Fix KeyError in session listing endpoint when accessing conversation reference (#9419)

- Add type and boundary checks for conv["reference"] access
- Prevent KeyError: 0 when reference list is empty or malformed
- Ensure reference is list type before indexing
- Handle cases where reference items are None or missing chunks
- Maintains backward compatibility with existing data structures

This resolves crashes in /api/v1/agents/<agent_id>/sessions endpoint
when conversation reference data is not properly structured.

### What problem does this PR solve?

This PR fixes a critical `KeyError: 0` that occurs in the
`/api/v1/agents/<agent_id>/sessions` endpoint when the system attempts
to access conversation reference data that is not properly structured.

**Background Context:**
The `list_agent_session` method in `api/apps/sdk/session.py` assumes
that `conv["reference"]` is always a properly indexed list with valid
dictionary structures. However, in real-world scenarios, this data can
be:
- Not a list type (could be None, string, or other types)
- An empty list when `chunk_num` tries to access index 0
- Contains None values or malformed dictionary structures
- Missing expected "chunks" keys in reference items

**Impact Before Fix:**
When malformed reference data is encountered, the API crashes with:
```json
{
    "code": 100,
    "data": null,
    "message": "KeyError(0)"
}
```
**Solution:**
Added comprehensive safety checks including type validation, boundary
checking, null safety, and structure validation to ensure the API
gracefully handles all reference data formats while maintaining backward
compatibility.

### Type of change

- [x] Bug Fix (non-breaking change which fixes an issue)
- [ ] New Feature (non-breaking change which adds functionality)
- [ ] Documentation Update
- [ ] Refactoring
- [ ] Performance Improvement
- [ ] Other (please describe):

api/apps/sdk/session.py

@@ -589,14 +589,22 @@ def list_agent_session(tenant_id, agent_id):
             if "prompt" in info:
                 info.pop("prompt")
         conv["agent_id"] = conv.pop("dialog_id")
+        # Fix for session listing endpoint
         if conv["reference"]:
             messages = conv["messages"]
             message_num = 0
             chunk_num = 0
+            # Ensure reference is a list type to prevent KeyError
+            if not isinstance(conv["reference"], list):
+                conv["reference"] = []
             while message_num < len(messages):
                 if message_num != 0 and messages[message_num]["role"] != "user":
                     chunk_list = []
-                    if "chunks" in conv["reference"][chunk_num]:
+                    # Add boundary and type checks to prevent KeyError
+                    if (chunk_num < len(conv["reference"]) and
+                            conv["reference"][chunk_num] is not None and
+                            isinstance(conv["reference"][chunk_num], dict) and
+                            "chunks" in conv["reference"][chunk_num]):
                         chunks = conv["reference"][chunk_num]["chunks"]
                         for chunk in chunks:
                             new_chunk = {