long-lived store with a security-scoped bookmark

Sandboxed clients keep one store created from the URL resolved from the bookmark, and make the folder accessible for each call. The README also points to 0.3.0.

Replace Worker and Database with a Mail.Store actor (#3)

* Replace Worker and Database with a Mail.Store actor

Store runs each operation on a private dispatch queue as part of the calling task, so task cancellation reaches SQLite and parsing without a token. Overlapping calls wait instead of failing with operationInProgress, and each operation closes its connection before it reads message files. Store.init validates the configuration, which adds a snapshot time limit. checkAccess() checks that the index can be opened. Operations run at the calling task's priority on macOS 14 and later. Cursors replace offsets for pagination. The new Envelope product re-exports Mail and Emlx and adds Store.content(for:), which checks the message's identity.

* Rewrite the README for Mail.Store

The usage examples use the Envelope product, cursor pagination, and task cancellation.

Add scoped reads that close the connection before returning (#2)

* Add scoped reads that close the connection before returning

Database.read runs a closure in one read transaction and closes the connection when it returns or throws. MessageFileReader.read(_:root:) finds the store from the Mail folder, so callers no longer carry versionURL from a closed database.

* Use scoped reads in the README examples

The read example no longer closes the database twice.

Revert "Skip XCTest discovery in the mutation run"

This reverts commit 768d5b2. The Swift 6.2 mutation run still stalled without XCTest discovery.