chore(8.0): delete vectorStore:mmap wiring — dead in the 8.0 provider world

The mmap-vector backend was a 2.x-era accelerator for the JS HNSW read path:
a native provider registered under 'vectorStore:mmap' supplied a single-file
mmap'd vector store, and JsHnswVectorIndex tried it before per-entity storage
reads with lazy write-back migration.

In the 8.0 provider world nothing registers that key — the native plugin's
3.0 line replaces the entire vector index under the 'vector' provider key
(vectors live inside its own index file), and the open-core path never had
an mmap provider. The wiring is unreachable; per the no-unwired-code rule
it goes away:

- src/hnsw/mmapVectorBackend.ts deleted (175 LOC)
- wireMmapVectorBackend() + its init call site removed from brainy.ts
- VectorStoreMmapProvider + VectorStoreMmapInstance contracts removed
  from plugin.ts
- JsHnswVectorIndex loses the vectorBackend field, setVectorBackend(),
  and the mmap-first branches in getVectorSafe/preloadVectors — the
  storage + UnifiedCache path is now the single read path
- tests/unit/hnsw/mmap-vector-backend.test.ts deleted

The 7.x line keeps the wiring and got the capacity-NaN bugfix as 7.31.3
(see the platform handoff mmap thread). EntityIdMapperProvider stays — the
connections codec and the id mapper still implement it.

1403/1403 tests, build clean.

tests/unit/hnsw/mmap-vector-backend.test.ts

@@ -1,242 +0,0 @@
-/**
- * @module hnsw/mmapVectorBackend.test
- * @description Unit tests for the `MmapVectorBackend` bridge — the brainy-side
- * wrapper that translates UUID-keyed vector reads/writes into stable int slot
- * ops against an `vectorStore:mmap` provider.
- *
- * Mocks the provider so the tests run without cortex installed (cortex is a
- * downstream consumer of brainy, not a dev dep). The real integration with
- * cortex's `NativeMmapVectorStore` is exercised when cortex 2.4.0 picks up
- * this brainy release and re-runs its cross-language parity suite.
- *
- * Coverage:
- * 1. Open-then-write-then-read round-trips for a single vector.
- * 2. Batch reads return an array aligned with the input UUIDs, with `null`
- *    entries for misses interleaved among hits — order preserved.
- * 3. Slot assignment is stable across multiple writes for the same UUID
- *    (no re-slot, no overwrite of an adjacent slot).
- * 4. Writes beyond the initial capacity grow the file (doubling) without
- *    losing the vectors already written.
- * 5. `readByUuid` returns `null` for both unknown UUIDs and UUIDs in the map
- *    whose slot has not yet been written.
- * 6. Open is idempotent — opening an already-existing file reuses it.
- */
-
-import { describe, it, expect, beforeEach, afterEach } from 'vitest'
-import { tmpdir } from 'node:os'
-import { mkdtemp, rm } from 'node:fs/promises'
-import { join } from 'node:path'
-import { MmapVectorBackend } from '../../../src/hnsw/mmapVectorBackend.js'
-import { EntityIdMapper } from '../../../src/utils/entityIdMapper.js'
-import type {
-  VectorStoreMmapInstance,
-  VectorStoreMmapProvider
-} from '../../../src/plugin.js'
-
-/**
- * Minimal storage stub for the EntityIdMapper. The mapper only touches storage
- * in init/flush; for these tests the mapper starts empty and is never flushed.
- */
-const stubStorage = {
-  getMetadata: async () => undefined,
-  saveMetadata: async () => {},
-  getNouns: async () => ({ totalCount: 0, items: [] })
-} as any
-
-/**
- * Pure in-memory mmap store. Mirrors cortex's NativeMmapVectorStore surface
- * just closely enough to exercise the backend's contract — no real mmap, no
- * file I/O, no f32 round-trip narrowing (the precision check is out of scope
- * here; that's covered by cortex's parity suite).
- */
-class MockMmapStore implements VectorStoreMmapInstance {
-  private readonly vectors: Array<number[] | undefined> = []
-  private highestWritten = -1
-  constructor(
-    public readonly dim: number,
-    private _capacity: number
-  ) {}
-  get count(): number {
-    return this.highestWritten + 1
-  }
-  get capacity(): number {
-    return this._capacity
-  }
-  writeVector(index: number, vector: number[]): void {
-    if (index >= this._capacity) {
-      throw new Error(`Slot ${index} >= capacity ${this._capacity}`)
-    }
-    if (vector.length !== this.dim) {
-      throw new Error(`Dim mismatch: expected ${this.dim}, got ${vector.length}`)
-    }
-    this.vectors[index] = [...vector]
-    if (index > this.highestWritten) this.highestWritten = index
-  }
-  writeVectorsBatch(startIndex: number, vectorsFlat: number[]): number {
-    if (vectorsFlat.length % this.dim !== 0) {
-      throw new Error('vectorsFlat length not a multiple of dim')
-    }
-    const n = vectorsFlat.length / this.dim
-    for (let i = 0; i < n; i++) {
-      this.writeVector(startIndex + i, vectorsFlat.slice(i * this.dim, (i + 1) * this.dim))
-    }
-    return n
-  }
-  readVector(index: number): number[] {
-    const v = this.vectors[index]
-    if (!v) throw new Error(`Slot ${index} not written`)
-    return [...v]
-  }
-  readVectorsBatch(indices: number[]): number[] {
-    const flat: number[] = []
-    for (const i of indices) {
-      const v = this.vectors[i]
-      if (!v) throw new Error(`Slot ${i} not written`)
-      for (let k = 0; k < this.dim; k++) flat.push(v[k])
-    }
-    return flat
-  }
-  prefetch(_indices: number[]): void {
-    /* no-op in mock */
-  }
-  resize(newCapacity: number): void {
-    if (newCapacity < this._capacity) throw new Error('Cannot shrink')
-    this._capacity = newCapacity
-  }
-  flush(): void {
-    /* no-op in mock */
-  }
-}
-
-/**
- * Mock provider — keeps one MockMmapStore per path. open() throws if the path
- * doesn't exist yet (matches cortex semantics: open() is for existing files
- * only); create() throws if it does (cortex doesn't, but the brainy backend
- * does open-first-then-create, so the throw path is exercised).
- */
-class MockMmapProvider implements VectorStoreMmapProvider {
-  private files = new Map<string, MockMmapStore>()
-  create(path: string, dim: number, capacity: number): VectorStoreMmapInstance {
-    if (this.files.has(path)) throw new Error(`File exists at ${path}`)
-    const store = new MockMmapStore(dim, capacity)
-    this.files.set(path, store)
-    return store
-  }
-  open(path: string): VectorStoreMmapInstance {
-    const store = this.files.get(path)
-    if (!store) throw new Error(`No file at ${path}`)
-    return store
-  }
-  openReadOnly(path: string): VectorStoreMmapInstance {
-    return this.open(path)
-  }
-  /** Test helper — peek at the underlying store. */
-  _peek(path: string): MockMmapStore | undefined {
-    return this.files.get(path)
-  }
-}
-
-describe('MmapVectorBackend (2.4.0 #2 — wraps vectorStore:mmap provider)', () => {
-  let dir: string
-  let path: string
-  let idMapper: EntityIdMapper
-  let provider: MockMmapProvider
-
-  beforeEach(async () => {
-    dir = await mkdtemp(join(tmpdir(), 'brainy-mmap-vec-'))
-    path = join(dir, 'vectors.bin')
-    idMapper = new EntityIdMapper({ storage: stubStorage })
-    await idMapper.init()
-    provider = new MockMmapProvider()
-  })
-
-  afterEach(async () => {
-    await rm(dir, { recursive: true, force: true }).catch(() => {})
-  })
-
-  it('open creates a new file when none exists, then round-trips a vector by UUID', async () => {
-    const backend = await MmapVectorBackend.open(provider, path, 4, 16, idMapper)
-    expect(backend.dim).toBe(4)
-
-    backend.writeByUuid('alpha', [1, 2, 3, 4])
-    expect(backend.readByUuid('alpha')).toEqual([1, 2, 3, 4])
-  })
-
-  it('reads return null for unknown UUIDs and for UUIDs in the map but not yet written', async () => {
-    const backend = await MmapVectorBackend.open(provider, path, 2, 8, idMapper)
-
-    // Unknown — never seen by the mapper.
-    expect(backend.readByUuid('ghost')).toBeNull()
-
-    // Known to the mapper but no slot ever written. We assign through the
-    // mapper directly so the backend itself has not touched the slot.
-    idMapper.getOrAssign('reserved')
-    expect(backend.readByUuid('reserved')).toBeNull()
-  })
-
-  it('batch read returns an array aligned to the input UUIDs (nulls preserved in place)', async () => {
-    const backend = await MmapVectorBackend.open(provider, path, 3, 16, idMapper)
-    backend.writeByUuid('a', [1, 1, 1])
-    backend.writeByUuid('b', [2, 2, 2])
-    backend.writeByUuid('c', [3, 3, 3])
-
-    // Interleave hits + a never-seen UUID + a duplicate hit. Order preserved.
-    const result = backend.readBatchByUuid(['b', 'missing', 'a', 'c', 'missing-too', 'b'])
-    expect(result).toEqual([
-      [2, 2, 2],
-      null,
-      [1, 1, 1],
-      [3, 3, 3],
-      null,
-      [2, 2, 2]
-    ])
-  })
-
-  it('writes for the same UUID land in the same slot (stable id, no re-slotting)', async () => {
-    const backend = await MmapVectorBackend.open(provider, path, 2, 8, idMapper)
-    backend.writeByUuid('persistent', [1, 1])
-    const slotAfterFirstWrite = idMapper.getInt('persistent')
-
-    backend.writeByUuid('persistent', [9, 9]) // overwrite the same slot
-    expect(idMapper.getInt('persistent')).toBe(slotAfterFirstWrite)
-    expect(backend.readByUuid('persistent')).toEqual([9, 9])
-
-    // Another UUID gets a different slot, and the first vector is undisturbed.
-    backend.writeByUuid('other', [5, 5])
-    expect(idMapper.getInt('other')).not.toBe(slotAfterFirstWrite)
-    expect(backend.readByUuid('persistent')).toEqual([9, 9])
-    expect(backend.readByUuid('other')).toEqual([5, 5])
-  })
-
-  it('grows the file (doubling) when a write lands beyond capacity, without losing prior data', async () => {
-    // Start at the smallest sane initial capacity (clamped to 16 by the backend).
-    const backend = await MmapVectorBackend.open(provider, path, 2, 1, idMapper)
-    const store = provider._peek(path)!
-    expect(store.capacity).toBe(16) // backend floor
-
-    // Write 20 vectors so capacity must double at least once (16 → 32).
-    const uuids: string[] = []
-    for (let i = 0; i < 20; i++) {
-      const uuid = `u-${i}`
-      uuids.push(uuid)
-      backend.writeByUuid(uuid, [i, i * 2])
-    }
-    expect(store.capacity).toBeGreaterThanOrEqual(32)
-
-    // Every vector survived the growth — no slot got overwritten or lost.
-    for (let i = 0; i < uuids.length; i++) {
-      expect(backend.readByUuid(uuids[i])).toEqual([i, i * 2])
-    }
-  })
-
-  it('opens an existing file idempotently when the second open hits the same path', async () => {
-    // First open creates.
-    const backend1 = await MmapVectorBackend.open(provider, path, 2, 8, idMapper)
-    backend1.writeByUuid('persisted', [7, 7])
-
-    // Second open against the same path. The provider's create() throws on
-    // collision; the backend's open-first behaviour means we reuse the file.
-    const backend2 = await MmapVectorBackend.open(provider, path, 2, 8, idMapper)
-    expect(backend2.readByUuid('persisted')).toEqual([7, 7])
-  })
-})