feat(dashboardapi): diff-skip regen via flows:started predicate (#36)

Subscribes to Node-RED's flows:started runtime event, caches the {diff}
payload on the dashboardAPI source, and short-circuits the child.register
handler when none of {dashboardAPI id, child id, grandchild ids} appears in
diff.added/changed/removed/rewired. Predicate verified by S1 spike (#32).

- src/nodeClass.js: _attachLifecycleHook subscribes, _attachCloseHandler
  cleans up. No-op when RED.events isn't available (unit-test friendly).
- src/specificClass.js: subtreeChanged() predicate + subtreeIdsFor() helper.
- src/commands/handlers.js: registerChild consults predicate before composing;
  logs {event:'regen-skipped', outcome:'no-diff'} when skipping.
- test/basic/slice36-diff-predicate.basic.test.js: 8 cases — null/empty diff,
  affected/unaffected ids, tab-id over-triggering avoidance, grandchild
  inclusion, no-grandchild case.

Cold start (no cached diff yet) always regenerates — safe default. Edge case
documented in #32: when a brand-new child is wired to a registered parent,
the new child's id is in diff.added but not yet in registeredChildren when
flows:started fires. Mitigation (b) per spike findings: one-deploy race
accepted for R&D — next deploy picks up the new registration.

Closes #36

test/basic/slice36-diff-predicate.basic.test.js

@@ -0,0 +1,73 @@
+'use strict';
+
+const test = require('node:test');
+const assert = require('node:assert/strict');
+
+const DashboardApi = require('../../src/specificClass.js');
+
+test('subtreeChanged: null diff → always regen (safe default for cold start)', () => {
+  const api = new DashboardApi({});
+  assert.equal(api.subtreeChanged(null, new Set(['a', 'b'])), true);
+  assert.equal(api.subtreeChanged(undefined, new Set(['a', 'b'])), true);
+});
+
+test('subtreeChanged: empty diff arrays → no regen needed', () => {
+  const api = new DashboardApi({});
+  const diff = { added: [], changed: [], removed: [], rewired: [], linked: [], flowChanged: [] };
+  assert.equal(api.subtreeChanged(diff, new Set(['a', 'b'])), false);
+});
+
+test('subtreeChanged: id in added → regen', () => {
+  const api = new DashboardApi({});
+  const diff = { added: ['x', 'b'], changed: [], removed: [], rewired: [] };
+  assert.equal(api.subtreeChanged(diff, new Set(['a', 'b'])), true);
+});
+
+test('subtreeChanged: id in changed → regen', () => {
+  const api = new DashboardApi({});
+  const diff = { added: [], changed: ['a'], removed: [], rewired: [] };
+  assert.equal(api.subtreeChanged(diff, new Set(['a', 'b'])), true);
+});
+
+test('subtreeChanged: only unrelated ids → no regen', () => {
+  const api = new DashboardApi({});
+  const diff = { added: ['z'], changed: ['y'], removed: ['x'], rewired: ['w'] };
+  assert.equal(api.subtreeChanged(diff, new Set(['a', 'b'])), false);
+});
+
+test('subtreeChanged: tab id in diff but not in subtree → no regen', () => {
+  // Tab id over-triggering avoidance: when an unrelated tab changes, its
+  // tab id lands in changed/added but should not affect this dashboardAPI.
+  const api = new DashboardApi({});
+  const diff = { added: [], changed: ['unrelated_tab'], removed: [], rewired: [] };
+  assert.equal(api.subtreeChanged(diff, new Set(['dashboardApiId', 'childA'])), false);
+});
+
+test('subtreeIdsFor: includes dashboardAPI id + child id + grandchild ids', () => {
+  const api = new DashboardApi({});
+  const grandchild = {
+    config: { general: { id: 'gc-1' }, functionality: { softwareType: 'measurement' } },
+  };
+  const grandchildEntry = { child: grandchild, position: 'downstream', softwareType: 'measurement' };
+  const child = {
+    config: { general: { id: 'child-1' }, functionality: { softwareType: 'pumpingStation' } },
+    childRegistrationUtils: {
+      registeredChildren: new Map([['gc-1', grandchildEntry]]),
+    },
+  };
+  const ids = api.subtreeIdsFor('dApi-1', child);
+  assert.equal(ids.has('dApi-1'), true);
+  assert.equal(ids.has('child-1'), true);
+  assert.equal(ids.has('gc-1'), true);
+  assert.equal(ids.size, 3);
+});
+
+test('subtreeIdsFor: handles child with no grandchildren', () => {
+  const api = new DashboardApi({});
+  const child = {
+    config: { general: { id: 'child-1' }, functionality: { softwareType: 'measurement' } },
+  };
+  const ids = api.subtreeIdsFor('dApi-1', child);
+  assert.equal(ids.size, 2);
+  assert.ok(ids.has('dApi-1') && ids.has('child-1'));
+});