feat(vterm): F12 toggle that excludes claude and preserves geometry

vterm-toggle picked the most-recently-selected vterm buffer as F12's toggle target. After using F9 on a claude vterm, the most-recent vterm IS claude, so F12 ended up toggling claude, which has its own F9 / C-F9 / M-F9 surface in ai-vterm.el and shouldn't be affected. The display rule also had a hard-coded `(window-height . 0.7)` that overrode mouse-resize and orientation flips on every toggle.

I replaced the F12 binding with `cj/vterm-toggle` in `eshell-vterm-config.el`, mirroring the pattern shipped in ai-vterm.el:

- `cj/--vterm-toggle-buffer-p` excludes claude-prefixed buffers from F12's candidate set.
- `cj/--vterm-toggle-capture-state` records direction + body size at toggle-off.
- `cj/--vterm-toggle-display-saved` replays via `(body-columns . N)` / `(body-lines . N)` cons forms with the cardinal direction mapped to its frame-edge variant (`right` -> `rightmost`, `below` -> `bottom`, etc.) so vterm always lands at the captured edge regardless of selected window.
- `cj/vterm-toggle` uses `delete-window` (with `one-window-p` guard) on toggle-off so buffer-move scenarios don't leak ghost windows.

Default direction is `'below` to match F12's traditional bottom split. The vterm-toggle package stays installed so `M-x vterm-toggle` still works. Only the F12 binding changes.

19 new tests across three files: buffer-filter, dispatch, display. Full make test green.

Tradeoff: ~150 lines of geometry helpers and capture/display action logic are duplicated from ai-vterm.el. Worth extracting into a shared module now that two consumers exist. I filed it as a follow-up rather than blocking this ship.

1 files changed, 58 insertions, 0 deletions

diff --git a/tests/test-vterm-toggle--dispatch.el b/tests/test-vterm-toggle--dispatch.el
new file mode 100644
index 00000000..d63b3d35
--- /dev/null
+++ b/tests/test-vterm-toggle--dispatch.el
@@ -0,0 +1,58 @@
+;;; test-vterm-toggle--dispatch.el --- Tests for cj/--vterm-toggle-dispatch -*- lexical-binding: t; -*-
+
+;;; Commentary:
+;; Pure decision helper for F12.  Returns one of (toggle-off . WIN),
+;; (show-recent . BUFFER), or (create-new) based on whether a vterm
+;; window is currently displayed and whether any vterm buffers are
+;; alive.  Mocking the underlying helpers keeps the dispatch logic
+;; exercisable without touching real windows.
+
+;;; Code:
+
+(require 'ert)
+(require 'cl-lib)
+
+(add-to-list 'load-path (expand-file-name "modules" user-emacs-directory))
+(require 'eshell-vterm-config)
+
+(defun test-vterm-toggle--dispatch-cleanup ()
+  "Kill any leftover test buffers."
+  (dolist (b (buffer-list))
+    (let ((name (buffer-name b)))
+      (when (string-prefix-p "*test-vterm" name)
+        (kill-buffer b)))))
+
+(ert-deftest test-vterm-toggle--dispatch-window-displayed-returns-toggle-off ()
+  "Normal: displayed vterm window -> (toggle-off . WIN)."
+  (let ((sentinel-win 'fake-window))
+    (cl-letf (((symbol-function 'cj/--vterm-toggle-displayed-window)
+               (lambda (&optional _frame) sentinel-win)))
+      (should (equal (cj/--vterm-toggle-dispatch)
+                     (cons 'toggle-off sentinel-win))))))
+
+(ert-deftest test-vterm-toggle--dispatch-no-window-buffer-alive-returns-show-recent ()
+  "Normal: no displayed vterm, at least one alive -> show-recent + first."
+  (test-vterm-toggle--dispatch-cleanup)
+  (let ((b1 (get-buffer-create "*test-vterm-mru-1*"))
+        (b2 (get-buffer-create "*test-vterm-mru-2*")))
+    (unwind-protect
+        (cl-letf (((symbol-function 'cj/--vterm-toggle-displayed-window)
+                   (lambda (&optional _frame) nil))
+                  ((symbol-function 'cj/--vterm-toggle-buffers)
+                   (lambda () (list b1 b2))))
+          (should (equal (cj/--vterm-toggle-dispatch)
+                         (cons 'show-recent b1))))
+      (kill-buffer b1)
+      (kill-buffer b2))))
+
+(ert-deftest test-vterm-toggle--dispatch-no-window-no-buffer-returns-create-new ()
+  "Boundary: nothing displayed, no alive vterms -> create-new."
+  (test-vterm-toggle--dispatch-cleanup)
+  (cl-letf (((symbol-function 'cj/--vterm-toggle-displayed-window)
+             (lambda (&optional _frame) nil))
+            ((symbol-function 'cj/--vterm-toggle-buffers)
+             (lambda () nil)))
+    (should (equal (cj/--vterm-toggle-dispatch) '(create-new)))))
+
+(provide 'test-vterm-toggle--dispatch)
+;;; test-vterm-toggle--dispatch.el ends here