refactor(guild-discovery): drop serviceEndpoint (no longer needed)

Pairs with Dialectic.Backend@5cf4302 which removes the backend-driven
broadcast that was the only consumer of serviceEndpoint. With agent-
driven recruitment broadcasts via fabric-send-message, the
service-to-service URL distinction goes away (agents use the regular
guild endpoint).

Removed:
  - GuildNode.serviceEndpoint column (TypeORM will drop on next sync)
  - GET /api/auth/me/guilds + /api/nodes response fields
  - NodeAdminService.setServiceEndpoint()
  - cli 'node set-service-endpoint' subcommand

Kept:
  - GuildNode.purpose (used by fabric-guild-list for intent-based
    channel discovery — still wanted)

src/auth/auth.service.ts

@@ -192,6 +192,7 @@ export class AuthService {
       name: n.name,
       endpoint: n.endpoint,
       status: n.status,
+      purpose: n.purpose ?? null,
     }));
 
     const guildAccessTokens = guilds.map((g) => ({

src/cli.ts

@@ -19,6 +19,7 @@ function printUsageAndExit(): never {
   console.error('  node dist/cli.js user clear-admin');
   console.error('  node dist/cli.js user show-admin');
   console.error('  node dist/cli.js node register --node-id <id> --name <name> --endpoint <url>');
+  console.error('  node dist/cli.js node set-purpose --node-id <id> --purpose <text>');
   console.error(
     '  node dist/cli.js config oidc [--issuer <url>] [--client-id <id>] [--client-secret <s>]\n' +
       '      [--callback-url <url>] [--post-login-redirect <url>] [--scopes "openid email profile"]\n' +
@@ -91,6 +92,17 @@ async function main() {
       return;
     }
 
+    if (subject === 'node' && action === 'set-purpose') {
+      const nodeId = getArg('--node-id');
+      const purpose = getArg('--purpose');
+      if (!nodeId || purpose === null) printUsageAndExit();
+
+      const nodes = app.get(NodeAdminService);
+      const result = await nodes.setPurpose(nodeId, purpose);
+      process.stdout.write(JSON.stringify({ ok: true, node: result }) + '\n');
+      return;
+    }
+
     if (subject === 'config' && action === 'oidc') {
       const oidc = app.get(OidcService);
       const patch: Record<string, unknown> = {};

src/entities/guild-node.entity.ts

@@ -20,6 +20,15 @@ export class GuildNode {
   @Column()
   endpoint!: string;
 
+  // Free-form description of this guild's purpose — what it's used for,
+  // who its agents/users serve. Surfaced to agents via /auth/me/guilds so
+  // the cross-guild/cross-channel announce-target picker can find the
+  // right guild by intent ("which guild is about debate broadcasts?")
+  // without anything hard-coded into agent workflows. admin-only write
+  // (cli: `node set-purpose --node-id X --purpose Y`).
+  @Column({ type: 'text', nullable: true })
+  purpose!: string | null;
+
   @Column({ type: 'varchar', length: 255, nullable: true })
   apiKeyHash!: string | null;
 

src/nodes/node-admin.service.ts

@@ -1,4 +1,4 @@
-import { ConflictException, Injectable } from '@nestjs/common';
+import { ConflictException, Injectable, NotFoundException } from '@nestjs/common';
 import { InjectRepository } from '@nestjs/typeorm';
 import { Repository } from 'typeorm';
 import bcrypt from 'bcryptjs';
@@ -55,5 +55,26 @@ export class NodeAdminService {
       apiKey: rawApiKey,
     };
   }
+
+  // Admin-only via cli (never HTTP): set the free-form purpose string on
+  // a guild node. Pass an empty string to clear it (null).
+  async setPurpose(nodeId: string, purpose: string) {
+    const node = await this.nodeRepo.findOne({ where: { nodeId } });
+    if (!node) throw new NotFoundException(`node ${nodeId} not found`);
+    const trimmed = String(purpose ?? '').trim();
+    node.purpose = trimmed === '' ? null : trimmed;
+    const saved = await this.nodeRepo.save(node);
+    await this.audit.write({
+      action: 'node.set_purpose',
+      targetType: 'node',
+      targetId: saved.nodeId,
+      detail: JSON.stringify({ purpose: saved.purpose, via: 'cli' }),
+    });
+    return {
+      nodeId: saved.nodeId,
+      name: saved.name,
+      purpose: saved.purpose,
+    };
+  }
 }
 

src/nodes/nodes.controller.ts

@@ -119,6 +119,7 @@ export class NodesController {
         name: n.name,
         endpoint: n.endpoint,
         status: n.status,
+        purpose: n.purpose ?? null,
         lastHeartbeatAt: n.lastHeartbeatAt,
         createdAt: n.createdAt,
         updatedAt: n.updatedAt,