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--capture-state.el b/tests/test-ai-vterm--capture-state.el
new file mode 100644
index 000000000..cecb3ab8b
--- /dev/null
+++ b/tests/test-ai-vterm--capture-state.el
@@ -0,0 +1,64 @@
+;;; test-ai-vterm--capture-state.el --- Tests for cj/--ai-vterm-capture-state -*- lexical-binding: t; -*-
+
+;;; Commentary:
+;; The capture helper writes WINDOW's direction and size to module-
+;; level state vars `cj/--ai-vterm-last-direction' and
+;; `cj/--ai-vterm-last-size'.  Called from `cj/ai-vterm''s toggle-off
+;; branch so the next F9 display can restore the user's chosen
+;; orientation and size.  No-op on a dead window.
+
+;;; Code:
+
+(require 'ert)
+
+(add-to-list 'load-path (expand-file-name "modules" user-emacs-directory))
+(require 'ai-vterm)
+
+(ert-deftest test-ai-vterm--capture-state-right-split-sets-direction ()
+  "Normal: right-split window -> direction=right, size in (0.4, 0.6)."
+  (save-window-excursion
+    (delete-other-windows)
+    (let ((right (split-window (selected-window) nil 'right))
+          (cj/--ai-vterm-last-direction nil)
+          (cj/--ai-vterm-last-size nil))
+      (cj/--ai-vterm-capture-state right)
+      (should (eq cj/--ai-vterm-last-direction 'right))
+      (should (numberp cj/--ai-vterm-last-size))
+      (should (and (> cj/--ai-vterm-last-size 0.4)
+                   (< cj/--ai-vterm-last-size 0.6))))))
+
+(ert-deftest test-ai-vterm--capture-state-below-split-sets-direction ()
+  "Normal: below-split window -> direction=below, size in (0.4, 0.6)."
+  (save-window-excursion
+    (delete-other-windows)
+    (let ((below (split-window (selected-window) nil 'below))
+          (cj/--ai-vterm-last-direction nil)
+          (cj/--ai-vterm-last-size nil))
+      (cj/--ai-vterm-capture-state below)
+      (should (eq cj/--ai-vterm-last-direction 'below))
+      (should (and (> cj/--ai-vterm-last-size 0.4)
+                   (< cj/--ai-vterm-last-size 0.6))))))
+
+(ert-deftest test-ai-vterm--capture-state-noop-on-dead-window ()
+  "Boundary: nil window -> state remains unchanged."
+  (let ((cj/--ai-vterm-last-direction 'sentinel-dir)
+        (cj/--ai-vterm-last-size 0.123))
+    (cj/--ai-vterm-capture-state nil)
+    (should (eq cj/--ai-vterm-last-direction 'sentinel-dir))
+    (should (= cj/--ai-vterm-last-size 0.123))))
+
+(ert-deftest test-ai-vterm--capture-state-noop-on-deleted-window ()
+  "Boundary: deleted window -> state remains unchanged."
+  (let ((cj/--ai-vterm-last-direction 'sentinel-dir)
+        (cj/--ai-vterm-last-size 0.123)
+        (dead-win (save-window-excursion
+                    (delete-other-windows)
+                    (let ((w (split-window (selected-window) nil 'right)))
+                      (delete-window w)
+                      w))))
+    (cj/--ai-vterm-capture-state dead-win)
+    (should (eq cj/--ai-vterm-last-direction 'sentinel-dir))
+    (should (= cj/--ai-vterm-last-size 0.123))))
+
+(provide 'test-ai-vterm--capture-state)
+;;; test-ai-vterm--capture-state.el ends here