hermes-memory-installer: Memory Sidecar v3.5.1

Memory Sidecar v3.5.1 lands as a focused operational hardening release for the public agent-agnostic memory layer. If you’ve been running earlier iterations in production with multi-agent systems, you know the friction: dangling connections from failed sessions, unbounded retries hammering storage backends, and inconsistent transaction windows when multiple agents write simultaneously. This release doesn’t introduce new storage engines or retrieval strategies—it locks down the seams where real-world deployments bleed availability.

Operational Improvements

The core target is fault isolation and deterministic cleanup. Two concrete changes drive this:

Session Scoped Graceful Shutdown

Previously, when an agent task died ungracefully, the sidecar held onto memory handles until a timeout forced closure. In v3.5.1, every session lock is tied to a unique ephemeral token, and the sidecar’s heartbeat goroutine now detects stale tokens within half the lease interval. The shutdown path emits a final checkpoint before releasing storage, preventing orphaned write buffers.

Retry with Bounded Jitter

Retry logic now uses a capped exponential backoff (max 30s) with per-request jitter derived from the session ID. This avoids retry storms when a transient storage outage resolves—each agent sees staggered attempts, and the storage side sees smoothed load. The max_retries config defaults to 3 and can be overridden per deployment but is clamped at 5 to prevent tail latency blowups.

Code Example

The most visible improvement is the updated configure API for the memory connector. Here’s how you set up a hardened instance with retry policy and transaction logging:

from memory_sidecar import MemoryClient

client = MemoryClient(
    endpoint="unix:///var/run/mem-sidecar.sock",
    session_config={
        "heartbeat_interval_s": 10,
        "heartbeat_timeout_s": 25,
        "on_orhpan": "checkpoint_and_close"
    },
    retry_policy={
        "max_retries": 3,
        "base_delay_ms": 200,
        "cap_delay_s": 30,
        "jitter_factor": 0.25
    },
    transaction_log="/var/log/mem-sidecar-tx.jsonl"
)

Key points from this snippet:

• on_orphan replaces the old ambiguous timeout_action—now you explicitly choose between checkpoint_and_close or abort_quietly.
• transaction_log enables an append-only log of all memory mutations. This is off by default; enabling it costs ~2% throughput but gives you precise replay for debugging or audit trails.
• The jitter factor randomizes each retry interval within ±25% of the computed backoff, so two agents hitting the same outage don’t collide on retry.

Agent-Agnostic Benefits

Because Memory Sidecar remains agent-agnostic, these improvements automatically protect any adapter implementing the standard gRPC contract. Whether your agents are built on LangChain, custom Python workers, or Node services, the sidecar enforces the same session lifecycle and retry boundaries. The installer (hermes-memory-installer) now includes a --hardening-profile flag that applies these defaults to all new deployments.

Migration Notes

If you’re upgrading from v3.4.x, note that the timeout_ms field in session config is deprecated in favor of the two-parameter heartbeat model. The sidecar logs a warning if you use the old field but still respects it during migration. Remove timeout_ms when you can schedule a config cleanup.

Memory Sidecar v3.5.1 is available now through the hermes-memory-installer package. Run pip install --upgrade hermes-memory-installer and review the new config templates in /etc/memory-sidecar/. No database migrations required—this is purely a runtime stabilization cut.