diff --git a/app/application/messaging/chat.py b/app/application/messaging/chat.py
index 2e44b0f59..d85690fa8 100644
--- a/app/application/messaging/chat.py
+++ b/app/application/messaging/chat.py
@@ -14,6 +14,7 @@ from app.application.database import (
     AsyncDatabaseExecutor,
 )
 from app.application.messaging.recall import RecallService
+from app.domain.chat import normalize_display_timestamps
 from app.runtime.observability import record_metric
 from app.runtime.priority import INTERACTIVE_DATABASE_CAPACITY, is_interactive
 from app.schemas.agent import AgentChatSessionDetail, AgentChatSessionSummary
@@ -465,11 +466,16 @@ class AgentChatService:
     @classmethod
     def to_detail(cls, record: AgentChatRecord) -> AgentChatSessionDetail:
         """
-        把持久化投影转换为会话详情 DTO。
+        把持久化投影转换为会话详情 DTO，兼容旧消息缺失时间戳。
+
+        只修正响应副本，避免读取接口改写数据库或运行中的内存快照。
+
+        :param record: 已完成授权检查的会话持久化投影
+        :return: 所有展示消息都包含时间戳的会话详情
         """
         return AgentChatSessionDetail.model_validate({
                 **cls.to_summary(record).model_dump(),
-                "messages": record.messages,
+                "messages": normalize_display_timestamps(record.messages),
             })
 
     @staticmethod
diff --git a/app/domain/chat.py b/app/domain/chat.py
index 30cd2dd48..cb9005ff7 100644
--- a/app/domain/chat.py
+++ b/app/domain/chat.py
@@ -1,48 +1,79 @@
 """
-会话展示快照中选择结果的合并规则，不负责交互执行或持久化。
+会话展示快照的时间戳兼容与选择结果合并规则，不负责交互执行或持久化。
 """
 
 from copy import deepcopy
 from typing import Any
 
 
-def _choice_selections(messages: list[dict[str, Any]]) -> dict[str, dict[str, Any]]:
+def normalize_display_timestamps(messages: list[dict[str, Any]]) -> list[dict[str, Any]]:
+    """
+    为历史展示消息补齐缺失时间戳，不修改原快照或已有时间。
+
+    缺失值沿用前方最近的有效时间；开头缺失时使用后方首个有效时间。
+    整个快照没有时间时使用 0 表示未知，避免每次读取都改变历史时间。
+
+    :param messages: 可能含有缺失 createdAt 字段的历史展示快照
+    :return: 时间戳字段完整的快照；已有非法值仍由响应模型报错
+    """
+    timestamp = next((message["createdAt"] for message in messages
+                      if isinstance(message.get("createdAt"), (int, float))), 0)
+    result = []
+    for message in messages:
+        if isinstance(message.get("createdAt"), (int, float)):
+            timestamp = message["createdAt"]
+        result.append({"createdAt": timestamp, **message})
+    return result
+
+
+def _choice_receipts(messages: list[dict[str, Any]]) -> dict[str, dict[str, Any]]:
     """
     优先采用完整选择回执，旧记录只有已选卡片时从卡片恢复。
+
+    :param messages: 当前会话快照，旧回执可能缺少时间戳
+    :return: 以选择 ID 索引的回执，同时保留首次选择与对应时间
     """
-    selections: dict[str, dict[str, Any]] = {}
-    for message in messages:
+    receipts: dict[str, dict[str, Any]] = {}
+    normalized = normalize_display_timestamps(messages)
+    for message in normalized:
         selected = message.get("choice_selection")
         if isinstance(selected, dict) and selected.get("choice_id"):
-            selections.setdefault(str(selected["choice_id"]), selected)
-    for message in messages:
+            receipts.setdefault(str(selected["choice_id"]), {
+                "id": f"choice-selection-{selected['choice_id']}", "role": "user", "content": "",
+                "createdAt": message["createdAt"], "choice_selection": selected,
+            })
+    for message in normalized:
         for choice in message.get("choices") or []:
             if isinstance(choice, dict) and choice.get("status") == "selected" and choice.get("id"):
-                selections.setdefault(str(choice["id"]), {
-                    "choice_id": str(choice["id"]),
-                    "prompt": choice.get("prompt") or "",
-                    "buttons": choice.get("buttons") or [],
-                    "button_rows": choice.get("button_rows") or [],
-                    **{key: choice.get(key) for key in (
-                        "title", "selected_label", "selected_value", "selected_description",
-                    )},
+                receipts.setdefault(str(choice["id"]), {
+                    "id": f"choice-selection-{choice['id']}", "role": "user", "content": "",
+                    "createdAt": message["createdAt"],
+                    "choice_selection": {
+                        "choice_id": str(choice["id"]),
+                        "prompt": choice.get("prompt") or "",
+                        "buttons": choice.get("buttons") or [],
+                        "button_rows": choice.get("button_rows") or [],
+                        **{key: choice.get(key) for key in (
+                            "title", "selected_label", "selected_value", "selected_description",
+                        )},
+                    },
                 })
-    return selections
+    return receipts
 
 
 def merge_choice_state(
     previous: list[dict[str, Any]], messages: list[dict[str, Any]],
 ) -> list[dict[str, Any]]:
     """
-    保留首次已选结果，旧客户端的 pending 快照不能降级已选卡片。
+    保留首次已选结果及回执时间，旧客户端的 pending 快照不能降级已选卡片。
 
     :param previous: 当前持久化的权威快照
     :param messages: 本次准备保存的完整快照，不原地修改
     :return: 应用已选结果并按稳定 ID 合并选择回显后的快照
     """
-    selections = _choice_selections(previous)
-    for choice_id, selection in _choice_selections(messages).items():
-        selections.setdefault(choice_id, selection)
+    selection_receipts = _choice_receipts(previous)
+    for choice_id, receipt in _choice_receipts(messages).items():
+        selection_receipts.setdefault(choice_id, receipt)
     result: list[dict[str, Any]] = []
     receipts: dict[str, int] = {}
     received_choices: set[str] = set()
@@ -52,11 +83,13 @@ def merge_choice_state(
         if isinstance(selected, dict) and selected.get("choice_id"):
             choice_id = str(selected["choice_id"])
             received_choices.add(choice_id)
-            message["choice_selection"] = deepcopy(selections[choice_id])
+            receipt = selection_receipts[choice_id]
+            message["choice_selection"] = deepcopy(receipt["choice_selection"])
+            message["createdAt"] = receipt["createdAt"]
         for choice in message.get("choices") or []:
-            if not isinstance(choice, dict) or str(choice.get("id") or "") not in selections:
+            if not isinstance(choice, dict) or str(choice.get("id") or "") not in selection_receipts:
                 continue
-            selection = selections[str(choice["id"])]
+            selection = selection_receipts[str(choice["id"])]["choice_selection"]
             choice.update({"status": "selected", **{
                 key: selection.get(key) for key in ("selected_label", "selected_value", "selected_description")
             }})
@@ -67,10 +100,7 @@ def merge_choice_state(
             if key:
                 receipts[key] = len(result)
             result.append(message)
-    for choice_id, selection in selections.items():
+    for choice_id, receipt in selection_receipts.items():
         if choice_id not in received_choices:
-            result.append({
-                "id": f"choice-selection-{choice_id}", "role": "user", "content": "",
-                "choice_selection": deepcopy(selection),
-            })
+            result.append(deepcopy(receipt))
     return result
diff --git a/docs/architecture-overview.md b/docs/architecture-overview.md
index fd4881f78..789488a25 100644
--- a/docs/architecture-overview.md
+++ b/docs/architecture-overview.md
@@ -825,7 +825,7 @@ flowchart LR
 | 指标 | 当前值 |
 |---|---:|
 | Python 模块 | 1150 |
-| 内部导入边 | 9,963 |
+| 内部导入边 | 9,965 |
 | 非平凡 SCC | 1（29 个模块的 TMDB vendor 精确 containment） |
 | Application / Chain 具体 Adapter 直连 | 0 / 0 |
 | Direct egress | 51（精确 policy 准入，Application / Chain 均为 0） |
diff --git a/docs/mcp-api.md b/docs/mcp-api.md
index a996bb01d..d17e4a608 100644
--- a/docs/mcp-api.md
+++ b/docs/mcp-api.md
@@ -74,6 +74,8 @@
 后端按用户、会话和选择 ID 领取一次执行；入队前明确拒绝可重试，执行结果未知时不重放。
 `echo_user=false` 仅隐藏用户回显，选择结果仍保存；完整快照替换保留隐藏选择收据，
 即使旧快照不含卡片，也不能让后续快照把已选卡片改回 `pending`。普通消息仍按完整快照替换。
+选择回执合并时保留原始 `createdAt` 毫秒时间戳；旧历史缺少该字段时，读取和保存边界
+使用相邻消息时间补齐，不丢弃选择内容。整份快照都没有时间时以 `0` 表示未知。
 
 会话 `is_processing` 只表示实际执行或排队，空闲等待下一条消息的 worker 不计入。
 工具事件沿用 `tool_id` 与 `assistant_message_id`，跨 steering 后仍更新原助手段。
diff --git a/docs/rules/05-architecture.md b/docs/rules/05-architecture.md
index 38f8b2a91..2f7308c37 100644
--- a/docs/rules/05-architecture.md
+++ b/docs/rules/05-architecture.md
@@ -1342,7 +1342,7 @@ driven workflow registration.
 | `app/application/server/report.py` | Server reporting use cases over injected local readers and transport callbacks |
 | `app/application/server/share.py` | Server sharing use cases over injected repositories and transport callbacks |
 | `app/domain/plugin.py` | Pure local-source, generation-compatibility and Release-install-plan rules |
-| `app/domain/chat.py` | 会话展示快照的纯选择状态合并规则；保留首次选择，不读取交互管理器或持久化服务 |
+| `app/domain/chat.py` | 会话展示快照的纯时间戳兼容与选择状态合并规则；保留首次选择及回执时间，不读取交互管理器或持久化服务 |
 | `app/adapters/external/plugin/client.py` | `PluginMarketTransport`, the unique market transport, index/Release and local-candidate owner |
 | `app/adapters/system/plugin/package.py` | `PluginPackageManager`, the unique install, checkpoint, backup, restore and physical-delete owner |
 | `app/adapters/system/plugin/dependency.py` | `PluginDependencyInstaller`, enabled-source dependency inspection and constrained per-plugin recovery owner; `async_install` has two completion-owned worker boundaries for request preparation and fallback planning, while package subprocess cancellation remains with `PluginRuntimeHealth` |
diff --git a/tests/fixtures/architecture/dependency-baseline.json b/tests/fixtures/architecture/dependency-baseline.json
index 073c7a5cc..33fe40746 100644
--- a/tests/fixtures/architecture/dependency-baseline.json
+++ b/tests/fixtures/architecture/dependency-baseline.json
@@ -959,8 +959,8 @@
       "runtime_only": true
     }
   },
-  "edge_count": 9963,
-  "edge_sha256": "44cf52b7ca35534e04cf6fa3de8aadcaa7f54ccdeec543b79156f6d7aed3b8a0",
+  "edge_count": 9965,
+  "edge_sha256": "95b80752f6b6f2ab82c79f2c5464b52b74a57bc13aecadb452dcb51e587b400b",
   "edges": [
     "app -> app.foundation",
     "app -> app.foundation.environment",
@@ -3853,6 +3853,8 @@
     "app.application.messaging.chat -> app.application.database",
     "app.application.messaging.chat -> app.application.messaging",
     "app.application.messaging.chat -> app.application.messaging.recall",
+    "app.application.messaging.chat -> app.domain",
+    "app.application.messaging.chat -> app.domain.chat",
     "app.application.messaging.chat -> app.runtime",
     "app.application.messaging.chat -> app.runtime.observability",
     "app.application.messaging.chat -> app.runtime.priority",
diff --git a/tests/test_agent_chat_timestamps.py b/tests/test_agent_chat_timestamps.py
new file mode 100644
index 000000000..99e5d4b98
--- /dev/null
+++ b/tests/test_agent_chat_timestamps.py
@@ -0,0 +1,161 @@
+"""
+选择回执的时间戳保留及历史会话读取兼容回归。
+"""
+
+from copy import deepcopy
+from types import SimpleNamespace
+from uuid import uuid4
+
+import pytest
+from fastapi import FastAPI
+from fastapi.testclient import TestClient
+from pydantic import ValidationError
+
+from app.api.endpoints import agent as agent_endpoint
+from app.application.messaging.chat import get_configured_agent_chat_service
+from app.db.models.agentchat import AgentChat
+from app.db.oper.agentchat import AgentChatOper
+from app.db.session import SessionFactory
+from app.domain.chat import merge_choice_state, normalize_display_timestamps
+from app.schemas.agent import AgentChatMessage
+
+
+def _receipt(**fields: object) -> dict[str, object]:
+    """
+    构造带稳定标识的选择回执，允许省略时间戳以重放旧数据。
+
+    :param fields: 回执需要补充或覆盖的展示字段
+    :return: 用户选择电影的展示回执
+    """
+    return {
+        "id": "choice-selection-test", "role": "user", "content": "",
+        "choice_selection": {"choice_id": "test", "selected_label": "电影", "selected_value": "选择电影"},
+        **fields,
+    }
+
+
+def test_replacement_keeps_original_receipt_timestamp_across_stale_snapshots() -> None:
+    """
+    旧快照省略回执或重复提交回执时，首次选择和原始时间都保持稳定。
+    """
+    card = {"id": "card", "role": "assistant", "content": "", "createdAt": 1000,
+            "choices": [{"id": "test", "status": "pending"}]}
+    original = [card, _receipt(createdAt=1010)]
+    before = deepcopy(original)
+    saved = original
+    for incoming in ([card], [], [card, _receipt(createdAt=9000)], [card, _receipt()], [card]):
+        saved = merge_choice_state(saved, incoming)
+        receipt = next(message for message in saved if message.get("choice_selection"))
+        assert AgentChatMessage.model_validate(receipt).createdAt == 1010
+        assert receipt["choice_selection"] == original[1]["choice_selection"]
+    assert original == before
+
+
+def test_selected_card_recovery_supplies_receipt_timestamp() -> None:
+    """
+    旧记录只有已选卡片时，重建回执使用卡片时间并保留选择内容。
+    """
+    original = [{"id": "card", "role": "assistant", "content": "", "createdAt": 1234.5,
+                 "choices": [{"id": "test", "status": "selected", "selected_value": "选择电影"}]}]
+    result = merge_choice_state(original, [])
+    assert len(result) == 1
+    receipt = AgentChatMessage.model_validate(result[0])
+    assert receipt.id == "choice-selection-test"
+    assert receipt.createdAt == 1234.5
+    assert receipt.choice_selection.selected_value == "选择电影"
+
+
+@pytest.mark.parametrize("position", [0, 1, 2])
+def test_legacy_receipt_is_repaired_on_save_without_mutating_input(position: int) -> None:
+    """
+    历史回执缺少时间时借用相邻消息时间，保存后可读取且不修改旧内存快照。
+
+    :param position: 缺字段回执位于完整快照中的位置
+    """
+    original = [
+        {"id": "first", "role": "user", "createdAt": 1000},
+        {"id": "last", "role": "assistant", "createdAt": 2000},
+    ]
+    original.insert(position, _receipt())
+    before = deepcopy(original)
+    result = merge_choice_state([], original)
+    assert result[position]["createdAt"] == (2000 if position == 2 else 1000)
+    assert all(AgentChatMessage.model_validate(message) for message in result)
+    assert original == before
+
+
+def test_legacy_receipt_without_any_known_time_uses_stable_unknown_timestamp() -> None:
+    """
+    完全缺少时间的旧快照返回固定未知值，重复保存不会伪造不断变化的创建时间。
+    """
+    result = merge_choice_state([], [_receipt()])
+    assert AgentChatMessage.model_validate(result[0]).createdAt == 0
+    assert merge_choice_state(result, []) == result
+
+
+@pytest.mark.parametrize("timestamp", [None, "invalid"])
+def test_timestamp_compatibility_preserves_explicit_invalid_values(timestamp: object) -> None:
+    """
+    仅兼容缺失字段，显式非法值仍由原有模型验证报告。
+
+    :param timestamp: 已提供但不符合毫秒数值约定的字段值
+    """
+    result = normalize_display_timestamps([_receipt(createdAt=timestamp)])
+    with pytest.raises(ValidationError, match="createdAt"):
+        AgentChatMessage.model_validate(result[0])
+
+
+@pytest.mark.parametrize("replace_snapshot", [False, True])
+def test_history_endpoint_reads_legacy_receipt_and_survives_old_snapshot_save(
+    monkeypatch: pytest.MonkeyPatch, replace_snapshot: bool,
+) -> None:
+    """
+    实际详情路由能读取脏历史，且旧内存快照或缺少回执的快照再次写回后仍返回 200。
+
+    :param monkeypatch: 隔离运行中 Agent 管理器的 pytest 替换工具
+    :param replace_snapshot: 后续保存完整旧快照或省略回执的快照
+    """
+    session_id = f"web-agent:timestamps-{uuid4().hex}"
+    legacy = [
+        {"id": "first", "role": "user", "content": "选择电影", "createdAt": 1000},
+        _receipt(),
+        {"id": "last", "role": "assistant", "content": "继续", "createdAt": 2000},
+    ]
+    with SessionFactory() as db:
+        db.add(AgentChat(session_id=session_id, user_id="501", username="alice",
+                         display_messages=legacy, message_count=len(legacy)))
+        db.commit()
+    monkeypatch.setattr(agent_endpoint.agent_application, "get_running_agent_manager", lambda: None)
+    app = FastAPI()
+    app.include_router(agent_endpoint.router)
+    app.dependency_overrides[agent_endpoint.get_agent_chat_service] = get_configured_agent_chat_service
+    app.dependency_overrides[agent_endpoint.get_current_active_user] = lambda: SimpleNamespace(
+        id=501, name="alice", is_superuser=False,
+    )
+    with TestClient(app) as client:
+        for attempt in range(3):
+            response = client.get(f"/sessions/{session_id}")
+            assert response.status_code == 200, response.text
+            messages = response.json()["data"]["messages"]
+            assert len(messages) == 3
+            assert next(message for message in messages if message.get("choice_selection"))["createdAt"] == 1000
+            with SessionFactory() as db:
+                row = AgentChatOper(db).get(session_id)
+                if attempt == 0:
+                    assert row.display_messages == legacy
+                AgentChatOper(db).save_display_messages(
+                    session_id=session_id, user_id="501",
+                    messages=legacy if not replace_snapshot else [legacy[0], legacy[2]],
+                )
+                db.commit()
+    with SessionFactory() as db:
+        row = AgentChatOper(db).get(session_id)
+        assert all(AgentChatMessage.model_validate(message) for message in row.display_messages)
+
+
+def test_history_timestamp_compatibility_does_not_weaken_save_request_validation() -> None:
+    """
+    历史兼容只发生在读取和合并边界，客户端展示消息仍必须提供时间戳。
+    """
+    with pytest.raises(ValidationError, match="createdAt"):
+        AgentChatMessage.model_validate(_receipt())
diff --git a/tests/test_agent_session_consistency.py b/tests/test_agent_session_consistency.py
index a1563e440..8be7206c9 100644
--- a/tests/test_agent_session_consistency.py
+++ b/tests/test_agent_session_consistency.py
@@ -20,6 +20,7 @@ from app.application.messaging.interaction.agent import (
 from app.db.oper.agentchat import AgentChatOper
 from app.db.session import SessionFactory
 from app.domain.chat import merge_choice_state
+from app.schemas.agent import AgentChatMessage
 from app.schemas.types import NotificationChannel
 
 
@@ -75,6 +76,7 @@ async def test_choice_callback_persists_first_selection_and_replays_without_chan
         assert row.display_messages[0]["choices"][0]["selected_value"] == "选择电影"
         receipts = [message for message in row.display_messages if message.get("choice_selection")]
         assert len(receipts) == 1 and receipts[0]["content"] == ""
+        assert AgentChatMessage.model_validate(receipts[0]).createdAt > 0
 
 
 @pytest.mark.asyncio
@@ -148,6 +150,7 @@ def test_selected_card_survives_old_pending_snapshot_without_mutating_inputs(cho
     before_card = merge_choice_state(previous, [])
     assert before_card == [{
         "id": f"choice-selection-{request.request_id}", "role": "user", "content": "", "choice_selection": selected,
+        "createdAt": 0,
     }]
     result = merge_choice_state(before_card, original)
     assert result[0]["choices"][0]["status"] == "selected"