fix: validate mail transport executables and default debug off

`mail-config.el` had three related issues. SMTP transport debug was hard-coded to t, which is sensitive since mail bodies and headers land in debug buffers. The use-package `:config` was also setting `sendmail-program` and `mu4e-get-mail-command` directly from `executable-find` results. So a host without msmtp or mbsync silently got `nil` or `(concat nil " -a")` instead of a clear failure mode.

I added `cj/smtpmail-debug-enabled` (default nil) plus `cj/set-smtpmail-debug` and `cj/toggle-smtpmail-debug` for temporary troubleshooting, mirroring the pattern from `auth-config.el`.

I extracted `cj/mail--executable-or-warn` so a missing program emits a one-time `display-warning` and returns nil. `cj/mail-configure-smtpmail` and `cj/mail--mbsync-command` both use it. Missing msmtp now leaves `sendmail-program` nil with a warning. Missing mbsync produces a nil sync command instead of the broken `(concat nil " -a")` string. I also wrapped the mbsync executable path in `shell-quote-argument` so unusual install paths don't fall apart on the `" -a"` concat.

I added `tests/test-mail-config-transport.el` with seven tests across Normal / Boundary / Error: debug-default-off, toggle wiring, msmtp present and missing, mbsync present, mbsync path with spaces, and mbsync missing. The `test-mail-config--with-executables` macro stubs `executable-find` from an alist so each test names its own environment.

1 files changed, 88 insertions, 0 deletions

diff --git a/tests/test-mail-config-transport.el b/tests/test-mail-config-transport.el
new file mode 100644
index 00000000..2244b6dd
--- /dev/null
+++ b/tests/test-mail-config-transport.el
@@ -0,0 +1,88 @@
+;;; test-mail-config-transport.el --- Tests for mail transport setup -*- lexical-binding: t; -*-
+
+;;; Commentary:
+;; Verifies mail transport debug logging is opt-in and external mail
+;; executables are validated before command variables are assigned.
+
+;;; Code:
+
+(require 'ert)
+(require 'cl-lib)
+
+(add-to-list 'load-path (expand-file-name "modules" user-emacs-directory))
+(require 'mail-config)
+
+(defmacro test-mail-config--with-executables (executables &rest body)
+  "Run BODY with `executable-find' returning paths from EXECUTABLES.
+EXECUTABLES is an alist of program name strings to executable paths."
+  (declare (indent 1))
+  `(let (test-mail-config--warnings)
+     (cl-letf (((symbol-function 'executable-find)
+                (lambda (program)
+                  (cdr (assoc program ,executables))))
+               ((symbol-function 'display-warning)
+                (lambda (type message &rest _args)
+                  (push (cons type message) test-mail-config--warnings))))
+       ,@body)))
+
+(ert-deftest test-mail-config-transport-smtpmail-debug-defaults-off ()
+  "SMTP transport debug logging should default to disabled."
+  (test-mail-config--with-executables '(("msmtp" . "/usr/bin/msmtp"))
+    (let ((cj/smtpmail-debug-enabled nil)
+          (smtpmail-debug-info :before-load))
+      (cj/mail-configure-smtpmail)
+      (should-not smtpmail-debug-info))))
+
+(ert-deftest test-mail-config-transport-smtpmail-debug-toggle ()
+  "Troubleshooting command should update both SMTP debug variables."
+  (let ((cj/smtpmail-debug-enabled nil)
+        (smtpmail-debug-info nil))
+    (cl-letf (((symbol-function 'message) (lambda (&rest _args) nil)))
+      (cj/set-smtpmail-debug t)
+      (should cj/smtpmail-debug-enabled)
+      (should smtpmail-debug-info)
+      (cj/set-smtpmail-debug nil)
+      (should-not cj/smtpmail-debug-enabled)
+      (should-not smtpmail-debug-info))))
+
+(ert-deftest test-mail-config-transport-msmtp-present-configures-sendmail ()
+  "When msmtp exists, sendmail transport variables should be configured."
+  (test-mail-config--with-executables '(("msmtp" . "/usr/bin/msmtp"))
+    (let (sendmail-program send-mail-function message-send-mail-function
+                           message-sendmail-envelope-from)
+      (cj/mail-configure-smtpmail)
+      (should (equal sendmail-program "/usr/bin/msmtp"))
+      (should (eq send-mail-function 'message-send-mail-with-sendmail))
+      (should (eq message-send-mail-function 'message-send-mail-with-sendmail))
+      (should (eq message-sendmail-envelope-from 'header))
+      (should-not test-mail-config--warnings))))
+
+(ert-deftest test-mail-config-transport-msmtp-missing-warns-and-disables-program ()
+  "When msmtp is missing, sendmail-program should be nil and a warning emitted."
+  (test-mail-config--with-executables nil
+    (let ((sendmail-program "/old/msmtp"))
+      (cj/mail-configure-smtpmail)
+      (should-not sendmail-program)
+      (should (equal test-mail-config--warnings
+                     '((mail-config . "msmtp not found; SMTP mail sending unavailable")))))))
+
+(ert-deftest test-mail-config-transport-mbsync-present-builds-command ()
+  "When mbsync exists, build the mu4e sync command."
+  (test-mail-config--with-executables '(("mbsync" . "/usr/bin/mbsync"))
+    (should (equal (cj/mail--mbsync-command) "/usr/bin/mbsync -a"))
+    (should-not test-mail-config--warnings)))
+
+(ert-deftest test-mail-config-transport-mbsync-path-with-spaces-is-quoted ()
+  "The mu4e sync command should quote unusual executable paths."
+  (test-mail-config--with-executables '(("mbsync" . "/opt/mail tools/mbsync"))
+    (should (equal (cj/mail--mbsync-command) "/opt/mail\\ tools/mbsync -a"))))
+
+(ert-deftest test-mail-config-transport-mbsync-missing-returns-nil-and-warns ()
+  "When mbsync is missing, no unusable sync command should be assigned."
+  (test-mail-config--with-executables nil
+    (should-not (cj/mail--mbsync-command))
+    (should (equal test-mail-config--warnings
+                   '((mail-config . "mbsync not found; mu4e mail synchronization unavailable"))))))
+
+(provide 'test-mail-config-transport)
+;;; test-mail-config-transport.el ends here