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, 64 insertions, 0 deletions

diff --git a/tests/test-ai-vterm--displayed-claude-window.el b/tests/test-ai-vterm--displayed-claude-window.el
new file mode 100644
index 00000000..283a1b3c
--- /dev/null
+++ b/tests/test-ai-vterm--displayed-claude-window.el
@@ -0,0 +1,64 @@
+;;; test-ai-vterm--displayed-claude-window.el --- Tests for the displayed-window helper -*- lexical-binding: t; -*-
+
+;;; Commentary:
+;; The helper returns a window in the selected frame whose buffer
+;; satisfies `cj/--ai-vterm-buffer-p', or nil when no such window
+;; exists.  Used by F9 dispatch and M-F9 in-place replacement.
+
+;;; Code:
+
+(require 'ert)
+
+(add-to-list 'load-path (expand-file-name "modules" user-emacs-directory))
+(require 'ai-vterm)
+
+(defun test-ai-vterm--displayed-cleanup ()
+  "Kill any leftover claude-prefixed buffers."
+  (dolist (b (buffer-list))
+    (when (string-prefix-p "claude [" (buffer-name b))
+      (kill-buffer b))))
+
+(ert-deftest test-ai-vterm--displayed-claude-window-no-buffers-returns-nil ()
+  "Boundary: no claude buffers anywhere -> nil."
+  (test-ai-vterm--displayed-cleanup)
+  (save-window-excursion
+    (delete-other-windows)
+    (should-not (cj/--ai-vterm-displayed-claude-window))))
+
+(ert-deftest test-ai-vterm--displayed-claude-window-not-displayed-returns-nil ()
+  "Boundary: claude buffer exists but not in any window -> nil."
+  (test-ai-vterm--displayed-cleanup)
+  (let ((b1 (get-buffer-create "claude [hidden]")))
+    (unwind-protect
+        (save-window-excursion
+          (delete-other-windows)
+          (should-not (cj/--ai-vterm-displayed-claude-window)))
+      (kill-buffer b1))))
+
+(ert-deftest test-ai-vterm--displayed-claude-window-returns-window-when-displayed ()
+  "Normal: claude buffer in a window -> returns that window."
+  (test-ai-vterm--displayed-cleanup)
+  (let ((b1 (get-buffer-create "claude [shown]")))
+    (unwind-protect
+        (save-window-excursion
+          (delete-other-windows)
+          (let ((win (split-window-right)))
+            (set-window-buffer win b1)
+            (let ((result (cj/--ai-vterm-displayed-claude-window)))
+              (should (windowp result))
+              (should (eq (window-buffer result) b1)))))
+      (kill-buffer b1))))
+
+(ert-deftest test-ai-vterm--displayed-claude-window-ignores-non-claude-windows ()
+  "Boundary: only a non-claude buffer is displayed -> nil."
+  (test-ai-vterm--displayed-cleanup)
+  (let ((other (get-buffer-create "regular-displayed-buffer")))
+    (unwind-protect
+        (save-window-excursion
+          (delete-other-windows)
+          (set-window-buffer (selected-window) other)
+          (should-not (cj/--ai-vterm-displayed-claude-window)))
+      (kill-buffer other))))
+
+(provide 'test-ai-vterm--displayed-claude-window)
+;;; test-ai-vterm--displayed-claude-window.el ends here