ADR 0172: the lab is a module, and runs a bed when the mesh asks

02-DECISIONS/0172-the-lab-is-a-module-and-runs-a-bed-when-the-mesh-asks.md

@@ -0,0 +1,59 @@
+---
+topic: the mesh
+status: accepted
+date: 2026-10-02
+deciders: jochen
+reconstructed: false
+extends: 02-DECISIONS/0016-the-lab.md
+---
+
+# 172. The lab is a module, and runs a bed when the mesh asks
+
+## Context
+
+The lab raises virtual machines and runs the mesh on them, end to end, before a change reaches a real
+machine ([ADR 0016](0016-the-lab.md)). It runs on one machine of the mesh, the one with the
+virtualisation it needs. Until now the only way to start a bed there was to sign in to that machine and
+run the lab's command line by hand, with a dozen environment variables pointing at sibling checkouts.
+
+Nothing in the mesh could ask for it. An agent working through the mesh's own tools could build,
+merge and push a change, and could not prove it in the lab first. The operator's direction on
+2026-10-02: work on another machine goes through a mesh tool, not a shell on it.
+
+## Considered Options
+
+1. **Keep the lab a command line on one machine.** Every run is a person, or an agent with a shell on
+   that machine, outside the mesh.
+2. **The lab is a module.** Assigned to the machine that can run it, serving tools that run a bed
+   against named branches and say how it went.
+
+## Decision
+
+**Option 2.**
+
+- **A `lab` module, assigned where the lab can run**, serves five tools: whether this machine can run
+  beds, run beds against a branch per repository, a run's state, its log, and stopping it.
+- **A run is the lab's own suite**, against fresh checkouts of the named branches from the mesh's forge,
+  side by side as the lab expects them. It builds what the beds place from those checkouts, as the suite
+  already does. It answers at once with an id, like a build: a bed takes minutes, and a call does not.
+- **Only branches on the forge are run**, never code handed to the tool. What a run tested is what the
+  forge holds at the commit it names.
+- **The lab is reached over the mesh only.** Its tools travel the bus, and the module opens no port.
+- **No grant beyond the mesh's own.** Running a bed is root on the lab's machine, but anyone who can call
+  the mesh's tools can already do worse. The operator's judgement on 2026-10-02.
+
+## Consequences
+
+- An agent proves a change in the lab through the mesh, the same way it builds and pushes one.
+- The lab's machine carries a module whose runtime holds the virtualisation's and the container
+  runtime's sockets, and a toolchain to build the mesh with.
+- A run's checkouts are its own, so two runs never build from each other's tree. Old ones are removed
+  when their run ends.
+
+## How this is checked
+
+| Rule | Checked by |
+|---|---|
+| A run checks out exactly the named branches, and reports the commits it tested | the module's tests over a forge fixture, and each run's answer |
+| A run answers at once, and its state and log follow it to the end | by hand, the first run |
+| The module opens no port | the composed filter of the lab's machine |

02-DECISIONS/README.md

@@ -181,6 +181,7 @@ python3 00-META/checks/index.py            fail if stale
 - **0168** — [A converged machine is filtered by the mesh alone, and the host says what else refuses](0168-a-converged-machine-is-filtered-by-the-mesh-alone.md)
 - **0169** — [A machine joins through the tunnel, and the bus is never public](0169-a-machine-joins-through-the-tunnel-and-the-bus-is-never-public.md)
 - **0169** — [The firewall seat serves its verbs, and a foreign rule set is removed through one of them](0169-the-firewall-seat-serves-its-verbs.md)
+- **0172** — [The lab is a module, and runs a bed when the mesh asks](0172-the-lab-is-a-module-and-runs-a-bed-when-the-mesh-asks.md)
 
 ### Its tiers, from the bottom up