Opt-in: compact the conversation at the end of a goal while the session is still cached

Feature request

An opt-in setting that has Claude Code compact the conversation proactively at the end of a goal or task, while the session's prompt cache is still warm, instead of lazily on the next user turn.

Problem

Compaction currently triggers when the context fills up on a later turn. For long autonomous or unattended sessions, that turn often comes hours after the work finished, when I return to check on it. By then the prompt cache has expired, so the compaction request re-processes the full uncached transcript, and I sit waiting on it before I can interact with the session at all.

Proposed behavior

• A setting (off by default) such as compactAtGoalEnd or similar.
• When enabled, and the session reaches a natural end-of-work boundary (task complete, agent stops and hands back to the user) with the context near the compaction threshold, Claude compacts immediately while the transcript is still cached.
• The next user message then lands on an already-compacted, ready session.

Why it matters

• Compacting against a warm cache is cheaper than re-reading the whole transcript cold hours later.
• Removes the wait when resuming an unattended session.
• Opt-in, so users who prefer to see the full transcript before it is summarized are unaffected.

Repro of the current behavior

1. Run a long autonomous task that ends near the context limit.
2. Leave the session idle for several hours.
3. Send the next message. Compaction triggers then, against a cold cache, and the user waits for it.

Also submitted via /feedback, receipt d993c092-daad-4d41-90cd-e88e464bc21e.