category: reference
tags: [tasks, mcp, bug, multi-tenant]
last_updated: 2026-03-15
confidence: high

MCP Wiki Routing Bug

Problem

The MCP sidecar calls the otterwiki REST API at http://localhost:8000 without a Host header. The TenantResolver on port 8000 treats requests without a wiki subdomain as the default wiki (_default). All MCP reads and writes go to the wrong wiki.

This means:

• Pages written via MCP go to /srv/wikis/_default/, not the intended wiki
• Pages read via MCP return content from _default, not the wiki the user connected to
• Semantic search queries search the wrong index
• The three Tasks/ pages created today via MCP are in the _default wiki, not the dev wiki

Root cause

The MCP server (otterwiki-mcp) creates a WikiClient with OTTERWIKI_API_URL=http://localhost:8000. When it makes HTTP requests to the REST API, it doesn't set a Host header. The TenantResolver sees localhost and falls through to the default wiki.

On 3gw (single-tenant), this works because there's only one wiki. On robot.wtf (multi-tenant), the MCP sidecar needs to forward the wiki context.

Fix

The MCP sidecar receives requests on wiki subdomains (e.g., dev.robot.wtf/mcp). It needs to:

1. Extract the wiki slug from the incoming request's Host header
2. Pass Host: {slug}.robot.wtf on its API calls to http://localhost:8000
3. This way TenantResolver resolves the correct wiki for each API call

The WikiClient in otterwiki_mcp/api_client.py needs to accept a host_header parameter and include it in all requests. The MCP tool handlers need to know the current wiki slug (from the incoming request context) and pass it to the client.

Complication

FastMCP's tool handlers are async functions registered with @mcp.tool(). They don't have direct access to the HTTP request context (Host header). The wiki slug needs to be threaded through somehow — either via a context variable, or by creating a per-request WikiClient.

The V5 consent flow already extracts the wiki slug in the /authorize/callback handler. A similar pattern can be used for tool calls.