Headroom measured and blocked; Mouse-1 triage command built and run

docs/PLAN-INTERFACE.md

@@ -640,6 +640,30 @@ without the provider.
 to the company, not to a project. The finest granularity is one agent, which is what the
 `Agents>settings` model field already gives.
 
+### Measured afterwards: it does not work yet, and why
+
+A provider entry was added and removed again after testing, because requests fail:
+
+```
+POST http://192.168.20.13:8787/v1/chat/completions   → 502 {"code":"proxy_error"}
+POST http://192.168.20.13:8787/v1/messages           → 401 "invalid x-api-key" (Anthropic shape)
+POST http://192.168.20.13:20129/v1/chat/completions  → 400 (the router's own model naming)
+```
+
+Headroom's backend is `anthropic`: it speaks the Anthropic Messages API and authenticates with
+an Anthropic key, which this machine does not have. The omni router uses an OpenAI-shaped API
+with its own key. So headroom cannot be put in front of the agents as things stand.
+
+To use it, one of these is needed:
+
+1. an Anthropic-compatible credential in headroom, and agents moved to an Anthropic-shaped
+   provider;
+2. or headroom configured to accept the omni router's OpenAI API and key;
+3. or nothing — the omni router already does model routing, and headroom's only addition would be
+   prompt compression.
+
+The provider entry was removed so no agent can be pointed at a failing endpoint by accident.
+
 ## Mouse-1, measured
 
 The person supplied `docs/MOUSE-1-NOTES.md`, written from measurements on 2026-11-08/09. The