From fe6d824074b67ab7571d7fb07dac18830db3a9b4 Mon Sep 17 00:00:00 2001
From: MorAlekss <mor.aleksandr@yahoo.com>
Date: Mon, 22 Jun 2026 12:17:40 -0700
Subject: [PATCH 1/2] fix(compression): skip session rotation when compress
 returns messages unchanged

---
 agent/conversation_compression.py             | 10 +++++
 .../test_infinite_compaction_loop.py          | 40 +++++++++++++++++++
 2 files changed, 50 insertions(+)

diff --git a/agent/conversation_compression.py b/agent/conversation_compression.py
index 94fff28389349..9dff01dcc8c88 100644
--- a/agent/conversation_compression.py
+++ b/agent/conversation_compression.py
@@ -482,6 +482,16 @@ def _release_lock() -> None:
         _release_lock()  # compression aborted — no rotation will happen
         return messages, _existing_sp
 
+    # If compress() returned messages unchanged without setting
+    # _last_compress_aborted (e.g. compress_start >= compress_end),
+    # there is nothing to rotate — skip session rotation entirely.
+    if len(compressed) >= _pre_msg_count:
+        _existing_sp = getattr(agent, "_cached_system_prompt", None)
+        if not _existing_sp:
+            _existing_sp = agent._build_system_prompt(system_message)
+        _release_lock()  # no-op compression — no rotation will happen
+        return messages, _existing_sp
+
     summary_error = getattr(agent.context_compressor, "_last_summary_error", None)
     if summary_error:
         if getattr(agent, "_last_compression_summary_warning", None) != summary_error:
diff --git a/tests/run_agent/test_infinite_compaction_loop.py b/tests/run_agent/test_infinite_compaction_loop.py
index 930df3381cc1b..c40679f030fe6 100644
--- a/tests/run_agent/test_infinite_compaction_loop.py
+++ b/tests/run_agent/test_infinite_compaction_loop.py
@@ -248,3 +248,43 @@ def test_below_threshold_allows(self):
         comp = _make_compressor(config_context_length=96000)
         comp.last_prompt_tokens = 10_000
         assert not comp.should_compress(10_000)
+
+
+class TestNoOpCompressionSkipsRotation:
+    """When compress() returns messages unchanged (no-op), session rotation
+    must be skipped — no end_session, no new session_id."""
+
+    def test_no_op_compression_does_not_rotate_session(self):
+        """compress_start >= compress_end path must not trigger session rotation."""
+        from unittest.mock import MagicMock
+        from agent.conversation_compression import compress_context
+
+        messages = _build_session(10, words_per_turn=10)
+
+        agent = MagicMock()
+        agent.session_id = "test-no-op-session"
+        agent.compression_in_place = False
+        agent.compression_enabled = True
+        agent._compression_feasibility_checked = True
+        agent._cached_system_prompt = "system prompt"
+        agent._memory_manager = None
+        agent._todo_store = MagicMock()
+        agent._todo_store.format_for_injection.return_value = ""
+
+        session_db = MagicMock()
+        session_db.try_acquire_compression_lock.return_value = True
+        agent._session_db = session_db
+
+        compressor = MagicMock()
+        compressor._last_compress_aborted = False
+        compressor._last_summary_error = None
+        compressor._last_aux_model_failure_model = None
+        compressor.compress.return_value = list(messages)
+        agent.context_compressor = compressor
+
+        result_messages, _ = compress_context(agent, messages, "system", approx_tokens=1000)
+
+        session_db.end_session.assert_not_called()
+        assert agent.session_id == "test-no-op-session", (
+            "Session ID must not change when compression is a no-op"
+        )

From 0815845e1fd19d8a979b21b6d365484875350d21 Mon Sep 17 00:00:00 2001
From: MorAlekss <mor.aleksandr@yahoo.com>
Date: Mon, 22 Jun 2026 12:38:13 -0700
Subject: [PATCH 2/2] fix(compression): narrow no-op guard to savings_pct == 0
 to avoid blocking legitimate compression

---
 agent/conversation_compression.py                | 6 +++++-
 tests/run_agent/test_infinite_compaction_loop.py | 1 +
 2 files changed, 6 insertions(+), 1 deletion(-)

diff --git a/agent/conversation_compression.py b/agent/conversation_compression.py
index 9dff01dcc8c88..2064100a6f938 100644
--- a/agent/conversation_compression.py
+++ b/agent/conversation_compression.py
@@ -485,7 +485,11 @@ def _release_lock() -> None:
     # If compress() returned messages unchanged without setting
     # _last_compress_aborted (e.g. compress_start >= compress_end),
     # there is nothing to rotate — skip session rotation entirely.
-    if len(compressed) >= _pre_msg_count:
+    # Guard on both length (no reduction) AND savings_pct == 0 so that
+    # a legitimate compression that happens to produce the same message
+    # count (e.g. summary replaces many messages 1:1) is not blocked.
+    _savings_pct = getattr(agent.context_compressor, "_last_compression_savings_pct", 100.0)
+    if len(compressed) >= _pre_msg_count and _savings_pct == 0.0:
         _existing_sp = getattr(agent, "_cached_system_prompt", None)
         if not _existing_sp:
             _existing_sp = agent._build_system_prompt(system_message)
diff --git a/tests/run_agent/test_infinite_compaction_loop.py b/tests/run_agent/test_infinite_compaction_loop.py
index c40679f030fe6..f46766214d644 100644
--- a/tests/run_agent/test_infinite_compaction_loop.py
+++ b/tests/run_agent/test_infinite_compaction_loop.py
@@ -279,6 +279,7 @@ def test_no_op_compression_does_not_rotate_session(self):
         compressor._last_compress_aborted = False
         compressor._last_summary_error = None
         compressor._last_aux_model_failure_model = None
+        compressor._last_compression_savings_pct = 0.0
         compressor.compress.return_value = list(messages)
         agent.context_compressor = compressor