feat: proactive context compaction for agents

[rmdevpro]

Summary

LibreChat's agents endpoint currently uses a 'discard' context strategy — oldest messages are silently dropped once the context window fills. No summarization is triggered. The summarizeMessages() method on BaseClient throws if called; the summary prompts in summaryPrompts.js are unused scaffolding.

This issue tracks the design and implementation of proactive context compaction for agents.

Problem

• Context grows turn-by-turn until it hits maxContextTokens
• Oldest messages are then discarded silently — no summarization occurs
• Every prompt reconstructs the full context from MongoDB (no persistent state between turns)
• No cache-friendly compaction means near-full-window token costs on every turn once the window fills

Design

Algorithm

Triggered when current context token count reaches the configured threshold (default 80% of maxContextTokens):

1. Keep newest 10% of context as raw messages
2. Summarize everything older into a summary targeting ≤5% of the context window (token budget passed to model)
3. Prepend summary as a system message
4. Result: ~15% used (5% summary + 10% raw), ~85% free after each compaction

Agent Config Fields (schema addition)

Field	Type	Default	Description
autoCompact	boolean	false	Enable proactive compaction
compactThreshold	number	80	% of context window that triggers compaction

UI: toggle + plain number input (no slider) in the agent config screen.

Slash Command

/compact — manually triggers compaction on the current conversation regardless of threshold. Intercepted before submission reaches the model; calls POST /api/conversations/:id/compact.

Files Affected

Backend

• api/server/controllers/agents/client.js — implement summarizeMessages(), add proactive threshold logic, change contextStrategy
• api/app/clients/BaseClient.js — add proactive threshold check in handleContextStrategy
• api/app/clients/prompts/summaryPrompts.js — update prompt to accept token budget constraint
• New route: POST /api/conversations/:id/compact

Schema

• packages/data-provider/src/types/agents.ts (or equivalent) — add autoCompact, compactThreshold fields

Frontend

• Agent config screen — autocompact toggle + number input for threshold
• Message submission handler — /compact command interceptor
• client/src/locales/en/translation.json — localization strings

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Migrated from jmorrissette-RMDC/LibreChat