feat(gateway): inject stable human-readable message timestamps

Consolidates these related Amy fork patches:
- 429830f39 feat(gateway): inject message timestamps into user messages for LLM context
- 3c3d6fac0 fix: handle both ISO string and epoch float timestamps in history replay
- 2874f7725 feat: human-friendly timestamp format with weekday and timezone name
- 3735f4c8b fix: render gateway message timestamps once

run_agent.py

@@ -1472,16 +1472,21 @@ class AIAgent:
         that synthetic text leak into persisted transcripts or resumed session
         history. When an override is configured for the active turn, mutate the
         in-memory messages list in place so both persistence and returned
-        history stay clean.
+        history stay clean.  A paired timestamp override preserves the platform
+        event time as message metadata, rather than embedding it in content.
         """
         idx = getattr(self, "_persist_user_message_idx", None)
         override = getattr(self, "_persist_user_message_override", None)
-        if override is None or idx is None:
+        timestamp = getattr(self, "_persist_user_message_timestamp", None)
+        if idx is None or (override is None and timestamp is None):
             return
         if 0 <= idx < len(messages):
             msg = messages[idx]
             if isinstance(msg, dict) and msg.get("role") == "user":
-                msg["content"] = override
+                if override is not None:
+                    msg["content"] = override
+                if timestamp is not None:
+                    msg["timestamp"] = timestamp
 
     def _persist_session(self, messages: List[Dict], conversation_history: List[Dict] = None):
         """Save session state to both JSON log and SQLite on any exit path.
@@ -1639,6 +1644,7 @@ class AIAgent:
                     reasoning_details=msg.get("reasoning_details") if role == "assistant" else None,
                     codex_reasoning_items=msg.get("codex_reasoning_items") if role == "assistant" else None,
                     codex_message_items=msg.get("codex_message_items") if role == "assistant" else None,
+                    timestamp=msg.get("timestamp"),
                 )
                 flushed_ids.add(msg_id)
             self._last_flushed_db_idx = len(messages)
@@ -5218,10 +5224,20 @@ class AIAgent:
         task_id: str = None,
         stream_callback: Optional[callable] = None,
         persist_user_message: Optional[str] = None,
+        persist_user_timestamp: Optional[float] = None,
     ) -> Dict[str, Any]:
         """Forwarder — see ``agent.conversation_loop.run_conversation``."""
         from agent.conversation_loop import run_conversation
-        return run_conversation(self, user_message, system_message, conversation_history, task_id, stream_callback, persist_user_message)
+        return run_conversation(
+            self,
+            user_message,
+            system_message,
+            conversation_history,
+            task_id,
+            stream_callback,
+            persist_user_message,
+            persist_user_timestamp,
+        )
 
     def chat(self, message: str, stream_callback: Optional[callable] = None) -> str:
         """