Environment facts: ids, archived sandbox, Go missing, and the exact heartbeat test

Measured: six Pi agents and their ids, the user key rule, blocker endpoint, sandbox
archived (DELETE returned 500), scratch repo removed, Go not installed, repo has no
remote. The wake step is named as unproven with the endpoint that should trigger it.

README.md

@@ -11,6 +11,8 @@ If you are the person: read these in order:
 2. `docs/PLAN.md` — the plan: the four screens, the milestones, what is Paperclip's job and what is ours.
 3. `docs/PAPERCLIP-API-NOTES.md` — what we measured against your running Paperclip, with the endpoint and the response.
 4. `CHECKLIST.md` — the exact steps for the next session, in order, with boxes to tick.
+5. `docs/ENVIRONMENT-FACTS.md` — the ids, the installed tools, and the one step that is
+   still unproven.
 
 ## The one-line version
 
@@ -23,7 +25,8 @@ Nothing else.
 - Paperclip server running locally on `http://127.0.0.1:3100` (it is; 685 endpoints).
 - `PAPERCLIP_BOARD_KEY` in the environment — the **user** key. The terminal program uses
   this one. An agent key cannot write outside a heartbeat run.
-- Go toolchain, for the terminal program.
+- Go toolchain — **not installed yet**; add `go` to `/etc/nixos/configuration.nix` before
+  Milestone 2. See `docs/ENVIRONMENT-FACTS.md`.
 - Pi, which is already the worker adapter on your Paperclip agent.
 
 ## Rules for this project