[Bug] Handoffs between agents don't always work

**Describe the bug**
When assigning a piece of work to two agents in succession, the first agent sometimes fails to actually post the final handoff message - instead, I just get a file path returned

**To Reproduce:**
Ask one agent to do something and then hand off to a second agent. After a few times doing this you'll probably find the handoff fails - see the screenshot below.

**Expected behavior:**
I expect the first agent to complete the task and post an actual @-mention message to trigger the other agent.

**Supporting Material**

Me having to do this manually:

**Environment (please complete the following information):**
- OS: Ubuntu 26.04

No source file or test is named. Start by reproducing repeated handoffs between two agents on Ubuntu and trace the path that returns a file path instead of posting the final message. Done means the first agent completes the task and sends an actual @-mention that triggers the second agent.

Written by the indexing model from the issue text.