fix(term): land copy-mode cursor at column 0

Entering copy-mode from C-; x c left the cursor at the live column, far right after a prompt, so scrolling up ran the cursor up the right edge instead of the left.

In the tmux branch I append C-a after C-b [, which tmux's emacs copy-mode reads as start-of-line. It has to go after C-b [: before copy-mode is active, C-a would hit the shell's readline instead. In the non-tmux ghostel-copy-mode branch I call beginning-of-line after entering the view, for the same column-0 result. Both branches now run the cursor up the left edge.

The non-tmux test asserts ghostel-copy-mode runs before beginning-of-line, since the move only repositions inside an active copy view. Its tracker variable is dwim-order, not calls, to avoid clashing with the variable the tmux mock macro binds.

2 files changed, 32 insertions, 15 deletions

diff --git a/modules/term-config.el b/modules/term-config.el
index 7cd386dc..2daebe9b 100644
--- a/modules/term-config.el
+++ b/modules/term-config.el
@@ -29,10 +29,12 @@
 ;; Two ways to lift text out of a terminal, both with the same key story:
 ;;   - C-; x c  enters copy-mode via `cj/term-copy-mode-dwim'.  When a tmux
 ;;     client is attached (typical -- `cj/term-launch-tmux' auto-starts tmux),
-;;     sends tmux's prefix C-b [ so the user lands in tmux's own copy-mode with
-;;     the full pane history available.  Without tmux, falls back to
+;;     sends tmux's prefix C-b [ then C-a, so the user lands in tmux's own
+;;     copy-mode with the full pane history and the cursor at column 0 (so
+;;     scrolling up runs up the left, not the right).  Without tmux, falls back to
 ;;     `ghostel-copy-mode' (read-only standard-Emacs navigation over the
-;;     scrollback; M-w copies and stays, q / C-g exit).
+;;     scrollback; M-w copies and stays, q / C-g exit) and moves point to the
+;;     start of the line for the same column-0 reason.
 ;;   - C-; x h  captures the current tmux pane's full history into a temporary
 ;;     Emacs buffer.
 ;; In both copy surfaces, M-w copies the active region and stays open so several
@@ -190,13 +192,19 @@ cheap boolean predicate."
   "Enter copy-mode using the engine appropriate to this terminal.
 
 When tmux is attached, write tmux's default prefix sequence (C-b [) into the
-pty so the user lands in tmux's copy-mode with the full pane history.  Without
-tmux, falls through to `ghostel-copy-mode', a read-only standard-Emacs view of
-the scrollback (M-w copies and stays, q / C-g exit)."
+pty so the user lands in tmux's copy-mode with the full pane history, then
+C-a to land the cursor at the start of the line.  Without the trailing C-a
+the copy cursor inherits the live column (far right after a prompt) and
+scrolling up runs up the right edge; tmux's emacs copy-mode binds C-a to
+start-of-line, so column 0 makes it run up the left.  Without tmux, falls
+through to `ghostel-copy-mode' (a read-only standard-Emacs view of the
+scrollback; M-w copies and stays, q / C-g exit), then moves point to the
+start of the line for the same column-0 reason."
   (interactive)
   (if (cj/term--in-tmux-p)
-      (ghostel-send-string "\C-b[")
-    (ghostel-copy-mode)))
+      (ghostel-send-string "\C-b[\C-a")
+    (ghostel-copy-mode)
+    (beginning-of-line)))
 
 ;; ----------------------------- ghostel package -------------------------------
 
diff --git a/tests/test-term-tmux-history.el b/tests/test-term-tmux-history.el
index b7ab5351..51e9725c 100644
--- a/tests/test-term-tmux-history.el
+++ b/tests/test-term-tmux-history.el
@@ -260,8 +260,11 @@ ghostel-mode terminal."
         (should-not tmux-called)))))
 
 (ert-deftest test-term-copy-mode-dwim-sends-tmux-prefix-when-attached ()
-  "Normal: with tmux attached, dwim writes C-b [ into the pty so tmux enters
-its own copy-mode against the full pane history."
+  "Normal: with tmux attached, dwim writes C-b [ then C-a into the pty so
+tmux enters its own copy-mode and lands the cursor at the start of the
+line.  Without the trailing C-a the cursor inherits the live column (far
+right after a prompt) and scrolling up runs up the right edge; start-of-line
+puts it at column 0 so it runs up the left."
   (let ((agent (cj/test--make-fake-ghostel-buffer "agent [emacs.d]"))
         (sent nil)
         (copy-mode-called nil))
@@ -279,16 +282,20 @@ its own copy-mode against the full pane history."
                 '((("list-clients" "-F" "#{client_tty}\t#{pane_id}") 0
                    "/dev/pts/8\t%8\n"))
               (cj/term-copy-mode-dwim)
-              (should (equal sent '("\C-b[")))
+              (should (equal sent '("\C-b[\C-a")))
               (should-not copy-mode-called))))
       (when (buffer-live-p agent)
         (kill-buffer agent)))))
 
 (ert-deftest test-term-copy-mode-dwim-falls-back-without-tmux ()
-  "Boundary: without tmux, dwim calls `ghostel-copy-mode' and sends nothing."
+  "Boundary: without tmux, dwim calls `ghostel-copy-mode' then moves point
+to the start of the line and sends nothing to the pty.  The
+`beginning-of-line' must run after `ghostel-copy-mode' so it repositions
+inside the copy view; column 0 keeps the cursor on the left edge while
+scrolling, parity with the tmux branch's trailing C-a."
   (let ((agent (cj/test--make-fake-ghostel-buffer "agent [emacs.d]"))
         (sent nil)
-        (copy-mode-called nil))
+        (dwim-order nil))
     (unwind-protect
         (with-current-buffer agent
           (cl-letf (((symbol-function 'get-buffer-process)
@@ -298,13 +305,15 @@ its own copy-mode against the full pane history."
                     ((symbol-function 'ghostel-send-string)
                      (lambda (s) (push s sent)))
                     ((symbol-function 'ghostel-copy-mode)
-                     (lambda () (setq copy-mode-called t))))
+                     (lambda () (push 'copy-mode dwim-order)))
+                    ((symbol-function 'beginning-of-line)
+                     (lambda (&optional _n) (push 'beginning-of-line dwim-order))))
             (test-term-tmux-history--with-tmux-mock
                 '((("list-clients" "-F" "#{client_tty}\t#{pane_id}") 1
                    "no server running"))
               (cj/term-copy-mode-dwim)
               (should-not sent)
-              (should copy-mode-called))))
+              (should (equal (reverse dwim-order) '(copy-mode beginning-of-line))))))
       (when (buffer-live-p agent)
         (kill-buffer agent)))))