Add ghostel-default face for per-buffer default fg/bg customization

Previously, ghostel--apply-palette always read default foreground/background
from the global 'default face, making it impossible to theme ghostel terminal
buffers independently (e.g. dark terminal inside a light Emacs) without resorting
to defadvice.

Introduce 'ghostel-default' (inherits 'default) as the customization point,
following the same idiom as vterm-color-default, term-default-fg-color, etc.
Existing users see no change; those who want per-buffer theming can customize
the face directly.

Closes #178

Author: dakra

README.md

@@ -556,6 +556,17 @@ ghostel-color-white         ghostel-color-bright-white
 Themes that customize `term-color-*` faces automatically apply. Customize
 individual faces with `M-x customize-face`.
 
+Default foreground/background are read from the `ghostel-default` face,
+which inherits from `default`. Customize it to give ghostel terminals
+different default colors than the rest of Emacs (e.g. a dark terminal
+inside a light Emacs):
+
+```elisp
+(set-face-attribute 'ghostel-default nil
+                    :foreground "#cdd6f4"
+                    :background "#1e1e2e")
+```
+
 ## Configuration
 
 | Variable                         | Default              | Description                                              |

lisp/ghostel.el

@@ -2323,6 +2323,13 @@ file:// URL does not match the local machine, construct a TRAMP path."
 
 ;;; Palette
 
+(defface ghostel-default
+  '((t :inherit default))
+  "Base face used to derive ghostel terminal default fg/bg colors.
+Customize this to give ghostel buffers different default colors than
+the rest of Emacs (e.g. a dark terminal inside a light Emacs)."
+  :group 'ghostel)
+
 (defun ghostel--face-hex-color (face attr)
   "Extract hex color string from FACE's ATTR (:foreground or :background).
 Falls back to \"#000000\" if the color cannot be resolved."
@@ -2343,8 +2350,8 @@ Falls back to \"#000000\" if the color cannot be resolved."
   (when term
     (ghostel--set-default-colors
      term
-     (ghostel--face-hex-color 'default :foreground)
-     (ghostel--face-hex-color 'default :background))
+     (ghostel--face-hex-color 'ghostel-default :foreground)
+     (ghostel--face-hex-color 'ghostel-default :background))
     (when ghostel-color-palette
       (let ((colors
              (mapconcat

test/ghostel-test.el

@@ -4934,6 +4934,22 @@ rendered by `ghostel--delayed-redraw'.  This is the exact real-world path."
       (should-not default-colors-calls)
       (should-not palette-calls))))
 
+(ert-deftest ghostel-test-apply-palette-ghostel-default-face ()
+  "`ghostel--apply-palette' reads default fg/bg from `ghostel-default', not `default'."
+  (let ((looked-up nil))
+    (cl-letf (((symbol-function 'ghostel--set-default-colors) #'ignore)
+              ((symbol-function 'ghostel--set-palette) #'ignore)
+              ((symbol-function 'ghostel--face-hex-color)
+               (lambda (face _attr)
+                 (push face looked-up)
+                 "#000000")))
+      (ghostel--apply-palette 'fake-term)
+      ;; The two default-color lookups must target `ghostel-default',
+      ;; never `default' directly — otherwise buffer-local customization
+      ;; of the terminal's fg/bg is impossible (issue #178).
+      (should (memq 'ghostel-default looked-up))
+      (should-not (memq 'default looked-up)))))
+
 ;; -----------------------------------------------------------------------
 ;; OSC 51 elisp eval
 ;; -----------------------------------------------------------------------
@@ -7201,6 +7217,7 @@ while :; do sleep 0.1; done'\n")
     ghostel-test-prompt-navigation
     ghostel-test-sync-theme
     ghostel-test-apply-palette-default-colors
+    ghostel-test-apply-palette-ghostel-default-face
     ghostel-test-osc51-eval
     ghostel-test-osc51-eval-unknown
     ghostel-test-osc51-eval-catches-errors