refactor(tests): extract shared buffer-cleanup and fake-vterm helpers

Eight test files across the ai-vterm and vterm-toggle suites each shipped a small variant of the same cleanup loop: walk `buffer-list`, kill any buffer whose name starts with a given prefix. Each file also re-implemented the `(string-prefix-p ...)` check inline. One file additionally had its own fake-vterm-mode-buffer constructor for tests that needed `cj/--vterm-toggle-buffer-p` to fire.

I pulled the shared logic into `tests/testutil-vterm-buffers.el`:

- `cj/test--kill-buffers-matching-prefix` is the primitive.
- `cj/test--kill-claude-buffers` and `cj/test--kill-test-vterm-buffers` are thin wrappers for the two prefixes that actually appear.
- `cj/test--make-fake-vterm-buffer` constructs a buffer with `major-mode` set to `vterm-mode` without launching a real vterm process.

Each affected test file now `(require 'testutil-vterm-buffers)` and calls the shared helpers directly. `test-vterm-toggle--buffer-filter.el` keeps a 3-line wrapper that calls both kill helpers in sequence (the only place that needs both prefixes). Net diff: -116 / +72 across 8 test files, plus ~30 lines in the new testutil. Roughly -45 lines after the abstraction is paid for.

No behavior change. 80 ai-vterm tests, 15 vterm-toggle tests, 15 cj-window-geometry tests all pass. Full make test green.

1 files changed, 7 insertions, 11 deletions

diff --git a/tests/test-ai-vterm--pick-buffer-candidates.el b/tests/test-ai-vterm--pick-buffer-candidates.el
index 99ef73254..ddfd75294 100644
--- a/tests/test-ai-vterm--pick-buffer-candidates.el
+++ b/tests/test-ai-vterm--pick-buffer-candidates.el
@@ -16,23 +16,19 @@
 (require 'ert)
 
 (add-to-list 'load-path (expand-file-name "modules" user-emacs-directory))
+(add-to-list 'load-path (expand-file-name "tests" user-emacs-directory))
 (require 'ai-vterm)
-
-(defun test-ai-vterm--pbc-cleanup ()
-  "Kill any leftover claude-prefixed buffers."
-  (dolist (b (buffer-list))
-    (when (string-prefix-p "claude [" (buffer-name b))
-      (kill-buffer b))))
+(require 'testutil-vterm-buffers)
 
 (ert-deftest test-ai-vterm--pick-buffer-candidates-empty-buffers ()
   "Boundary: empty buffer list -> empty alist regardless of shown."
-  (test-ai-vterm--pbc-cleanup)
+  (cj/test--kill-claude-buffers)
   (should (null (cj/--ai-vterm-pick-buffer-candidates nil nil)))
   (should (null (cj/--ai-vterm-pick-buffer-candidates nil 'sentinel))))
 
 (ert-deftest test-ai-vterm--pick-buffer-candidates-shown-nil ()
   "Normal: shown is nil -> straight alist in input order, no marker."
-  (test-ai-vterm--pbc-cleanup)
+  (cj/test--kill-claude-buffers)
   (let ((b1 (get-buffer-create "claude [a]"))
         (b2 (get-buffer-create "claude [b]")))
     (unwind-protect
@@ -44,7 +40,7 @@
 
 (ert-deftest test-ai-vterm--pick-buffer-candidates-shown-promotes-non-shown ()
   "Normal: shown buffer sorts last with [shown] suffix; others first."
-  (test-ai-vterm--pbc-cleanup)
+  (cj/test--kill-claude-buffers)
   (let ((b1 (get-buffer-create "claude [a]"))
         (b2 (get-buffer-create "claude [b]"))
         (b3 (get-buffer-create "claude [c]")))
@@ -61,7 +57,7 @@
 
 (ert-deftest test-ai-vterm--pick-buffer-candidates-shown-only-buffer ()
   "Boundary: shown is the only entry -> single cell with [shown] marker."
-  (test-ai-vterm--pbc-cleanup)
+  (cj/test--kill-claude-buffers)
   (let ((b1 (get-buffer-create "claude [a]")))
     (unwind-protect
         (let ((result (cj/--ai-vterm-pick-buffer-candidates (list b1) b1)))
@@ -70,7 +66,7 @@
 
 (ert-deftest test-ai-vterm--pick-buffer-candidates-shown-not-in-buffers ()
   "Boundary: stale shown buffer not in list -> all cells are non-shown."
-  (test-ai-vterm--pbc-cleanup)
+  (cj/test--kill-claude-buffers)
   (let ((b1 (get-buffer-create "claude [a]"))
         (b-stale (get-buffer-create "claude [stale]")))
     (unwind-protect