feat: queue messages for SMTP before encryption

Headers like From and Autocrypt are now added late,
right before sending the message over SMTP.
This way we advertise the latest list of transports
and use the correct From address in the encrypted part
even for messages queued while being offline.

BCC-self recipients are also added late.
For unencrypted messages we only want to send a copy
to the sending address, but we don't know the sending address
when queueing the message.
Adding bcc-self recipients when dequeuing the message
also makes it possible to send copies to updated list of relays.

docs/schema.sql

@@ -400,14 +400,51 @@ CREATE TABLE bobstate (
     chat_id INTEGER NOT NULL
 );
 
-CREATE TABLE smtp (
-  id INTEGER PRIMARY KEY AUTOINCREMENT,
-  rfc724_mid TEXT NOT NULL,          -- Message-ID
-  mime TEXT NOT NULL,                -- SMTP payload
-  msg_id INTEGER NOT NULL,           -- ID of the message in `msgs` table
-  recipients TEXT NOT NULL,          -- List of recipients separated by space
-  retries INTEGER NOT NULL DEFAULT 0 -- Number of failed attempts to send the message
-);
+CREATE TABLE smtp2 (
+    id INTEGER PRIMARY KEY AUTOINCREMENT,
+    display_name TEXT NOT NULL, -- Display name to put into the From field.
+    rfc724_mid TEXT NOT NULL, -- Message-ID
+
+    -- Unencrypted payload with some headers.
+    mime BLOB NOT NULL,
+
+    -- True if Autocrypt header should be added before sending.
+    should_attach_pubkey INTEGER NOT NULL,
+
+    -- True if OpenPGP-encrypted message may use compression.
+    should_compress INTEGER NOT NULL,
+
+    -- True if encrypted message should be signed.
+    should_sign INTEGER NOT NULL,
+
+    -- ID of the message in `msgs` table
+    msg_id INTEGER NOT NULL,
+
+    -- Space-separated recipient addresses.
+    recipients TEXT NOT NULL,
+
+    -- Space-separated addresses the message was sent to.
+    sent_to TEXT NOT NULL DEFAULT '',
+
+    -- If true, copy should be sent to self in addition to the recipient list.
+    --
+    -- For encrypted messages copy is sent to all addresses.
+    -- For unencrypted messages, copy is sent to the From address only.
+    bcc_self INTEGER NOT NULL,
+
+    -- True if the message is encrypted.
+    -- If true, at most one of the shared_secret or encryption_fingerprints should be non-empty.
+    -- If false, both must be empty.
+    is_encrypted INTEGER NOT NULL,
+
+    -- Shared secret if the message is to be encrypted symmetrically.
+    shared_secret TEXT NOT NULL DEFAULT '',
+
+    -- Space-separated fingerprints of the keys the message should be encrypted to.
+    encryption_fingerprints TEXT NOT NULL DEFAULT '',
+
+    retries INTEGER NOT NULL DEFAULT 0 -- Number of failed attempts to send the message
+) STRICT;
 
 CREATE TABLE smtp_mdns (
     msg_id INTEGER NOT NULL, -- id of the message in msgs table which requested MDN (DEPRECATED 2024-06-21)
@@ -781,3 +818,13 @@ CREATE TABLE sending_domains(
     domain TEXT PRIMARY KEY,
     dkim_works INTEGER DEFAULT 0
 );
+
+-- Replaced with smtp2.
+CREATE TABLE smtp (
+  id INTEGER PRIMARY KEY AUTOINCREMENT,
+  rfc724_mid TEXT NOT NULL,          -- Message-ID
+  mime TEXT NOT NULL,                -- SMTP payload
+  msg_id INTEGER NOT NULL,           -- ID of the message in `msgs` table
+  recipients TEXT NOT NULL,          -- List of recipients separated by space
+  retries INTEGER NOT NULL DEFAULT 0 -- Number of failed attempts to send the message
+);