refactor(integrations): five hygiene fixes from the module-by-module re-review

- markdown-config.el: two related fixes on `markdown-preview'.
  First, the URL was `https://localhost:8080/imp' but simple-httpd
  serves plaintext on port 8080 -- the browser hit a TLS handshake
  against a non-TLS listener and the preview never rendered.  Changed
  to `http://' and switched from `browse-url-generic' to plain
  `browse-url' so the user's default protocol handler picks the
  browser.  Second, the function used to start the network listener
  as a side effect of opening a preview; that's split into a
  separate `cj/markdown-preview-server-start' command and
  `markdown-preview' now signals a `user-error' (with the recovery
  command in the message) when the server isn't running.

- slack-config.el: wrap the
  `which-key-add-keymap-based-replacements' call in
  `with-eval-after-load 'which-key'.  Matches the pattern other
  config modules use and means a slow / missing which-key load
  won't block requiring slack-config.

- ai-vterm.el: pass the inner shell-command-string through
  `shell-quote-argument' before wrapping in the tmux invocation.
  The default value with embedded double quotes was safe under the
  prior literal-single-quote wrap, but a user-customized
  `cj/ai-vterm-agent-command' containing a single quote silently
  broke the shell parse.  Two existing tests updated to tolerate
  the post-quote escape shape; new regression test asserts a
  single-quote-bearing custom command survives.

- eshell-config.el: scope the `TERM=xterm-256color' override to
  eshell-spawned processes only via an `eshell-mode' hook that
  prepends to a buffer-local `process-environment'.  The previous
  global `setenv' at config-time changed `TERM' for every
  subsequent `start-process' across the Emacs session, so any
  subprocess (not just eshell pipelines) inherited
  `xterm-256color' regardless of whether the receiver could
  interpret the escapes.

1 files changed, 21 insertions, 3 deletions

diff --git a/modules/markdown-config.el b/modules/markdown-config.el
index 2536904a..1fc4cb0e 100644
--- a/modules/markdown-config.el
+++ b/modules/markdown-config.el
@@ -33,16 +33,34 @@
 
 ;;;; --------------------- WIP: Markdown-Preview ---------------------
 
+(defun cj/markdown-preview-server-start ()
+  "Start the simple-httpd listener that serves the live markdown preview.
+Idempotent: re-running while the server is already up is a no-op."
+  (interactive)
+  (require 'simple-httpd)
+  (httpd-start)
+  (message "markdown preview server running on http://localhost:8080/imp"))
+
 ;; the filter to apply to markdown before impatient-mode pushes it to the server
 (defun markdown-preview ()
+  "Open the current buffer as a live HTML preview at http://localhost:8080/imp.
+The simple-httpd listener must already be running -- see
+`cj/markdown-preview-server-start'.  Starting a network listener as a
+side effect of opening a preview is surprising, so the server start
+lives in a separate command."
   (interactive)
-  (httpd-start)
+  (unless (and (boundp 'httpd-process) httpd-process)
+    (user-error "markdown preview server not running; run `M-x cj/markdown-preview-server-start' first"))
   (impatient-mode 1)
   (setq imp-user-filter #'cj/markdown-html)
   (cl-incf imp-last-state)
   (imp--notify-clients)
-  ;;  (browse-url-generic-function 'browse-url-xdg-open)
-  (browse-url-generic "https://localhost:8080/imp" 1))
+  ;; Use plain `browse-url' (not `browse-url-generic') so the user's
+  ;; default protocol handler picks the browser, and use `http://' --
+  ;; simple-httpd serves plaintext; the previous `https://' URL caused
+  ;; a TLS handshake against a non-TLS listener and the preview never
+  ;; rendered.
+  (browse-url "http://localhost:8080/imp"))
 
 (defun cj/markdown-html (buffer)
   (princ (with-current-buffer buffer