feat(ai-vterm): F9 toggle/redisplay/pick + persistent split geometry

F9 was a single command that always opened the project picker. Three small frustrations stacked up. With one claude buffer open and not visible, F9 was a redundant prompt to pick a project that already had a session. With claude visible, there was no way to bury it without M-x quit-window. With two projects' buffers alive, swapping between them was a buffer-switch chore.

F9 is now a dispatch:

- Claude visible in this frame: quit the window (toggle off) and capture the geometry first.
- Exactly one claude buffer alive but hidden: re-display it (DWIM single-buffer case).
- Zero or two-plus alive: fall through to the project picker.

C-F9 is the always-pick-project entry point for explicit project switches. M-F9 is a buffer picker over the alive claude buffers. If a claude window is currently shown, the picked buffer replaces it in that window so the split orientation and size carry over. The shown buffer sorts last in the picker with a [shown] marker so RET picks "the other one."

Split geometry persists across toggles. Two module-level vars (cj/--ai-vterm-last-direction, cj/--ai-vterm-last-size) capture at toggle-off and feed a custom display action. After M-S-t flips claude from right to bottom, F9 toggle-off-then-on returns it at the bottom. After a mouse resize, the next toggle restores that fraction. State is per-session. Restarts reset to default right/0.5.

Two display-buffer fixes came out of testing:

- save-window-excursion around (vterm name) keeps the dashboard from being buried on a fresh F9 at startup. vterm calls pop-to-buffer-same-window internally, which would otherwise replace the selected window's buffer before the alist could route the new one.
- The action chain swaps display-buffer-use-some-window for a more specific cj/--ai-vterm-reuse-existing-claude. The generic version stole non-claude windows on C-F9 when the user was focused inside claude (claude on bottom, code on top -> new project landed in the code window). The specific version only reuses windows that already show a claude buffer.

I reclaimed C-F9 from the gptel toggle in ai-config.el. C-; a t still binds gptel.

I added eight new test files (claude-buffers, displayed-claude-window, dispatch, pick-buffer-candidates, window-geometry, capture-state, display-saved, reuse-existing-claude) plus a regression test on cj/--ai-vterm-show-or-create for the dashboard-preservation fix. All 73 ai-vterm tests pass and the full make test suite is green.

1 files changed, 39 insertions, 0 deletions

diff --git a/tests/test-ai-vterm--show-or-create.el b/tests/test-ai-vterm--show-or-create.el
index 3faf5f03..3fee4883 100644
--- a/tests/test-ai-vterm--show-or-create.el
+++ b/tests/test-ai-vterm--show-or-create.el
@@ -105,6 +105,45 @@ VARS is a plist of capture variable names: :calls, :strings, :returns,
               (should-not (buffer-live-p stale)))))
       (test-ai-vterm--cleanup name))))
 
+(ert-deftest test-ai-vterm--show-or-create-preserves-selected-window ()
+  "Regression: vterm's pop-to-buffer-same-window must not bury the dashboard.
+
+Real `vterm' replaces the selected window's buffer as a side-effect of
+construction.  On a fresh-boot frame (one window showing the dashboard),
+that side-effect previously left the original window pointing at the new
+claude buffer; the dashboard was buried, the alist-routed split then
+created a second window also showing claude.  The wrapper must restore
+the original window state before `display-buffer' fires so dashboard
+stays put and the alist places claude into a fresh right-side split.
+
+This test stubs `vterm' to mimic the pop-to-buffer-same-window side-effect
+and asserts the originally-selected window still shows its original buffer
+after `cj/--ai-vterm-show-or-create' returns."
+  (let ((claude-name "claude [preserve-window-test]")
+        (orig-name "*test-original-buffer*"))
+    (test-ai-vterm--cleanup claude-name)
+    (when (get-buffer orig-name) (kill-buffer orig-name))
+    (unwind-protect
+        (save-window-excursion
+          (delete-other-windows)
+          (let ((orig-buf (get-buffer-create orig-name))
+                (orig-win (selected-window)))
+            (set-window-buffer orig-win orig-buf)
+            (cl-letf
+                (((symbol-function 'vterm)
+                  (lambda (&optional name)
+                    (let ((buf (get-buffer-create name)))
+                      (set-window-buffer (selected-window) buf)
+                      buf)))
+                 ((symbol-function 'vterm-send-string)
+                  (lambda (_s &optional _) nil))
+                 ((symbol-function 'vterm-send-return)
+                  (lambda () nil)))
+              (cj/--ai-vterm-show-or-create "/tmp/preserve" claude-name)
+              (should (eq (window-buffer orig-win) orig-buf)))))
+      (test-ai-vterm--cleanup claude-name)
+      (when (get-buffer orig-name) (kill-buffer orig-name)))))
+
 (ert-deftest test-ai-vterm--show-or-create-returns-buffer ()
   "Normal: return value is the vterm buffer."
   (let ((name "claude [return-test]"))