Keep point with the prompt across streamed fragment inserts

README.org

@@ -27,6 +27,7 @@ A soft fork of [[https://github.com/xenodium/agent-shell][agent-shell]] with ext
 - Live-validate workflow doc (=.agents/commands/live-validate.md=) describing the batch-mode rendering verification used for rendering-pipeline changes ([[https://github.com/timvisher-dd/agent-shell-plus/pull/7][#7]])
 - =gfm-mode= compose buffer for the interactive =agent-shell-queue-request=, replacing the read-string minibuffer prompt (non-interactive callers still pass =PROMPT= directly) ([[https://github.com/timvisher-dd/agent-shell-plus/pull/9][#9]])
 - =agent-shell-resume-session= repurposed from an ID-prompt command into a session-picker entry point: opens the same fuzzy-completion picker that =agent-shell-session-strategy= ='prompt= uses, and force-shows session IDs in the picker (via a new =:show-session-id= keyword on =agent-shell--start=) so users with an ID in hand can find it via their completion framework ([[https://github.com/timvisher-dd/agent-shell-plus/pull/11][#11]])
+- Fix streaming cursor drop: a streamed message fragment inserted at the prompt no longer strands point above the inserted text. The shell render path relied on shell-maker's insertion-type nil =save-excursion=, which stays before text inserted at point, so when the cursor sat at an empty prompt (or the start of pending input) with auto-scroll suppressed it was left behind the freshly streamed block. A new =agent-shell--with-preserved-point= saves point in an insertion-type t marker (mirroring the tool-output path) and snaps to =point-max= when point was at end-of-buffer, so the cursor always tracks the prompt
 
 -----
 

agent-shell.el

@@ -3050,6 +3050,31 @@ live process-mark is pushed forward by the insertion."
             (marker-position (process-mark ,proc-sym)))
            (set-marker ,saved-sym nil))))))
 
+(defmacro agent-shell--with-preserved-point (&rest body)
+  "Evaluate BODY, then restore point so it stays with the prompt.
+Fragment updates insert text at the insert-cursor, which can sit
+exactly at point when the prompt is empty or point is at the start
+of the input area.  shell-maker's `save-excursion'-based point
+preservation uses an insertion-type nil marker, which stays BEFORE
+text inserted at point, stranding point above the freshly inserted
+fragment (the cursor appears to \"drop behind\" streamed text).
+
+Save point in a marker with insertion-type t so it advances past
+insertions made at point, and snap to `point-max' when point was at
+end-of-buffer — the prompt — so a streaming chunk never leaves the
+cursor behind regardless of shell-maker's auto-scroll decision."
+  (declare (indent 0) (debug body))
+  (let ((was-at-end-sym (make-symbol "was-at-end"))
+        (saved-sym (make-symbol "saved-point")))
+    `(let ((,was-at-end-sym (eobp))
+           (,saved-sym (copy-marker (point) t)))
+       (unwind-protect
+           (progn ,@body)
+         (if ,was-at-end-sym
+             (goto-char (point-max))
+           (goto-char ,saved-sym))
+         (set-marker ,saved-sym nil)))))
+
 (defun agent-shell--insert-cursor ()
   "Return the insertion cursor for the current shell buffer.
 The cursor is a marker with insertion-type t that advances past
@@ -3249,7 +3274,8 @@ by default, RENDER-BODY-IMAGES to enable inline image rendering in body."
                  (equal (current-buffer)
                         (map-elt state :buffer)))
       (error "Editing the wrong buffer: %s" (current-buffer)))
-    (agent-shell--with-preserved-process-mark
+    (agent-shell--with-preserved-point
+     (agent-shell--with-preserved-process-mark
       (shell-maker-with-auto-scroll-edit
        (when-let* ((range (agent-shell-ui-update-fragment
                          (agent-shell-ui-make-fragment-model
@@ -3290,7 +3316,7 @@ by default, RENDER-BODY-IMAGES to enable inline image rendering in body."
               (append "append")
               (t "rebuild"))
         (or namespace-id (map-elt state :request-count))
-        block-id append))))))
+        block-id append)))))))
 
 (cl-defun agent-shell--update-text (&key state namespace-id block-id text append create-new)
   "Update plain text entry in the shell buffer.
@@ -3316,7 +3342,8 @@ APPEND and CREATE-NEW control update behavior."
            :create-new create-new
            :no-undo t))))
     (with-current-buffer (map-elt state :buffer)
-      (agent-shell--with-preserved-process-mark
+      (agent-shell--with-preserved-point
+       (agent-shell--with-preserved-process-mark
         (shell-maker-with-auto-scroll-edit
          (when-let* ((range (agent-shell-ui-update-text
                              :namespace-id ns
@@ -3334,7 +3361,7 @@ APPEND and CREATE-NEW control update behavior."
             (cond (create-new "create")
                   (append "append")
                   (t "rebuild"))
-            ns block-id append)))))))
+            ns block-id append))))))))
 
 (defun agent-shell-toggle-logging ()
   "Toggle logging."

tests/agent-shell-streaming-tests.el

@@ -723,6 +723,57 @@ must appear before the prompt text, not after it."
       (should (string-suffix-p "hello\n\n"
                                (buffer-substring-no-properties (point-min) (point-max)))))))
 
+;;; Point preservation across streaming insertions (cursor drop regression)
+
+(ert-deftest agent-shell--with-preserved-point-keeps-cursor-at-empty-prompt-test ()
+  "A streaming insertion at point must not strand the cursor behind it.
+Regression: when point sits at the insert-cursor position (an empty
+prompt at end-of-buffer) and shell-maker's non-auto-scroll branch
+preserves point with an insertion-type nil `save-excursion' marker,
+text inserted at point leaves that marker — and thus point — BEFORE
+the inserted text, so the cursor appears to drop behind streamed
+output.  `agent-shell--with-preserved-point' must snap point back to
+the prompt at `point-max'."
+  (with-temp-buffer
+    (insert "previous output\n\nClaude Code> ")
+    ;; Point is at the (empty) prompt = where a streaming fragment is
+    ;; inserted = end-of-buffer.
+    (let ((insert-pos (point)))
+      (agent-shell--with-preserved-point
+        ;; Mimic shell-maker-with-auto-scroll-edit's non-auto-scroll
+        ;; branch: an insertion-type nil save-excursion around an
+        ;; insertion made at the insert-cursor (= point).
+        (save-excursion
+          (goto-char insert-pos)
+          (insert "STREAMED")))
+      ;; Without the fix point would be stranded at INSERT-POS, behind
+      ;; "STREAMED"; it must instead stay with the prompt at point-max.
+      (should (= (point) (point-max)))
+      (should (string-suffix-p "STREAMED"
+                               (buffer-substring-no-properties (point-min) (point-max)))))))
+
+(ert-deftest agent-shell--with-preserved-point-advances-past-insertion-test ()
+  "Point not at end-of-buffer must advance past text inserted at point.
+When the user has moved point to the start of their pending input (the
+insert-cursor position) but is not at end-of-buffer, a streamed
+fragment inserted there must push point forward with the input rather
+than leaving it stranded above the inserted text."
+  (with-temp-buffer
+    (insert "previous output\n\nClaude Code> hello")
+    ;; Move point to the start of the input, the insert-cursor position,
+    ;; but NOT end-of-buffer.
+    (goto-char (- (point) (length "hello")))
+    (let ((insert-pos (point)))
+      (agent-shell--with-preserved-point
+        (save-excursion
+          (goto-char insert-pos)
+          (insert "STREAMED")))
+      ;; Point must sit just after the inserted text, still at the start
+      ;; of "hello" — not stranded above "STREAMED".
+      (should (looking-at-p "hello"))
+      (should (string= (buffer-substring-no-properties (point) (point-max))
+                       "hello")))))
+
 (ert-deftest agent-shell--mark-tool-calls-cancelled-with-nil-transcript-test ()
   "Cancelling in-flight tool calls must not signal when transcript-file is nil.
 agent-shell--mark-tool-calls-cancelled invokes handle-tool-call-final