feat(ai-vterm): show [running] in picker and F9 redisplays last-used

The C-F9 project picker now flags projects whose claude buffer is alive with a " [running]" suffix on the abbreviated path. I added `cj/--ai-vterm-format-candidate` to compute the display name and routed the picker through it. Before the change, the picker showed every candidate identically, so you couldn't tell at a glance whether picking a project would attach to an existing session or start a fresh one.

F9 with two or more alive claude buffers used to open the project picker. That meant after toggling claude-A off, opening claude-B via C-F9, then toggling B off, the next F9 dropped into a picker rather than redisplaying B (the one you just toggled off). I renamed `redisplay-single` to `redisplay-recent` in `cj/--ai-vterm-dispatch` and broadened the trigger from "exactly one alive" to "one or more alive". F9 now redisplays the MRU claude buffer, so it consistently means "toggle THE claude I was last using". The project picker stays explicit on C-F9 for "start a different project", and M-F9 still picks among existing claudes.

2 new tests for the indicator (`format-candidate` flagged + unflagged), 2 dispatch tests renamed to match the new contract. 80 ai-vterm tests pass. Full make test green.

2 files changed, 34 insertions, 9 deletions

diff --git a/tests/test-ai-vterm--dispatch.el b/tests/test-ai-vterm--dispatch.el
index 3c0ae766..030b200d 100644
--- a/tests/test-ai-vterm--dispatch.el
+++ b/tests/test-ai-vterm--dispatch.el
@@ -2,10 +2,10 @@
 
 ;;; Commentary:
 ;; The dispatch helper is a pure decision function used by F9.
-;; Returns one of (toggle-off . WIN), (redisplay-single . BUF),
+;; Returns one of (toggle-off . WIN), (redisplay-recent . BUF),
 ;; or (pick-project) based on whether a claude buffer is currently
-;; displayed and how many alive claude buffers exist.  Tests mock the
-;; two underlying helpers so the dispatch logic can be exercised
+;; displayed and whether any alive claude buffers exist.  Tests mock
+;; the two underlying helpers so the dispatch logic can be exercised
 ;; without touching real windows.
 
 ;;; Code:
@@ -30,8 +30,8 @@
       (should (equal (cj/--ai-vterm-dispatch)
                      (cons 'toggle-off sentinel-win))))))
 
-(ert-deftest test-ai-vterm--dispatch-no-window-single-buffer-returns-redisplay ()
-  "Normal: no displayed claude, exactly one alive buffer -> redisplay-single."
+(ert-deftest test-ai-vterm--dispatch-no-window-single-buffer-returns-redisplay-recent ()
+  "Normal: no displayed claude, one alive buffer -> redisplay-recent + buffer."
   (test-ai-vterm--dispatch-cleanup)
   (let ((b1 (get-buffer-create "claude [single]")))
     (unwind-protect
@@ -40,11 +40,14 @@
                   ((symbol-function 'cj/--ai-vterm-claude-buffers)
                    (lambda () (list b1))))
           (should (equal (cj/--ai-vterm-dispatch)
-                         (cons 'redisplay-single b1))))
+                         (cons 'redisplay-recent b1))))
       (kill-buffer b1))))
 
-(ert-deftest test-ai-vterm--dispatch-no-window-multiple-buffers-returns-pick-project ()
-  "Normal: no displayed claude, 2+ alive buffers -> pick-project."
+(ert-deftest test-ai-vterm--dispatch-no-window-multiple-buffers-returns-redisplay-recent ()
+  "Normal: no displayed claude, 2+ alive buffers -> redisplay-recent + MRU.
+F9 redisplays the most-recently-selected claude (head of buffer-list
+order) rather than opening the project picker, so the user toggles
+THE claude they were last using.  Other claudes are reachable via M-F9."
   (test-ai-vterm--dispatch-cleanup)
   (let ((b1 (get-buffer-create "claude [a]"))
         (b2 (get-buffer-create "claude [b]")))
@@ -53,7 +56,8 @@
                    (lambda (&optional _frame) nil))
                   ((symbol-function 'cj/--ai-vterm-claude-buffers)
                    (lambda () (list b1 b2))))
-          (should (equal (cj/--ai-vterm-dispatch) '(pick-project))))
+          (should (equal (cj/--ai-vterm-dispatch)
+                         (cons 'redisplay-recent b1))))
       (kill-buffer b1)
       (kill-buffer b2))))
 
diff --git a/tests/test-ai-vterm--pick-project.el b/tests/test-ai-vterm--pick-project.el
index 6fa2d185..fd5295bf 100644
--- a/tests/test-ai-vterm--pick-project.el
+++ b/tests/test-ai-vterm--pick-project.el
@@ -44,5 +44,26 @@
       (cj/--ai-vterm-pick-project)
       (should (equal (caar received-collection) "~/code/foo")))))
 
+(ert-deftest test-ai-vterm--format-candidate-flags-running-project ()
+  "Normal: a path whose claude buffer has a live process gets a [running] suffix."
+  (let* ((path (expand-file-name "~/code/already-running"))
+         (buffer-name (cj/--ai-vterm-buffer-name path))
+         (buf (get-buffer-create buffer-name)))
+    (unwind-protect
+        (cl-letf (((symbol-function 'cj/--ai-vterm-process-live-p)
+                   (lambda (b) (eq b buf))))
+          (should (equal (cj/--ai-vterm-format-candidate path)
+                         (format "%s [running]" (abbreviate-file-name path)))))
+      (kill-buffer buf))))
+
+(ert-deftest test-ai-vterm--format-candidate-omits-flag-when-not-running ()
+  "Boundary: a path with no buffer or no live process -> plain abbreviated path."
+  (let ((path (expand-file-name "~/code/not-running")))
+    ;; Make sure no claude buffer exists for this path.
+    (let ((bn (cj/--ai-vterm-buffer-name path)))
+      (when (get-buffer bn) (kill-buffer bn)))
+    (should (equal (cj/--ai-vterm-format-candidate path)
+                   (abbreviate-file-name path)))))
+
 (provide 'test-ai-vterm--pick-project)
 ;;; test-ai-vterm--pick-project.el ends here