feat(cmail): add --cc/--bcc and threading headers to cmail-action send

cmail-action send couldn't do a proper reply (no Cc/Bcc, no In-Reply-To/References), so an org-drill session that needed to reply to an upstream maintainer hand-rolled a raw MIME message through msmtp instead. I extended build_message (the pure function) with cc, bcc, in_reply_to, and references, wired the matching --cc/--bcc (repeatable), --in-reply-to, and --references flags through cmd_send, and wrote the tests first. send_message derives recipients from the To/Cc/Bcc headers and strips Bcc, so no manual recipient list is needed.

1 files changed, 52 insertions, 1 deletions

diff --git a/.ai/scripts/tests/test_cmail_action.py b/.ai/scripts/tests/test_cmail_action.py
index 3f77ca3..6788464 100644
--- a/.ai/scripts/tests/test_cmail_action.py
+++ b/.ai/scripts/tests/test_cmail_action.py
@@ -526,6 +526,52 @@ class TestBuildMessage:
         assert parsed["Subject"] == "日本語 ñ ü"
         assert "café" in parsed.get_content()
 
+    def test_cc_and_bcc_headers_set_from_lists(self, cmail_action):
+        msg = cmail_action.build_message(
+            from_addr="c@cjennings.net",
+            to_addr="to@example.com",
+            subject="Re: thread",
+            body="body",
+            cc=["cc1@example.com", "cc2@example.com"],
+            bcc=["bcc@example.com"],
+        )
+        assert msg["Cc"] == "cc1@example.com, cc2@example.com"
+        assert msg["Bcc"] == "bcc@example.com"
+
+    def test_threading_headers_set(self, cmail_action):
+        msg = cmail_action.build_message(
+            from_addr="c@cjennings.net",
+            to_addr="to@example.com",
+            subject="Re: thread",
+            body="body",
+            in_reply_to="<abc@host>",
+            references="<root@host> <abc@host>",
+        )
+        assert msg["In-Reply-To"] == "<abc@host>"
+        assert msg["References"] == "<root@host> <abc@host>"
+
+    def test_no_cc_bcc_or_threading_headers_when_omitted(self, cmail_action):
+        msg = cmail_action.build_message(
+            from_addr="c@cjennings.net",
+            to_addr="to@example.com",
+            subject="plain",
+            body="body",
+        )
+        assert msg["Cc"] is None
+        assert msg["Bcc"] is None
+        assert msg["In-Reply-To"] is None
+        assert msg["References"] is None
+
+    def test_cc_accepts_a_bare_string(self, cmail_action):
+        msg = cmail_action.build_message(
+            from_addr="c@cjennings.net",
+            to_addr="to@example.com",
+            subject="s",
+            body="b",
+            cc="solo@example.com",
+        )
+        assert msg["Cc"] == "solo@example.com"
+
 
 # ---------------------------------------------------------------------------
 # load_attachment — file I/O via tmp_path
@@ -580,12 +626,17 @@ class TestCmdSend:
 
     @staticmethod
     def _args(to="r@example.com", subject="s", body="b", body_file=None,
-              attach=None, stdin=False):
+              attach=None, stdin=False, cc=None, bcc=None,
+              in_reply_to=None, references=None):
         return SimpleNamespace(
             to=to, subject=subject,
             body=None if stdin else body,
             body_file=body_file,
             attach=attach or [],
+            cc=cc or [],
+            bcc=bcc or [],
+            in_reply_to=in_reply_to,
+            references=references,
         )
 
     def test_normal_inline_body_calls_send_message(self, cmail_action):