Feature: Background/non-blocking compacting to reduce developer wait time

Problem

Compacting currently blocks the entire conversation, causing significant productivity loss for power users. In my workflow:

• Compacting triggers approximately every 10 minutes
• Each compacting event causes a noticeable pause
• Estimated ~30% of development time is lost waiting for compacting

This makes extended coding sessions with Claude Code frustratingly stop-and-go.

Proposed Solution: Background Compacting

Instead of blocking when the context limit is reached, start compacting proactively in the background before hitting the limit:

1. At ~80% context capacity: set a marker and start background summarization of everything before the marker
2. Continue the conversation normally — new turns accumulate after the marker
3. When the background summary completes: replace pre-marker context with the summary, append post-marker turns
4. Fallback: if the hard limit is reached before the background summary finishes, block as today

Context: [Turn 1 ............ Turn 15 ... Turn 18 ... Turn 20]
                                ↑                        ↑
                          Marker set                 Limit reached
                          Background compact
                          starts (Turn 1-15)

Result:  [Summary(1-15)] + [Turn 16-20 uncompacted]

Why this works without consistency issues

• Everything after the marker is preserved in full — no information loss
• The summary only covers turns before the marker, which are frozen and won't change
• This is identical to current compacting behavior, just started earlier and non-blocking

Benefits

• Near-zero perceived compacting latency for most cases
• No change in summary quality (same input, same process)
• Graceful fallback to current blocking behavior if needed
• Massive UX improvement for power users in long sessions

Current Workaround

Manually managing context by starting new conversations frequently, which breaks flow and requires re-establishing context via CLAUDE.md and file references.