feat: enhance messaging system with improved API and tests

- Refactor messaging API endpoints for admin, shop, and vendor
- Add message-specific exceptions (ConversationNotFoundException, etc.)
- Enhance messaging service with additional helper methods
- Add comprehensive test fixtures for messaging
- Add integration tests for admin and vendor messaging APIs
- Add unit tests for messaging and attachment services

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

app/api/v1/vendor/messages.py

@@ -14,12 +14,19 @@ Uses get_current_vendor_api dependency which guarantees token_vendor_id is prese
 import logging
 from typing import Any
 
-from fastapi import APIRouter, Depends, File, Form, HTTPException, Query, UploadFile
+from fastapi import APIRouter, Depends, File, Form, Query, UploadFile
 from pydantic import BaseModel
 from sqlalchemy.orm import Session
 
 from app.api.deps import get_current_vendor_api
 from app.core.database import get_db
+from app.exceptions import (
+    ConversationClosedException,
+    ConversationNotFoundException,
+    InvalidConversationTypeException,
+    InvalidRecipientTypeException,
+    MessageAttachmentException,
+)
 from app.services.message_attachment_service import message_attachment_service
 from app.services.messaging_service import messaging_service
 from models.database.message import ConversationType, ParticipantType
@@ -230,41 +237,30 @@ def get_recipients(
     current_user: User = Depends(get_current_vendor_api),
 ) -> RecipientListResponse:
     """Get list of available recipients for compose modal."""
-    from models.database.customer import Customer
-
     vendor_id = current_user.token_vendor_id
-    recipients = []
 
     if recipient_type == ParticipantType.CUSTOMER:
         # List customers for this vendor (for vendor_customer conversations)
-        query = db.query(Customer).filter(
-            Customer.vendor_id == vendor_id,
-            Customer.is_active == True,  # noqa: E712
+        recipient_data, total = messaging_service.get_customer_recipients(
+            db=db,
+            vendor_id=vendor_id,
+            search=search,
+            skip=skip,
+            limit=limit,
         )
-        if search:
-            search_pattern = f"%{search}%"
-            query = query.filter(
-                (Customer.email.ilike(search_pattern))
-                | (Customer.first_name.ilike(search_pattern))
-                | (Customer.last_name.ilike(search_pattern))
-            )
-
-        total = query.count()
-        results = query.offset(skip).limit(limit).all()
-
-        for customer in results:
-            name = f"{customer.first_name or ''} {customer.last_name or ''}".strip()
-            recipients.append(
-                RecipientOption(
-                    id=customer.id,
-                    type=ParticipantType.CUSTOMER,
-                    name=name or customer.email,
-                    email=customer.email,
-                    vendor_id=customer.vendor_id,
-                )
+        recipients = [
+            RecipientOption(
+                id=r["id"],
+                type=r["type"],
+                name=r["name"],
+                email=r["email"],
+                vendor_id=r["vendor_id"],
             )
+            for r in recipient_data
+        ]
     else:
         # Vendors can't start conversations with admins - admins initiate those
+        recipients = []
         total = 0
 
     return RecipientListResponse(recipients=recipients, total=total)
@@ -286,15 +282,15 @@ def create_conversation(
 
     # Vendors can only create vendor_customer conversations
     if data.conversation_type != ConversationType.VENDOR_CUSTOMER:
-        raise HTTPException(
-            status_code=400,
-            detail="Vendors can only create vendor_customer conversations",
+        raise InvalidConversationTypeException(
+            message="Vendors can only create vendor_customer conversations",
+            allowed_types=["vendor_customer"],
         )
 
     if data.recipient_type != ParticipantType.CUSTOMER:
-        raise HTTPException(
-            status_code=400,
-            detail="vendor_customer conversations require a customer recipient",
+        raise InvalidRecipientTypeException(
+            conversation_type="vendor_customer",
+            expected_recipient_type="customer",
         )
 
     # Create conversation
@@ -416,11 +412,11 @@ def get_conversation(
     )
 
     if not conversation:
-        raise HTTPException(status_code=404, detail="Conversation not found")
+        raise ConversationNotFoundException(str(conversation_id))
 
     # Verify vendor context
     if conversation.vendor_id and conversation.vendor_id != vendor_id:
-        raise HTTPException(status_code=404, detail="Conversation not found")
+        raise ConversationNotFoundException(str(conversation_id))
 
     # Mark as read if requested
     if mark_read:
@@ -460,16 +456,14 @@ async def send_message(
     )
 
     if not conversation:
-        raise HTTPException(status_code=404, detail="Conversation not found")
+        raise ConversationNotFoundException(str(conversation_id))
 
     # Verify vendor context
     if conversation.vendor_id and conversation.vendor_id != vendor_id:
-        raise HTTPException(status_code=404, detail="Conversation not found")
+        raise ConversationNotFoundException(str(conversation_id))
 
     if conversation.is_closed:
-        raise HTTPException(
-            status_code=400, detail="Cannot send messages to a closed conversation"
-        )
+        raise ConversationClosedException(conversation_id)
 
     # Process attachments
     attachments = []
@@ -480,7 +474,7 @@ async def send_message(
             )
             attachments.append(att_data)
         except ValueError as e:
-            raise HTTPException(status_code=400, detail=str(e))
+            raise MessageAttachmentException(str(e))
 
     # Send message
     message = messaging_service.send_message(
@@ -525,10 +519,10 @@ def close_conversation(
     )
 
     if not conversation:
-        raise HTTPException(status_code=404, detail="Conversation not found")
+        raise ConversationNotFoundException(str(conversation_id))
 
     if conversation.vendor_id and conversation.vendor_id != vendor_id:
-        raise HTTPException(status_code=404, detail="Conversation not found")
+        raise ConversationNotFoundException(str(conversation_id))
 
     conversation = messaging_service.close_conversation(
         db=db,
@@ -567,10 +561,10 @@ def reopen_conversation(
     )
 
     if not conversation:
-        raise HTTPException(status_code=404, detail="Conversation not found")
+        raise ConversationNotFoundException(str(conversation_id))
 
     if conversation.vendor_id and conversation.vendor_id != vendor_id:
-        raise HTTPException(status_code=404, detail="Conversation not found")
+        raise ConversationNotFoundException(str(conversation_id))
 
     conversation = messaging_service.reopen_conversation(
         db=db,