feat(markdown): start the preview server from F2 when it's down

cj/markdown-preview now brings up the simple-httpd listener itself instead of signaling a user-error pointing at cj/markdown-preview-server-start. The two-command flow guarded against a surprise network listener, but the preview is the only reason the listener exists, so the guard was just an extra step. I kept the start command for manual use.

1 files changed, 52 insertions, 0 deletions

diff --git a/tests/test-markdown-config-preview-autostart.el b/tests/test-markdown-config-preview-autostart.el
new file mode 100644
index 00000000..247c75d7
--- /dev/null
+++ b/tests/test-markdown-config-preview-autostart.el
@@ -0,0 +1,52 @@
+;;; test-markdown-config-preview-autostart.el --- preview server autostart -*- lexical-binding: t; -*-
+
+;;; Commentary:
+;; Tests for `cj/--markdown-preview-ensure-server': F2 preview starts the
+;; simple-httpd listener itself when it isn't running (per the 2026-07-01
+;; cj comment), and leaves a running server alone.  simple-httpd isn't
+;; installed in batch, so the tests provide a stub feature with the two
+;; functions the helper touches.
+
+;;; Code:
+
+(require 'ert)
+
+(add-to-list 'load-path (expand-file-name "modules" user-emacs-directory))
+
+(require 'markdown-config)
+
+;; Stand in for the elpa package: `require' in the helper becomes a
+;; no-op.  Tests mock httpd-running-p explicitly (works whether the
+;; real simple-httpd or this stub is loaded), so the stub bodies never
+;; matter.
+(require 'cl-lib)
+(unless (featurep 'simple-httpd)
+  (defun httpd-running-p () nil)
+  (defun httpd-start () nil)
+  (provide 'simple-httpd))
+
+(ert-deftest test-markdown-config-ensure-server-starts-when-down ()
+  "Normal: a stopped server gets started."
+  (let ((started nil))
+    (cl-letf (((symbol-function 'httpd-running-p) (lambda () nil))
+              ((symbol-function 'cj/markdown-preview-server-start)
+               (lambda () (setq started t))))
+      (cj/--markdown-preview-ensure-server)
+      (should started))))
+
+(ert-deftest test-markdown-config-ensure-server-noop-when-running ()
+  "Boundary: a running server is left alone."
+  (let ((started nil))
+    (cl-letf (((symbol-function 'httpd-running-p) (lambda () t))
+              ((symbol-function 'cj/markdown-preview-server-start)
+               (lambda () (setq started t))))
+      (cj/--markdown-preview-ensure-server)
+      (should-not started))))
+
+(ert-deftest test-markdown-config-preview-no-longer-signals-user-error ()
+  "Error-path regression: the old user-error on a stopped server is gone."
+  (should-not (string-match-p "user-error"
+                              (format "%S" (symbol-function 'cj/markdown-preview)))))
+
+(provide 'test-markdown-config-preview-autostart)
+;;; test-markdown-config-preview-autostart.el ends here