Ran overnight in regular mode (not Autopilot) listing a directory tree and compacting memory - refund requested plz.

### Describe the bug

Bug: Agent enters infinite compaction/directory-list loop on long sessions

Product: GitHub Copilot CLI
Model: Claude Sonnet 4.6
Session: e6fd398f (~136 turns)

Trigger:
Complex multi-part prompt with a PDF attachment sent on a 136-turn session near context limit. Agent response
was NULL and the loop began immediately.

Behavior:

Compacting conversation history...
→ List directory . (54 files)
→ List directory (6 files)
→ Compacting conversation history...
→ [repeat indefinitely, ~6–8 hours]

No self-termination. No clarification request. Subsequent user messages produced NULL responses.
When confronted, agent falsely attributed the behavior to "another agent."

Root cause:
Context compaction on a long session lost enough state that the agent couldn't determine next action. It
defaulted to directory enumeration as the only available anchor, which immediately triggered another
compaction, creating a stable infinite loop.

Impact: Several million tokens consumed in wasted compaction passes. Conservative cost estimate: dozens of
dollars.

Expected behavior: Agent should detect no-progress loops and either self-terminate or emit a visible "I'm
stuck" message.

### Affected version

_No response_

### Steps to reproduce the behavior

Intermittent

### Expected behavior

No runaway prompts.

### Additional context

_No response_

この報告では、ソースファイル、テスト、エントリーポイントは指定されていません。まず、コンテキストの上限近くまである PDF 添付ファイルを使った長時間セッションでコンテキストの圧縮を調査し、ディレクトリ一覧の取得と圧縮が繰り返し発生するかを観察してください。完了とは、セッションが無期限に実行され続けるのではなく、終了するか、停止していることを示すメッセージを目に見える形で表示することです。

索引モデルが issue の本文から書いたものです。