feat(tools): fabric-guild-list returns serviceEndpoint for announce targets

FabricSession.guilds type + fabric-guild-list response now carry the
new serviceEndpoint field (added to GuildNode in Fabric.Backend.Center).
The tool description teaches agents the distinction: 'endpoint' is the
client-facing URL (which they themselves use to call the guild from
plugin context), 'serviceEndpoint' is what to plumb into
dialectic_propose_topic's announce_guild_base_url so the dialectic
backend can dial it from inside the deployment.

Fixes bug #2 from the first e2e debate run: agent-supplied
'http://server.t3:7002' wasn't backend-reachable; agent now
supplies 'http://fabric-backend-guild:7002' via serviceEndpoint
and broadcasts actually land.

src/tools.ts

@@ -367,10 +367,15 @@ export function registerFabricTools(
     name: 'fabric-guild-list',
     description:
       'List guilds the calling agent is a member of. Returns ' +
-      '{nodeId, name, purpose, status} per row. `purpose` is a free-form ' +
-      "description of what each guild is for. Use this BEFORE " +
-      'fabric-channel-list when a workflow asks you to pick the ' +
-      'right guild by intent (no guild ids hardcoded into workflows).',
+      '{nodeId, name, purpose, status, serviceEndpoint} per row. ' +
+      "`purpose` is a free-form description of what each guild is for — " +
+      'pick the guild whose purpose matches your intent. ' +
+      '`serviceEndpoint` is the internal URL another backend service ' +
+      'uses to reach this guild (NOT the client-facing url): pass it as ' +
+      '`announce_guild_base_url` to dialectic_propose_topic when you ' +
+      'want the dialectic-backend to broadcast topic lifecycle to a ' +
+      "channel in this guild. Use this tool BEFORE fabric-channel-list " +
+      'when a workflow asks you to pick the right guild by intent.',
     parameters: {
       type: 'object',
       additionalProperties: false,
@@ -411,6 +416,13 @@ export function registerFabricTools(
           name: g.name,
           status: g.status,
           purpose: g.purpose ?? null,
+          // serviceEndpoint is what an in-deployment service uses to
+          // reach this guild — pass this into announce_guild_base_url
+          // on dialectic_propose_topic, NOT the client-facing endpoint.
+          // Null when the admin hasn't configured it (broadcasts will
+          // fail until set; ask hangman to run
+          // `cli node set-service-endpoint --node-id <id> --endpoint <url>`).
+          serviceEndpoint: g.serviceEndpoint ?? null,
         })),
       };
     },