Store the person uuid the master issues, so renames keep our identity

The welcome now carries a personId; it lands in the instance_id setting
and rides on every hello and HTTP report from then on. The master keys
the person by that uuid, so changing instance_name moves our history to
the new name instead of starting a stranger. Read-only in Settings on
purpose — editing it by hand would detach this machine from its person.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

lib/master-link.ts

@@ -15,7 +15,7 @@
  * master you control, and prefer https so it cannot be redirected in transit.
  */
 
-import { getSetting, getInstruments, getRunnerHeartbeat, RUNNER_TIMEOUT_MS } from './db';
+import { getSetting, setSetting, getInstruments, getRunnerHeartbeat, RUNNER_TIMEOUT_MS } from './db';
 import { runTrade, startScheduler, stopScheduler, getSchedulerStatus } from './auto-trade';
 import { FIRMS, automationKey } from './automations';
 import { POINT_VALUES } from './trading-logic';
@@ -217,9 +217,14 @@ function connect() {
     s.ready = false;
 
     socket.addEventListener('open', () => {
+        // The stored uuid, once the master has issued one — it, not the name,
+        // is who this instance is, so renaming instance_name keeps the same
+        // person (and their accounting history) on the master.
+        const instanceId = getSetting('instance_id');
         socket.send(JSON.stringify({
             type: 'hello',
             instance,
+            id: instanceId || undefined,
             capabilities: collectCapabilities(),
         } satisfies InstanceMessage));
     });
@@ -235,6 +240,9 @@ function connect() {
         if (msg.type === 'welcome') {
             s.ready = true;
             s.attempt = 0;
+            if (msg.personId && msg.personId !== getSetting('instance_id')) {
+                setSetting('instance_id', msg.personId);
+            }
             console.log(`[master-link] connected to ${url} as "${instance}"`);
             return;
         }