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

A session for the mesh itself, addressed as the mesh, differing from a
node's in exactly three things: the context it starts in, its engram,
and its licence binding. Not a new kind of agent — the same mechanism
pointed at a different root. Two implementations of one mechanism drift,
and the vocabulary collision 0001 exists to undo began exactly that way.

It runs on the control-plane node, and the reasoning is easy to get
backwards: not "the important agent on the important machine", but that
this node is already the one place excepted from "compromise of a node
is compromise of that node". Placed anywhere else it would create a
second such place.

It is an addition to per-node messaging and never a replacement. 0001
holds that losing the control plane costs change, not operation — and a
mesh whose only conversational surface lived there would lose the
ability to ask anything while every machine kept running perfectly.

Writing it up exposed that the node session's setup was never designed
at all. 0004 gives behaviour and stops: nothing said how a session
starts, where its context lives, or how a broker message becomes a
prompt. That gap was invisible until something had to be built *like* a
node session. 15-the-agent-session.md covers both as one mechanism.

It also makes "a consumer that is not a machine" undeferrable. The
control-plane node now hosts two sessions that must hold different
licences, and a per-machine binding cannot express that at all. Noted in
14-model-access.md against the gap it was already recorded as.

Also completes the to-be index, which stopped at 10 and omitted four
documents. Pre-existing broken ADR references in the older rows are left
alone rather than guessed at.

03-DESIGN/01-to-be/README.md

@@ -20,6 +20,11 @@ document is written and this one's status becomes `implemented`.
 | [`08-connectivity.md`](08-connectivity.md) | One context in full — overlay, resolution, exposure, filtering, certificates | [ADR 0007](../../02-DECISIONS/0007-connectivity.md), [0050](../../02-DECISIONS/0007-connectivity.md), [0051](../../02-DECISIONS/0004-a-node-and-how-it-joins.md), [0055](../../02-DECISIONS/0006-the-substrate-and-the-control-plane.md) |
 | [`09-the-node-lifecycle.md`](09-the-node-lifecycle.md) | How a machine becomes a node, stays one, and stops being one | [ADR 0004](../../02-DECISIONS/0004-a-node-and-how-it-joins.md), [0051](../../02-DECISIONS/0004-a-node-and-how-it-joins.md) |
 | [`10-delivery.md`](10-delivery.md) | Modules, the three edges, and how a change becomes a running thing | [ADR 0010](../../02-DECISIONS/0010-delivery.md), [0064](../../02-DECISIONS/0009-modules-and-the-graph.md), [0065](../../02-DECISIONS/0009-modules-and-the-graph.md) |
+| [`11-a-board.md`](11-a-board.md) | What a person sees of the mesh, and why it is read from what runs | [ADR 0008](../../02-DECISIONS/0008-a-context-owns-its-store.md), [ADR 0001](../../02-DECISIONS/0001-mesh-brokers-nodes-host-agents-think.md) |
+| [`12-a-module-repository.md`](12-a-module-repository.md) | A module repository, and what builds it | [ADR 0009](../../02-DECISIONS/0009-modules-and-the-graph.md), [ADR 0010](../../02-DECISIONS/0010-delivery.md), [ADR 0005](../../02-DECISIONS/0005-the-node-host.md) |
+| [`13-credentials-and-their-rotation.md`](13-credentials-and-their-rotation.md) | Credentials, and moving them without a consumer holding one the provider does not know about | [ADR 0001](../../02-DECISIONS/0001-mesh-brokers-nodes-host-agents-think.md), [ADR 0009](../../02-DECISIONS/0009-modules-and-the-graph.md) |
+| [`14-model-access.md`](14-model-access.md) | Model access as a provision, and what a licence is bound to | [ADR 0024](../../02-DECISIONS/0024-model-access-is-a-provision.md), [ADR 0009](../../02-DECISIONS/0009-modules-and-the-graph.md) |
+| [`15-the-agent-session.md`](15-the-agent-session.md) | One mechanism started twice — a node's session and the mesh's | [ADR 0004](../../02-DECISIONS/0004-a-node-and-how-it-joins.md), [ADR 0026](../../02-DECISIONS/0026-the-mesh-has-a-session-of-its-own.md) |
 
 ## Not yet written