agent-kernel: Skill for Claude Code

Adding a New Multimodal Storage Backend

This guide walks through adding a new attachment storage backend to Agent Kernel's multimodal subsystem. Use the existing Redis (ak-py/src/agentkernel/core/multimodal/storage/redis.py) and DynamoDB (ak-py/src/agentkernel/core/multimodal/storage/dynamodb.py) implementations as reference.

Existing Backends

Backend	Config value	Features	Extras
In-memory	in_memory	Ephemeral ClassVar dict, zero setup, single-process only	None
Redis	redis	Persistent, TTL, shared RedisDriver (lazy connect, retry, ping/reconnect), distributed	agentkernel[multimodal,redis]
DynamoDB	dynamodb	Serverless/AWS, TTL via expiry_time, fully managed	agentkernel[multimodal,aws]
Session cache	session_cache	Legacy — stores in session nv_cache (causes bloat, not recommended)	None

To run multimodal end-to-end (hooks/tools), you typically need agentkernel[multimodal] plus the backend-specific extra shown above (for example: agentkernel[multimodal,redis] or agentkernel[multimodal,aws]).

Architecture Overview

The multimodal storage system uses a simple pluggable pattern:

1. AttachmentStore (storage/base.py) — abstract base class with save(), get(), delete()
2. AttachmentData (storage/base.py) — dataclass representing a stored attachment (id, type, data, name, mime_type, description, timestamp, url)
3. AttachmentStorageManager (storage/storage_manager.py) — high-level API that reads configuration, instantiates the correct AttachmentStore via _build_driver(), and provides save_attachment() / get_attachment_data() methods
4. Callers: MultimodalPreHook saves attachments; AnalyzeAttachmentsTool retrieves them

MultimodalPreHook / AnalyzeAttachmentsTool
    → AttachmentStorageManager(session_id)
        → _build_driver(session_id)          # reads config.multimodal.storage_type
            → InMemoryAttachmentStore        # or Redis, DynamoDB, etc.
        → save_attachment() / get_attachment_data()
            → AttachmentStore.save() / .get()