diff --git a/agent-office/app/agents/stock.py b/agent-office/app/agents/stock.py
index d6de585..c59bd4a 100644
--- a/agent-office/app/agents/stock.py
+++ b/agent-office/app/agents/stock.py
@@ -48,7 +48,9 @@ class StockAgent(BaseAgent):
             })
 
             if not tg_result.get("ok"):
-                add_log(self.agent_id, "Telegram send failed", "warning", task_id)
+                desc = tg_result.get("description") or "unknown"
+                code = tg_result.get("error_code")
+                add_log(self.agent_id, f"Telegram send failed: [{code}] {desc}", "warning", task_id)
                 if self._ws_manager:
                     await self._ws_manager.send_notification(
                         self.agent_id, "telegram_failed", task_id, "텔레그램 전송 실패"
diff --git a/agent-office/app/telegram/formatter.py b/agent-office/app/telegram/formatter.py
index 0fc9b4e..4345a24 100644
--- a/agent-office/app/telegram/formatter.py
+++ b/agent-office/app/telegram/formatter.py
@@ -1,4 +1,5 @@
 """에이전트 메시지 포맷팅."""
+from html import escape as _h
 from typing import Literal, Optional
 
 from .agent_registry import get_agent_meta
@@ -23,9 +24,14 @@ def format_agent_message(
 ) -> str:
     meta = get_agent_meta(agent_id)
     icon = KIND_ICONS.get(kind, "")
-    header = f"{icon} <b>[{meta['emoji']} {meta['display_name']}]</b> {title}"
+    header = f"{icon} <b>[{_h(meta['emoji'])} {_h(meta['display_name'])}]</b> {_h(title)}"
 
-    lines = [header, "━" * 20, body]
+    # Telegram 단일 메시지 4096자 제한 대응 (헤더/푸터 여유 512자 확보)
+    safe_body = _h(body)
+    if len(safe_body) > 3500:
+        safe_body = safe_body[:3500] + "\n…(생략)"
+
+    lines = [header, "━" * 20, safe_body]
 
     if metadata:
         footer_parts = []
@@ -38,6 +44,6 @@ def format_agent_message(
             footer_parts.append(f"🤖 {metadata['model']}")
         if footer_parts:
             lines.append("")
-            lines.append(f"<i>{' · '.join(footer_parts)}</i>")
+            lines.append(f"<i>{_h(' · '.join(footer_parts))}</i>")
 
     return "\n".join(lines)
diff --git a/agent-office/app/telegram/messaging.py b/agent-office/app/telegram/messaging.py
index 7d13636..75dfb4d 100644
--- a/agent-office/app/telegram/messaging.py
+++ b/agent-office/app/telegram/messaging.py
@@ -20,9 +20,12 @@ async def send_raw(text: str, reply_markup: Optional[dict] = None) -> dict:
     if reply_markup:
         payload["reply_markup"] = reply_markup
     result = await api_call("sendMessage", payload)
+    ok = result.get("ok", False)
     return {
-        "ok": result.get("ok", False),
-        "message_id": result.get("result", {}).get("message_id") if result.get("ok") else None,
+        "ok": ok,
+        "message_id": result.get("result", {}).get("message_id") if ok else None,
+        "description": result.get("description") if not ok else None,
+        "error_code": result.get("error_code") if not ok else None,
     }