diff --git a/pi-coding-agent-menu.el b/pi-coding-agent-menu.el
index 13bfbc8..e7f3e32 100644
--- a/pi-coding-agent-menu.el
+++ b/pi-coding-agent-menu.el
@@ -273,6 +273,7 @@ Used when starting a new session."
   (when-let* ((chat-buf (pi-coding-agent--get-chat-buffer)))
     (with-current-buffer chat-buf
       (let ((inhibit-read-only t))
+        (pi-coding-agent--clear-render-artifacts)
         (erase-buffer)
         (insert (pi-coding-agent--format-startup-header))
         (insert "\n")
diff --git a/pi-coding-agent-render.el b/pi-coding-agent-render.el
index 9307e2b..0a6106c 100644
--- a/pi-coding-agent-render.el
+++ b/pi-coding-agent-render.el
@@ -927,6 +927,16 @@ Returns a plist with:
               :hidden-lines (if (and truncated-first-line (= hidden 0)) 1 hidden)
               :line-map line-map-vec)))))
 
+(defun pi-coding-agent--clear-render-artifacts ()
+  "Delete pi-owned render overlays in the current chat buffer.
+This removes completed/pending tool overlays and diff overlays before
+buffer reset or history rebuild, then clears the pending overlay slot so
+buffer state and overlay state stay consistent.  Tree-sitter overlays are
+left alone."
+  (remove-overlays (point-min) (point-max) 'pi-coding-agent-tool-block t)
+  (remove-overlays (point-min) (point-max) 'pi-coding-agent-diff-overlay t)
+  (setq pi-coding-agent--pending-tool-overlay nil))
+
 (defun pi-coding-agent--tool-overlay-create (tool-name &optional path)
   "Create overlay for tool block TOOL-NAME at point.
 Optional PATH stores the file path for navigation.
@@ -1831,6 +1841,7 @@ Note: When called from async callbacks, pass CHAT-BUF explicitly."
   (when (and chat-buf (buffer-live-p chat-buf))
     (with-current-buffer chat-buf
       (let ((inhibit-read-only t))
+        (pi-coding-agent--clear-render-artifacts)
         (erase-buffer)
         (insert (pi-coding-agent--format-startup-header) "\n")
         (when (vectorp messages)
diff --git a/test/pi-coding-agent-menu-test.el b/test/pi-coding-agent-menu-test.el
index e45cb64..a84be6d 100644
--- a/test/pi-coding-agent-menu-test.el
+++ b/test/pi-coding-agent-menu-test.el
@@ -125,6 +125,37 @@
     ;; Tool args cache should be empty
     (should (= 0 (hash-table-count pi-coding-agent--tool-args-cache)))))
 
+(ert-deftest pi-coding-agent-test-clear-chat-buffer-removes-pi-owned-render-overlays ()
+  "Clearing chat buffer removes stale pi-owned tool and diff overlays."
+  (with-temp-buffer
+    (pi-coding-agent-chat-mode)
+    (let ((inhibit-read-only t))
+      (insert "tool\n+ 1 added\n- 2 removed\n"))
+    (let ((tool-ov (make-overlay 1 5 nil nil nil))
+          (tool-count 0)
+          (diff-count 0))
+      (overlay-put tool-ov 'pi-coding-agent-tool-block t)
+      (setq pi-coding-agent--pending-tool-overlay tool-ov)
+      (pi-coding-agent--apply-diff-overlays 6 (point-max))
+      (dolist (ov (overlays-in (point-min) (point-max)))
+        (when (overlay-get ov 'pi-coding-agent-tool-block)
+          (setq tool-count (1+ tool-count)))
+        (when (overlay-get ov 'pi-coding-agent-diff-overlay)
+          (setq diff-count (1+ diff-count))))
+      (should (= tool-count 1))
+      (should (= diff-count 4)))
+    (pi-coding-agent--clear-chat-buffer)
+    (let ((tool-count 0)
+          (diff-count 0))
+      (dolist (ov (overlays-in (point-min) (point-max)))
+        (when (overlay-get ov 'pi-coding-agent-tool-block)
+          (setq tool-count (1+ tool-count)))
+        (when (overlay-get ov 'pi-coding-agent-diff-overlay)
+          (setq diff-count (1+ diff-count))))
+      (should (= tool-count 0))
+      (should (= diff-count 0))
+      (should-not pi-coding-agent--pending-tool-overlay))))
+
 (ert-deftest pi-coding-agent-test-new-session-clears-buffer-from-different-context ()
   "New session clears buffer and updates state even when callback runs elsewhere.
 This tests that the async callback properly captures the chat buffer reference,
diff --git a/test/pi-coding-agent-render-test.el b/test/pi-coding-agent-render-test.el
index af75102..7fb7232 100644
--- a/test/pi-coding-agent-render-test.el
+++ b/test/pi-coding-agent-render-test.el
@@ -388,6 +388,33 @@ agent_end + next section's leading newline must not create triple newlines."
     (should (cl-some (lambda (ov) (overlay-get ov 'pi-coding-agent-tool-block))
                      (overlays-in (point-min) (point-max))))))
 
+(ert-deftest pi-coding-agent-test-display-session-history-does-not-accumulate-stale-tool-overlays ()
+  "Rebuilding session history removes stale pi-owned tool overlays first."
+  (with-temp-buffer
+    (pi-coding-agent-chat-mode)
+    (let ((messages [(:role "assistant"
+                      :content [(:type "text" :text "Let me check.")
+                                (:type "toolCall" :id "tc1"
+                                 :name "bash"
+                                 :arguments (:command "ls -la"))]
+                      :timestamp 1704067200000)
+                     (:role "toolResult" :toolCallId "tc1"
+                      :toolName "bash"
+                      :content [(:type "text" :text "total 42")]
+                      :isError :json-false
+                      :timestamp 1704067201000)]))
+      (pi-coding-agent--display-session-history messages (current-buffer))
+      (pi-coding-agent--display-session-history messages (current-buffer))
+      (let ((tool-count 0)
+            (zero-tool-count 0))
+        (dolist (ov (overlays-in (point-min) (point-max)))
+          (when (overlay-get ov 'pi-coding-agent-tool-block)
+            (setq tool-count (1+ tool-count))
+            (when (= (overlay-start ov) (overlay-end ov))
+              (setq zero-tool-count (1+ zero-tool-count)))))
+        (should (= tool-count 1))
+        (should (= zero-tool-count 0))))))
+
 (ert-deftest pi-coding-agent-test-history-renders-multiple-tools-in-order ()
   "Multiple tool calls render with headers and output in order."
   (with-temp-buffer