DAG-based context that refuses to lose a message

What it does

hermes-lcm plugs into Hermes Agent and replaces the default context compressor. Instead of asking an auxiliary model to summarize and discard older turns, it persists raw messages in a local SQLite store, compacts them into depth-aware summary nodes, and assembles the active prompt from a bounded mix of system instructions, hierarchical summaries, and a protected fresh tail. If the agent needs a specific fact from a compacted turn, it uses built-in recall tools to pull exact excerpts back into scope.

The interesting bit

The clever part is the DAG structure: summaries retain source lineage and can be condensed further into higher-level nodes, creating a hierarchical memory the agent can navigate without dumping the entire conversation history into the prompt. It is essentially a lossy-on-the-surface, lossless-in-the-archive design that treats context window limits as a retrieval problem rather than a deletion event.

Key highlights

• SQLite-backed message store with FTS metadata and optional semantic retrieval.
• Hierarchical summary DAG that preserves lineage and supports drill-down.
• 15 built-in agent tools for recall, search, state inspection, and diagnostics (lcm_grep, lcm_recall, lcm_expand, etc.).
• Optional redaction of API keys and bearer tokens before storage.
• No required third-party runtime dependencies; runs fully offline.

Caveats

• The README notes this is a v0.21.0-rc2 release with additive schema changes; operators should back up lcm.db before updating.
• Several advanced features—semantic retrieval, temporal memory, and assertion sidecars—are opt-in and default-off, so the out-of-box experience is intentionally narrower than the full feature set.
• Requires Hermes Agent host and Python 3.11+; not a standalone context manager.

Verdict

Worth a look if you run Hermes Agent and are tired of watching your agent’s “memory” get creatively rewritten by summaries. Skip it if you are not using Hermes or if you prefer your context compression simple and irreversible.