01-RESEARCH/024-state-a-module-keeps-on-the-bus/00-overview.md

@@ -0,0 +1,147 @@
+---
+status: graduated
+initiated: 2026-10-04
+touches: [the bus, what a module declares, the tool runtime, the SDK, the bus grants, 03-DESIGN/01-to-be/25-the-bus-on-nats.md, 03-DESIGN/01-to-be/32-what-a-module-declares.md]
+became: [02-DECISIONS/0201-a-module-keeps-its-current-state-in-key-value-buckets-it-declares-and-reaches-through-the-runtime.md, 03-DESIGN/01-to-be/32-what-a-module-declares.md, 03-DESIGN/01-to-be/25-the-bus-on-nats.md]
+---
+
+# 024 — State a module keeps on the bus
+
+## What is investigated
+
+A place on the bus where a module's own code keeps **current state** — not history — that every
+machine sees, including a machine that joins after the state was written: put, get, delete, list and
+watch, reached through the node's runtime the way a bundle already publishes, asks and subscribes
+([ADR 0198](../../02-DECISIONS/0198-a-modules-long-running-code-is-launched-by-the-node-runtime-and-reaches-the-bus-through-it.md)).
+On NATS that is a key-value bucket. The questions are what a module declares, who creates the
+bucket, what the grants are, what the runtime's verbs are, and what may never be stored.
+
+## Why
+
+The mesh carries two kinds of module traffic and a third is missing.
+
+- **Events** land in the EVENTS stream: limits retention, seven days, ten thousand messages per
+  subject, a durable consumer per consuming module that replays what it missed. Never a secret
+  ([design 32](../../03-DESIGN/01-to-be/32-what-a-module-declares.md) §10).
+- **Requests** are core request/reply — tool calls, a bundle's `mesh/ask` — and are kept nowhere.
+
+Neither is *the current value of something*. Two cases from the first module that needs it, the
+operator's agent on a machine ([design 36](../../03-DESIGN/01-to-be/36-the-operators-agent-on-a-machine.md)):
+
+1. **An MCP server registered for every machine.** Registering emits an event every machine's copy
+   of the module consumes. A machine the module is assigned to *after* the registration has no
+   durable consumer yet — the consumer is created at assignment — so it never hears of it. Wanted
+   instead: one entry per server, for every machine or for one; every machine reads the whole current
+   set when it starts and watches for changes; unregistering is a delete; any machine can list it.
+2. **Which licence a machine is bound to** ([design 39](../../03-DESIGN/01-to-be/39-the-anthropic-licence-manager.md)).
+   As events, a machine that was off for a day replays every rotation since and asks for a token
+   after each. It needs only the latest binding and its generation. The token itself stays on
+   request/reply and is never stored.
+
+The design already expects this. [Design 25](../../03-DESIGN/01-to-be/25-the-bus-on-nats.md) §1:
+"conditions and observed state in key-value buckets that anything may watch".
+[Research 017](../017-a-mesh-that-heals-itself/01-the-intended-behaviour.md) wants a provisioner's
+"what I applied" and a rotation's step kept in one rather than in memory. Nothing implements it.
+
+## What exists, measured 2026-10-04
+
+| | fact | where |
+|---|---|---|
+| streams | five kinds of mesh stream: CONTROL (work queue), NODES and ASSIGNMENTS (last per subject), EVENTS (limits: 7 days, 10 000 per subject), one work queue per seat that accepts | the controller's broker streams |
+| the state relationship | [design 32](../../03-DESIGN/01-to-be/32-what-a-module-declares.md) §4 already names *state* — 1:1, last per subject — and says it is "declared: the mesh's own". Two streams use it, both written by the controller. No module can declare it | design 32, the controller |
+| key-value buckets | none, anywhere | all four code repositories |
+| the runtime's bus verbs | `mesh/publish`, `mesh/ask`, `mesh/subscribe`; delivery back to the bundle is `mesh/event` | the runtime's launcher |
+| the runtime's principal | one bus user per machine carries every assigned module; its grant is the union of theirs. That one module's code does not act as another is the runtime's to keep: it publishes under the module's own name by construction | the controller's grant composition, the runtime's bus |
+| what a bundle is issued | a membership per assignment, last per subject, read directly by the runtime: where it serves, where it emits, what it reaches | ADR 0160 |
+| who creates bus objects | the controller only — mesh streams on every raise, a seat's stream at registration, a module's consumer at assignment. No module reaches the JetStream API | design 25 §3 |
+
+### What a key-value bucket needs from a grant, against a real server
+
+Measured against nats-server 2.10 with the Go client the runtime already uses, a bucket created by
+an unrestricted user and used by two users holding only the subjects below (`B` is the bucket):
+
+| operation | subject published | writer | reader |
+|---|---|---|---|
+| bind to the bucket | `$JS.API.STREAM.INFO.KV_B` | yes | yes |
+| get | `$JS.API.DIRECT.GET.KV_B.>` | yes | yes |
+| put, delete | `$KV.B.>` | yes | **refused** |
+| list keys, watch | `$JS.API.CONSUMER.CREATE.KV_B.>` — an ordered, ephemeral consumer | yes | yes |
+| stop a watch cleanly | `$JS.API.CONSUMER.DELETE.KV_B.>` | yes | yes |
+| answers | its own inbox, which every principal already subscribes | — | — |
+
+Three things the measurement showed that reading the documentation would not have:
+
+1. **A refused put is not an error to the caller; it is a timeout.** The server reports the
+   permission violation asynchronously, on the connection, and the client waits out its deadline
+   for an acknowledgement that never comes. So a runtime that relies on the grant alone tells a
+   bundle "timed out" for "you may not write this" — it must refuse first, from what the module was
+   issued, with the reason.
+2. **A watch's current values include deletions.** A key deleted earlier arrives among the initial
+   values as a delete marker, before the end-of-current marker. A bundle asking "what is there now"
+   must not be handed those.
+3. **Without the consumer-delete grant, stopping a watch hangs** until its deadline, and the
+   ephemeral consumer lingers on the server until it times out by itself.
+
+### Whether the events shape is enough instead
+
+Honestly compared, because a new primitive is a cost:
+
+- **EVENTS cannot be made last-per-subject for some subjects.** Retention is per stream, and
+  JetStream refuses a second stream overlapping the first (verified and recorded in design 32 §3).
+  A state subject inside `mesh.mod.*.event.>` keeps EVENTS' seven days: a licence binding unchanged
+  for a week disappears.
+- **A separate last-per-subject stream per module** is possible — it is exactly what a key-value
+  bucket *is* on the server: a stream with one message per subject, a rollup for purge, and direct
+  reads. Building it by hand gives up the client's get, list, delete and watch, which are the
+  operations both cases need, and would be the mesh writing NATS's own key-value layer again.
+- **Consumers are the wrong reader.** A durable consumer per reading module is created at
+  assignment and replays from where it is; state wants "everything current, now, then changes",
+  which an ordered ephemeral consumer from the last value per subject gives and a durable does not.
+
+So key-value is not a convenience over events; it is the state relationship design 32 already
+names, opened to modules.
+
+## Questions, and what this effort proposes
+
+1. **What a manifest says.** `state` names the buckets a module owns, by local name — every
+   instance of the module may write them and read them. `reads` names another module's bucket as
+   `<module>.<name>`, read-only. Names only, never a bucket or subject (design 32 §1). A bucket's
+   options — how many past values it keeps, how long a value lives — are the owner's to declare,
+   the way a seat declares its own retention (design 32 §3).
+2. **Scope.** One bucket per module per name, mesh-wide. A key may carry a machine by the module's
+   own convention (`all.<server>`, `<machine>.<server>`). A bucket per machine was considered and
+   not proposed: "list every server for every machine" becomes a walk over buckets, and the grant
+   could only narrow writes, which nothing asked for — every instance of the owner already writes.
+3. **Who creates the bucket.** The controller, from the catalogue, on every raise — a bucket exists
+   from registration, like a seat's stream, so a reader can watch before the owner is assigned
+   anywhere. Never a module.
+4. **The runtime's verbs.** `mesh/state.get`, `mesh/state.put`, `mesh/state.delete`,
+   `mesh/state.keys`, `mesh/state.watch`, each naming the bucket as the module named it. A watch
+   is answered once the current values are on their way, then each change is delivered to the
+   bundle as a `mesh/state` request it answers — current values first (no deletions among them), an
+   end-of-current marker, then changes. A child that restarts watches again, as it subscribes
+   again. The runtime refuses, with the reason, a bucket the module was not issued, and a write to
+   one it only reads.
+5. **Secrets.** None in a bucket, sealed or not: a bucket is a stream (design 32 §10). Sealed values
+   are plain base64 and cannot be recognised, so the mechanical check is partial and said to be: the
+   runtime refuses a value carrying a field whose name says it is a credential (`password`,
+   `secret`, `token`, `authorization`, …), which catches the ordinary mistake and not a determined
+   one. For the first consumer this has a concrete consequence: an MCP server registered with an
+   authorisation header keeps that header out of the bucket.
+6. **History, lifetime, size.** One value per key unless the owner says more; no expiry unless it
+   says one; a value at most 256 KiB and a bucket at most 64 MiB, the mesh's caps rather than a
+   module's. **A bucket outlives its module's assignment** — what a module stored is data, and data
+   outlives what declared it ([ADR 0030](../../02-DECISIONS/0030-data-outlives-the-mesh-that-declared-it.md));
+   unassigning is not cleaning up. A bucket whose declaration is gone is reported, never removed.
+7. **Events or state.** State (above).
+
+## The work, once decided
+
+1. A decision record, then design 32 (*state* becomes a relationship a module declares) and design
+   25 (key-value buckets are part of the bus) amended.
+2. The controller: the manifest's two words and their registration check; buckets asserted on every
+   raise; the grants for owners' and readers' runtimes; the buckets issued in each membership.
+3. The runtime: the five verbs, the watch delivery, the refusals; tested against a real server.
+4. The SDK, TypeScript and Go: a small state surface over the verbs.
+5. Proved on a running mesh with one small module, then handed to the operator's agent, whose
+   registered servers move from events to a bucket.

02-DECISIONS/0201-a-module-keeps-its-current-state-in-key-value-buckets-it-declares-and-reaches-through-the-runtime.md

@@ -0,0 +1,106 @@
+---
+topic: what runs on it
+status: accepted
+date: 2026-10-04
+deciders: jochen
+reconstructed: false
+extends: 02-DECISIONS/0198-a-modules-long-running-code-is-launched-by-the-node-runtime-and-reaches-the-bus-through-it.md
+---
+
+# 201. A module keeps its current state in key-value buckets it declares, and reaches them through the runtime
+
+## Context
+
+A module's code reaches the bus through the node's runtime: it publishes events, subscribes to them
+and asks tools ([ADR 0198](0198-a-modules-long-running-code-is-launched-by-the-node-runtime-and-reaches-the-bus-through-it.md)).
+Events are kept for a week and replayed to a consumer that was away; requests are kept nowhere. What
+neither gives is **the current value of something**, seen by every machine, including one that joins
+after it was written. The first module to need it — the operator's agent on a machine — registers MCP
+servers for every machine as events, and a machine assigned later never hears of them; and it would
+replay a week of licence rotations where it needs only the binding that holds now. Research
+[024](../01-RESEARCH/024-state-a-module-keeps-on-the-bus/00-overview.md) measured the alternatives and
+the grants against a real server.
+
+[Design 32](../03-DESIGN/01-to-be/32-what-a-module-declares.md) §4 already names *state* as one of the
+mesh's relationships — 1:1, last per subject — and reserves it to the mesh's own declarations.
+[Design 25](../03-DESIGN/01-to-be/25-the-bus-on-nats.md) §1 expects key-value buckets on the bus.
+
+## Considered Options
+
+1. **Key-value buckets a module declares, created by the controller, reached through the runtime.**
+   Chosen.
+2. **State as events on EVENTS, read last-per-subject.** Rejected: retention is per stream and EVENTS
+   keeps seven days, so a value unchanged for a week disappears; a second stream over the same subjects
+   is refused by the server (design 32 §3). And events give no get, list or delete.
+3. **A last-per-subject stream per module, written by hand.** Rejected: it is what a key-value bucket
+   is on the server, without the client's get, list, delete and watch — the mesh writing NATS's
+   key-value layer again.
+4. **State in a module's own files or database, shared by asking a tool.** Rejected for state every
+   machine must see: a machine joining later has to know whom to ask and poll, and an owner that is
+   down answers nothing — the property the bus exists to remove.
+
+## Decision
+
+**1. A module declares its state by name.** `state` names the buckets it owns, by local name; every
+instance of the module may write and read them. `reads` names another module's bucket as
+`<module>.<name>`, read-only. A bucket's options are its owner's: how many past values a key keeps,
+and how long a value lives. A manifest names no bucket, stream or subject (design 32 §1).
+
+**2. One bucket per module per name, mesh-wide.** A key may name a machine by the module's own
+convention; the mesh does not scope buckets per machine.
+
+**3. The controller creates the buckets, from the catalogue, on every raise** — from registration,
+like a seat's stream, so a reader can watch a bucket whose owner is not yet assigned anywhere. A module
+never creates one. The runtime's grant on each bucket is the union of what its carried modules may do:
+an owner's instances write and read, a reader's read.
+
+**4. Each assignment is issued its buckets in its membership** ([ADR 0160](0160-the-mesh-issues-an-assignments-subjects-and-a-runtime-serves-what-it-is-issued.md)),
+by the name the module uses for each and whether it may write. The runtime serves `mesh/state.get`,
+`put`, `delete`, `keys` and `watch` on the bundle's channel from that list, and refuses — with the
+reason — a bucket the module was not issued and a write to one it only reads. A watch delivers the
+current values first, without deletions, then an end-of-current marker, then every change, each as a
+`mesh/state` request the bundle answers.
+
+**5. No secret is stored in a bucket, sealed or not.** A bucket is a stream, and design 32 §10 keeps
+every secret off streams. A value that needs a secret names it; the secret travels on request/reply.
+
+**6. The mesh caps size; a bucket outlives its module.** One value per key and no expiry unless the
+owner says otherwise; at most 256 KiB a value and 64 MiB a bucket. Unassigning a module leaves its
+buckets and what is in them ([ADR 0030](0030-data-outlives-the-mesh-that-declared-it.md)); a bucket
+whose declaration is gone from the catalogue is reported, never removed by the mesh.
+
+## Consequences
+
+- A machine that joins reads the current state at once, and every machine sees a change as it
+  happens, with no consumer created per reader and nothing replayed.
+- The runtime's channel has a sixth verb family, and the SDKs a small state surface over it — a
+  contract, which ADR 0039 admits: it changes when the verbs do, rarely, and every module should be
+  rebuilt when it does.
+- What got harder: the runtime must keep each module to its own buckets, because one principal per
+  machine carries all of them and the server enforces only the union. A write the server refuses
+  surfaces to a client as a timeout, not a refusal, so the runtime's own refusal is what a module sees.
+- The secrets rule is only partly mechanical. Sealed values cannot be recognised; the runtime refuses
+  a value with a field whose name says it is a credential, which catches the ordinary mistake and not a
+  determined one. For the operator's agent this means an MCP server's authorisation header stays out of
+  its bucket.
+- Buckets accumulate as modules come and go; that they are reported rather than removed is the price
+  of not deleting data.
+
+## How it is checked
+
+| Rule | Checked by |
+|---|---|
+| A manifest's state names are local, and a read names a bucket its owner declares | the catalogue's registration check, per manifest; a catalogue test that every `reads` whose owner is present names a bucket that owner declares |
+| Buckets exist for every declared state | the controller's raise asserts them idempotently; its test over a real bus |
+| Owners write, readers only read | the composer's test of the grants, per principal kind; the runtime's refusal test over a real bus |
+| A watch hands current values first, without deletions, then changes | the runtime's test over a real bus |
+| No credential-named field in a value | the runtime's refusal test |
+| Live | one module puts on one machine and another machine's watch sees it; a machine assigned afterwards reads it at start |
+
+## References
+
+- Research [024](../01-RESEARCH/024-state-a-module-keeps-on-the-bus/00-overview.md)
+- [Design 32](../03-DESIGN/01-to-be/32-what-a-module-declares.md) §4 and §10, [design 25](../03-DESIGN/01-to-be/25-the-bus-on-nats.md) §1 and §3
+- [ADR 0030](0030-data-outlives-the-mesh-that-declared-it.md), [ADR 0039](0039-what-the-sdk-holds-and-refuses.md),
+  [ADR 0160](0160-the-mesh-issues-an-assignments-subjects-and-a-runtime-serves-what-it-is-issued.md),
+  [ADR 0198](0198-a-modules-long-running-code-is-launched-by-the-node-runtime-and-reaches-the-bus-through-it.md)

02-DECISIONS/README.md

@@ -298,6 +298,7 @@ python3 00-META/checks/index.py            fail if stale
 - **0195** — [The mesh's tools are found by address, not announced whole](0195-the-meshs-tools-are-found-by-address-not-announced-whole.md)
 - **0197** — [Every tool announces itself on the bus, in the NATS services protocol](0197-every-tool-announces-itself-on-the-bus-in-the-nats-services-protocol.md)
 - **0198** — [A module's long-running code is launched by the node's runtime, and reaches the bus through it](0198-a-modules-long-running-code-is-launched-by-the-node-runtime-and-reaches-the-bus-through-it.md)
+- **0201** — [A module keeps its current state in key-value buckets it declares, and reaches them through the runtime](0201-a-module-keeps-its-current-state-in-key-value-buckets-it-declares-and-reaches-through-the-runtime.md)
 
 ### How it is built
 

03-DESIGN/01-to-be/25-the-bus-on-nats.md

@@ -7,8 +7,10 @@ code:
   - mesh-tools src/broker-amqp.ts (to be replaced)
   - mesh-catalog modules/nats (to be written)
   - mesh-sdk src (the protocol's NATS binding, step 3)
-updated: 2026-10-02
+  - mesh-tools node-tools/internal/bus (a module's state, ADR 0201)
+updated: 2026-10-04
 decisions:
+  - 02-DECISIONS/0201-a-module-keeps-its-current-state-in-key-value-buckets-it-declares-and-reaches-through-the-runtime.md
   - 02-DECISIONS/0167-a-membership-carries-what-its-module-receives-and-who-the-mesh-is.md
   - 02-DECISIONS/0160-the-mesh-issues-an-assignments-subjects-and-a-runtime-serves-what-it-is-issued.md
   - 02-DECISIONS/0157-a-build-says-what-it-does-on-the-bus-as-it-happens.md
@@ -48,6 +50,7 @@ mesh's own state lives, and where what a module may say is decided by what it de
 | **events** — a module says something happened | 1:many | delivered to every consumer that declared it; dead-lettered when it cannot be |
 | **tools** — a module or a person asks another's tool | request/reply | one answer, from one server, or a timeout |
 | **work to a role** — a module submits to a capability without knowing who provides it | job | exactly one holder does it; it queues while nobody does |
+| **state** — a module's current value of something, every machine reading it | key-value | the newest per key, kept until replaced or deleted; read whole by a machine that joins later |
 
 The last two rows are the ones worth dwelling on, because they are not messaging in the sense of
 carrying bytes from A to B. **A role is addressable**, so a caller names the capability and never
@@ -56,7 +59,8 @@ changing ([ADR 0126](../../02-DECISIONS/0126-a-module-declares-its-own-seats.md)
 property of the mesh's architecture that happens to be expressed in subjects.
 
 And more of the mesh lands here as it is built: conditions and observed state in key-value
-buckets that anything may watch, the server's own advisories becoming observations like any other
+buckets that anything may watch — the first of them a module's own declared state, *2026-10-04*
+([ADR 0201](../../02-DECISIONS/0201-a-module-keeps-its-current-state-in-key-value-buckets-it-declares-and-reaches-through-the-runtime.md)) — the server's own advisories becoming observations like any other
 ([research 017](../../01-RESEARCH/017-a-mesh-that-heals-itself/00-overview.md)), and a person's
 client speaking the bus directly rather than through a surface built over it (§7). None of that
 is a message being moved; all of it is the bus being the mesh's centre.
@@ -84,8 +88,16 @@ mesh.seat.<seat>.event.<verb>     a role's own event           (JetStream: EVENT
 mesh.seat.<seat>.tool.<verb>      a role's tool                (core request/reply)
 mesh.ask.<node>.<command>         the controller's command api (core request/reply)
 mesh.assignment.<node>.<module>   an assignment's membership   (JetStream: ASSIGNMENTS, last-per-subject)
+$KV.<module>_<name>.<key>          a module's state             (JetStream: a key-value bucket per declared name)
 ```
 
+**Added 2026-10-04** ([ADR 0201](../../02-DECISIONS/0201-a-module-keeps-its-current-state-in-key-value-buckets-it-declares-and-reaches-through-the-runtime.md)):
+the last row is outside `mesh.` on purpose. A key-value bucket is NATS's own construct and lives
+under NATS's own prefix, which is what lets the server's key-value layer — direct reads, rollups,
+delete markers, watches — do the work instead of the mesh writing it again. The bucket is named for
+the module and the local name joined by an underscore, which neither may contain, so two modules can
+never derive one bucket.
+
 **Revised 2026-10-01** ([ADR 0160](../../02-DECISIONS/0160-the-mesh-issues-an-assignments-subjects-and-a-runtime-serves-what-it-is-issued.md)): the rows above
 for a module's and a seat's tools are the shapes the controller *issues*, not rules a runtime carries.
 Every assignment is published a membership — what it serves and where, in which queue, its seat verbs,
@@ -155,6 +167,7 @@ Core NATS is at-most-once. Everything the mesh must not lose lives in a JetStrea
 | CONTROL | `mesh.control.>` except `alive` (a build's outcome moved to its seat, ADR 0121) | work queue, one consumer (the controller), explicit ack | the store-window guarantee ([ADR 0083](../../02-DECISIONS/0083-one-push-leaves-the-mesh-consistent.md)): the controller `nak`s with a delay while its store is away and the message is redelivered; nothing is dropped |
 | NODES | `mesh.node.>` | last per subject | one declaration per node, always the newest |
 | EVENTS | `mesh.mod.*.event.>` and `mesh.seat.*.event.>` | limits (age, size), durable consumer per subscribing module | a subscriber that was down catches up; after `max-deliver` attempts the advisory feeds `mesh.events.dead` (its own small stream). *2026-10-01:* a build's whole log is here too, as the build-machine seat's `log.<build id>` events ([ADR 0157](../../02-DECISIONS/0157-a-build-says-what-it-does-on-the-bus-as-it-happens.md)) — one subject per build, a week of retention, read back by `builds --log <id>` with a consumer that is gone when the reading is done |
+| `KV_<module>_<name>` | `$KV.<module>_<name>.>` | the newest value per key — as many past values as the owner declared — no age unless the owner declared one; a value at most 256 KiB, a bucket at most 64 MiB | a module's state (ADR 0201): one per name in a manifest's `state`, created from the catalogue on every raise, so it exists before its owner runs anywhere; kept when the module is unassigned, because what it holds is data |
 
 Tool calls and heartbeats stay on core NATS: a lost heartbeat is the next heartbeat; a lost tool
 call is a timeout the caller already handles.
@@ -234,6 +247,14 @@ expresses this exactly, per subject, and better than a vhost could:
   permissions for each consumed event's subject, its tool subjects, and that same inbox prefix.
   Nothing else. A module that tries to publish outside its emits is refused by the server, not by
   convention.
+- **A module's state** (ADR 0201), for whichever principal carries the module — today the machine's
+  runtime, whose grant is the union of its modules': binding to the bucket, reading a key directly,
+  and an ordered consumer for listing and watching, created and deleted on the bucket's own stream
+  and nothing else's; and, for the owner's instances only, publishing under the bucket's own
+  `$KV.<bucket>.>`. *Measured 2026-10-04 against a running server:* without the consumer-delete
+  grant a watch cannot be stopped cleanly, and a write the server refuses reaches the writer as a
+  timeout rather than a refusal — so the runtime refuses first, from the membership, and the grant
+  is the second line.
 - **The controller's user** owns `mesh.control.>`, `mesh.node.>` and the streams, and may submit work
   to the seats the mesh's own flows use — a build, for one (ADR 0121).
   **A host's user** may publish its own `mesh.control.<node>.>` and subscribe its own

03-DESIGN/01-to-be/32-what-a-module-declares.md

@@ -11,8 +11,10 @@ code:
   - mesh-host internal/apply/apply.go
   - mesh-tools src/main.ts
   - mesh-catalog modules/mesh-catalog
-updated: 2026-10-02
+  - mesh-tools node-tools/internal/runtime (a module's state, ADR 0201)
+updated: 2026-10-04
 decisions:
+  - 02-DECISIONS/0201-a-module-keeps-its-current-state-in-key-value-buckets-it-declares-and-reaches-through-the-runtime.md
   - 02-DECISIONS/0160-the-mesh-issues-an-assignments-subjects-and-a-runtime-serves-what-it-is-issued.md
   - 02-DECISIONS/0126-a-module-declares-its-own-seats.md
   - 02-DECISIONS/0131-everything-on-the-mesh-speaks-to-the-broker-seat.md
@@ -67,6 +69,8 @@ the catalogue, and the mesh would have hundreds of copies of a decision it made
 | `tools: status` | queue-group subscription on `mesh.mod.<module>.tool.status` |
 | seat `telegram-sender`, `accepts: send` | work-queue consumer on `mesh.seat.telegram-sender.accept.send` |
 | `uses: telegram-sender` | publish on that seat's `accept` subjects, and nothing else |
+| `state: servers` | a key-value bucket for the module, created by the controller; its instances write and read it |
+| `reads: billing.orders` | read and watch billing's `orders` bucket, and nothing else of it |
 
 **Wildcards, and they are the mesh's rather than a bus's.** *Added 2026-09-27, from
 [issue 127](../../04-ISSUES/127-a-module-event-derives-a-subject-nothing-publishes/00-report.md).* A
@@ -221,7 +225,7 @@ service" versus "one worker per machine".
 | credential | sealed, per consumer | none | none | none | none |
 | reply | — | none | none, or an event later | a report | awaited |
 | retention | — | age and size | work queue, explicit ack | **last per subject** | none |
-| declared | `provides`/`requires` | `emits`/`consumes` | seat `accepts` / `uses` | the mesh's own | `serves` |
+| declared | `provides`/`requires` | `emits`/`consumes` | seat `accepts` / `uses` | the mesh's own; a module's `state` / `reads` | `serves` |
 
 **Job** is the one [ADR 0041](../../02-DECISIONS/0041-events-are-a-relationship.md) had no room
 for. Its table has events at 1:many and provisions at 1:1; a module submitting work to a service
@@ -236,6 +240,31 @@ last-per-subject retention, and a node that has seen sequence *n* refuses *n−1
 That is the wire-level answer to
 [issue 107](../../04-ISSUES/107-a-declaration-carries-no-order/00-report.md).
 
+**A module declares state too.** *Added 2026-10-04,
+[ADR 0201](../../02-DECISIONS/0201-a-module-keeps-its-current-state-in-key-value-buckets-it-declares-and-reaches-through-the-runtime.md).*
+State was the mesh's alone, and modules had the same need with nowhere to put it: an MCP server
+registered for every machine, sent as an event, never reached a machine assigned afterwards — its
+consumer did not exist yet when the event passed — and a licence binding sent as events replays a
+week of rotations where only the latest matters. So a module names the state it **owns** with
+`state`, and another module's it **reads** with `reads: <module>.<name>`. Each is a key-value bucket
+the controller creates from the catalogue, mesh-wide, existing from registration so a reader can
+watch before the owner runs anywhere ([design 25](25-the-bus-on-nats.md) §3). Every instance of the
+owner writes; a reader reads and watches. A key may name a machine by the module's own convention;
+the mesh keeps one bucket per name, not one per machine, because "every server, for every machine"
+is then one list rather than a walk.
+
+What a module sees is what it named. Its assignment's membership lists its buckets by those names,
+with whether it may write, and the runtime answers `get`, `put`, `delete`, `keys` and `watch` for
+them on the bundle's channel — refusing, with the reason, a name it was not issued or a write to a
+bucket it only reads. A watch hands the current values first, then every change: a bundle that starts
+late, or starts again, has the whole of the state before it has any of the news.
+
+The owner says how many past values a key keeps and how long a value lives, as a seat says how long
+its backlog survives (§3); the mesh caps a value's size and a bucket's. **A bucket outlives its
+module's assignment** — what a module stored is data
+([ADR 0030](../../02-DECISIONS/0030-data-outlives-the-mesh-that-declared-it.md)) — and one whose
+declaration is gone is reported, never removed by the mesh.
+
 ## 5. Seats
 
 A module declares a seat with its protocol, and the mesh enforces one holder at its scope
@@ -454,6 +483,14 @@ sealing key leaks, that stream is an archive rather than a moment. So:
   existing discipline — *fetched from it, not carried* — applied to the one payload where carrying
   it is worst.
 
+**A key-value bucket is a stream, so the same holds for it.** *Added 2026-10-04,
+[ADR 0201](../../02-DECISIONS/0201-a-module-keeps-its-current-state-in-key-value-buckets-it-declares-and-reaches-through-the-runtime.md).*
+No secret is put in a module's state, sealed or not: state is exactly what a machine joining a year
+later reads in full. A value that needs a secret names it, and the secret travels on request/reply.
+Sealed values are plain text to anything inspecting them, so this is checked only partly — the
+runtime refuses a value carrying a field whose name says it is a credential, which catches the
+ordinary mistake and not a determined one.
+
 **The bootstrap, which is circular and has a precedent.** The vault makes every secret
 ([ADR 0113](../../02-DECISIONS/0113-the-vault-makes-every-secret.md)), including the bus's own
 passwords. The vault is a module, and a module needs a bus account, whose password the vault
@@ -523,3 +560,9 @@ billing existing under that name.
   on, and exactly those two are rebuilt.
 - **A stale declaration is refused.** A bed: replay sequence *n−1* after *n*, and the node refuses
   it rather than applying it.
+- **A module reaches only the state it declared.** The composer's test: an owner's runtime may write
+  its buckets, a reader's may only read, and nothing else is granted; the runtime's test over a real
+  bus: a name not issued and a reader's write are refused with the reason.
+- **State is current at once.** The runtime's test over a real bus: a watch hands the current values
+  without deletions, then an end-of-current marker, then changes. Live: a machine assigned after a put
+  reads it at start.