fix(fleet): heartbeat consistency — MOSAIC_HOME path + configurable interval (#595)

Co-authored-by: Jason Woltje <jason@diversecanvas.com>
Co-committed-by: Jason Woltje <jason@diversecanvas.com>

packages/mosaic/src/commands/fleet.spec.ts

@@ -851,6 +851,23 @@ describe('fleet ps — heartbeat parsing', () => {
     expect(hb.health).toBe('unknown');
     expect(hb.ts).toBeNull();
   });
+
+  it('honors MOSAIC_HEARTBEAT_INTERVAL for the freshness threshold', () => {
+    const prev = process.env.MOSAIC_HEARTBEAT_INTERVAL;
+    try {
+      // A 60s-old beat is STALE at the default 15s interval (3x15 = 45s)...
+      const ts = new Date(NOW - 60_000).toISOString();
+      const content = `ts=${ts}\npid=1\nstatus=ok\n`;
+      delete process.env.MOSAIC_HEARTBEAT_INTERVAL;
+      expect(parseHeartbeat(content, NOW).health).toBe('stale');
+      // ...but HEALTHY when the operator widened the interval to 30s (3x30 = 90s).
+      process.env.MOSAIC_HEARTBEAT_INTERVAL = '30';
+      expect(parseHeartbeat(content, NOW).health).toBe('healthy');
+    } finally {
+      if (prev === undefined) delete process.env.MOSAIC_HEARTBEAT_INTERVAL;
+      else process.env.MOSAIC_HEARTBEAT_INTERVAL = prev;
+    }
+  });
 });
 
 describe('fleet ps — systemd show parsing', () => {