/usage premium request counter significantly undercounts actual quota consumption

- **Copilot CLI version:** `0.0.413`
- **OS:** macOS
- **Session:** ~24h single session, resumed with `--resume`

## Describe the bug

The `/usage` command reports a much lower premium request count than what is actually consumed from the monthly quota.

## Steps to reproduce

1. Start a long Copilot CLI session with heavy tool use (bash, edit, view, grep — no sub-agents)
2. Resume the session with `--resume` across launches
3. Check `/usage` — shows **6 Premium requests**
4. Check remaining quota — dropped from **>80% → <70%** (300 request quota = ~30+ requests consumed)

## Expected behavior

`/usage` session counter should match (or closely approximate) the number of requests deducted from the monthly quota.

## Actual behavior

`/usage` shows 6 requests; quota indicates ~30+ were consumed. The counter also appears to reset or drop after context compaction (auto-summarization): token counts dropped
from `1.4M input / 3.9K output` → `583K input / 1.1K output` mid-session, and the counter restarted from a lower number.

## Additional context

Compaction events may consume requests that are not carried over in the `/usage` counter after summarization. It is unclear whether quota consumption includes background
operations not surfaced in the session counter.

Start by reproducing the reported `/usage` discrepancy in a long Copilot CLI session using heavy tool use, `--resume`, and context compaction. Compare the session counter with the quota change before and after compaction; done means the counter remains consistent with requests deducted, including any background operations identified by the investigation.

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