Outline collection pushed; Obsidian note links the map and the collection; Headroom paths recorded

docs/PLAN-INTERFACE.md

@@ -771,3 +771,24 @@ the earlier test was trying, and it fails today only because LiteLLM does not kn
 
 **What the person does:** choose A or B. A needs no file edits. B needs the two files above and a
 container restart, and then one agent's model changed.
+
+### Headroom, final state after testing every path
+
+Tested on a throwaway container on a spare port, so the running one was not touched.
+
+| Configuration tried | Result |
+|---|---|
+| default image (`HEADROOM_BACKEND` unset, so `anthropic`) with our router key | `502 proxy_error` |
+| plus `OPENAI_API_KEY` | `openai/deepseek-v4-flash` → `404 No active credentials for provider: openai`; `deepseek/deepseek-v4-flash` → `502` |
+| plus `HEADROOM_BACKEND=openai` | `502 proxy_error` |
+
+Headroom's own `/stats` reports `api_requests: 0` for those calls, so the proxy refuses or fails
+before it forwards anything. The `404 … provider: openai` is the **router** answering, which means
+it parsed `openai/` as a provider name and had no key for it — not a headroom misconfiguration.
+
+What works, and was re-checked: `POST /v1/compress` answers 200 and reports `tokens_before` and
+`tokens_after`. That is the endpoint `headroom-bridge` uses, and `headroom-ai` is installed on all
+three machines.
+
+So: **use the tool path.** The provider path needs someone to work on headroom's own deployment
+with its logs in front of them; it is not something our software can fix.