diff --git a/chktime.py b/chktime.py
index c7f9378..dae983d 100644
--- a/chktime.py
+++ b/chktime.py
@@ -1312,8 +1312,14 @@ def collect_blocks(store, project_id, start, end, gap_min=N8N_GAP_MIN, min_min=N
                     }
                 )
                 out.append(block)
-    out.sort(key=lambda b: b["startEpoch"])
-    return out
+    # 会話を続けると新しいセッションのファイルに前の履歴が同じ時刻のまま写されるので、
+    # 開始時刻 (ミリ秒) が同じ区間は写しとみなし、いちばん後まで続いているものだけを残す。
+    unique = {}
+    for block in out:
+        key = int(round(block["startEpoch"] * 1000))
+        if key not in unique or block["endEpoch"] > unique[key]["endEpoch"]:
+            unique[key] = block
+    return sorted(unique.values(), key=lambda b: b["startEpoch"])
 
 
 def mark_blocks(blocks, rows, deleted_sources, now=None):
diff --git a/tests/test_n8n.py b/tests/test_n8n.py
index e76e9c5..9279d27 100644
--- a/tests/test_n8n.py
+++ b/tests/test_n8n.py
@@ -153,6 +153,16 @@ class CollectAndMarkTest(unittest.TestCase):
         self.assertEqual([b["date"] for b in day1], ["2026-01-05"])
         self.assertEqual(day2, [])
 
+    def test_continued_session_copies_are_listed_once(self):
+        # 会話を続けると、新しいセッションのファイルに前の履歴が同じ時刻のまま写される
+        old = [(0, "user", "設計して"), (10, "assistant", "ok")]
+        write_session(self.root, "C--debug-demo", "old", old, r"C:\debug\demo")
+        write_session(self.root, "C--debug-demo", "new",
+                      old + [(20, "user", "続き"), (25, "assistant", "ok"), (90, "user", "次"), (100, "assistant", "ok")],
+                      r"C:\debug\demo")
+        blocks = chktime.collect_blocks(self.store, "", date(2026, 1, 5), date(2026, 1, 5), 30, 5, now=LATER)
+        self.assertEqual([(b["sessionId"], b["minutes"]) for b in blocks], [("new", 25), ("new", 10)])
+
     def test_mark_blocks(self):
         b1 = {"source": "chktime:a:1", "startEpoch": BASE, "endEpoch": BASE + 600, "start": "", "end": "", "taskName": "A"}
         b2 = {"source": "chktime:b:2", "startEpoch": BASE + 600, "endEpoch": BASE + 1200, "start": "", "end": "", "taskName": "B"}