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.

4 files changed, 160 insertions, 10 deletions

diff --git a/.ai/scripts/cmail-action.py b/.ai/scripts/cmail-action.py
index 10eb215..0acd82d 100755
--- a/.ai/scripts/cmail-action.py
+++ b/.ai/scripts/cmail-action.py
@@ -120,17 +120,31 @@ def extract_body(msg):
     return msg.get_content()
 
 
-def build_message(from_addr, to_addr, subject, body, attachments=None):
+def build_message(from_addr, to_addr, subject, body, attachments=None,
+                  cc=None, bcc=None, in_reply_to=None, references=None):
     """Construct an EmailMessage from the given fields and attachments.
 
     attachments is a list of (filename, maintype, subtype, content_bytes)
-    tuples — typically the return value of load_attachment per file. Pure
-    function: no I/O, no SMTP.
+    tuples — typically the return value of load_attachment per file.
+
+    cc and bcc accept either a list of addresses or a single string; the
+    Cc/Bcc headers are set when present (smtplib.send_message reads them for
+    delivery and strips Bcc before sending). in_reply_to and references set
+    the In-Reply-To and References headers so a reply threads on the
+    recipient's end. Pure function: no I/O, no SMTP.
     """
     msg = EmailMessage()
     msg["From"] = from_addr
     msg["To"] = to_addr
+    if cc:
+        msg["Cc"] = ", ".join(cc) if isinstance(cc, (list, tuple)) else cc
+    if bcc:
+        msg["Bcc"] = ", ".join(bcc) if isinstance(bcc, (list, tuple)) else bcc
     msg["Subject"] = subject
+    if in_reply_to:
+        msg["In-Reply-To"] = in_reply_to
+    if references:
+        msg["References"] = references
     msg.set_content(body)
     for filename, maintype, subtype, content in (attachments or []):
         msg.add_attachment(content, maintype=maintype, subtype=subtype,
@@ -310,7 +324,9 @@ def cmd_send(args):
         body = Path(args.body_file).read_text()
     else:
         body = sys.stdin.read()
-    msg = build_message(USER, args.to, args.subject, body, attachments)
+    msg = build_message(USER, args.to, args.subject, body, attachments,
+                        cc=args.cc, bcc=args.bcc,
+                        in_reply_to=args.in_reply_to, references=args.references)
     smtp = smtp_connect()
     try:
         smtp.send_message(msg)
@@ -377,6 +393,14 @@ def main():
                             "contents become the body")
     p_send.add_argument("--attach", action="append", default=[],
                         help="path to attach (repeatable)")
+    p_send.add_argument("--cc", action="append", default=[],
+                        help="Cc address (repeatable)")
+    p_send.add_argument("--bcc", action="append", default=[],
+                        help="Bcc address (repeatable)")
+    p_send.add_argument("--in-reply-to",
+                        help="Message-ID this replies to (threads on the recipient's end)")
+    p_send.add_argument("--references",
+                        help="References header (space-separated Message-IDs)")
     p_send.set_defaults(func=cmd_send)
 
     args = p.parse_args()
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):
diff --git a/claude-templates/.ai/scripts/cmail-action.py b/claude-templates/.ai/scripts/cmail-action.py
index 10eb215..0acd82d 100755
--- a/claude-templates/.ai/scripts/cmail-action.py
+++ b/claude-templates/.ai/scripts/cmail-action.py
@@ -120,17 +120,31 @@ def extract_body(msg):
     return msg.get_content()
 
 
-def build_message(from_addr, to_addr, subject, body, attachments=None):
+def build_message(from_addr, to_addr, subject, body, attachments=None,
+                  cc=None, bcc=None, in_reply_to=None, references=None):
     """Construct an EmailMessage from the given fields and attachments.
 
     attachments is a list of (filename, maintype, subtype, content_bytes)
-    tuples — typically the return value of load_attachment per file. Pure
-    function: no I/O, no SMTP.
+    tuples — typically the return value of load_attachment per file.
+
+    cc and bcc accept either a list of addresses or a single string; the
+    Cc/Bcc headers are set when present (smtplib.send_message reads them for
+    delivery and strips Bcc before sending). in_reply_to and references set
+    the In-Reply-To and References headers so a reply threads on the
+    recipient's end. Pure function: no I/O, no SMTP.
     """
     msg = EmailMessage()
     msg["From"] = from_addr
     msg["To"] = to_addr
+    if cc:
+        msg["Cc"] = ", ".join(cc) if isinstance(cc, (list, tuple)) else cc
+    if bcc:
+        msg["Bcc"] = ", ".join(bcc) if isinstance(bcc, (list, tuple)) else bcc
     msg["Subject"] = subject
+    if in_reply_to:
+        msg["In-Reply-To"] = in_reply_to
+    if references:
+        msg["References"] = references
     msg.set_content(body)
     for filename, maintype, subtype, content in (attachments or []):
         msg.add_attachment(content, maintype=maintype, subtype=subtype,
@@ -310,7 +324,9 @@ def cmd_send(args):
         body = Path(args.body_file).read_text()
     else:
         body = sys.stdin.read()
-    msg = build_message(USER, args.to, args.subject, body, attachments)
+    msg = build_message(USER, args.to, args.subject, body, attachments,
+                        cc=args.cc, bcc=args.bcc,
+                        in_reply_to=args.in_reply_to, references=args.references)
     smtp = smtp_connect()
     try:
         smtp.send_message(msg)
@@ -377,6 +393,14 @@ def main():
                             "contents become the body")
     p_send.add_argument("--attach", action="append", default=[],
                         help="path to attach (repeatable)")
+    p_send.add_argument("--cc", action="append", default=[],
+                        help="Cc address (repeatable)")
+    p_send.add_argument("--bcc", action="append", default=[],
+                        help="Bcc address (repeatable)")
+    p_send.add_argument("--in-reply-to",
+                        help="Message-ID this replies to (threads on the recipient's end)")
+    p_send.add_argument("--references",
+                        help="References header (space-separated Message-IDs)")
     p_send.set_defaults(func=cmd_send)
 
     args = p.parse_args()
diff --git a/claude-templates/.ai/scripts/tests/test_cmail_action.py b/claude-templates/.ai/scripts/tests/test_cmail_action.py
index 3f77ca3..6788464 100644
--- a/claude-templates/.ai/scripts/tests/test_cmail_action.py
+++ b/claude-templates/.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):