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, 85 insertions, 0 deletions

diff --git a/tests/test-ai-vterm--window-geometry.el b/tests/test-ai-vterm--window-geometry.el
new file mode 100644
index 000000000..62b78baf8
--- /dev/null
+++ b/tests/test-ai-vterm--window-geometry.el
@@ -0,0 +1,85 @@
+;;; test-ai-vterm--window-geometry.el --- Tests for direction + fraction helpers -*- lexical-binding: t; -*-
+
+;;; Commentary:
+;; Two pure helpers used by F9's geometry-preservation feature:
+;;
+;; - `cj/--ai-vterm-window-direction' classifies a window's position
+;;   relative to its frame as right / below / left / above (with a
+;;   right fallback when the window fills the frame).
+;;
+;; - `cj/--ai-vterm-window-fraction' returns the window's size on
+;;   the matching axis as a fraction of the frame.
+;;
+;; Tests use real window splits in `save-window-excursion' rather
+;; than mocking, since the helpers consume `window-edges' and
+;; `frame-width' / `frame-height' directly.
+
+;;; Code:
+
+(require 'ert)
+
+(add-to-list 'load-path (expand-file-name "modules" user-emacs-directory))
+(require 'ai-vterm)
+
+(ert-deftest test-ai-vterm--window-direction-right-split ()
+  "Normal: 2-window vertical split, right-side window -> right."
+  (save-window-excursion
+    (delete-other-windows)
+    (let ((right (split-window (selected-window) nil 'right)))
+      (should (eq (cj/--ai-vterm-window-direction right) 'right)))))
+
+(ert-deftest test-ai-vterm--window-direction-left-split ()
+  "Normal: 2-window vertical split, left-side window -> left."
+  (save-window-excursion
+    (delete-other-windows)
+    (split-window (selected-window) nil 'right)
+    (should (eq (cj/--ai-vterm-window-direction (selected-window)) 'left))))
+
+(ert-deftest test-ai-vterm--window-direction-below-split ()
+  "Normal: 2-window horizontal split, bottom window -> below."
+  (save-window-excursion
+    (delete-other-windows)
+    (let ((below (split-window (selected-window) nil 'below)))
+      (should (eq (cj/--ai-vterm-window-direction below) 'below)))))
+
+(ert-deftest test-ai-vterm--window-direction-above-split ()
+  "Normal: 2-window horizontal split, top window -> above."
+  (save-window-excursion
+    (delete-other-windows)
+    (split-window (selected-window) nil 'below)
+    (should (eq (cj/--ai-vterm-window-direction (selected-window)) 'above))))
+
+(ert-deftest test-ai-vterm--window-direction-single-window-fallback ()
+  "Boundary: single-window frame -> default right."
+  (save-window-excursion
+    (delete-other-windows)
+    (should (eq (cj/--ai-vterm-window-direction (selected-window)) 'right))))
+
+(ert-deftest test-ai-vterm--window-fraction-right-split-half ()
+  "Normal: right window of equal vertical split -> ~0.5 width fraction."
+  (save-window-excursion
+    (delete-other-windows)
+    (let* ((right (split-window (selected-window) nil 'right))
+           (frac (cj/--ai-vterm-window-fraction right 'right)))
+      (should (and (> frac 0.4) (< frac 0.6))))))
+
+(ert-deftest test-ai-vterm--window-fraction-below-split-half ()
+  "Normal: bottom window of equal horizontal split -> ~0.5 height fraction."
+  (save-window-excursion
+    (delete-other-windows)
+    (let* ((below (split-window (selected-window) nil 'below))
+           (frac (cj/--ai-vterm-window-fraction below 'below)))
+      (should (and (> frac 0.4) (< frac 0.6))))))
+
+(ert-deftest test-ai-vterm--window-fraction-narrow-right-split ()
+  "Normal: right window at 1/4 width -> fraction within that range."
+  (save-window-excursion
+    (delete-other-windows)
+    (let* ((frame-w (frame-width))
+           (target-cols (/ frame-w 4))
+           (right (split-window (selected-window) (- target-cols) 'right))
+           (frac (cj/--ai-vterm-window-fraction right 'right)))
+      (should (and (> frac 0.15) (< frac 0.35))))))
+
+(provide 'test-ai-vterm--window-geometry)
+;;; test-ai-vterm--window-geometry.el ends here