lossless-hermes-py 0.1.0

Lossless Context Management (LCM) for Hermes Agent — DAG-based conversation summarization that never forgets

lossless-hermes-py

DAG-based lossless context management for LLM conversations. Never lose a message — summarize them into a directed acyclic graph.

A Python port of lossless-claw for use with Hermes Agent or as a standalone library.

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What It Does

Long conversations with LLMs hit context window limits. The typical solution is to truncate or naively summarize, losing information permanently. Lossless Context Management (LCM) takes a different approach: it builds a directed acyclic graph of summaries that compresses older messages while preserving the ability to drill back into any detail.

Your conversation never loses information. It just gets more compact.

See the animated visualization at losslesscontext.ai.

How It Works

LCM operates in two compaction passes that build a summary DAG:

Leaf pass — When the context window fills up, raw messages (excluding a protected "fresh tail" of recent messages) are chunked and summarized into leaf nodes at depth 0. Each leaf summary covers a group of messages and links back to the originals.

Condensed pass — When enough leaf summaries accumulate, they are themselves summarized into condensed nodes at depth 1. This process repeats upward: depth-1 summaries get condensed into depth-2, and so on. The result is a tree-like DAG where the root captures the entire conversation at high compression, and any branch can be expanded to recover full detail.

Context assembly reconstructs the optimal prompt by combining:

• The highest-level summaries (covering the full history compactly)
• The fresh tail (recent messages kept verbatim for continuity)

Cache-aware compaction adapts to prompt caching behavior. When the cache is hot (high hit rate), compaction backs off to avoid invalidating cached prefixes. When the cache is cold, compaction runs more aggressively.

Agent tools (lcm_grep, lcm_expand, lcm_describe) let the LLM search and drill into compacted history on demand, recovering detail without keeping everything in context.

Installation

Hermes Agent Plugin (recommended)

hermes plugins install mssteuer/lossless-hermes-py

Then enable the engine in ~/.hermes/config.yaml (top level, not under agent:):

context:
  engine: lcm

(Optional) Configure a dedicated summarization model via environment variables in ~/.hermes/.env:

LCM_SUMMARY_MODEL=gemini-2.5-flash
LCM_SUMMARY_PROVIDER=openai          # your litellm provider name

Or edit the plugin's plugin.yaml directly:

nano ~/.hermes/plugins/lossless-hermes/plugin.yaml

Restart the gateway:

hermes gateway restart

The agent will now have lcm_grep, lcm_describe, and lcm_expand tools available.

Via pip

pip install lossless-hermes-py

This is useful for standalone library usage (see below) or if you prefer managing Python packages separately. For use with Hermes, the hermes plugins install method above is simpler.

Standalone Usage

LCM also works as a standalone library without Hermes:

from lossless_hermes import LcmContextEngine

engine = LcmContextEngine(
    model="gemini-2.5-flash",
    provider="openai",
    config_context_length=128000,
)

# Start a session
engine.on_session_start("my-session")

# Check if compaction is needed
if engine.should_compress(prompt_tokens=100000):
    compressed = engine.compress(messages, current_tokens=100000)

Configuration

Settings are resolved with three-tier precedence: environment variables > plugin.yaml > defaults.

Key Settings

Setting	Default	Description
enabled	true	Enable/disable LCM
context_threshold	0.75	Fraction of context window that triggers compaction
fresh_tail_count	64	Number of recent messages kept verbatim
fresh_tail_max_tokens	null	Optional token budget cap for fresh tail
leaf_chunk_tokens	20000	Max tokens per leaf chunk
leaf_target_tokens	2400	Target summary size for leaf nodes
condensed_target_tokens	2000	Target summary size for condensed nodes
leaf_min_fanout	8	Minimum messages per leaf chunk
condensed_min_fanout	4	Minimum summaries per condensed chunk
condensed_min_fanout_hard	2	Hard minimum for condensed chunks
incremental_max_depth	1	Max depth levels to compact per pass
summary_provider	""	LLM provider for summarization (falls back to host agent's provider)
summary_model	""	Model for summarization (falls back to host agent's model)
summary_timeout_ms	60000	Timeout for summarization calls
circuit_breaker_threshold	5	Consecutive failures before circuit opens
circuit_breaker_cooldown_ms	1800000	Cooldown before retrying after circuit break (30 min)

Cache-Aware Compaction

config:
  cache_aware_compaction:
    enabled: true
    cache_ttl_seconds: 300
    max_cold_cache_catchup_passes: 2
    hot_cache_pressure_factor: 4
    hot_cache_budget_headroom_ratio: 0.2
    cold_cache_observation_threshold: 3

Dynamic Leaf Chunk Sizing

config:
  dynamic_leaf_chunk_tokens:
    enabled: true
    max: 40000

Environment Variables

All config keys can be set via environment variables with the LCM_ prefix:

export LCM_SUMMARY_MODEL="gemini-2.5-flash"
export LCM_FRESH_TAIL_COUNT=32
export LCM_CONTEXT_THRESHOLD=0.8

Tools

LCM exposes three tools that the agent can call to interact with compacted history:

lcm_grep

Search conversation history and summaries using FTS5 full-text search or regex.

{
  "query": "database migration strategy",
  "mode": "full_text",
  "include_messages": true,
  "include_summaries": true,
  "limit": 20
}

lcm_describe

Get the current LCM state: summary statistics, DAG depth, message counts, recent compaction activity.

{
  "include_stats": true,
  "include_recent": true
}

lcm_expand

Drill into specific content. Expand a message to see its full text, a summary to see its children and linked messages, or search for related content across conversations.

{
  "target_type": "summary",
  "target_id": "abc123"
}

{
  "target_type": "related",
  "query": "authentication flow",
  "limit": 10
}

Architecture

src/lossless_hermes/
    __init__.py          # LcmContextEngine — main plugin class, Hermes integration
    compaction.py        # CompactionEngine — leaf/condensed passes, cache-aware policy
    assembler.py         # ContextAssembler — reconstructs optimal context from DAG
    summarizer.py        # LLM summarization with circuit breaker pattern
    retrieval.py         # RetrievalEngine — FTS5 search, related content discovery
    tokens.py            # Unicode-aware token estimation (CJK, emoji)
    tools.py             # lcm_grep, lcm_describe, lcm_expand tool implementations
    db/
        config.py        # Three-tier config resolution (env > yaml > defaults)
        connection.py    # SQLite connection management (WAL mode)
        migration.py     # Schema migrations
    store/
        conversation.py  # ConversationStore — messages, parts, sequences
        summary.py       # SummaryStore — DAG nodes, edges, depth stats
        identity.py      # Content identity hashing for deduplication

Storage

SQLite with WAL mode for concurrent reads. FTS5 virtual tables for full-text search across messages and summaries. All data is local — no external services beyond the LLM provider.

Differences from the TypeScript Version

This is a Python port of the original lossless-claw TypeScript implementation. Key adaptations:

• Target platform: Hermes Agent (NousResearch) Python plugin system instead of OpenClaw
• Plugin interface: Implements ContextEngine base class from agent.context_engine with register() entry point
• LLM calls: Provider-agnostic via configurable summarizer (supports litellm, direct API calls) rather than being tied to a specific SDK
• Default summarization model: Gemini 2.5 Flash (configurable to any model)
• Async model: Synchronous by default (matching the Hermes plugin interface) rather than async-first
• Config resolution: Three-tier env/yaml/defaults pattern adapted for Python conventions
• Token estimation: Custom Unicode-aware estimator (tokens.py) with CJK and emoji handling
• Database: Same SQLite/FTS5 approach, using Python's built-in sqlite3 module
• Standalone support: Works both as a Hermes plugin and as a standalone library — the ContextEngine import is optional

The core algorithm — DAG-based compaction with leaf and condensed passes, fresh-tail protection, cache-aware compaction policies — is a faithful port of the original.

Credits

• lossless-claw by Josh Lehman / Martian Engineering (MIT License) — the original TypeScript implementation this project is ported from
• The LCM Paper by Voltropy — the academic foundation for lossless context management
• Hermes Agent by NousResearch — the target platform whose context engine plugin system this integrates with

License

MIT