From e9387f8aa5285f0b49e674e382b4014b179a7ec0 Mon Sep 17 00:00:00 2001
From: Rod Boev <rod.boev@gmail.com>
Date: Mon, 29 Jun 2026 14:29:47 -0400
Subject: [PATCH] fix(session): fail closed on ambiguous truncate context
 matches (#5134)

---
 api/session_ops.py                         | 68 +++++++++++++---------
 tests/test_issue_branch_context_at_fork.py | 14 +++++
 2 files changed, 56 insertions(+), 26 deletions(-)

diff --git a/api/session_ops.py b/api/session_ops.py
index b4a3d166..19969239 100644
--- a/api/session_ops.py
+++ b/api/session_ops.py
@@ -6,6 +6,7 @@ Behavior parity reference: gateway/run.py:_handle_*_command in
 the hermes-agent repo.
 """
 from __future__ import annotations
+import json
 import logging
 from typing import Any
 
@@ -114,37 +115,52 @@ def truncate_context_for_display_keep(
     if len(msgs) == 0:
         return []
 
-    def _row_matches(context_row: Any, msg_row: Any) -> bool:
-        """Match rows by stable id, then (role, content, timestamp), then
-        (role, content)."""
-        if not isinstance(context_row, dict) or not isinstance(msg_row, dict):
-            return False
-
-        context_id = context_row.get('id')
-        msg_id = msg_row.get('id')
-        if context_id is not None and msg_id is not None and context_id == msg_id:
-            return True
-
-        context_ts = context_row.get('timestamp')
-        msg_ts = msg_row.get('timestamp')
-        if context_ts is not None and msg_ts is not None:
-            if (
-                context_row.get('role') == msg_row.get('role')
-                and context_row.get('content') == msg_row.get('content')
-                and context_ts == msg_ts
-            ):
-                return True
-
+    def _row_signature(row: Any) -> tuple[str, ...] | None:
+        if not isinstance(row, dict):
+            return None
+        tool_calls = row.get('tool_calls')
+        tool_calls_sig = json.dumps(tool_calls, sort_keys=True, default=str) if tool_calls else ''
         return (
-            context_row.get('role') == msg_row.get('role')
-            and context_row.get('content') == msg_row.get('content')
+            str(row.get('role') or ''),
+            str(row.get('content') or ''),
+            str(row.get('tool_call_id') or ''),
+            str(row.get('tool_use_id') or ''),
+            str(row.get('tool_name') or row.get('name') or ''),
+            tool_calls_sig,
         )
 
     def _first_match_from(message: Any, start_idx: int) -> int | None:
+        msg_sig = _row_signature(message)
+        if msg_sig is None:
+            return None
+        msg_id = message.get('id')
+        msg_ts = message.get('timestamp')
+        weak_matches: list[int] = []
         for idx in range(start_idx, len(ctx)):
-            if _row_matches(ctx[idx], message):
-                return idx
-        return None
+            context_row = ctx[idx]
+            context_sig = _row_signature(context_row)
+            if context_sig is None:
+                continue
+
+            context_id = context_row.get('id')
+            if context_id is not None and msg_id is not None:
+                if context_id == msg_id:
+                    return idx
+                continue
+
+            if context_sig != msg_sig:
+                continue
+
+            context_ts = context_row.get('timestamp')
+            if context_ts is not None and msg_ts is not None:
+                if context_ts == msg_ts:
+                    return idx
+                continue
+
+            weak_matches.append(idx)
+            if len(weak_matches) > 1:
+                return None
+        return weak_matches[0] if len(weak_matches) == 1 else None
 
     matches = [None] * len(msgs)
     next_ctx_idx = 0
diff --git a/tests/test_issue_branch_context_at_fork.py b/tests/test_issue_branch_context_at_fork.py
index 5c69faaf..44cd5984 100644
--- a/tests/test_issue_branch_context_at_fork.py
+++ b/tests/test_issue_branch_context_at_fork.py
@@ -120,3 +120,17 @@ def test_truncate_context_for_display_keep_prefers_compact_summary_fallback():
     ]
     out = truncate_context_for_display_keep(ctx, msgs, 2)
     assert out == ctx[:2]
+
+
+def test_truncate_context_for_display_keep_keeps_real_user_turn_when_duplicate_rows_lack_identity():
+    msgs = [
+        {"role": "user", "content": "u1"},
+        {"role": "assistant", "content": "a1"},
+    ]
+    ctx = [
+        {"role": "user", "content": "u1"},
+        {"role": "user", "content": "u1"},
+        {"role": "assistant", "content": "a1"},
+    ]
+    out = truncate_context_for_display_keep(ctx, msgs, 1)
+    assert [row["content"] for row in out] == ["u1", "u1"]