A custom, scoped MCP channel for bidirectional communication between Home Assistant and the Friday container, replacing the existing broadly permissive HA MCP.

Problem

The Friday container runs Claude Code with --dangerously-skip-permissions. The current Home Assistant MCP gives full read/write access to everything in HA. That combination means Claude could control anything in the house without guardrails. We need a scoped replacement that lets Paul decide exactly what Friday can see and do.

Core Concept

• A single custom MCP server inside the Friday Docker container handling both directions
• Inbound (HA → Claude): Subscribes to HA's WebSocket API using subscribe_trigger with filtered entity subscriptions. Friday receives only the events Paul chooses to expose. No firehose.
• Outbound (Claude → HA): Exposes scoped action tools (not full HA call_service). Only whitelisted actions are available.
• Replaces the existing broadly permissive HA MCP in the Friday container entirely.

Architecture

Event Flow (Inbound)

flowchart LR
    A["Home Assistant"] -->|WebSocket subscribe_trigger| B["MCP Channel Server"]
    B -->|channel tag| C["Claude Code (Friday)"]

• Channel server connects to HA's WebSocket API (ws://ha-host:8123/api/websocket)
• Uses subscribe_trigger (not subscribe_events) so HA filters server-side. Only matching entity state changes are sent over the socket.
• Entity allowlist is defined in a config and translated into WebSocket subscription parameters at connect time.

Action Flow (Outbound)

flowchart LR
    C["Claude Code (Friday)"] -->|MCP tool call| B["MCP Channel Server"]
    B -->|call_service| A["Home Assistant"]

• MCP exposes scoped tools, not arbitrary call_service access
• Each permitted action is defined explicitly in config
• Claude can only call actions that have been whitelisted