[Bug] /ultrareview returns empty findings array with full Extra Usage charge billed

Bug Description
Title: /ultrareview returns empty findings but bills full Extra Usage cost

Body:

## Summary

Ran /ultrareview on a branch. The remote agent completed (status: completed, summary: "Remote review completed"), but returned
an empty findings array []. Extra Usage was billed in full (~$20).

## Reproduction

• Command: /ultrareview (no arg, reviewing current branch)
• Branch: main
• Session: https://claude.ai/code/session_01DpwYsg2trvBMiLb7Qs6aAu
• Task ID: rsc6s73ni

## Expected

Either (a) the remote review produces findings proportional to the diff scope, or (b) if the agent genuinely had nothing to flag,
that outcome should be communicated clearly with a non-billable / refunded result. A 7k-line diff returning zero findings with no
explanation looks like a silent failure, not a clean review.

## Actual

task-notification arrived with status: completed and findings []. No diagnostic output, no indication of whether the agent
actually reviewed the diff or failed early. Full Extra Usage cost charged.
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