[Bug] Unexpected high token consumption with delegated sub-agents in Fable

**Bug Description**
my usage this morning was not consumed by these sessions yet jumped to over 50% in about 17mins. i had used fable and had told it to delegate to token efficient sub agents. this shouldn't have happened and i feel like i did nothing different to cause this. Fable had genuinely not accomplished anything to get to 50% usage, no massive fan out, nothing.

**Environment Info**
- Platform: win32
- Terminal: vscode
- Version: 2.1.270
- Feedback ID: c3ae439a-53ed-4ed3-a7e6-cc4bcc323920

**Errors**
```json
[]
```

Start by reviewing the reported session and usage data associated with feedback ID c3ae439a-53ed-4ed3-a7e6-cc4bcc323920, focusing on the delegated sub-agent activity in Fable. Compare the token consumption with the reported lack of fan-out or completed work; done means identifying and reproducing the unexpected usage or documenting why it occurred, with a regression check if the cause is found.

Written by the indexing model from the issue text.