From 78b8032301080b8c84a8d904d24dd78ca96e28bd Mon Sep 17 00:00:00 2001
From: teknium1 <127238744+teknium1@users.noreply.github.com>
Date: Thu, 24 Sep 2026 05:36:51 -0700
Subject: [PATCH] fix: streamed reply no longer repeats a word when edits fall
 back to a new message

_continuation_text backed the cut up to the previous space even when the visible
preview already ended on a whole word, so the continuation re-sent that word at
the seam ("the answer" + "answer to your question."). Back up only when the cut
lands inside a word (#116312 behaviour kept).

Found by the platforms E2E suite (#121409).
---
 gateway/stream_consumer_fallback.py                    | 4 +++-
 tests/gateway/test_stream_consumer_continuation_cut.py | 6 ++++++
 2 files changed, 9 insertions(+), 1 deletion(-)

diff --git a/gateway/stream_consumer_fallback.py b/gateway/stream_consumer_fallback.py
index 44ca80fae5..135915d857 100644
--- a/gateway/stream_consumer_fallback.py
+++ b/gateway/stream_consumer_fallback.py
@@ -58,7 +58,9 @@ class StreamFallbackMixin:
             # the continuation re-sends the broken word's tail and reads as an
             # ordinary continuation.  A prefix with no boundary (one very long
             # token) keeps the original cut rather than re-sending the whole reply.
-            if cut < len(final_text):
+            # A prefix that already ends on a whole word needs no back-up: doing it
+            # re-sent that word at the seam.
+            if cut < len(final_text) and not final_text[cut].isspace() and not final_text[cut - 1].isspace():
                 boundary = max(
                     final_text.rfind(" ", 0, cut),
                     final_text.rfind("\n", 0, cut),
diff --git a/tests/gateway/test_stream_consumer_continuation_cut.py b/tests/gateway/test_stream_consumer_continuation_cut.py
index e17300b27d..6137246ed9 100644
--- a/tests/gateway/test_stream_consumer_continuation_cut.py
+++ b/tests/gateway/test_stream_consumer_continuation_cut.py
@@ -49,3 +49,9 @@ class TestContinuationWordBoundary:
         consumer._last_sent_text = "у" * 100
         final_text = ("у" * 100) + ("д" * 20)
         assert consumer._continuation_text(final_text) == "д" * 20
+
+    def test_whole_word_prefix_is_not_resent(self):
+        # The preview ends exactly on a word; the continuation must not repeat it.
+        consumer = _make_consumer()
+        consumer._last_sent_text = "Here is the answer ▉"
+        assert consumer._continuation_text("Here is the answer to your question.") == "to your question."