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.

CHECKLIST.md

@@ -10,8 +10,9 @@ Tick each line. Nothing after the first unchecked line should be started early.
 
 ## Milestone 1 — one task, really run (no interface)
 
-- [ ] Read the sandbox from `docs/PAPERCLIP-API-NOTES.md`; it has two tasks, the second blocked by the first.
-- [ ] Give the first task to the Pi agent on the task (assign it) and let a heartbeat run it.
+- [ ] Read `docs/ENVIRONMENT-FACTS.md` for the company id, agent ids and toolchain facts.
+- [ ] Make a sandbox project (payload in `docs/PAPERCLIP-API-NOTES.md`) with two tasks, the second blocked by the first.
+- [ ] Assign the first task to `Builder` and force a wake with `POST /api/agents/{id}/heartbeat/invoke`. **Unproven** — if no run appears, record the response and stop.
 - [ ] Watch: the task goes `todo` → `in_progress` → `done`.
 - [ ] Confirm a comment written by Pi holds what it did.
 - [ ] Confirm the cost appears: `GET /api/issues/{id}/cost-summary`.