Drop dropped-turn excerpts when the summary ledger is included

The ledger supersedes the "Earlier conversation excerpts" message, as on
main; sending both duplicated dropped-turn content. Removal is consistent
whenever the ledger is included, so the cached prefix stays stable.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

blueprints/conversation/context.py

@@ -506,6 +506,15 @@ def trim_history(
             "Omitting optional conversation summary to preserve current request"
         )
         return trimmed
+    # The ledger supersedes excerpts of dropped turns; whenever it is included
+    # they are consistently absent, so this doesn't disturb the cached prefix.
+    if (
+        with_room
+        and isinstance(with_room[0], AIMessage)
+        and isinstance(with_room[0].content, str)
+        and with_room[0].content.startswith("Earlier conversation excerpts")
+    ):
+        with_room = with_room[1:]
     # The ledger changes every turn, so place it just before the current turn:
     # system, tools and retained history then stay byte-identical for the
     # prompt cache. Turns start at a HumanMessage, so the last one opens the

tests/unit/test_context_trim.py

@@ -501,8 +501,16 @@ def test_summary_placed_before_current_turn_when_turns_dropped():
     assert cost(out) <= 6000
     assert out[-4:] == [summary, question, messages[-2], messages[-1]]
     assert out.count(summary) == 1
-    # Excerpts of dropped turns stay at the head; they only change with the cut.
-    assert out[0].content.startswith("Earlier conversation excerpts")
+    # The ledger supersedes excerpts of dropped turns; don't send both.
+    assert not any(
+        isinstance(m.content, str)
+        and m.content.startswith("Earlier conversation excerpts")
+        for m in out
+    )
+    assert isinstance(out[0], HumanMessage)
+    # Without a ledger, the excerpts still cover the dropped turns.
+    plain = trim_history(messages, token_budget=6000)
+    assert plain[0].content.startswith("Earlier conversation excerpts")
     assert_valid_sequence(out)