Allow the input buffer to navigate chat while keeping focus

pi-coding-agent-input.el

@@ -37,6 +37,8 @@
 ;;   `pi-coding-agent-quit'                  Close session
 ;;   `pi-coding-agent-previous-input'        History backward (M-p)
 ;;   `pi-coding-agent-next-input'            History forward (M-n)
+;;   `pi-coding-agent-input-previous-message' Navigate previous chat message
+;;   `pi-coding-agent-input-next-message'    Navigate next chat message
 ;;   `pi-coding-agent-history-isearch-backward'  History search (C-r)
 ;;   `pi-coding-agent-queue-steering'        Steering message (C-c C-s)
 
@@ -252,6 +254,31 @@ markdown highlighting while preserving mode identity and keybindings."
   (add-hook 'isearch-mode-hook #'pi-coding-agent--history-isearch-setup nil t)
   (add-hook 'kill-buffer-hook #'pi-coding-agent--cleanup-input-on-kill nil t))
 
+;;;; Input-Buffer Chat Navigation
+
+(defun pi-coding-agent--call-in-visible-chat-window (fn)
+  "Call FN in the visible linked chat window, preserving input focus."
+  (let* ((chat-buf (pi-coding-agent--get-chat-buffer))
+         (win (and (buffer-live-p chat-buf)
+                   (get-buffer-window chat-buf))))
+    (if (window-live-p win)
+        (save-selected-window
+          (select-window win)
+          (funcall fn))
+      (user-error "No chat window visible"))))
+
+(defun pi-coding-agent-input-next-message ()
+  "Move chat to the next user message, keeping focus in input."
+  (interactive)
+  (pi-coding-agent--call-in-visible-chat-window
+   #'pi-coding-agent-next-message))
+
+(defun pi-coding-agent-input-previous-message ()
+  "Move chat to the previous user message, keeping focus in input."
+  (interactive)
+  (pi-coding-agent--call-in-visible-chat-window
+   #'pi-coding-agent-previous-message))
+
 ;;;; Sending Prompts
 
 (defun pi-coding-agent--accept-input-text (text)

pi-coding-agent-ui.el

@@ -423,7 +423,6 @@ Returns the position of the heading line start, or nil if not found."
           (when (get-buffer-window) (recenter 0)))
       (message "No previous message"))))
 
-
 ;;;; Copy Visible Text
 
 (defun pi-coding-agent--visible-text (beg end)
@@ -623,8 +622,12 @@ new live processes in interactive sessions."
   "Reference to the chat buffer for this session.")
 
 (defun pi-coding-agent--set-chat-buffer (buffer)
-  "Set the chat BUFFER reference for this session."
-  (setq pi-coding-agent--chat-buffer buffer))
+  "Set the chat BUFFER reference for this session.
+In input buffers, also store BUFFER in `other-window-scroll-buffer'
+so built-in other-window scrolling commands target the linked chat."
+  (setq pi-coding-agent--chat-buffer buffer)
+  (when (derived-mode-p 'pi-coding-agent-input-mode)
+    (setq-local other-window-scroll-buffer buffer)))
 
 (defvar-local pi-coding-agent--input-buffer nil
   "Reference to the input buffer for this session.")

test/pi-coding-agent-input-test.el

@@ -2915,5 +2915,88 @@ no spurious faces are applied to plain colon-ending lines."
     (should (eq (key-binding (kbd "TAB")) 'pi-coding-agent-complete))
     (should (eq (key-binding (kbd "C-c C-s")) 'pi-coding-agent-queue-steering))))
 
+;;; Input-Buffer Chat Navigation
+
+(ert-deftest pi-coding-agent-test-input-next-message-moves-chat ()
+  "Input-side next-message moves the linked chat and keeps focus."
+  (let ((chat-buf (generate-new-buffer "*test-chat*"))
+        (input-buf (generate-new-buffer "*test-input*")))
+    (unwind-protect
+        (progn
+          (delete-other-windows)
+          (switch-to-buffer chat-buf)
+          (with-current-buffer chat-buf
+            (pi-coding-agent-chat-mode)
+            (let ((inhibit-read-only t))
+              (pi-coding-agent-test--insert-chat-turns))
+            (pi-coding-agent--set-input-buffer input-buf)
+            (goto-char (point-min)))
+          (let ((input-win (split-window nil -10 'below)))
+            (set-window-buffer input-win input-buf)
+            (with-current-buffer input-buf
+              (pi-coding-agent-input-mode)
+              (pi-coding-agent--set-chat-buffer chat-buf))
+            (select-window input-win)
+            (pi-coding-agent-input-next-message)
+            (with-current-buffer chat-buf
+              (should (looking-at "You · 10:00")))
+            (should (eq (window-buffer (selected-window)) input-buf))))
+      (kill-buffer chat-buf)
+      (kill-buffer input-buf)
+      (delete-other-windows))))
+
+(ert-deftest pi-coding-agent-test-input-previous-message-moves-linked-chat ()
+  "Input-side previous-message uses the linked chat, not scroll state."
+  (let ((chat-a (generate-new-buffer "*test-chat-a*"))
+        (chat-b (generate-new-buffer "*test-chat-b*"))
+        (input-buf (generate-new-buffer "*test-input*")))
+    (unwind-protect
+        (progn
+          (delete-other-windows)
+          (switch-to-buffer chat-a)
+          (let* ((chat-win-a (selected-window))
+                 (input-win (split-window chat-win-a -10 'below))
+                 (chat-win-b (split-window chat-win-a nil 'right)))
+            (set-window-buffer input-win input-buf)
+            (set-window-buffer chat-win-b chat-b)
+            (with-current-buffer chat-a
+              (pi-coding-agent-chat-mode)
+              (let ((inhibit-read-only t))
+                (pi-coding-agent-test--insert-chat-turns))
+              (goto-char (point-max))
+              (re-search-backward "^You · 10:10$" nil t))
+            (with-current-buffer chat-b
+              (pi-coding-agent-chat-mode)
+              (let ((inhibit-read-only t))
+                (pi-coding-agent-test--insert-chat-turns))
+              (goto-char (point-max))
+              (re-search-backward "^You · 10:10$" nil t))
+            (with-current-buffer input-buf
+              (pi-coding-agent-input-mode)
+              (pi-coding-agent--set-chat-buffer chat-a)
+              (setq-local other-window-scroll-buffer chat-b))
+            (select-window input-win)
+            (pi-coding-agent-input-previous-message)
+            (with-current-buffer chat-a
+              (should (looking-at "You · 10:05")))
+            (with-current-buffer chat-b
+              (should (looking-at "You · 10:10")))
+            (should (eq (window-buffer (selected-window)) input-buf))))
+      (kill-buffer chat-a)
+      (kill-buffer chat-b)
+      (kill-buffer input-buf)
+      (delete-other-windows))))
+
+(ert-deftest pi-coding-agent-test-input-previous-message-no-chat-window-errors ()
+  "Navigating from input without a visible linked chat signals error."
+  (let ((chat-buf (generate-new-buffer "*test-chat-hidden*")))
+    (unwind-protect
+        (with-temp-buffer
+          (pi-coding-agent-input-mode)
+          (pi-coding-agent--set-chat-buffer chat-buf)
+          (should-error (pi-coding-agent-input-previous-message)
+                        :type 'user-error))
+      (kill-buffer chat-buf))))
+
 (provide 'pi-coding-agent-input-test)
 ;;; pi-coding-agent-input-test.el ends here

test/pi-coding-agent-ui-test.el

@@ -446,6 +446,66 @@ Buffer is read-only with `inhibit-read-only' used for insertion.
       (should (= (point) pos))
       (should (equal shown-message "No previous message")))))
 
+(ert-deftest pi-coding-agent-test-other-window-scroll-buffer-set-locally ()
+  "Session setup stores `other-window-scroll-buffer' as input-local state."
+  (let ((root "/tmp/pi-coding-agent-test-scroll-other/")
+        (original-default (default-value 'other-window-scroll-buffer)))
+    (make-directory root t)
+    (cl-letf (((symbol-function 'project-current) (lambda (&rest _) nil))
+              ((symbol-function 'pi-coding-agent--start-process) (lambda (_) nil))
+              ((symbol-function 'pi-coding-agent--display-buffers) #'ignore))
+      (unwind-protect
+          (progn
+            (let ((default-directory root))
+              (pi-coding-agent))
+            (let ((chat (get-buffer (pi-coding-agent-test--chat-buffer-name root)))
+                  (input (get-buffer (pi-coding-agent-test--input-buffer-name root))))
+              (with-current-buffer input
+                (should (local-variable-p 'other-window-scroll-buffer))
+                (should (eq other-window-scroll-buffer chat)))
+              (should (eq (default-value 'other-window-scroll-buffer)
+                          original-default))))
+        (set-default 'other-window-scroll-buffer original-default)
+        (pi-coding-agent-test--kill-session-buffers root)))))
+
+(ert-deftest pi-coding-agent-test-other-window-for-scrolling-tracks-each-input-session ()
+  "Each input buffer scrolls its own chat buffer."
+  (let ((root-a "/tmp/pi-coding-agent-test-scroll-a/")
+        (root-b "/tmp/pi-coding-agent-test-scroll-b/")
+        (original-default (default-value 'other-window-scroll-buffer)))
+    (make-directory root-a t)
+    (make-directory root-b t)
+    (cl-letf (((symbol-function 'project-current) (lambda (&rest _) nil))
+              ((symbol-function 'pi-coding-agent--start-process) (lambda (_) nil))
+              ((symbol-function 'pi-coding-agent--display-buffers) #'ignore))
+      (unwind-protect
+          (progn
+            (let ((default-directory root-a))
+              (pi-coding-agent))
+            (let ((default-directory root-b))
+              (pi-coding-agent))
+            (let* ((chat-a (get-buffer (pi-coding-agent-test--chat-buffer-name root-a)))
+                   (input-a (get-buffer (pi-coding-agent-test--input-buffer-name root-a)))
+                   (chat-b (get-buffer (pi-coding-agent-test--chat-buffer-name root-b)))
+                   (input-b (get-buffer (pi-coding-agent-test--input-buffer-name root-b))))
+              (delete-other-windows)
+              (switch-to-buffer chat-a)
+              (let* ((chat-win-a (selected-window))
+                     (input-win-a (split-window chat-win-a -10 'below))
+                     (chat-win-b (split-window chat-win-a nil 'right))
+                     input-win-b)
+                (set-window-buffer input-win-a input-a)
+                (set-window-buffer chat-win-b chat-b)
+                (setq input-win-b (split-window chat-win-b -10 'below))
+                (set-window-buffer input-win-b input-b)
+                (select-window input-win-a)
+                (should (eq (window-buffer (other-window-for-scrolling)) chat-a))
+                (select-window input-win-b)
+                (should (eq (window-buffer (other-window-for-scrolling)) chat-b)))))
+        (set-default 'other-window-scroll-buffer original-default)
+        (pi-coding-agent-test--kill-session-buffers root-a)
+        (pi-coding-agent-test--kill-session-buffers root-b)))))
+
 ;;; Turn Detection
 
 (ert-deftest pi-coding-agent-test-turn-index-on-first-heading ()