test(dashboardapi): perf + uid-uniqueness for multi-child composition (#35)

Architectural note: existing composition is "1 dashboardAPI → root dashboard
+ 1 per child", not "1 dashboardAPI → 1 dashboard with N panels" as the PRD
assumed. Each generated dashboard is laid out at template-authoring time
(explicit gridPos per panel inside config/<softwareType>.json); the composer's
job is to substitute per-instance templating variables and assemble the
cross-link list. So the PRD's "non-overlapping gridPos for N panels" lands as:

- perf: 50 children compose in <500ms (PRD N-1).
- uid-uniqueness: stableUid keyed on softwareType:nodeId never collides.
- byte-identical idempotency (PRD N-2): two consecutive compositions match.
- root links: one link per registered child.

No production code change — this slice just adds the perf/uniqueness/idempotency
guarantees as explicit tests so we can't regress.

Closes #35

test/basic/slice35-graph-perf-and-uid-uniqueness.basic.test.js

@@ -0,0 +1,75 @@
+'use strict';
+
+const test = require('node:test');
+const assert = require('node:assert/strict');
+
+const DashboardApi = require('../../src/specificClass.js');
+
+function makeChild(i, softwareType = 'measurement', positionVsParent = 'downstream') {
+  return {
+    child: {
+      config: {
+        general: { id: `child-${i}`, name: `Child ${i}` },
+        functionality: { softwareType, positionVsParent },
+      },
+    },
+    softwareType,
+    position: positionVsParent,
+    registeredAt: Date.now(),
+  };
+}
+
+function makeRoot(children) {
+  const map = new Map();
+  for (const c of children) map.set(c.child.config.general.id, c);
+  return {
+    config: {
+      general: { id: 'root-1', name: 'Root' },
+      functionality: { softwareType: 'dashboardapi', positionVsParent: 'atequipment' },
+    },
+    childRegistrationUtils: { registeredChildren: map },
+  };
+}
+
+test('generateDashboardsForGraph composes 50 children in <500ms', () => {
+  const api = new DashboardApi({});
+  const children = Array.from({ length: 50 }, (_, i) => makeChild(i));
+  const root = makeRoot(children);
+
+  const t0 = process.hrtime.bigint();
+  const dashboards = api.generateDashboardsForGraph(root, { includeChildren: true });
+  const t1 = process.hrtime.bigint();
+
+  const durationMs = Number(t1 - t0) / 1e6;
+  assert.ok(durationMs < 500, `composition took ${durationMs.toFixed(1)}ms, expected <500ms`);
+  assert.ok(dashboards.length >= 1, 'should produce at least the root dashboard');
+});
+
+test('uids are unique across all generated dashboards (no collision risk)', () => {
+  const api = new DashboardApi({});
+  const children = Array.from({ length: 30 }, (_, i) => makeChild(i, 'measurement'));
+  const root = makeRoot(children);
+  const dashboards = api.generateDashboardsForGraph(root);
+  const uids = dashboards.map((d) => d.uid);
+  const unique = new Set(uids);
+  assert.equal(unique.size, uids.length, `expected ${uids.length} unique uids, got ${unique.size}`);
+});
+
+test('byte-identical composition under repeat (idempotency)', () => {
+  const api = new DashboardApi({});
+  const children = Array.from({ length: 5 }, (_, i) => makeChild(i));
+  const root = makeRoot(children);
+  const first = JSON.stringify(api.generateDashboardsForGraph(root).map((d) => d.dashboard));
+  const second = JSON.stringify(api.generateDashboardsForGraph(root).map((d) => d.dashboard));
+  assert.equal(first, second, 'two consecutive compositions should produce byte-identical JSON');
+});
+
+test('root dashboard links to every child dashboard', () => {
+  const api = new DashboardApi({});
+  const children = Array.from({ length: 4 }, (_, i) => makeChild(i));
+  const root = makeRoot(children);
+  const dashboards = api.generateDashboardsForGraph(root);
+  const rootDash = dashboards[0].dashboard;
+  assert.ok(Array.isArray(rootDash.links), 'root dashboard should have links array');
+  assert.equal(rootDash.links.length, 4, 'one link per registered child');
+});