runtime: RPC replies ride mesh.rpc; an invoke subcommand (ADR 0052)

Replies go through the RPC exchange keyed by the caller's reply-queue name, not
the default exchange — so a serving module's scoped account answers with write
on mesh.rpc alone, never the default exchange (which would let it publish into
any queue). 'mesh-tools invoke <module> <tool> [args]' is the caller's side, the
sibling of emit. Verified against a real broker: a scoped account serves its
tool and is refused another module's serve queue.

src/broker-amqp.ts

@@ -75,6 +75,10 @@ export async function connectAmqp(
   async function ensureReply(): Promise<string> {
     if (replyQueue) return replyQueue;
     const { queue } = await ch.assertQueue("", { exclusive: true });
+    // Replies come back through the RPC exchange keyed by this queue's own name, not the default
+    // exchange (novox/hq ADR 0052): a serving module's scoped account may write to mesh.rpc but not
+    // the default exchange, which would let it publish into any queue on the broker.
+    await ch.bindQueue(queue, RPC_EXCHANGE, queue);
     replyQueue = queue;
     await ch.consume(
       queue,
@@ -161,7 +165,9 @@ export async function connectAmqp(
             reply = { error: err instanceof Error ? err.message : String(err) };
           }
           if (msg.properties.replyTo) {
-            ch.sendToQueue(msg.properties.replyTo, Buffer.from(JSON.stringify(reply)), {
+            // Reply through the RPC exchange, keyed by the caller's reply-queue name, so a scoped
+            // account answers with write on mesh.rpc alone — never the default exchange (ADR 0052).
+            ch.publish(RPC_EXCHANGE, msg.properties.replyTo, Buffer.from(JSON.stringify(reply)), {
               correlationId: msg.properties.correlationId,
             });
           }

src/main.ts

@@ -17,6 +17,7 @@ import { readFileSync } from "node:fs";
 import { connectAmqp } from "./broker-amqp.js";
 import type { Credential } from "./broker-amqp.js";
 import { runTools } from "./runtime.js";
+import { invokeTool } from "@novox/mesh-sdk/tools";
 import { useBroker } from "@novox/mesh-sdk/messaging";
 import type { Broker } from "@novox/mesh-sdk/messaging";
 import { emit } from "@novox/mesh-sdk/events";
@@ -92,8 +93,33 @@ async function emitOnce(type: string, bodyJson: string): Promise<void> {
   await broker.close();
 }
 
+async function invokeOnce(module: string, tool: string, argsJson: string): Promise<void> {
+  let args: Record<string, unknown> = {};
+  if (argsJson) {
+    try {
+      args = JSON.parse(argsJson) as Record<string, unknown>;
+    } catch {
+      console.error(`mesh-tools invoke: args are not JSON: ${argsJson}`);
+      process.exit(1);
+    }
+  }
+  const broker = await connectBroker();
+  const result = await invokeTool(broker, module, tool, args);
+  process.stdout.write(JSON.stringify(result) + "\n");
+  await broker.close();
+}
+
 async function main(): Promise<void> {
   const [command, ...rest] = process.argv.slice(2);
+  if (command === "invoke") {
+    const [module, tool] = rest;
+    if (!module || !tool) {
+      console.error("mesh-tools invoke <module> <tool> [json-args] — a module and tool are required");
+      process.exit(1);
+    }
+    await invokeOnce(module, tool, rest[2] ?? "");
+    return;
+  }
   if (command === "emit") {
     const type = rest[0];
     if (!type) {