diff --git a/src/acp/observer.lisp b/src/acp/observer.lisp
index d2e224be..5a426898 100644
--- a/src/acp/observer.lisp
+++ b/src/acp/observer.lisp
@@ -139,10 +139,11 @@
 (defmethod agent-observer-text ((observer acp-observer) text)
   "Stream assistant text and retain its length for nonstreamed response reconciliation."
   (acp-session-check-cancelled (acp-observer-session observer))
-  (with-lock-held ((acp-observer-lock observer))
-    (text-buffer-append (acp-observer-streamed-text observer) text)
-    (acp-observer--send observer
-                        (agentcomms:acp-update-agent-message (agentcomms:acp-text-content text))))
+  (when (plusp (length text))
+    (with-lock-held ((acp-observer-lock observer))
+      (text-buffer-append (acp-observer-streamed-text observer) text)
+      (acp-observer--send observer
+                          (agentcomms:acp-update-agent-message (agentcomms:acp-text-content text)))))
   nil)
 
 (defmethod agent-observer-reasoning ((observer acp-observer) text)
diff --git a/tests/acp-observer-tests.lisp b/tests/acp-observer-tests.lisp
index 35a27ff7..0c07b6f9 100644
--- a/tests/acp-observer-tests.lisp
+++ b/tests/acp-observer-tests.lisp
@@ -200,6 +200,9 @@
                (agent-observer-status observer ':provider-request-started nil)
                (agent-observer-reasoning observer "before ")
                (agent-observer-reasoning observer "approval")
+               (agent-observer-reasoning observer "continued ")
+               (agent-observer-text observer "")
+               (agent-observer-reasoning observer "thought")
                (test-assert
                 (acp-observer--approval observer "shell.run" (json-object "command" "pwd") '(:command))
                 "the editor can approve after receiving pending thoughts")
@@ -209,7 +212,8 @@
                          (mapcar #'agentcomms:acp-update-kind updates))
                   "thought batches precede the next message and permission request")
                  (test-assert
-                  (equal (list (format nil "first thought~2%next thought") "answer" "before approval")
+                  (equal (list (format nil "first thought~2%next thought") "answer"
+                               (format nil "before approvalcontinued thought"))
                          (mapcar (lambda (update)
                                    (agentcomms:acp-content-text (agentcomms:json-get update "content")))
                                  updates))