`compactOnExit: true` — one setting, three problems solved

[!IMPORTANT] tl;dr — compactOnExit: true in settings.json. The compaction pipeline already exists. The exit path just needs to call it.

The auto-compact feature is genuinely one of the best parts of Claude Code. This is about closing one gap in its reach.

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The problems

Three issues, same root cause.

🐌 Slow resumes

Resuming a large uncompacted session means reading and parsing the full transcript before the first prompt loads. A 3.5 GB JSONL is not the same experience as a compact summary.

🧠 Wasted context budget

Resumed sessions that never hit the auto-compact threshold load full, uncompressed history into the context window. Users burn that budget before typing a word.

💾 Disk accumulation

Uncompacted sessions write the full raw transcript to disk and leave it there. One machine: 4,850 session files, 8.9 GB, with individual sessions at 3.5 GB and 2.3 GB. Compacted sessions store a summary. Uncompacted sessions store everything.

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Proposed change

// settings.json (global or project level)
{
  "compactOnExit": true
}

Runs the existing /compact logic when the session closes. Nothing else changes.

| Unchanged | |
|---|---|
| Compaction pipeline | ✅ untouched |
| Hook system | ✅ untouched |
| API surface | ✅ untouched |
| Session teardown logic | ✅ one call added |

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What this is not

[!NOTE] Not a request for BeforeSessionEnd hooks or a memory lifecycle API (see #39392, #47023). Those tackle a bigger problem and I hope they move forward. This is a single boolean for users who want clean resumes without building a plugin.

Users are already doing this by hand before every exit. They just can't make it automatic.

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Why current options fall short

| Approach | Why it doesn't work |
|---|---|
| autoCompactEnabled | Only fires at threshold — short sessions never compact |
| Stop hook | Fires after every response, not just the last |
| SessionEnd hook | Runs after process exit — too late for in-process compaction |
| Manual /compact | Works, requires discipline |

Two open issues (#39392, #47023) show users pushing on this from different angles for months. This is the smallest ask that closes the gap without waiting on a broader lifecycle API.

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I'd write the patch today if the repo were open — the exit path and compaction call site are both clear. Happy to help test or spec it out if that's useful.