// The tool runtime's broker client, on NATS.
//
// **The sdk's contract does not change** (novox/hq ADR 0106, ADR 0039): a module is written
// against `request`, `handle`, `publish`, `subscribe`, `close`, and the runtime implements them.
// 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.
//
// Underneath, everything is a subject and durability is JetStream (novox/hq design 25,
// design 29).
//
//   mesh.mod.<module>.event.<type>   an event this module emits
//   mesh.mod.<module>.tool.<tool>    a tool this module serves
//   mesh.seat.<seat>.accept.<verb>   work submitted to a role
//
// The module never writes one of those: it names its events and tools locally and the mesh
// derives the subject (design 29 §1), so reorganising the subject space leaves every module
// correct.

import { AsyncLocalStorage } from "node:async_hooks";
import { createHash } from "node:crypto";
import net from "node:net";
import tls from "node:tls";
import { connect as natsConnect, headers as natsHeaders, StringCodec, type JsMsg, type Subscription, type TlsOptions } from "nats";
import type { Broker, Envelope, EventHeaders } from "@novox/mesh-sdk/messaging";

const sc = StringCodec();

/** Requests wait this long for an answer before failing. Unchanged from what modules already
 *  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 {}

/** A broker credential as the mesh delivers it (novox/hq ADR 0120): the bus's address, the
 *  fingerprint of the certificate it must present, and the node and module the account is scoped
 *  to — the runtime derives its subjects from those rather than being told them. */
export interface Credential {
  url: string;
  fingerprint?: string;
  node?: string;
  module?: string;
  user?: string;
  password?: string;
  /** The seats this module claims, with the verbs each promises (novox/hq ADR 0159). The runtime
   *  serves each claimed seat's verbs with its tools of the same name; the bus admits only the
   *  holder's subscription, so claiming and not holding costs a refused subscription and nothing else. */
  claims?: { seat: string; scope?: string; serves?: string[] }[];
}

/**
 * What the mesh issued this assignment (novox/hq ADR 0160): where its tools are served, in which
 * queue, the verbs of the seats it holds, where its events land, what it may reach. Read from the
 * ASSIGNMENTS stream at `mesh.assignment.<node>.<module>` — the one subject a runtime derives for
 * itself — and followed live. Absent for a mesh older than the membership, and then the runtime
 * serves the shape it always derived, and says so.
 */
export interface Membership {
  node: string;
  module: string;
  /** Addresses a tool is answered on; `{tool}` stands for the tool's name. */
  serves: { subject: string; queue?: string }[];
  seats?: { seat: string; verb: string; subject: string }[];
  emits: string;
  reaches?: Record<string, string[]>;
  tools: string;
}

/** What a tool call answers: the module's own result, and which machine answered it
 *  (novox/hq ADR 0159) — a module on several machines is otherwise an answer from nowhere. */
export interface Answered<Res> {
  result: Res;
  node?: string;
}

/** The bus as the runtime sees it: the sdk's contract, and the few things only the runtime needs —
 *  an answer that says which machine gave it, serving a subject that is not a module's own tool
 *  (a seat's verb), and following the memberships of the modules it serves beside its own. */
export interface RuntimeBroker extends Broker {
  /** Call a tool by key, or — when `on` names a subject the mesh listed for it (ADR 0160) — there. */
  ask<Req, Res>(key: string, body: Req, on?: string): Promise<Answered<Res>>;
  handleSubject<Req, Res>(subject: string, handler: (body: Req) => Promise<Res>): Promise<() => void>;
  /**
   * Serve another module's tools from this connection: read its membership on this machine and
   * follow it, so `handle("<module>.<tool>")` is served where the mesh issued that module (novox/hq
   * ADR 0175: one runtime per node, every assigned module's tools). The account must be allowed
   * to read that membership and to subscribe its subjects — the node's is; a module's own is not,
   * and is refused by the bus, not here.
   */
  follow(module: string): Promise<void>;
  /** What the mesh issued this assignment — this module's when none is named — or undefined when
   *  nothing has been issued yet. */
  membership(module?: string): Membership | undefined;
  /** Called when the mesh issues a new membership to any module this connection follows; the
   *  runtime re-serves on it. The membership says which module it is for. */
  onMembership(handler: (m: Membership) => void): void;
  /** The modules whose memberships this connection follows: its own and every one `follow` added. */
  serving(): string[];
  /** The module this connection is: what its credential named, and what a bare key serves as. */
  readonly module: string;
  /** Where a served module's tool is answered right now (ADR 0197: what it serves, it announces). */
  servedOn?(module: string, tool: string): { subject: string; queue?: string }[];
  /** Answer a subject in a format of its own, not a tool's reply envelope — the NATS services
   *  protocol's discovery (novox/hq ADR 0197). An undefined answer is no reply. */
  raw?(subject: string, answer: (subject: string, data: Uint8Array) => Uint8Array | undefined): () => void;
  /** The machine this connection serves on, when its credential names one. */
  readonly node?: string;
}

/**
 * Which module's tool is at work on this connection, when one is (novox/hq ADR 0175). One runtime
 * carries many modules' tools, and an event a tool emits must land on the emitting *module's*
 * subject, not the runtime's — so the runtime runs each tool inside this store, and `publish`
 * reads the module from it. Outside a tool the connection's own module stands.
 */
export const atWork = new AsyncLocalStorage<{ module: string }>();

const ASSIGNMENTS_STREAM = "ASSIGNMENTS";

/** The one address a runtime derives for itself (ADR 0160). */
export function membershipSubject(node: string, module: string): string {
  return `mesh.assignment.${node}.${module}`;
}

/** Whether a connection failure is worth retrying, or is a fact about this configuration that
 *  retrying cannot change. The runtime's supervisor asks this and does not need to know what it
 *  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 };
  const message = typeof e?.message === "string" ? e.message : String(err);
  if (e?.code === "ERR_INVALID_URL" || /invalid url/i.test(message)) {
    return "the bus address is not a usable URL";
  }
  if (/authorization violation|user authentication expired|permissions violation/i.test(message)) {
    return "the bus refused this account";
  }
  return null;
}

/**
 * Connect to the mesh bus and return a Broker.
 *
 * **A module's subjects come from its credential, not from its calls.** `node` and `module` name
 * the account the mesh issued, and every subject this client publishes or subscribes is derived
 * from them — so a module cannot name another's namespace even by mistake, and what it emits
 * matches what the mesh authorised (ADR 0074's identity rule).
 */
export async function connectNats(
  target: string | Credential,
  opts: { module?: string } = {},
): Promise<RuntimeBroker> {
  const cred: Credential = typeof target === "string" ? { url: target } : target;
  const self = cred.module ?? opts.module;
  if (!self) {
    throw new Error(
      "a broker credential with no module: the runtime derives its subjects from the account " +
        "the mesh issued, and cannot guess which module it is",
    );
  }

  const conn = await natsConnect({
    servers: cred.url,
    user: cred.user,
    pass: cred.password,
    name: `${cred.node ?? "?"}.${self}`,
    tls: cred.fingerprint ? await pinnedTls(cred.url, cred.fingerprint) : undefined,
    // Its own inbox, not a random one: every user's inbox is private to it (design 25 §4), and the
    // grant names `_INBOX.<user>.>` — a reply space the client invented would be refused, and with
    // it every pull for the next message and every answer to a tool call.
    inboxPrefix: cred.user ? `_INBOX.${cred.user}` : undefined,
    // Reconnect forever: the bus being restarted is an upgrade, not a reason for every module on
    // the mesh to exit. `close()` stays the only thing that ends the connection.
    maxReconnectAttempts: -1,
  });
  const js = conn.jetstream();

  const subs: Subscription[] = [];
  // Every registration, and the one reader that dispatches to them. A module has one durable
  // consumer; the loop belongs to the connection rather than to a subscription.
  const listeners: { pattern: string; handler: (env: Envelope<unknown>) => Promise<void> }[] = [];
  let reading: Awaited<ReturnType<Awaited<ReturnType<typeof js.consumers.get>>["consume"]>> | undefined;
  let closed = false;

  const node = cred.node;

  // The memberships, one per module this connection serves, each read once and followed. A
  // module's own runtime follows one, its own; the node's runtime follows one per assigned module
  // (novox/hq ADR 0175) — the same subject shape, the same stream, read as many times as there are
  // modules, and nothing on the bus learns a new shape for it. A direct get is one request on the
  // stream's API, which is the whole of what an account may ask JetStream for a subject it is
  // granted; a 404 is a mesh that has not issued one, which is a fact to say and not an error to
  // retry.
  const issued = new Map<string, Membership | undefined>();
  const issuedHandlers: ((m: Membership) => void)[] = [];
  const follow = async (module: string): Promise<void> => {
    if (!node || issued.has(module)) return;
    issued.set(module, undefined);
    const subjectOfTheirs = membershipSubject(node, module);
    try {
      // The subject-addressed form of a direct get — the stream, then the subject, nothing in
      // the body — because that is the one address the mesh grants this account on the
      // stream's API; the body form asks the stream's root, which it may not.
      const got = await conn.request(`$JS.API.DIRECT.GET.${ASSIGNMENTS_STREAM}.${subjectOfTheirs}`,
        new Uint8Array(0), { timeout: 5_000 });
      const status = got.headers?.code ?? 0;
      if (status === 0 && got.data.length > 0) {
        issued.set(module, JSON.parse(sc.decode(got.data)) as Membership);
      }
    } catch {
      // Not readable here: an older mesh, a stream not yet asserted, or no grant. Said below.
    }
    if (!issued.get(module)) {
      console.log(`[mesh-tools] no membership issued for ${module} on ${node} yet; serving the derived shape until one arrives`);
    }
    try {
      const live = conn.subscribe(subjectOfTheirs);
      subs.push(live);
      void (async () => {
        for await (const msg of live) {
          try {
            const m = JSON.parse(sc.decode(msg.data)) as Membership;
            issued.set(module, m);
            console.log(`[mesh-tools] ${module} on ${node} was issued a new membership; re-serving on it`);
            for (const h of issuedHandlers) h(m);
          } catch (err) {
            console.log(`[mesh-tools] a membership arrived that is not one: ${err}`);
          }
        }
      })();
    } catch {
      // A subscription this account may not make is a mesh older than the membership.
    }
  };
  await follow(self);

  /** The subjects a tool of a served module is served on: from that module's membership when
   *  issued, derived otherwise (the shape the mesh issues on day one, so the two agree). */
  const servedOn = (module: string, tool: string): { subject: string; queue?: string }[] => {
    const m = issued.get(module);
    if (m) {
      const out = m.serves.map((s) => ({ subject: s.subject.replace("{tool}", tool), queue: s.queue }));
      // The verb that lists what this module serves is answered on the mesh's plain address for it
      // whatever the placement — one answer suffices, so a queue — and on this machine's beside it.
      if (tool === "tools" && m.tools && !out.some((s) => s.subject === m.tools)) {
        out.unshift({ subject: m.tools, queue: `serve.${module}` });
      }
      return out;
    }
    const base = `mesh.mod.${module}.tool.${tool}`;
    const out: { subject: string; queue?: string }[] = [{ subject: base, queue: `serve.${module}` }];
    if (node) out.push({ subject: `${base}.${node}` });
    return out;
  };

  /** Where a call by key goes: a subject this connection's own membership says it reaches, when it
   *  says one — the machine's when named — else the derived shape. */
  const reachedAt = (key: string): string => {
    const [name, wanted] = key.split("@", 2);
    const reach = issued.get(self)?.reaches?.[name];
    if (reach && reach.length > 0) {
      if (wanted) {
        const at = reach.find((s) => s.endsWith(`.${wanted}`));
        if (at) return at;
      } else {
        return reach[0];
      }
    }
    return toolSubject(key, self);
  };

  /** Answer one subject with one handler, and say which machine answered (novox/hq ADR 0159). */
  const answerOn = <Req, Res>(
    subject: string,
    queue: string | undefined,
    handler: (body: Req) => Promise<Res>,
  ): (() => void) => {
    const sub = conn.subscribe(subject, queue ? { queue } : {});
    subs.push(sub);
    void (async () => {
      // **A refused subscription is said, never fatal** (novox/hq 04-ISSUES/218, as 217 for the
      // announcements). The grants are the mesh's word on what this account may answer; a subject
      // they leave out — a seat claimed here and held elsewhere — costs that subject, never the
      // module's other tools, its handlers and its provisioning. Unhandled, the refusal ended the
      // process and a module's runtime crash-looped on 2026-10-04.
      try {
        for await (const msg of sub) {
          let reply: { result?: Res; error?: string; node?: string };
          try {
            reply = { result: await handler(JSON.parse(sc.decode(msg.data)) as Req) };
          } catch (err) {
            // The caller is told, rather than left to time out: a handler that threw is a
            // different failure from a tool nobody serves, and only one of them is worth retrying.
            reply = { error: err instanceof Error ? err.message : String(err) };
          }
          if (node) reply.node = node;
          msg.respond(sc.encode(JSON.stringify(reply)));
        }
      } catch (err) {
        console.log(`[mesh-tools] the bus refused ${subject}: ${err instanceof Error ? err.message : String(err)}; ` +
          "not served here, and the rest serves on");
      }
    })();
    return () => sub.unsubscribe();
  };

  /**
   * Ask one question and await one answer, with the machine that gave it.
   *
   * Core NATS request/reply, not JetStream: a tool call must never be persisted (design 25 §3),
   * and a lost one is a timeout the caller already handles. The reply travels on the inbox the
   * request carries, which the responder may answer because its account has `allow_responses`
   * — one reply to a message it actually received, and nothing wider.
   */
  const ask = async <Req, Res>(key: string, body: Req, on?: string): Promise<Answered<Res>> => {
    const msg = await conn.request(on ?? reachedAt(key), sc.encode(JSON.stringify(body)), {
      timeout: REQUEST_TIMEOUT_MS,
    });
    const reply = JSON.parse(sc.decode(msg.data)) as { result?: Res; error?: string; node?: string };
    if (reply.error) throw new Error(reply.error);
    return { result: reply.result as Res, node: reply.node };
  };

  return {
    async request<Req, Res>(key: string, body: Req): Promise<Res> {
      return (await ask<Req, Res>(key, body)).result;
    },

    ask,

    /**
     * Answer a question, two ways (novox/hq ADR 0159): on the module's subject in a queue group,
     * so several machines may serve one tool and exactly one of them answers each call; and on the
     * same subject with this machine as its last token, so a caller that names the machine reaches
     * this instance and no other. A runtime that does not know its machine serves only the first,
     * which is how it always behaved.
     */
    async handle<Req, Res>(key: string, handler: (body: Req) => Promise<Res>): Promise<() => void> {
      // A seat's verb named outright is served on the seat's subject as given, for a holder that
      // knows its role without a membership; everything else is a served module's own tool, served
      // where the mesh issued that module (ADR 0160). A key naming a module this connection does
      // not follow is not served here at all: a module serves its own tools, and the node's
      // runtime those of the modules it was given (ADR 0175) — never a stranger's.
      if (key.startsWith("seat:")) {
        const stop = answerOn(toolSubject(key, self), undefined, handler);
        return () => stop();
      }
      const dot = key.indexOf(".");
      const module = dot < 0 ? self : key.slice(0, dot);
      if (!issued.has(module) && module !== self) {
        throw new Error(
          `${self} cannot serve ${key}: a module serves its own tools, and a runtime those of the ` +
            "modules it follows",
        );
      }
      const tool = dot < 0 ? key : key.slice(dot + 1);
      let stops = servedOn(module, tool).map((s) => answerOn(s.subject, s.queue, handler));
      // When that module's new membership arrives, serve where it now says and stop serving where
      // it no longer does.
      issuedHandlers.push((m) => {
        if (m.module !== module) return;
        stops.forEach((stop) => stop());
        stops = servedOn(module, tool).map((s) => answerOn(s.subject, s.queue, handler));
      });
      return () => stops.forEach((stop) => stop());
    },

    module: self,
    node,
    servedOn,
    raw(subject: string, answer: (subject: string, data: Uint8Array) => Uint8Array | undefined): () => void {
      const sub = conn.subscribe(subject);
      subs.push(sub);
      void (async () => {
        // **A refusal here is said, never fatal** (novox/hq 04-ISSUES/217). This serves discovery —
        // what the runtime says about itself — not the work; a bus that refuses it costs the mesh
        // seeing this runtime, not the runtime's tools and handlers. Unhandled, the refusal ended the
        // process and every per-module container crash-looped on 2026-10-03.
        try {
          for await (const msg of sub) {
            const body = answer(msg.subject, msg.data);
            if (body) msg.respond(body);
          }
        } catch (err) {
          console.log(`[mesh-tools] the bus refused ${subject}: ${err instanceof Error ? err.message : String(err)}; ` +
            "discovery will not see this runtime there, and it serves on");
        }
      })();
      return () => sub.unsubscribe();
    },
    follow,
    serving: () => [...issued.keys()],
    membership: (module?: string) => issued.get(module ?? self),
    onMembership: (handler: (m: Membership) => void) => {
      issuedHandlers.push(handler);
    },

    async handleSubject<Req, Res>(subject: string, handler: (body: Req) => Promise<Res>): Promise<() => void> {
      return answerOn(subject, undefined, handler);
    },

    /**
     * Emit an event.
     *
     * 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).
     *
     * `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** (ADR 0042). That shape
      // is what the conformance suite pins: 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)) {
        if (v != null) h.set(k, String(v));
      }
      if (!meta["content-type"]) h.set("content-type", "application/json");
      if (env.node) h.set("x-node", env.node);

      // The emitting module's subject: the tool at work's when a served module's tool emits from
      // the node's runtime (ADR 0175), this connection's own otherwise.
      await js.publish(eventSubject(env.key, atWork.getStore()?.module ?? self), sc.encode(JSON.stringify(env.body)), {
        headers: h,
        // De-duplicated by the server inside its window, so a redelivery after a crash between
        // publishing and acknowledging is not seen twice. Only the emitter can make this id.
        msgID: meta["x-event-id"],
      });
    },

    /**
     * React to events.
     *
     * The durable consumer is the **mesh's** to create, from what this module declared it
     * consumes (design 29 §3) — this binds to it and never creates one. A runtime that created
     * its own would be a module deciding its own delivery semantics, and its account cannot
     * reach the JetStream API to do it anyway.
     *
     * **One consumer, one loop, however many patterns a module registers.** A module has exactly one
     * durable consumer, so two loops reading it would each take half the messages — and a loop that
     * received one its own pattern does not match acknowledges it, which is the right answer for a
     * filter wider than anything registered and silent loss when it is another handler's. Every
     * registration is therefore dispatched from one reader, and a message is acknowledged once every
     * handler it is for has taken it.
     */
    async subscribe<T>(
      pattern: string,
      handler: (env: Envelope<T>) => Promise<void>,
    ): Promise<() => void> {
      const listener = { pattern, handler: handler as (env: Envelope<unknown>) => Promise<void> };
      listeners.push(listener);
      if (!reading) {
        const durable = `${cred.node ?? "?"}_${self}`;
        const consumer = await js.consumers.get("EVENTS", durable);
        const messages = await consumer.consume();
        reading = messages;
        void (async () => {
          for await (const msg of messages) {
            await deliver(msg, listeners);
          }
        })();
      }
      return () => {
        const at = listeners.indexOf(listener);
        if (at >= 0) listeners.splice(at, 1);
        if (listeners.length === 0 && reading) {
          void reading.close();
          reading = undefined;
        }
      };
    },

    async close(): Promise<void> {
      if (closed) return;
      closed = true;
      for (const sub of subs) sub.unsubscribe();
      // Drain rather than close: an in-flight reply is finished instead of dropped, which for a
      // tool call is the difference between an answer and an unexplained timeout at the caller.
      await conn.drain();
    },
  };
}

/**
 * Deliver one event to every handler it is for, acknowledging only once each has taken it.
 *
 * Several registrations share one durable consumer, so matching happens here rather than by having
 * each registration read the stream: two readers of one consumer would split it between them, and a
 * message that reached the wrong one would be acknowledged as not-for-me and lost.
 */
async function deliver(
  msg: JsMsg,
  listeners: { pattern: string; handler: (env: Envelope<unknown>) => Promise<void> }[],
): Promise<void> {
  let env: Envelope<unknown>;
  try {
    env = toEnvelope<unknown>(msg);
  } catch {
    // Unparseable: terminate it. Redelivering a message no version of this code can read is
    // an infinite loop, and what the mesh keeps of a message given up on (DEAD_LETTERS,
    // novox/hq issue 330) is for handlers that fail, not for bytes that were never an envelope.
    msg.term();
    return;
  }
  const forThis = listeners.filter((l) => topicMatches(l.pattern, env.key));
  if (forThis.length === 0) {
    // The consumer's filters are the mesh's, derived from what the module declared it
    // consumes, and may be wider than anything it registered a handler for. Acknowledge it, or it
    // would be redelivered until it expired.
    msg.ack();
    return;
  }
  try {
    for (const l of forThis) await l.handler(env);
    msg.ack();
  } catch {
    // Negative-acknowledge with a delay, so a handler failing on a transient cause gets another
    // attempt, and one failing permanently exhausts max-deliver rather than spinning: the consumer
    // gives the event up, and the mesh keeps it in DEAD_LETTERS until a person delivers it
    // again or drops it (novox/hq issue 330). Delivered again, it arrives under
    // `mesh.again.<consumer>.…`, and keyFromSubject reads the same key from it. The consumer's
    // limits are the mesh's; this only says "not done".
    msg.nak(5_000);
  }
}

/** Rebuild the envelope a module sees, from the subject, the headers and the payload — the
 *  mirror of publish, and the reason both live beside each other. */
function toEnvelope<T>(msg: JsMsg): Envelope<T> {
  const headers: Record<string, string> = {};
  if (msg.headers) {
    for (const k of msg.headers.keys()) headers[k] = msg.headers.get(k);
  }
  return {
    // The event's own key, recovered from the subject: `mesh.mod.<module>.event.<key>`. The
    // module never sees the subject, only the key it declared.
    key: keyFromSubject(msg.subject),
    node: headers["x-node"] ?? "",
    body: JSON.parse(sc.decode(msg.data)) as T,
    headers: headers as EventHeaders,
  };
}

/** The event key a module sees: the emitter and the event, which is exactly how its manifest names
 *  what it consumes (novox/hq design 29 §1, 04-ISSUES/127).
 *
 *  **One vocabulary for the declaration and the handler.** This returned the event name alone, so a
 *  manifest declaring `consumes: builder.built` produced a handler pattern that could never match
 *  the key it was compared against — and a module consuming the same event from two emitters could
 *  not tell them apart except by reading a header. The subject already carries the emitter; naming it
 *  here makes a mismatch between manifest and code a typo rather than a category error. */
function keyFromSubject(subject: string): string {
  const marker = ".event.";
  const at = subject.indexOf(marker);
  if (at < 0) return subject;
  const event = subject.slice(at + marker.length);
  // `mesh.mod.<emitter>.event.…` — the emitter is the token before the marker.
  const before = subject.slice(0, at).split(".");
  const emitter = before[before.length - 1];
  return emitter ? `${emitter}.${event}` : event;
}

/** A module's own event subject. Derived, never taken from the caller: the module names its
 *  event and the mesh decides where it lands (design 29 §1). */
function eventSubject(type: string, self: string): string {
  return `mesh.mod.${self}.event.${type}`;
}

/** A tool's subject. A bare name is this module's own tool; `<module>.<tool>` addresses
 *  another's, which is how a request reaches a module that is not this one; `seat:<seat>.<verb>`
 *  addresses a role's tool, answered by whoever holds the seat (novox/hq ADR 0132) — with
 *  `seat:<seat>.<verb>@<node>` for a node-scoped seat, whose tool carries the machine (design 33 §4). */
function toolSubject(key: string, self: string): string {
  if (key.startsWith("seat:")) {
    const rest = key.slice("seat:".length);
    const dot = rest.indexOf(".");
    if (dot < 0) throw new Error(`"${key}" names a seat and no verb: seat:<seat>.<verb>`);
    const seat = rest.slice(0, dot);
    const [verb, node] = rest.slice(dot + 1).split("@", 2);
    return node ? `mesh.seat.${seat}.tool.${verb}.${node}` : `mesh.seat.${seat}.tool.${verb}`;
  }
  // `<module>.<tool>@<node>` names the machine (novox/hq ADR 0159): the same subject with the
  // machine as its last token, which is what that instance serves beside the queue.
  const [name, node] = key.split("@", 2);
  const dot = name.indexOf(".");
  const base = dot < 0
    ? `mesh.mod.${self}.tool.${name}`
    : `mesh.mod.${name.slice(0, dot)}.tool.${name.slice(dot + 1)}`;
  return node ? `${base}.${node}` : base;
}

/** A seat's verb, as its holder serves it: flat for a mesh seat, carrying the machine for a
 *  node-scoped one (design 33 §4) — the same shape the mesh grants. */
export function seatToolSubject(seat: string, verb: string, scope: string | undefined, node: string | undefined): string {
  const base = `mesh.seat.${seat}.tool.${verb}`;
  return scope === "node" && node ? `${base}.${node}` : base;
}

function normalizeFingerprint(fingerprint: string): string {
  return fingerprint.replace(/^sha256:/i, "").replace(/:/g, "").toLowerCase();
}

/**
 * Dial once to see the certificate, and refuse unless it is exactly the one the mesh pinned.
 * 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.
 *
 * **The pin is the only check.** What comes back is handed to the client as its TLS options, and
 * the client's transport spreads them into Node's own `tls.connect` — so the pinned certificate
 * is the one authority the handshake accepts, and the hostname check beside it is replaced with
 * one that always passes. Pinning the exact certificate makes verifying its name redundant, and
 * the bus's certificate names the seat (`mesh-broker`), not the address a machine happens to
 * dial it by: every module on the mesh met "does not match certificate's altnames" the first time
 * it reached the handshake (2026-09-28).
 */
async function pinnedTls(rawUrl: string, fingerprint: string): Promise<TlsOptions> {
  const url = new URL(rawUrl.includes("://") ? rawUrl : `nats://${rawUrl}`);
  const port = url.port ? Number(url.port) : 4222;
  // **The bus speaks first, in the clear.** A NATS server sends its INFO line before TLS begins,
  // and only then expects the client to start the handshake; a raw TLS connect to that port reads
  // the INFO line as a TLS record and fails with "wrong version number" — which is what every
  // module met the first time it dialled the bus being built (2026-09-28). So: connect, wait for
  // INFO, then start TLS on the same socket, and read the certificate the server presents.
  const certificate = await new Promise<tls.DetailedPeerCertificate>((resolve, reject) => {
    const plain = net.connect({ host: url.hostname, port }, () => {});
    let seenInfo = false;
    let buffered = "";
    plain.on("error", reject);
    plain.on("data", (chunk: Buffer) => {
      if (seenInfo) return;
      buffered += chunk.toString("utf8");
      if (!buffered.includes("\r\n")) return;
      seenInfo = true;
      plain.removeAllListeners("data");
      const secure = tls.connect(
        { socket: plain, rejectUnauthorized: false, servername: url.hostname },
        () => {
          const peer = secure.getPeerCertificate(true);
          secure.end();
          resolve(peer);
        },
      );
      secure.on("error", reject);
    });
  });
  const seen = createHash("sha256").update(certificate.raw).digest("hex");
  if (seen !== normalizeFingerprint(fingerprint)) {
    throw new PinMismatchError(
      `the bus at ${url.hostname}:${port} presented ${seen}, not the pinned ${normalizeFingerprint(fingerprint)}`,
    );
  }
  const pem = `-----BEGIN CERTIFICATE-----\n${certificate.raw.toString("base64").replace(/(.{64})/g, "$1\n")}\n-----END CERTIFICATE-----\n`;
  // Node's option, not the client's: the transport passes the whole object on. `undefined` from
  // checkServerIdentity is "the name is fine"; the pin above already decided the rest.
  return { ca: pem, checkServerIdentity: () => undefined } as TlsOptions;
}

/** The mesh's topic matching: `*` is one token, `#` the rest. This is the module's vocabulary —
 *  a module's `consumes` pattern is matched here, and the subject it becomes is the mesh's
 *  business, not the module's. */
export function topicMatches(pattern: string, key: string): boolean {
  return matchFrom(pattern.split("."), 0, key.split("."), 0);
}

function matchFrom(p: string[], pi: number, k: string[], ki: number): boolean {
  if (pi === p.length) return ki === k.length;
  // `**` is the mesh's wildcard for the rest of a name; `#` is the old bus's, accepted so a pattern
  // written either way behaves the same while both buses ship (novox/hq design 29 §1).
  if (p[pi] === "#" || p[pi] === "**") {
    for (let skip = ki; skip <= k.length; skip++) {
      if (matchFrom(p, pi + 1, k, skip)) return true;
    }
    return false;
  }
  if (ki === k.length) return false;
  if (p[pi] !== "*" && p[pi] !== k[ki]) return false;
  return matchFrom(p, pi + 1, k, ki + 1);
}