perf(8.0): negation/absence where-operators via roaring-bitmap difference

The JS metadata index served `ne`, `exists:false`, and `missing:true` by
materializing the ENTIRE id universe as an array of UUID strings, building a Set
of the excluded ids, and filtering — O(N) heap and two full passes on the
open-core path, on the most common shape (`deleted !== true`).

Compute the complement as a roaring-bitmap difference over the int-id universe
instead (`complementIds(excludeInts)` = universe \ exclude), converting only the
result back to UUIDs. The exclude set is small (the matching value), so this
avoids the full-corpus string materialization entirely. Behaviour is unchanged,
including the load-bearing soft-delete semantic that `field !== value` includes
entities with no such field. New focused tests pin `ne`/`exists:false`/
`missing:true`/`exists:true` result sets and that the complement reflects deletes.

Full gate green: unit 1520, integration 607.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

tests/unit/brainy/find-complement-operators.test.ts

@@ -0,0 +1,60 @@
+/**
+ * @module tests/unit/brainy/find-complement-operators
+ * @description The negation/absence where-operators (`ne`, `exists:false`,
+ * `missing:true`) are served as a roaring-bitmap difference over the int-id
+ * universe (rather than materializing the whole corpus as UUID strings to
+ * filter). These tests pin the exact result set — including the load-bearing
+ * soft-delete semantic: `field !== value` MUST include entities that have no
+ * such field at all.
+ */
+import { describe, it, expect, beforeEach } from 'vitest'
+import { Brainy } from '../../../src/brainy'
+import { NounType } from '../../../src/types/graphTypes'
+
+describe('find() complement operators (ne / exists:false / missing:true)', () => {
+  let brain: Brainy<any>
+  // Three entities WITH a `status` field, two WITHOUT it.
+  const ids: Record<string, string> = {}
+
+  beforeEach(async () => {
+    brain = new Brainy({ requireSubtype: false, storage: { type: 'memory' } })
+    await brain.init()
+    ids.active1 = await brain.add({ data: 'a1', type: NounType.Thing, metadata: { status: 'active' } })
+    ids.active2 = await brain.add({ data: 'a2', type: NounType.Thing, metadata: { status: 'active' } })
+    ids.closed = await brain.add({ data: 'c', type: NounType.Thing, metadata: { status: 'closed' } })
+    ids.noField1 = await brain.add({ data: 'n1', type: NounType.Thing, metadata: { other: 1 } })
+    ids.noField2 = await brain.add({ data: 'n2', type: NounType.Thing, metadata: { other: 2 } })
+  })
+
+  it('ne returns everything except the matching value — INCLUDING entities without the field', async () => {
+    const rows = await brain.find({ where: { status: { ne: 'active' } }, limit: 100 })
+    const got = new Set(rows.map((r) => r.id))
+    // closed (status≠active) + the two without a status field at all.
+    expect(got).toEqual(new Set([ids.closed, ids.noField1, ids.noField2]))
+    expect(got.has(ids.active1)).toBe(false)
+    expect(got.has(ids.active2)).toBe(false)
+  })
+
+  it('exists:false returns exactly the entities without the field', async () => {
+    const rows = await brain.find({ where: { status: { exists: false } }, limit: 100 })
+    expect(new Set(rows.map((r) => r.id))).toEqual(new Set([ids.noField1, ids.noField2]))
+  })
+
+  it('missing:true matches exists:false (entities without the field)', async () => {
+    const rows = await brain.find({ where: { status: { missing: true } }, limit: 100 })
+    expect(new Set(rows.map((r) => r.id))).toEqual(new Set([ids.noField1, ids.noField2]))
+  })
+
+  it('exists:true returns exactly the entities with the field', async () => {
+    const rows = await brain.find({ where: { status: { exists: true } }, limit: 100 })
+    expect(new Set(rows.map((r) => r.id))).toEqual(new Set([ids.active1, ids.active2, ids.closed]))
+  })
+
+  it('the complement reflects deletes (a removed entity drops out of ne / exists:false)', async () => {
+    await brain.remove(ids.noField1)
+    const ne = await brain.find({ where: { status: { ne: 'active' } }, limit: 100 })
+    expect(new Set(ne.map((r) => r.id))).toEqual(new Set([ids.closed, ids.noField2]))
+    const absent = await brain.find({ where: { status: { exists: false } }, limit: 100 })
+    expect(new Set(absent.map((r) => r.id))).toEqual(new Set([ids.noField2]))
+  })
+})