Repository navigation
[v2] No idle-time compaction: a large session is re-sent uncached after its prompt cache expires #50777
Description
Description
When a session sits idle longer than the provider's prompt-cache lifetime (Anthropic 5 min or 1 h, OpenAI 30 min), the next message re-sends the whole context uncached. On a long session that is the most expensive request it makes. Compacting an idle session before the user comes back avoids that, but OpenCode v2 has no way to do it:
- No idle trigger. Compaction runs only on context overflow (
compaction.auto) or manually. - Plugins can't do it either. The plugin context's
ctx.sessionexposescreate,get,switchAgent,switchModel,prompt,generate,command,synthetic,interrupt,update,move,waitandcontext, but notcompact. The core session service hascompact(packages/core/src/session.ts) and the server hasPOST /api/session/:sessionID/compact. The only built-in commands areinitandreview, and calling the HTTP route from a plugin would need the server password, which in service mode comes from the service config, not the environment.
The built-in warming option shows the gap: it keeps an idle session warm, but when warming ends nothing can compact the session.
Expected: either an idle-compaction option (for example compaction.idle: { after: "4 hours", minTokens: 100000 }), or compact exposed on the plugin session API so a plugin can do it. The second looks small: add compact to the host session object (packages/core/src/plugin/host.ts), one adaptApiMethod line in packages/core/src/plugin/promise.ts, and "compact" in SessionDomain in packages/plugin/src/promise/session.ts and packages/plugin/src/effect/session.ts.
Plugins
A local server plugin that keeps idle Anthropic sessions warm and compacts them at the end of the idle window. It feature-detects ctx.session.compact.
OpenCode version
2.0.14 (source checked on the v2 branch at 1746672)
Steps to reproduce
- Write a server plugin that calls
ctx.session.compact({ sessionID }). typeof ctx.session.compactis"undefined", and no other plugin API compacts a session.- Leave a large session idle past the cache lifetime. Nothing compacts it, and the next message pays for a full uncached write of the context.
Operating System
Ubuntu 26.04 LTS
Terminal
N/A (background service, opencode serve --service)
Activity
github-actions commentedon Sep 23, 2026
This issue might be a duplicate of existing issues. Please check:
session.compactis not projected in the plugin context (SessionDomainPick omits it), with the same proposed fix (one-line forwarding change). Item 1 in that issue is identical to the plugin half of this report.context.session.compact(...)be exposed to the v2 plugin API, with the same motivation of coordinating compaction from a plugin.compaction.idle: { after: ..., minTokens: ... }) proposed here.If the plugin API gap is the primary concern, #49389 is the closest match and may be the best place to continue discussion.
[-][v2] No idle compaction, and plugins cannot trigger compaction (session.compact missing from the plugin context)[/-][+][v2] No idle-time compaction: a large session is re-sent uncached after its prompt cache expires[/+]sergiopadure commentedon Sep 23, 2026
Thanks for the pointers. The plugin half of this report duplicates #49389 (item 1) and #47229, so I'll follow those for
session.compacton the plugin context.I'm narrowing this issue to the part none of them covers: compaction after idle time. #40113 asks for a size-based threshold, which v2 already has as
compaction.auto. This one is about compacting a large session before its prompt cache expires, so the first message after a long break doesn't re-send the whole context uncached. Retitled to match.opencodejr commentedon Oct 28, 2026
Thanks for the detailed write-up, @sergiopadure! You're asking for a way to compact a large idle session before its prompt cache expires: either a built-in idle-compaction option, or
compactexposed to plugins.ctx.session.compactis already available. It was added in #52385 and has shipped since v2.0.22. That PR made the changes you describe: the hostsessionobject, the promise adapter, and"compact"inSessionDomainfor both the promise and effect APIs. You're on 2.0.14, and thev2branch you checked is out of date (it was promoted todevon 2026-10-10). Since your plugin already checks whetherctx.session.compactexists, it should start compacting once you upgrade, for example:This adds a compaction to the session's inbox, and you can pass
delivery: "queue"if needed.There is no built-in idle compaction yet. Compaction runs only on context overflow (
compaction.auto) or when you start it manually, andwarmingdoesn't compact a session when warming ends. I've marked this as a feature request, and maintainers will consider an option likecompaction.idle. In the meantime, a plugin like yours is the way to get this behaviour.Related issues:
compactto plugins