feat(dashboardapi): manual regen via msg.topic == regenerate-dashboard (#41)

Adds an explicit topic for operators (and the dashboardAPI v2 manual escape
hatch from PRD F-12). On `regenerate-dashboard`, dashboardAPI iterates every
child source cached by prior `child.register` messages and re-emits Grafana
upsert messages — bypassing the diff-skip predicate from #36.

- src/specificClass.js: light state cache (recordChild / cachedChildSources).
- src/commands/handlers.js: refactor shared emit path; emitDashboardsFor()
  used by both child.register and regenerateDashboard; meta.trigger
  distinguishes the two for downstream filtering.
- src/commands/index.js: register 'regenerate-dashboard' (alias 'regen').
- CONTRACT.md: document the new topic.
- test/basic/slice41-manual-regen.basic.test.js: 5 cases covering cache
  semantics, no-op for empty cache, bypass-predicate, trigger stamp on both
  paths, registry exposure.

Closes #41

test/basic/slice41-manual-regen.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');
+const handlers = require('../../src/commands/handlers.js');
+
+function makeCtx(sends, nodeId = 'dApi-1') {
+  return {
+    node: { id: nodeId },
+    RED: { nodes: { getNode: () => null } },
+    send: (m) => sends.push(m),
+    logger: null,
+  };
+}
+
+function makeChildPayload(id, softwareType = 'measurement') {
+  return {
+    config: {
+      general: { id, name: id },
+      functionality: { softwareType, positionVsParent: 'downstream' },
+    },
+  };
+}
+
+test('recordChild caches child source by id; subsequent ones replace by id', () => {
+  const api = new DashboardApi({});
+  api.recordChild(makeChildPayload('a'));
+  api.recordChild(makeChildPayload('b'));
+  api.recordChild(makeChildPayload('a')); // replace
+  assert.equal(api.cachedChildSources().length, 2);
+});
+
+test('regenerate-dashboard with no cached children is a no-op (no msgs emitted)', () => {
+  const api = new DashboardApi({});
+  const sends = [];
+  handlers.regenerateDashboard(api, { topic: 'regenerate-dashboard', payload: {} }, makeCtx(sends));
+  assert.equal(sends.length, 0);
+});
+
+test('regenerate-dashboard re-emits for each cached child, bypassing diff', () => {
+  const api = new DashboardApi({});
+  // Pre-populate cache as if two children had registered.
+  api.recordChild(makeChildPayload('m-1'));
+  api.recordChild(makeChildPayload('m-2'));
+
+  // Set a diff that says nothing changed — registerChild would skip, but
+  // regenerateDashboard should ignore the predicate.
+  api.lastFlowsStartedDiff = { added: [], changed: [], removed: [], rewired: [] };
+
+  const sends = [];
+  handlers.regenerateDashboard(api, { topic: 'regenerate-dashboard', payload: {} }, makeCtx(sends));
+  // Each child yields at least one dashboard message (the root for the child's view).
+  assert.ok(sends.length >= 2, `expected ≥2 emitted msgs, got ${sends.length}`);
+  // Every emitted msg carries trigger: 'manual' in meta.
+  for (const m of sends) assert.equal(m.meta?.trigger, 'manual');
+});
+
+test('child.register stamps trigger: child.register in emitted msg meta', () => {
+  const api = new DashboardApi({});
+  api.lastFlowsStartedDiff = null; // cold-start → always regen
+  const sends = [];
+  handlers.registerChild(api, { topic: 'child.register', payload: makeChildPayload('m-3') }, makeCtx(sends));
+  assert.ok(sends.length >= 1);
+  for (const m of sends) assert.equal(m.meta?.trigger, 'child.register');
+});
+
+test('command registry exposes regenerate-dashboard with regen alias', () => {
+  const registry = require('../../src/commands/index.js');
+  const entry = registry.find((e) => e.topic === 'regenerate-dashboard');
+  assert.ok(entry, 'topic registered');
+  assert.deepEqual(entry.aliases, ['regen']);
+  assert.equal(typeof entry.handler, 'function');
+});