fix: preserve repeated state rows in replay delta

api/models.py

@@ -3270,21 +3270,19 @@ def state_db_delta_after_context(sidecar_context: list, state_messages: list) ->
     if best_len < 2:
         return state_messages
 
-    sidecar_key_set = set(sidecar_keys)
-    last_represented_state_index = best_len - 1
-    for idx, key in enumerate(state_keys[best_len:], start=best_len):
-        if key in sidecar_key_set:
-            last_represented_state_index = idx
-
-    delta = []
-    for msg, key in zip(
-        state_messages[last_represented_state_index + 1:],
-        state_keys[last_represented_state_index + 1:],
-    ):
-        if key in sidecar_key_set:
-            continue
-        delta.append(msg)
-    return delta
+    # Drop only rows that can be aligned with the remaining sidecar context in
+    # order. This still tolerates stale state-only rows between mirrored context
+    # rows, but once the sidecar context is exhausted every later state row is a
+    # real delta, even if it repeats a short earlier message.
+    sidecar_index = best_len
+    state_index = best_len
+    while sidecar_index < len(sidecar_keys) and state_index < len(state_keys):
+        if state_keys[state_index] == sidecar_keys[sidecar_index]:
+            sidecar_index += 1
+        state_index += 1
+    if sidecar_index == len(sidecar_keys):
+        return state_messages[state_index:]
+    return state_messages[best_len:]
 
 
 def merge_session_messages_append_only(sidecar_messages: list, state_messages: list) -> list:

tests/test_issue1217_transcript_compaction.py

@@ -4,7 +4,7 @@ import json
 import sys
 from types import SimpleNamespace
 
-from api.models import Session, reconciled_state_db_messages_for_session
+from api.models import Session, reconciled_state_db_messages_for_session, state_db_delta_after_context
 
 from api.streaming import (
     _assistant_reply_added_after_current_turn,
@@ -513,6 +513,26 @@ def test_prefer_context_reconcile_starts_after_last_state_row_seen_in_context():
         {"role": "user", "content": "new after represented boundary", "timestamp": 200.0},
     ]
 
+
+
+def test_state_db_delta_preserves_fresh_rows_before_repeated_context_message():
+    sidecar_context = [
+        {"role": "user", "content": "ok"},
+        {"role": "assistant", "content": "ready"},
+    ]
+    state_messages = [
+        {"role": "user", "content": "ok", "timestamp": 1.0},
+        {"role": "assistant", "content": "ready", "timestamp": 2.0},
+        {"role": "user", "content": "fresh question", "timestamp": 3.0},
+        {"role": "user", "content": "ok", "timestamp": 4.0},
+        {"role": "assistant", "content": "after repeat", "timestamp": 5.0},
+    ]
+
+    delta = state_db_delta_after_context(sidecar_context, state_messages)
+
+    assert [m["content"] for m in delta] == ["fresh question", "ok", "after repeat"]
+
+
 def test_non_streaming_chat_writeback_dedupes_full_context_replay():
     previous_context = [
         {"role": "assistant", "content": "cron banner"},