mosquitto: a consumer's grant is the topics it asks for, and its binding says the port

mqtt-topic served nothing: with two listens the mesh could not say which port a consumer dials, so a
consumer had to type 1883 into its config. It now serves the MQTT listener's port (the machine's,
once assigned) and the scheme, so `${bound:mqtt-topic:port}` fills.

The provisioner confined every consumer to `<as>/#`, which leaves nothing for the consumers the
broker exists for: Home Assistant discovers under homeassistant/# and tasmota/discovery/#, and
Node-RED's flows follow the devices' own topics. A consumer now contributes `topics` (MQTT topic
filters) to its mqtt-topic requirement and is granted exactly those; with none, its own subtree as
before. Settings merge into contributions, so an operator narrows a grant per assignment. The role
is brought to exactly the wanted ACLs (stale ones removed), `holds` checks the ACLs too, and an
invalid list is refused, never quietly narrowed. Only the role named for the consumer is touched:
a client carried from the predecessor's password file keeps its own.

modules/mosquitto/provisioner/index.ts

@@ -5,7 +5,14 @@
 //
 // The `mqtt-topic` interface: a consumer connects as `as` with the password the mesh minted, and
 // publishes and subscribes under `<as>/#`, isolated from every other consumer by a Dynamic Security
-// role scoped to exactly that subtree.
+// role scoped to exactly that subtree — unless it contributed `topics`, the MQTT topic filters its
+// work needs (a home-automation hub needs the devices' topics); then the role grants exactly those
+// (topics.ts). A list that is not valid topic filters is refused, and the consumer is not created
+// or changed until it is fixed.
+//
+// What a consumer is told (its binding): `at` — the broker's machine — and `port`, the machine port
+// of the MQTT listener (the manifest's `serves`); `as` is its login, and its copy of the password is
+// the pair credential the mesh delivers to it.
 //
 // **The login and password are the mesh's, not the provisioner's (ADR 0048).** The mesh derives the
 // login and hands it to both ends so they agree, and mints the password and delivers a copy to each.
@@ -15,6 +22,7 @@
 import { runProvisioner, type Provision } from "@novox/mesh-sdk/provisioner";
 import { emit } from "@novox/mesh-sdk/events";
 import { MosquittoClient } from "../client.js";
+import { topicFilters } from "../topics.js";
 
 const mosquitto = MosquittoClient.fromEnv();
 
@@ -29,13 +37,20 @@ async function announce(type: string, body: Record<string, string>): Promise<voi
 
 runProvisioner("mqtt-topic", {
   async create(p: Provision): Promise<void> {
-    // The topic subtree is scoped to the consumer's own login, so one cannot read another's topics.
-    const topicPrefix = p.as;
-    await mosquitto.createScopedClient(p.as, p.password, topicPrefix);
+    // By default the consumer's own subtree, so one cannot read another's topics; what it
+    // contributed as `topics` otherwise.
+    const granted = topicFilters(p.values, p.as);
+    if ("problem" in granted) {
+      // Thrown, so the harness logs it and retries: the consumer stays as it was (or absent) until
+      // its contribution is valid, rather than being given a grant it did not ask for.
+      throw new Error(`${p.as}: ${granted.problem}`);
+    }
+    await mosquitto.createScopedClient(p.as, p.password, granted.filters);
     await announce("topic.provisioned", {
       consumer: p.consumer ?? "",
       username: p.as,
-      topicPrefix,
+      topicPrefix: granted.own ? p.as : "",
+      topics: granted.filters.join(" "),
     });
   },
 
@@ -46,6 +61,9 @@ runProvisioner("mqtt-topic", {
   // Asked every minute by the harness: whether the backend still holds this consumer exactly as
   // the mesh gave it, so a login lost behind the provisioner's back is made again (novox/hq issue 120).
   async holds(p: Provision): Promise<boolean> {
-    return mosquitto.holdsClient(p.as, p.password);
+    const granted = topicFilters(p.values, p.as);
+    // An invalid list was never applied; create refuses it again, loudly, on every pass.
+    if ("problem" in granted) return false;
+    return mosquitto.holdsClient(p.as, p.password, granted.filters);
   },
 });