Describe the client on its own terms

Same cleanup: the comments explained each decision by contrast with what
came before instead of stating it. The certificate constraint stays — it is
a fact about the mesh's certificates, not a comparison.

src/broker-nats.ts

@@ -5,8 +5,8 @@
 // That is why a module built before any of this runs on the new runtime without a rebuild, and
 // why the sdk's own diff for the whole bus change is three comments.
 //
-// What changes is underneath: exchanges and per-tool queues become subjects, and durability
+// Underneath, everything is a subject and durability is JetStream (novox/hq design 25,
-// becomes JetStream (novox/hq design 25, design 29).
+// design 29).
 //
 //   mesh.mod.<module>.event.<type>   an event this module emits
 //   mesh.mod.<module>.tool.<tool>    a tool this module serves
@@ -23,8 +23,8 @@ import type { Broker, Envelope, EventHeaders } from "@novox/mesh-sdk/messaging";
 
 const sc = StringCodec();
 
-/** Requests wait this long for an answer before failing, matching the AMQP client's behaviour so
+/** Requests wait this long for an answer before failing. Unchanged from what modules already
- *  a module's timeout handling does not change with the transport. */
+ *  expect, so a module's timeout handling is not something the bus quietly redefines. */
 const REQUEST_TIMEOUT_MS = 30_000;
 
 export class PinMismatchError extends Error {}
@@ -42,8 +42,8 @@ export interface Credential {
 }
 
 /** Whether a connection failure is worth retrying, or is a fact about this configuration that
- *  retrying cannot change. Mirrors the AMQP client's judgement so the runtime's supervisor does
+ *  retrying cannot change. The runtime's supervisor asks this and does not need to know what it
- *  not have to know which transport it is on. */
+ *  is connected to. */
 export function fatalBrokerReason(err: unknown): string | null {
   if (err instanceof PinMismatchError) return "the bus's certificate does not match the pin";
   const e = err as { code?: string; message?: string };
@@ -85,8 +85,7 @@ export async function connectNats(
     name: `${cred.node ?? "?"}.${self}`,
     tls: cred.fingerprint ? await pinnedTls(cred.url, cred.fingerprint) : undefined,
     // Reconnect forever: the bus being restarted is an upgrade, not a reason for every module on
-    // the mesh to exit. The AMQP client's supervisor did this a level up; here the library does
+    // the mesh to exit. `close()` stays the only thing that ends the connection.
-    // it, and `close()` is still the only thing that ends the connection.
     maxReconnectAttempts: -1,
   });
   const js = conn.jetstream();
@@ -116,7 +115,7 @@ export async function connectNats(
      * Answer a question.
      *
      * A queue group, so several nodes may serve one tool and exactly one of them answers each
-     * call — the same property the AMQP client got from a shared durable queue.
+     * call.
      */
     async handle<Req, Res>(key: string, handler: (body: Req) => Promise<Res>): Promise<() => void> {
       const sub = conn.subscribe(toolSubject(key, self), { queue: `serve.${self}` });
@@ -144,17 +143,15 @@ export async function connectNats(
      *
      * Published into JetStream and awaited, so a publish the bus never accepted fails the emit
      * rather than vanishing — at-least-once starts at the emitter, not only the consumer
-     * (ADR 0042), which is what the AMQP client's confirm channel was for.
+     * (ADR 0042).
      *
      * `msgID` is the event's own id, so a redelivery after a crash between publishing and
      * acknowledging is de-duplicated by the server inside its window rather than seen twice.
      */
     async publish<T>(env: Envelope<T>): Promise<void> {
-      // **The body is the payload and the metadata rides as headers**, exactly as on AMQP
+      // **The body is the payload and the metadata rides as headers** (ADR 0042). That shape
-      // (ADR 0042). NATS has headers of its own, so the envelope's shape on the wire is
+      // is what the conformance suite pins: an implementation that nested the whole envelope in
-      // preserved rather than re-encoded — which matters because that shape is what the
+      // the body would pass every one of its own tests and agree with nobody.
-      // conformance suite pins, and an implementation that nested the whole envelope in the
-      // body would pass every one of its own tests and agree with nobody.
       const meta = (env.headers ?? {}) as Record<string, string>;
       const h = natsHeaders();
       for (const [k, v] of Object.entries(meta)) {
@@ -288,13 +285,12 @@ function normalizeFingerprint(fingerprint: string): string {
  * A certificate authority is not consulted: the mesh issued this and knows its fingerprint,
  * which is stronger than trusting whoever a machine's trust store happens to contain.
  *
- * **One behaviour differs from the AMQP client, and it is a constraint on the mesh rather than a
+ * **A constraint on the mesh, not a detail of this file.** Pinning the exact certificate makes
- * detail of this file.** That client passed `checkServerIdentity: () => undefined`, because
+ * hostname verification redundant in principle, but the NATS client exposes no hook to replace
- * pinning the exact certificate makes hostname verification redundant. The NATS client exposes no
+ * it — its TLS options are file paths and PEM strings, with no verify callback. So the
- * such hook — its TLS options are file paths and PEM strings, with no verify callback — so the
+ * certificate the mesh issues the bus **must carry a subject-alternative name matching the
- * certificate the mesh issues the bus **must carry a subject-alternative name matching the address
+ * address nodes dial it by**. The fingerprint check below still happens and is still the real
- * nodes dial it by**. The fingerprint check below still happens and is still the real guarantee;
+ * guarantee; what cannot be switched off is the check *beside* it.
- * what cannot be switched off is the check *beside* it.
  */
 async function pinnedTls(rawUrl: string, fingerprint: string): Promise<{ ca: string }> {
   const url = new URL(rawUrl.includes("://") ? rawUrl : `nats://${rawUrl}`);
@@ -320,9 +316,9 @@ async function pinnedTls(rawUrl: string, fingerprint: string): Promise<{ ca: str
   return { ca: pem };
 }
 
-/** The mesh's topic matching, unchanged from AMQP: `*` is one token, `#` the rest. Kept because
+/** The mesh's topic matching: `*` is one token, `#` the rest. This is the module's vocabulary —
- *  it is the module's vocabulary — a module's `consumes` pattern reads the same as it always did,
+ *  a module's `consumes` pattern is matched here, and the subject it becomes is the mesh's
- *  and the subject it becomes is the mesh's business. */
+ *  business, not the module's. */
 export function topicMatches(pattern: string, key: string): boolean {
   return matchFrom(pattern.split("."), 0, key.split("."), 0);
 }