diff --git a/src/backend/bisheng/message/domain/repositories/implementations/inbox_message_read_repository_impl.py b/src/backend/bisheng/message/domain/repositories/implementations/inbox_message_read_repository_impl.py
index 4c52af507..a3424890a 100644
--- a/src/backend/bisheng/message/domain/repositories/implementations/inbox_message_read_repository_impl.py
+++ b/src/backend/bisheng/message/domain/repositories/implementations/inbox_message_read_repository_impl.py
@@ -1,8 +1,7 @@
 import logging
-from typing import List
 
-from sqlalchemy import func
-from sqlmodel import select, col
+from sqlalchemy.exc import IntegrityError
+from sqlmodel import col, select
 from sqlmodel.ext.asyncio.session import AsyncSession
 
 from bisheng.common.repositories.implementations.base_repository_impl import BaseRepositoryImpl
@@ -25,42 +24,74 @@ class InboxMessageReadRepositoryImpl(BaseRepositoryImpl[InboxMessageRead, int],
             return existing
 
         record = InboxMessageRead(message_id=message_id, user_id=user_id)
-        return await self.save(record)
+        try:
+            return await self.save(record)
+        except IntegrityError:
+            # A concurrent request inserted the same (message_id, user_id) between
+            # our find_one and save, tripping the ix_inbox_message_read_msg_user
+            # unique index. Roll back and return the row that won the race so
+            # marking-as-read stays idempotent instead of surfacing a 500.
+            await self.session.rollback()
+            existing = await self.find_one(message_id=message_id, user_id=user_id)
+            if existing:
+                return existing
+            raise  # not a duplicate-key race — a real failure, surface it
 
-    async def batch_mark_as_read(self, message_ids: List[int], user_id: int) -> int:
-        """Batch mark messages as read. Returns number of newly marked records."""
+    async def batch_mark_as_read(self, message_ids: list[int], user_id: int) -> int:
+        """Batch mark messages as read. Returns number of newly marked records.
+
+        Idempotent under concurrency: if a competing request inserts the same
+        (message_id, user_id) in the SELECT->INSERT window, one unique-constraint
+        conflict would otherwise roll back the *whole* batch (leaving every
+        message unread and 500ing the API). Instead we roll back, re-read what
+        now exists and insert only the still-missing ids. Same dialect-agnostic
+        pattern as ChannelInfoSourceRepositoryImpl.batch_add.
+        """
         if not message_ids:
             return 0
 
-        # Find which messages are already read
+        new_records = await self._build_unread_records(message_ids, user_id)
+        if not new_records:
+            return 0
+
+        try:
+            self.session.add_all(new_records)
+            await self.session.commit()
+            return len(new_records)
+        except IntegrityError:
+            await self.session.rollback()
+            remaining = await self._build_unread_records(message_ids, user_id)
+            if remaining:
+                self.session.add_all(remaining)
+                await self.session.commit()
+            return len(remaining)
+
+    async def _build_unread_records(self, message_ids: list[int], user_id: int) -> list[InboxMessageRead]:
+        """Build read-records for ids not yet read by the user.
+
+        Dedupes the input (``dict.fromkeys`` preserves order) so duplicate ids in
+        a single request cannot self-collide on the unique index.
+        """
         query = select(InboxMessageRead.message_id).where(
             InboxMessageRead.user_id == user_id,
-            col(InboxMessageRead.message_id).in_(message_ids)
+            col(InboxMessageRead.message_id).in_(message_ids),
         )
         result = await self.session.exec(query)
         already_read_ids = set(result.all())
 
-        # Create records for unread messages only
-        new_records = []
-        for msg_id in message_ids:
-            if msg_id not in already_read_ids:
-                new_records.append(InboxMessageRead(message_id=msg_id, user_id=user_id))
-
-        if new_records:
-            self.session.add_all(new_records)
-            await self.session.commit()
-
-        return len(new_records)
+        return [
+            InboxMessageRead(message_id=msg_id, user_id=user_id)
+            for msg_id in dict.fromkeys(message_ids)
+            if msg_id not in already_read_ids
+        ]
 
     async def is_read(self, message_id: int, user_id: int) -> bool:
         """Check if a message has been read by a specific user."""
         existing = await self.find_one(message_id=message_id, user_id=user_id)
         return existing is not None
 
-    async def get_read_message_ids(self, user_id: int) -> List[int]:
+    async def get_read_message_ids(self, user_id: int) -> list[int]:
         """Get all read message IDs for a specific user."""
-        query = select(InboxMessageRead.message_id).where(
-            InboxMessageRead.user_id == user_id
-        )
+        query = select(InboxMessageRead.message_id).where(InboxMessageRead.user_id == user_id)
         result = await self.session.exec(query)
         return list(result.all())
diff --git a/src/backend/bisheng/message/domain/services/message_service.py b/src/backend/bisheng/message/domain/services/message_service.py
index 59a582164..0f801acaa 100644
--- a/src/backend/bisheng/message/domain/services/message_service.py
+++ b/src/backend/bisheng/message/domain/services/message_service.py
@@ -1,28 +1,31 @@
 import copy
 import logging
-from typing import List, Optional, Any, Dict
+from typing import Any
+
+from sqlalchemy.exc import IntegrityError
 
 from bisheng.common.dependencies.user_deps import UserPayload
 from bisheng.common.errcode.message import (
+    MessageAlreadyApprovedError,
     MessageNotFoundError,
     MessagePermissionDeniedError,
-    MessageAlreadyApprovedError,
 )
-from bisheng.message.domain.models.inbox_message import InboxMessage, MessageTypeEnum, MessageStatusEnum
+from bisheng.database.models.user_group import UserGroupDao
+from bisheng.message.domain.models.inbox_message import InboxMessage, MessageStatusEnum, MessageTypeEnum
 from bisheng.message.domain.repositories.interfaces.inbox_message_read_repository import InboxMessageReadRepository
 from bisheng.message.domain.repositories.interfaces.inbox_message_repository import InboxMessageRepository
 from bisheng.message.domain.schemas.message_schema import (
+    ApprovalActionEnum,
+    MessageContentItem,
     MessageItemResponse,
     MessagePageResponse,
+    TabTypeEnum,
     UnreadCountResponse,
-    ApprovalActionEnum,
-    TabTypeEnum, MessageContentItem,
 )
 from bisheng.message.domain.services.approval_handler import ApprovalHandler
 from bisheng.message.domain.services.notification_content import infer_action_code
-from bisheng.database.models.user_group import UserGroupDao
-from bisheng.user.domain.models.user import UserDao
 from bisheng.notification.forwarder import maybe_forward_external
+from bisheng.user.domain.models.user import UserDao
 
 logger = logging.getLogger(__name__)
 
@@ -44,14 +47,14 @@ class MessageService:
     """Service layer for in-app messaging (inbox) operations."""
 
     def __init__(
-            self,
-            message_repository: 'InboxMessageRepository',
-            message_read_repository: 'InboxMessageReadRepository',
-            approval_handlers: Optional[List[ApprovalHandler]] = None,
+        self,
+        message_repository: "InboxMessageRepository",
+        message_read_repository: "InboxMessageReadRepository",
+        approval_handlers: list[ApprovalHandler] | None = None,
     ):
         self.message_repository = message_repository
         self.message_read_repository = message_read_repository
-        self._handler_map: Dict[str, ApprovalHandler] = {}
+        self._handler_map: dict[str, ApprovalHandler] = {}
 
         for handler in approval_handlers or []:
             action_code = handler.get_action_code()
@@ -60,13 +63,13 @@ class MessageService:
             self._handler_map[action_code] = handler
 
     async def send_message(
-            self,
-            content: List[Dict[str, Any]],
-            sender: int,
-            message_type: MessageTypeEnum,
-            receiver: List[int],
-            status: MessageStatusEnum = MessageStatusEnum.WAIT_APPROVE,
-            action_code: Optional[str] = None,
+        self,
+        content: list[dict[str, Any]],
+        sender: int,
+        message_type: MessageTypeEnum,
+        receiver: list[int],
+        status: MessageStatusEnum = MessageStatusEnum.WAIT_APPROVE,
+        action_code: str | None = None,
     ) -> InboxMessage:
         """Create and save a new inbox message.
 
@@ -84,7 +87,10 @@ class MessageService:
         saved_message = await self.message_repository.save(message)
         logger.info(
             "Inbox message sent: id=%s, type=%s, sender=%s, receivers=%s",
-            saved_message.id, message_type.value, sender, receiver,
+            saved_message.id,
+            message_type.value,
+            sender,
+            receiver,
         )
 
         # E+ forwarding hook — sync, lightweight; HTTP fires via asyncio task
@@ -97,13 +103,13 @@ class MessageService:
         return saved_message
 
     async def get_message_list(
-            self,
-            login_user: UserPayload,
-            tab: TabTypeEnum = TabTypeEnum.ALL,
-            only_unread: bool = False,
-            keyword: Optional[str] = None,
-            page: int = 1,
-            page_size: int = 20,
+        self,
+        login_user: UserPayload,
+        tab: TabTypeEnum = TabTypeEnum.ALL,
+        only_unread: bool = False,
+        keyword: str | None = None,
+        page: int = 1,
+        page_size: int = 20,
     ) -> MessagePageResponse:
         """Get paginated message list for the current user with read status annotation."""
         # 1. Get read message IDs for this user
@@ -141,7 +147,7 @@ class MessageService:
 
         # 5. Batch query sender user names
         sender_ids = list({m.sender for m in messages})
-        sender_map: Dict[int, str] = {}
+        sender_map: dict[int, str] = {}
         if sender_ids:
             users = await UserDao.aget_user_by_ids(sender_ids)
             sender_map = {u.user_id: u.user_name for u in users}
@@ -153,76 +159,75 @@ class MessageService:
         # 7. Build response
         items = []
         for msg in messages:
-            items.append(MessageItemResponse(
-                id=msg.id,
-                content=self._enrich_message_content_with_group_names(msg.content, user_group_name_map),
-                sender=msg.sender,
-                sender_name=sender_map.get(msg.sender),
-                message_type=msg.message_type.value,
-                status=msg.status.value,
-                action_code=msg.action_code,
-                operator_user_id=msg.operator_user_id,
-                is_read=msg.id in read_set,
-                create_time=msg.create_time,
-                update_time=msg.update_time,
-            ))
+            items.append(
+                MessageItemResponse(
+                    id=msg.id,
+                    content=self._enrich_message_content_with_group_names(msg.content, user_group_name_map),
+                    sender=msg.sender,
+                    sender_name=sender_map.get(msg.sender),
+                    message_type=msg.message_type.value,
+                    status=msg.status.value,
+                    action_code=msg.action_code,
+                    operator_user_id=msg.operator_user_id,
+                    is_read=msg.id in read_set,
+                    create_time=msg.create_time,
+                    update_time=msg.update_time,
+                )
+            )
 
         return MessagePageResponse(data=items, total=total)
 
     @staticmethod
-    def _extract_content_user_ids(messages: List[InboxMessage]) -> List[int]:
+    def _extract_content_user_ids(messages: list[InboxMessage]) -> list[int]:
         """Extract distinct user IDs from content items with type=user."""
         user_ids: set[int] = set()
         for message in messages:
             for item in message.content or []:
-                if item.get('type') != 'user':
+                if item.get("type") != "user":
                     continue
 
-                metadata = item.get('metadata') or {}
-                user_id = metadata.get('user_id')
+                metadata = item.get("metadata") or {}
+                user_id = metadata.get("user_id")
                 if isinstance(user_id, int):
                     user_ids.add(user_id)
 
         return list(user_ids)
 
     @staticmethod
-    async def _build_user_group_name_map(user_ids: List[int]) -> Dict[int, List[str]]:
+    async def _build_user_group_name_map(user_ids: list[int]) -> dict[int, list[str]]:
         """Build a map from user_id to the user's group names."""
         if not user_ids:
             return {}
 
         user_groups_map = await UserGroupDao.aget_user_groups_batch(user_ids)
-        return {
-            user_id: [group.group_name for group in groups]
-            for user_id, groups in user_groups_map.items()
-        }
+        return {user_id: [group.group_name for group in groups] for user_id, groups in user_groups_map.items()}
 
     @staticmethod
     def _enrich_message_content_with_group_names(
-            content: List[Dict[str, Any]],
-            user_group_name_map: Dict[int, List[str]],
-    ) -> List[Dict[str, Any]]:
+        content: list[dict[str, Any]],
+        user_group_name_map: dict[int, list[str]],
+    ) -> list[dict[str, Any]]:
         """Attach group_names into metadata for content items with type=user."""
         enriched_content = []
         for item in content or []:
-            if item.get('type') != 'user':
+            if item.get("type") != "user":
                 enriched_content.append(item)
                 continue
 
-            metadata = item.get('metadata')
+            metadata = item.get("metadata")
             if not isinstance(metadata, dict):
                 enriched_content.append(item)
                 continue
 
-            user_id = metadata.get('user_id')
+            user_id = metadata.get("user_id")
             if not isinstance(user_id, int):
                 enriched_content.append(item)
                 continue
 
             new_item = dict(item)
             new_metadata = dict(metadata)
-            new_metadata['group_names'] = user_group_name_map.get(user_id, [])
-            new_item['metadata'] = new_metadata
+            new_metadata["group_names"] = user_group_name_map.get(user_id, [])
+            new_item["metadata"] = new_metadata
             enriched_content.append(new_item)
 
         return enriched_content
@@ -250,7 +255,7 @@ class MessageService:
 
         return UnreadCountResponse(total=total, notify=notify_count, approve=approve_count)
 
-    async def mark_as_read(self, message_ids: List[int], login_user: UserPayload) -> int:
+    async def mark_as_read(self, message_ids: list[int], login_user: UserPayload) -> int:
         """Mark specific messages as read for the current user."""
         return await self.message_read_repository.batch_mark_as_read(message_ids, login_user.user_id)
 
@@ -270,10 +275,10 @@ class MessageService:
         return await self.message_read_repository.batch_mark_as_read(unread_ids, login_user.user_id)
 
     async def handle_approval(
-            self,
-            message_id: int,
-            action: ApprovalActionEnum,
-            login_user: UserPayload,
+        self,
+        message_id: int,
+        action: ApprovalActionEnum,
+        login_user: UserPayload,
     ) -> InboxMessage:
         """
         Handle approval action (agree/reject) on an approval message.
@@ -294,11 +299,7 @@ class MessageService:
             raise MessageAlreadyApprovedError()
 
         # 4. Determine new status
-        new_status = (
-            MessageStatusEnum.APPROVED
-            if action == ApprovalActionEnum.AGREE
-            else MessageStatusEnum.REJECTED
-        )
+        new_status = MessageStatusEnum.APPROVED if action == ApprovalActionEnum.AGREE else MessageStatusEnum.REJECTED
 
         original_content = copy.deepcopy(message.content)
         action_code = self._extract_action_code(message)
@@ -333,21 +334,33 @@ class MessageService:
             operator_user_id=login_user.user_id,
         )
 
-        # 8. Auto-mark as read after action
-        await self.message_read_repository.mark_as_read(message_id, login_user.user_id)
+        # 8. Auto-mark as read after action (best-effort). The approval has already
+        #    executed its handler and committed the status change above; the
+        #    auto-read is a pure convenience side-step. A concurrent-insert race on
+        #    the read record must never surface the finished approval as a 500.
+        try:
+            await self.message_read_repository.mark_as_read(message_id, login_user.user_id)
+        except IntegrityError:
+            logger.warning(
+                "Auto mark-as-read raced on approval message_id=%s user_id=%s; already read, ignoring",
+                message_id,
+                login_user.user_id,
+            )
 
         logger.info(
             "Approval action processed: message_id=%s, action=%s, operator=%s",
-            message_id, action.value, login_user.user_id,
+            message_id,
+            action.value,
+            login_user.user_id,
         )
 
         return updated_message
 
     @staticmethod
     def _update_content_after_approval(
-            content: List[Dict[str, Any]],
-            action: ApprovalActionEnum,
-    ) -> List[Dict[str, Any]]:
+        content: list[dict[str, Any]],
+        action: ApprovalActionEnum,
+    ) -> list[dict[str, Any]]:
         """
         Update message content after approval action.
         - Preserve 'user' and 'business_url' types for continued clickability
@@ -356,10 +369,10 @@ class MessageService:
         updated = []
         for item in content:
             new_item = dict(item)
-            item_type = item.get('type', '')
+            item_type = item.get("type", "")
 
-            if item_type == 'agree_reject_button':
-                new_item['content'] = action.value
+            if item_type == "agree_reject_button":
+                new_item["content"] = action.value
 
             updated.append(new_item)
 
@@ -378,19 +391,19 @@ class MessageService:
 
     @staticmethod
     def build_generic_notify_content(
-            content_list: List[MessageContentItem | Dict],
-    ) -> List[Dict[str, Any]]:
+        content_list: list[MessageContentItem | dict],
+    ) -> list[dict[str, Any]]:
         """
         Build generic notification content.
         """
         return [one if isinstance(one, dict) else one.to_message() for one in content_list]
 
     async def send_generic_notify(
-            self,
-            sender: int,
-            receiver_user_ids: List[int],
-            content_item_list: List[MessageContentItem | Dict],
-            action_code: Optional[str] = None,
+        self,
+        sender: int,
+        receiver_user_ids: list[int],
+        content_item_list: list[MessageContentItem | dict],
+        action_code: str | None = None,
     ) -> InboxMessage:
         """
         Send a generic notification message to specific receivers.
@@ -410,16 +423,16 @@ class MessageService:
 
     @staticmethod
     def build_generic_approval_content(
-            applicant_user_id: int,
-            applicant_user_name: str,
-            action_code: str,
-            business_type: str,
-            business_id: str,
-            business_name: str,
-            button_action_code: str,
-            approval_message_id: Optional[int] = None,
-            scenario_code: Optional[str] = None,
-    ) -> List[Dict[str, Any]]:
+        applicant_user_id: int,
+        applicant_user_name: str,
+        action_code: str,
+        business_type: str,
+        business_id: str,
+        business_name: str,
+        button_action_code: str,
+        approval_message_id: int | None = None,
+        scenario_code: str | None = None,
+    ) -> list[dict[str, Any]]:
         """
         Build the generic message content structure for a business approval request.
         """
@@ -459,16 +472,16 @@ class MessageService:
         return content
 
     async def send_generic_approval(
-            self,
-            applicant_user_id: int,
-            applicant_user_name: str,
-            action_code: str,
-            business_type: str,
-            business_id: str,
-            business_name: str,
-            button_action_code: str,
-            receiver_user_ids: List[int],
-            scenario_code: Optional[str] = None,
+        self,
+        applicant_user_id: int,
+        applicant_user_name: str,
+        action_code: str,
+        business_type: str,
+        business_id: str,
+        business_name: str,
+        button_action_code: str,
+        receiver_user_ids: list[int],
+        scenario_code: str | None = None,
     ) -> InboxMessage:
         """
         Send a generic approval notification to specific receivers.
@@ -499,12 +512,12 @@ class MessageService:
         updated_content = []
         for item in content:
             new_item = dict(item)
-            if item.get('type') == 'agree_reject_button':
-                metadata = dict(item.get('metadata', {}))
-                data = dict(metadata.get('data', {}))
-                data['approval_id'] = str(message.id)
-                metadata['data'] = data
-                new_item['metadata'] = metadata
+            if item.get("type") == "agree_reject_button":
+                metadata = dict(item.get("metadata", {}))
+                data = dict(metadata.get("data", {}))
+                data["approval_id"] = str(message.id)
+                metadata["data"] = data
+                new_item["metadata"] = metadata
             updated_content.append(new_item)
 
         updated_message = await self.message_repository.update_message_content(message.id, updated_content)
@@ -522,21 +535,21 @@ class MessageService:
             return message.action_code
 
         # Fallback: extract from content JSON (supports both old key 'business_type' and new key 'action_code')
-        for item in (message.content or []):
-            if item.get('type') != 'agree_reject_button':
+        for item in message.content or []:
+            if item.get("type") != "agree_reject_button":
                 continue
 
-            metadata = item.get('metadata', {})
-            code = metadata.get('action_code') or metadata.get('business_type')
+            metadata = item.get("metadata", {})
+            code = metadata.get("action_code") or metadata.get("business_type")
             if isinstance(code, str):
                 return code
 
         return ""
 
     async def batch_approve_channel_subscription_messages(
-            self,
-            channel_id: str,
-            operator_user_id: int,
+        self,
+        channel_id: str,
+        operator_user_id: int,
     ) -> int:
         """
         Batch approve all pending channel subscription messages for a specific channel.
@@ -553,6 +566,8 @@ class MessageService:
         if count > 0:
             logger.info(
                 "Batch approved %d channel subscription messages for channel_id=%s, operator=%s",
-                count, channel_id, operator_user_id,
+                count,
+                channel_id,
+                operator_user_id,
             )
         return count
diff --git a/src/backend/test/message/test_inbox_message_read_concurrency.py b/src/backend/test/message/test_inbox_message_read_concurrency.py
new file mode 100644
index 000000000..94ee6d490
--- /dev/null
+++ b/src/backend/test/message/test_inbox_message_read_concurrency.py
@@ -0,0 +1,152 @@
+"""Concurrency regression tests for inbox message read-status writes.
+
+Reproduces the production race condition (trace 19d54fcc… / 66d16bfb…):
+``batch_mark_as_read`` / ``mark_as_read`` used a check-then-insert pattern with
+no protection against a concurrent transaction inserting the same
+``(message_id, user_id)`` between the SELECT and the INSERT, so the second
+committer hit the ``ix_inbox_message_read_msg_user`` unique constraint
+(dmPython IntegrityError -6602 / SQLAlchemy gkpj) and the whole batch rolled
+back — every message in that request stayed unread and the API 500'd.
+
+These tests drive two *independent* DB connections sharing one in-memory
+database and inject a competing insert into the exact window between the
+read-status SELECT and the batch INSERT, deterministically (no timing luck).
+"""
+
+from __future__ import annotations
+
+import itertools
+
+import pytest
+from sqlalchemy.ext.asyncio import create_async_engine
+from sqlalchemy.pool import StaticPool
+from sqlmodel import select
+from sqlmodel.ext.asyncio.session import AsyncSession
+
+from bisheng.message.domain.models.inbox_message_read import InboxMessageRead
+from bisheng.message.domain.repositories.implementations.inbox_message_read_repository_impl import (
+    InboxMessageReadRepositoryImpl,
+)
+
+# Each test gets a distinct shared-cache in-memory DB name so committed rows
+# from one test never bleed into the next (a shared-cache DB lives as long as
+# any connection to that name is open).
+_db_counter = itertools.count()
+
+
+def _make_engine(db_name: str):
+    # Shared-cache in-memory DB: multiple connections see the same tables/rows,
+    # but each connection runs its own transaction (unlike StaticPool ':memory:',
+    # which is a single connection with no isolation between sessions).
+    # StaticPool keeps exactly one live connection per engine so the shared
+    # in-memory DB is never torn down while a session is open.
+    uri = f"sqlite+aiosqlite:///file:{db_name}?mode=memory&cache=shared&uri=true"
+    return create_async_engine(
+        uri,
+        connect_args={"check_same_thread": False, "uri": True},
+        poolclass=StaticPool,
+    )
+
+
+@pytest.fixture()
+async def race_sessions():
+    """Two AsyncSessions on independent connections over one shared in-memory DB."""
+    db_name = f"inbox_read_race_{next(_db_counter)}"
+    engine_a = _make_engine(db_name)
+    engine_b = _make_engine(db_name)
+
+    async with engine_a.begin() as conn:
+        await conn.run_sync(InboxMessageRead.__table__.create)
+
+    session_a = AsyncSession(bind=engine_a, expire_on_commit=False)
+    session_b = AsyncSession(bind=engine_b, expire_on_commit=False)
+    try:
+        yield session_a, session_b
+    finally:
+        await session_a.close()
+        await session_b.close()
+        await engine_a.dispose()
+        await engine_b.dispose()
+
+
+async def _count_rows(session: AsyncSession, message_id: int, user_id: int) -> int:
+    result = await session.exec(
+        select(InboxMessageRead).where(
+            InboxMessageRead.message_id == message_id,
+            InboxMessageRead.user_id == user_id,
+        )
+    )
+    return len(list(result.all()))
+
+
+def _inject_competing_insert_after_first_query(session_a, session_b, message_id, user_id):
+    """Patch session_a.exec so that, right after the FIRST query returns (the
+    read-status SELECT), a competing transaction on session_b inserts
+    ``(message_id, user_id)`` and commits — landing us in the exact race window.
+
+    Only the first exec is hijacked; the repository's own retry re-query runs
+    unhijacked so it can observe the competitor's row.
+    """
+    state = {"fired": False}
+    orig_exec = session_a.exec
+
+    async def exec_with_injection(*args, **kwargs):
+        result = await orig_exec(*args, **kwargs)
+        if not state["fired"]:
+            state["fired"] = True
+            session_b.add(InboxMessageRead(message_id=message_id, user_id=user_id))
+            await session_b.commit()
+        return result
+
+    session_a.exec = exec_with_injection
+
+
+async def test_batch_mark_as_read_is_idempotent_under_concurrent_insert(race_sessions):
+    session_a, session_b = race_sessions
+    user_id = 1
+    shared_id = 123  # both requests try to mark this one
+    only_a_id = 456  # only request A marks this one
+
+    repo_a = InboxMessageReadRepositoryImpl(session_a)
+    _inject_competing_insert_after_first_query(session_a, session_b, shared_id, user_id)
+
+    # Must NOT raise IntegrityError even though `shared_id` gets inserted by the
+    # competitor in the SELECT→INSERT window.
+    newly_marked = await repo_a.batch_mark_as_read([shared_id, only_a_id], user_id)
+
+    # A only newly marked `only_a_id`; `shared_id` was won by the competitor.
+    assert newly_marked == 1
+    # Exactly one row per (message_id, user_id) — no duplicates, nothing lost.
+    assert await _count_rows(session_a, shared_id, user_id) == 1
+    assert await _count_rows(session_a, only_a_id, user_id) == 1
+
+
+async def test_mark_as_read_is_idempotent_under_concurrent_insert(race_sessions):
+    session_a, session_b = race_sessions
+    user_id = 7
+    shared_id = 999
+
+    repo_a = InboxMessageReadRepositoryImpl(session_a)
+    _inject_competing_insert_after_first_query(session_a, session_b, shared_id, user_id)
+
+    # find_one (the first exec) returns empty, competitor inserts, then save()
+    # would hit the unique constraint. Must be swallowed idempotently.
+    record = await repo_a.mark_as_read(shared_id, user_id)
+
+    assert record is not None
+    assert record.message_id == shared_id
+    assert record.user_id == user_id
+    assert await _count_rows(session_a, shared_id, user_id) == 1
+
+
+async def test_batch_mark_as_read_dedupes_duplicate_ids(race_sessions):
+    """Duplicate ids within one request must not self-collide on the unique index."""
+    session_a, _ = race_sessions
+    user_id = 3
+    repo_a = InboxMessageReadRepositoryImpl(session_a)
+
+    newly_marked = await repo_a.batch_mark_as_read([555, 555, 666], user_id)
+
+    assert newly_marked == 2
+    assert await _count_rows(session_a, 555, user_id) == 1
+    assert await _count_rows(session_a, 666, user_id) == 1