Snap point to buffer end on scroll-on-input

When point is in scrollback (e.g. after pixel-scroll-precision-mode, mouse
wheel, M-v, or any scrolling command that moves point) and the user types or
pastes, ghostel--scroll-bottom resets the terminal viewport but leaves Emacs
point above viewport-start. The delayed redraw then preserves point via
saved-marker and skips the set-window-start anchor, so the window stays showing
scrollback.

Factor the terminal-viewport reset + point snap + redraw bump into
ghostel--snap-to-input, and call it from self-insert, send-event, and the shared
paste/yank/drop path (ghostel--paste-text). The terminal-engine
responsibility (scroll-bottom) stays in the native module; the Emacs-buffer
responsibility (goto-char) stays in Elisp, with one composition point.

Fixes #113

Author: dakra

ghostel.el

@@ -1057,12 +1057,24 @@ Returns the sequence string, or nil for unknown keys."
       (format "\e[%d;%d~" param (1+ mod-num))
     (format "\e[%d~" param)))
 
+(defun ghostel--snap-to-input ()
+  "Return the window to the live viewport on user input.
+Resets the terminal engine's viewport out of scrollback and moves
+Emacs point to `point-max' so the delayed redraw anchors
+`window-start' to the viewport and clears any pixel vscroll left
+by `pixel-scroll-precision-mode' or similar scrollers.  No-op
+when `ghostel-scroll-on-input' is nil.  Call from any path where
+the user's action implies \"show me the prompt\" — typed input,
+paste, yank, drop."
+  (when (and ghostel-scroll-on-input ghostel--term)
+    (ghostel--scroll-bottom ghostel--term)
+    (goto-char (point-max))
+    (setq ghostel--force-next-redraw t)))
+
 (defun ghostel--self-insert ()
   "Send the last typed character to the terminal."
   (interactive)
-  (when (and ghostel-scroll-on-input ghostel--term)
-    (ghostel--scroll-bottom ghostel--term)
-    (setq ghostel--force-next-redraw t))
+  (ghostel--snap-to-input)
   (let* ((keys (this-command-keys))
          (char (aref keys (1- (length keys))))
          (str (if (and (characterp char) (< char 128))
@@ -1076,9 +1088,7 @@ Extracts the base key name and modifiers from `last-command-event'
 and routes through the ghostty key encoder, which respects terminal
 modes (application cursor keys, Kitty keyboard protocol, etc.)."
   (interactive)
-  (when (and ghostel-scroll-on-input ghostel--term)
-    (ghostel--scroll-bottom ghostel--term)
-    (setq ghostel--force-next-redraw t))
+  (ghostel--snap-to-input)
   (let* ((event last-command-event)
          (base (event-basic-type event))
          (mods (event-modifiers event))
@@ -1155,6 +1165,7 @@ Clears `quit-flag' which Emacs sets when \\`C-g' is pressed with
 (defun ghostel--paste-text (text)
   "Send TEXT to the terminal, using bracketed paste if the terminal wants it."
   (when (and text ghostel--process (process-live-p ghostel--process))
+    (ghostel--snap-to-input)
     (process-send-string ghostel--process
                          (if (ghostel--bracketed-paste-p)
                              (concat "\e[200~" text "\e[201~")

test/ghostel-test.el

@@ -3703,12 +3703,16 @@ buffer and hand nil to the native module."
                (lambda (_term) (setq scroll-bottom-called t)))
               ((symbol-function 'ghostel--send-key)
                (lambda (str) (setq sent-key str))))
-      (let ((last-command-event ?a))
-        (cl-letf (((symbol-function 'this-command-keys) (lambda () "a")))
-          (ghostel--self-insert)))
-      (should scroll-bottom-called)
-      (should ghostel--force-next-redraw)
-      (should (equal "a" sent-key)))))
+      (with-temp-buffer
+        (insert "scrollback\nscrollback\nscrollback\n")
+        (goto-char (point-min))
+        (let ((last-command-event ?a))
+          (cl-letf (((symbol-function 'this-command-keys) (lambda () "a")))
+            (ghostel--self-insert)))
+        (should scroll-bottom-called)
+        (should ghostel--force-next-redraw)
+        (should (equal "a" sent-key))
+        (should (= (point) (point-max)))))))
 
 (ert-deftest ghostel-test-scroll-on-input-send-event ()
   "Send-event scrolls to bottom when `ghostel-scroll-on-input' is non-nil."
@@ -3720,10 +3724,14 @@ buffer and hand nil to the native module."
                (lambda (_term) (setq scroll-bottom-called t)))
               ((symbol-function 'ghostel--send-encoded)
                (lambda (_key _mods &optional _utf8) nil)))
-      (let ((last-command-event (aref (kbd "<return>") 0)))
-        (ghostel--send-event))
-      (should scroll-bottom-called)
-      (should ghostel--force-next-redraw))))
+      (with-temp-buffer
+        (insert "scrollback\nscrollback\nscrollback\n")
+        (goto-char (point-min))
+        (let ((last-command-event (aref (kbd "<return>") 0)))
+          (ghostel--send-event))
+        (should scroll-bottom-called)
+        (should ghostel--force-next-redraw)
+        (should (= (point) (point-max)))))))
 
 (ert-deftest ghostel-test-scroll-on-input-disabled ()
   "Self-insert does not scroll when `ghostel-scroll-on-input' is nil."
@@ -3735,11 +3743,41 @@ buffer and hand nil to the native module."
                (lambda (_term) (setq scroll-bottom-called t)))
               ((symbol-function 'ghostel--send-key)
                (lambda (_str) nil)))
-      (cl-letf (((symbol-function 'this-command-keys) (lambda () "a")))
-        (let ((last-command-event ?a))
-          (ghostel--self-insert)))
-      (should-not scroll-bottom-called)
-      (should-not ghostel--force-next-redraw))))
+      (with-temp-buffer
+        (insert "scrollback\nscrollback\nscrollback\n")
+        (goto-char (point-min))
+        (let ((start (point)))
+          (cl-letf (((symbol-function 'this-command-keys) (lambda () "a")))
+            (let ((last-command-event ?a))
+              (ghostel--self-insert)))
+          (should-not scroll-bottom-called)
+          (should-not ghostel--force-next-redraw)
+          (should (= (point) start)))))))
+
+(ert-deftest ghostel-test-scroll-on-input-paste ()
+  "Paste via `ghostel--paste-text' snaps point to the prompt."
+  (let ((ghostel--term 'fake)
+        (ghostel--process 'fake-proc)
+        (ghostel--force-next-redraw nil)
+        (ghostel-scroll-on-input t)
+        (scroll-bottom-called nil)
+        (sent-text nil))
+    (cl-letf (((symbol-function 'ghostel--scroll-bottom)
+               (lambda (_term) (setq scroll-bottom-called t)))
+              ((symbol-function 'ghostel--bracketed-paste-p)
+               (lambda () nil))
+              ((symbol-function 'process-live-p)
+               (lambda (_p) t))
+              ((symbol-function 'process-send-string)
+               (lambda (_p s) (setq sent-text s))))
+      (with-temp-buffer
+        (insert "scrollback\nscrollback\nscrollback\n")
+        (goto-char (point-min))
+        (ghostel--paste-text "hello")
+        (should scroll-bottom-called)
+        (should ghostel--force-next-redraw)
+        (should (equal "hello" sent-text))
+        (should (= (point) (point-max)))))))
 
 (ert-deftest ghostel-test-scroll-intercept-forwards-mouse-tracking ()
   "Scroll intercept forwards events when mouse tracking is active."
@@ -4349,6 +4387,7 @@ while :; do sleep 0.1; done'\n")
     ghostel-test-scroll-on-input-self-insert
     ghostel-test-scroll-on-input-send-event
     ghostel-test-scroll-on-input-disabled
+    ghostel-test-scroll-on-input-paste
     ghostel-test-scroll-intercept-forwards-mouse-tracking
     ghostel-test-scroll-intercept-fallthrough
     ghostel-test-control-key-bindings