---
topic: what runs on it
status: accepted
date: 2026-08-31
deciders: jochen
reconstructed: false
extends: 02-DECISIONS/0004-a-node-and-how-it-joins.md
---

# 26. The mesh has a session of its own, and it is the node session's mechanism

## Context

[ADR 0004](0004-a-node-and-how-it-joins.md) gives every node a session: one per node, permanent,
remembering across callers, its system prompt the node's engram, reachable over the broker like
everything else. **Any node can message any node**, and that is called the one part of the system
that is genuinely a mesh — symmetric, with no centre.

**There is no way to address the mesh itself.** A question that spans machines — *what is running
across all of this*, *which nodes are behind*, *why is it built this way* — has to be put to some
node, which then asks the others. That works, and it makes a mesh-wide question **nobody's
question**: every node answers it as a foreigner, from a position where the whole is not in view.

**Three things independently arrived at the same missing piece.**

[ADR 0025](0025-the-design-record-is-read-not-copied.md), taken hours before this one, commits to
an agent that reads the design repository directly and answers into search. That agent has to
exist, run somewhere, and be askable — and nothing in the record says what it is or where it
lives.

[`14-model-access.md`](../03-DESIGN/01-to-be/14-model-access.md) records, as a gap deliberately
not half-built: *this worker uses that licence is a binding to an agent, not to a node* — and the
provisions model has no consumer identity other than a node. A session that must be assigned a
licence is exactly that consumer, and node sessions are already one.

**And ADR 0004 never said how a session is set up.** It describes behaviour and stops: nothing
states how a session starts, where its context lives, how the engram reaches it, or how a message
off the broker becomes a prompt. There is no design document for it. That gap was invisible until
something had to be built *like* a node session, because describing a second instance of a
mechanism requires the mechanism to have been described once.

## Considered Options

1. **No mesh session; keep relaying through a node.** Costs nothing and works today. **Rejected.**
   It leaves mesh-wide questions belonging to nobody, and it does not survive contact with
   ADR 0025 — that agent still needs a home, so the thing gets built anyway, unnamed, as an
   attachment to whichever node happened to host it.

2. **A new kind of agent, built separately.** Purpose-built for the whole mesh. **Rejected.** It
   would hold a session, a memory, a licence and broker plumbing — every one of which the node
   session already has. Two implementations of one mechanism drift, and the vocabulary collision
   that [ADR 0001](0001-mesh-brokers-nodes-host-agents-think.md) exists to undo began exactly this
   way: two things that were nearly the same, built twice, until neither word meant one thing.

3. **The same mechanism, started in a different context.** **Adopted.**

## Decision

**The mesh has one session, addressed as the mesh, and it is a node session in every respect but
three.**

| | |
|---|---|
| **the context it starts in** | the mesh's, not a machine's — this is the whole of what makes it different |
| **its engram** | the mesh's system prompt, as a node's engram is that node's |
| **its licence binding** | assigned in its own right, not inherited from the machine it runs on |

Everything else is unchanged and deliberately so: it is permanent, it remembers, it is reachable
over the broker, it holds its own tools, and switched off it still answers *I am switched off*
rather than falling silent.

**It runs on the node that holds the control plane** — not for convenience, but because that node
is already the one place excepted from *compromise of a node is compromise of that node*
(ADR 0004). An agent able to reach everything, placed anywhere else, creates a **second** such
place. Putting it where the authority already sits concentrates nothing new.

**It is an addition to per-node messaging and never a replacement.** Every node remains directly
addressable. This is not a preference: ADR 0001 holds that losing the control plane costs *change,
not operation*, and a mesh whose only conversational surface lives on that node would lose the
ability to ask anything while every machine kept running perfectly. **The front door may not be
the single point.**

**It is not an employee** ([ADR 0003](0003-agents-are-persistent-employees.md)). Nobody hires it,
it holds no task queue, it is never drained or reassigned. What it does with work that belongs
somewhere else is **dispatch it** — to node sessions, or to workers — which is what a node session
already does when asked something it does not have.

**It is ADR 0025's reader.** The agent that reads the design repository and answers into search is
this session, not a second one. One agent, one memory, one place to reach; two would both need
that repository and would eventually disagree about what it says.

**"One per node" is about address, not about process count.** ADR 0004's rule — *two and nothing
decides which replies* — forbids ambiguity in who answers when a **node** is addressed. The mesh
session answers when the **mesh** is addressed. The control-plane node therefore hosts two
sessions and no ambiguity, and stating this here is what stops it reading as a contradiction
later.

## Consequences

**The node session's setup must now be designed, and it never was.** This decision is expressed as
*the same as a node session, elsewhere*, which is only meaningful once that mechanism is written
down. The design document covering both is the immediate consequence of this record, not a
follow-up to it.

**A consumer that is not a machine stops being deferrable.** The licence binding above is the gap
`14-model-access.md` names, and it now has two consumers rather than a hypothetical one. Until it
exists, a session's model access can only be expressed as *this module on this machine*, which
cannot say *this node's session uses the personal licence and the mesh's uses the company one* —
the thing the binding is for.

**Symmetry is preserved, and it is worth being precise about why.** ADR 0004's claim is about what
a node can reach, and it is untouched: node-to-node messaging is unchanged, nothing is routed
through the mesh session, and it is a participant rather than a hop. What arrives is a
participant that happens to be the one a person usually addresses.

**Availability degrades to inconvenience rather than to silence** — but only because of the
addition rule above. If that rule is ever relaxed, this consequence inverts, and it inverts
quietly: everything keeps working and nobody can ask about it.

**The surface a person uses is not decided here.** That a board is a good place to talk to it is
likely and is not this record's business; the session is reachable over the broker like everything
else, and what puts a text box in front of it is a separate choice.

## References

- [ADR 0004](0004-a-node-and-how-it-joins.md) — the node session this extends
- [ADR 0025](0025-the-design-record-is-read-not-copied.md) — the reader this session is
- [ADR 0003](0003-agents-are-persistent-employees.md) — the vocabulary this is not
- [`03-DESIGN/01-to-be/14-model-access.md`](../03-DESIGN/01-to-be/14-model-access.md) — *a
  consumer that is not a machine*, the gap this makes concrete