fix(webui): preserve casual chat compaction guard

api/streaming.py

@@ -2332,21 +2332,22 @@ def _has_task_resume_compaction_marker(messages):
     return False
 
 
+def _new_turn_context_from_messages(messages, msg_text):
+    """Return provider-facing history for a new user turn from a message list."""
+    history = _drop_checkpointed_current_user_from_context(messages, msg_text)
+    if _is_casual_fresh_chat_message(msg_text) and _has_task_resume_compaction_marker(history):
+        return []
+    return history
+
+
 def _context_messages_for_new_turn(session, msg_text):
     """Return provider-facing history for a new user turn.
 
     Compacted agent sessions can carry a hidden "resume the active task" summary
-    long after the visible UI looks like normal chat.  A short greeting should
-    not silently reactivate that old task; explicit continuation prompts still
-    keep the full compacted context.
+    in context_messages. If the user starts a fresh casual greeting in that old
+    session, do not feed that stale active-task summary back to the model.
     """
-    history = _drop_checkpointed_current_user_from_context(
-        _session_context_messages(session),
-        msg_text,
-    )
-    if _is_casual_fresh_chat_message(msg_text) and _has_task_resume_compaction_marker(history):
-        return []
-    return history
+    return _new_turn_context_from_messages(_session_context_messages(session), msg_text)
 
 
 def _stream_writeback_is_current(session, stream_id):
@@ -3965,7 +3966,7 @@ def _run_agent_streaming(
                     state_messages=_external_state_messages,
                 ) or []
             )
-            _previous_context_messages = _drop_checkpointed_current_user_from_context(
+            _previous_context_messages = _new_turn_context_from_messages(
                 reconciled_state_db_messages_for_session(
                     s,
                     prefer_context=True,

tests/test_issue1217_transcript_compaction.py

@@ -1,10 +1,12 @@
-from api.models import Session
+from api.models import Session, reconciled_state_db_messages_for_session
 import contextlib
+from types import SimpleNamespace
 
 from api.streaming import (
     _assistant_reply_added_after_current_turn,
     _context_messages_for_new_turn,
     _merge_display_messages_after_agent_result,
+    _new_turn_context_from_messages,
     _sanitize_messages_for_api,
     _session_context_messages,
 )
@@ -314,6 +316,40 @@ def test_explicit_continue_keeps_compacted_active_task_context(tmp_path):
     assert _context_messages_for_new_turn(session, "继续") == compacted_task_context
 
 
+def test_streaming_reconciled_context_keeps_casual_greeting_suppression():
+    compacted_task_context = [
+        {
+            "role": "user",
+            "content": (
+                "[CONTEXT COMPACTION — REFERENCE ONLY] Earlier turns were compacted. "
+                "Your current task is identified in the Active Task section — resume exactly from there."
+            ),
+            "timestamp": 1.0,
+        },
+        {"role": "assistant", "content": "I will inspect api/config.py next.", "timestamp": 2.0},
+    ]
+    session = SimpleNamespace(
+        session_id="issue2308-streaming",
+        messages=[{"role": "user", "content": "old task", "timestamp": 0.5}],
+        context_messages=compacted_task_context,
+    )
+    external_state_messages = list(compacted_task_context)
+
+    # Mirror the streaming pre-turn assembly for prefer_context=True: reconcile
+    # sidecar context with one state.db snapshot, then apply the normal new-turn
+    # context filter that suppresses casual greetings from resuming stale tasks.
+    previous_context_messages = _new_turn_context_from_messages(
+        reconciled_state_db_messages_for_session(
+            session,
+            prefer_context=True,
+            state_messages=external_state_messages,
+        ),
+        "你好",
+    )
+
+    assert previous_context_messages == []
+
+
 def test_all_cjk_greetings_drop_stale_compaction_context(tmp_path):
     """Pin every CJK greeting in the casual-fresh-chat set against a stale
     compaction context. Catches typos like \\u5616 (嘖, "click of tongue")