refactor: extract window-geometry helpers shared by F9 and F12

`ai-vterm.el` (F9) and `eshell-vterm-config.el` (F12) both grew the same geometry-preservation pattern: classify a window's position, capture its body size, map cardinal direction to its frame-edge variant. The shared helpers were sitting as near-duplicates in both modules. With two real consumers established, the abstraction has the right shape. I pulled them into `cj-window-geometry.el`.

The new module exposes three pure helpers:

- `cj/window-direction` returns right/below/left/above based on edges relative to `frame-root-window`. Takes an optional DEFAULT for the single-window-frame fallback so each consumer picks its own (ai-vterm wants 'right, vterm-toggle wants 'below).
- `cj/window-body-size` returns body-cols (right/left) or body-lines (below/above). Same body-vs-total reasoning as before: divider-independent, matches what the user sees.
- `cj/cardinal-to-edge-direction` maps right/left/below/above to rightmost/leftmost/bottom/top, used by each consumer's `display-saved` action.

`ai-vterm.el` and `eshell-vterm-config.el` now `(require 'cj-window-geometry)` and call the shared helpers directly. The consumer-specific `capture-state` and `display-saved` bodies stay in each module because they bind to consumer-specific state vars. Extracting those would either need parameter-passing-via-symbol or a macro, both heavier than the duplication they would remove.

Tests: 15 in `test-cj-window-geometry.el` covering all four directions, body-size on both axes, cardinal-to-edge mapping, default-arg fallback, and the unknown-direction nil case. Deleted `test-ai-vterm--window-geometry.el` (now redundant) and trimmed four duplicate window-direction/size tests from `test-vterm-toggle--display.el`. Net LOC: each consumer ~40-50 lines lighter, with the new module + tests paying roughly half that back. Full make test green. make validate-modules green.

1 files changed, 0 insertions, 88 deletions

diff --git a/tests/test-ai-vterm--window-geometry.el b/tests/test-ai-vterm--window-geometry.el
deleted file mode 100644
index c22002739..000000000
--- a/tests/test-ai-vterm--window-geometry.el
+++ /dev/null
@@ -1,88 +0,0 @@
-;;; 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-size-right-split-returns-body-cols ()
-  "Normal: right window -> integer body-cols matching window-body-width."
-  (save-window-excursion
-    (delete-other-windows)
-    (let* ((right (split-window (selected-window) nil 'right))
-           (size (cj/--ai-vterm-window-size right 'right)))
-      (should (integerp size))
-      (should (= size (window-body-width right))))))
-
-(ert-deftest test-ai-vterm--window-size-below-split-returns-body-lines ()
-  "Normal: bottom window -> integer body-lines matching window-body-height."
-  (save-window-excursion
-    (delete-other-windows)
-    (let* ((below (split-window (selected-window) nil 'below))
-           (size (cj/--ai-vterm-window-size below 'below)))
-      (should (integerp size))
-      (should (= size (window-body-height below))))))
-
-(ert-deftest test-ai-vterm--window-size-narrow-right-split ()
-  "Normal: deliberately narrow right window -> matching body-col count."
-  (save-window-excursion
-    (delete-other-windows)
-    (let* ((frame-w (frame-width))
-           (target-cols (/ frame-w 4))
-           (right (split-window (selected-window) (- target-cols) 'right))
-           (size (cj/--ai-vterm-window-size right 'right)))
-      (should (integerp size))
-      (should (= size (window-body-width right))))))
-
-(provide 'test-ai-vterm--window-geometry)
-;;; test-ai-vterm--window-geometry.el ends here