Send cc and bcc through the six providers that were dropping them

[pcbeingused333]

Closes #58.

Options accepts cc: and bcc: on every email, but six providers never read them, so the addresses went out discarded with no warning. This adds them, in the shape each API takes, through the address_list helper from #61:

provider	shape
Mailgun	cc / bcc, comma-separated line
MailPace	cc / bcc, comma-separated line
Postmark	Cc / Bcc, comma-separated line
Mailjet	Cc / Bcc, array of {"Email" => …}
SendGrid	cc / bcc inside the personalization, array of {"email" => …}
SparkPost	see below

Empty and whitespace-only values are dropped rather than sent, same as the providers that already used the helper.

SparkPost

SparkPost has no cc/bcc field. Every copy is an entry in recipients, and a copy is only shown as one if its address is repeated in the CC header — so the difference between a cc and a bcc is the header, not the recipient list. header_to carries the To line for all of them, which is also what keeps a bcc hidden: without it SparkPost sets each recipient's visible To to their own address, so the bcc would see itself addressed directly.

{"content" => {..., "headers" => {"CC" => "copy@example.com"}},
 "recipients" => [
   {"address" => {"email" => "first@example.com",  "header_to" => "first@example.com, second@example.com"}},
   {"address" => {"email" => "second@example.com", "header_to" => "first@example.com, second@example.com"}},
   {"address" => {"email" => "copy@example.com",   "header_to" => "first@example.com, second@example.com"}},
   {"address" => {"email" => "archive@example.com","header_to" => "first@example.com, second@example.com"}}]}

No cc means no headers key at all, so a send without copies keeps the body it had.

A second bug this fixes

Reading the recipients through the same helper also fixes #59. That issue is closed, but it still reproduces on main at 4d25da7 — and not only in Mailjet: SendGrid and SparkPost put a multi-address to into a single address object too.

options = Courrier::Email::Options.new(from: "d@example.com", to: "a@example.com, b@example.com", subject: "s", text: "t")

Courrier::Email::Providers::Mailjet.new(api_key: "k", options: options, provider_options: config).body
# => "To" => [{"Email" => "a@example.com, b@example.com"}]
Courrier::Email::Providers::Sendgrid.new(api_key: "k", options: options).body["personalizations"]
# => [{"to" => [{"email" => "a@example.com, b@example.com"}]}]
Courrier::Email::Providers::Sparkpost.new(api_key: "k", options: options).body["recipients"]
# => [{"address" => {"email" => "a@example.com, b@example.com"}}]

Happy to pull that out into its own PR if you'd rather review it separately, but it is the same one-line change per provider as the cc/bcc work, so splitting it would leave To broken next to a working Cc.

Left alone

Loops and Userlist address a single contact through a template API and have nowhere to put a copy, so they still ignore cc/bcc. Worth a note in the README, or a raise, but that is a decision rather than a fix — happy to follow whichever you prefer.

Tests

Postmark, SendGrid, SparkPost and MailPace had no test files; they have one now, covering the body shape, the empty-value handling and the auth header. Mailgun's and Mailjet's were extended.

bundle exec rake test on Ruby 3.4: 159 runs, 302 assertions, 0 failures, 0 errors. standardrb clean. With lib/ reverted and the new tests kept, 8 of them fail — verified rather than assumed.

[eelcoj]

Thanks again for this @pcbeingused333! ❤️ Will push a new version shorttly.