fix(ai-vterm): harden F9 toggle across multi-window and buffer-move

Live-testing surfaced four edge-case failures in the F9 toggle geometry preservation. Each gets a dedicated regression test.

- Multi-window squeeze: a captured fraction-of-frame replayed at the wrong size in 3+ window layouts because `display-buffer-in-direction` interprets float widths as fractions of the new window's parent, not the frame. In a flat 3-window layout the parent is the root, but in nested splits it's a sub-tree, and the captured fraction blew the layout up. I switched to absolute integer body-cols and body-lines as the captured unit. The unit is layout-independent.

- One-col peek: a claude window captured rightmost (no right divider, body=total) replayed into a middle position (with divider, body=total-1) showed 1 col of the sibling buffer peeking through where claude should have ended. I wrap the integer size in a `(body-columns . N)` / `(body-lines . N)` cons so `display-buffer-in-direction` sets the body explicitly, divider-independent.

- Position swap and compounding gap: `direction=right` in `display-buffer-in-direction` splits the selected window, not the frame edge. In multi-window layouts the new claude landed mid-frame instead of where it came from. Each toggle compounded a 1-col loss because the new position picked up a divider the original lacked. I map the cardinal direction to its frame-edge variant (`right` -> `rightmost`, `below` -> `bottom`, etc.) so claude always returns to the captured edge.

- Extra window after buffer-move: buffer-move (C-M-arrows) doesn't update the claude window's `quit-restore` parameter, so `quit-window` falls through to bury rather than delete. The window stays alive showing some other buffer. Toggle-on doesn't recognize it and creates a fresh side window, landing at N+1 windows. I switched to `delete-window` with a `one-window-p` guard for the single-window-frame case.

One tradeoff: in a layout where claude was deliberately in a middle position (e.g. agenda | claude | todo), the next toggle pulls it to the frame edge rather than the middle. The side-panel pattern is the design intent and the common case.

7 new regression tests covering each scenario. 80 ai-vterm tests pass. Full make test green.

1 files changed, 6 insertions, 7 deletions

diff --git a/tests/test-ai-vterm--capture-state.el b/tests/test-ai-vterm--capture-state.el
index cecb3ab8b..88a7784b2 100644
--- a/tests/test-ai-vterm--capture-state.el
+++ b/tests/test-ai-vterm--capture-state.el
@@ -15,7 +15,7 @@
 (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)."
+  "Normal: right-split window -> direction=right, integer body-cols matching window."
   (save-window-excursion
     (delete-other-windows)
     (let ((right (split-window (selected-window) nil 'right))
@@ -23,12 +23,11 @@
           (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))))))
+      (should (integerp cj/--ai-vterm-last-size))
+      (should (= cj/--ai-vterm-last-size (window-body-width right))))))
 
 (ert-deftest test-ai-vterm--capture-state-below-split-sets-direction ()
-  "Normal: below-split window -> direction=below, size in (0.4, 0.6)."
+  "Normal: below-split window -> direction=below, integer body-lines matching window."
   (save-window-excursion
     (delete-other-windows)
     (let ((below (split-window (selected-window) nil 'below))
@@ -36,8 +35,8 @@
           (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))))))
+      (should (integerp cj/--ai-vterm-last-size))
+      (should (= cj/--ai-vterm-last-size (window-body-height below))))))
 
 (ert-deftest test-ai-vterm--capture-state-noop-on-dead-window ()
   "Boundary: nil window -> state remains unchanged."