fix: one field-resolution law across aggregation hooks, source.where, removeMany, and find() spellings

Four fixes from a consumer conformance report, one root disease — two
field-resolution regimes where there must be one:

- The delete/update aggregation hooks fed the engine a partial entity
  view (type/service/data/metadata only), so a reserved-field groupBy
  (subtype, visibility, ...) resolved to a nonexistent group on the way
  down: counts drifted upward forever after deletes, and updates moving
  an entity between reserved-field groups double-counted. The hooks now
  pass the full-fidelity view via entityForAggFromRawRecord (every
  reserved field top-level, mirroring the add path); the update sites
  pass the full get() view instead of a hand-rolled subset.
- Aggregation source.where resolved fields only against the custom
  metadata bag, so where on a reserved field silently matched nothing.
  The matcher now resolves each filtered field through
  resolveEntityField — the same single source of truth groupBy uses.
- removeMany() with no usable selector (bare array passed positionally,
  empty params, ids: []) resolved successfully having deleted nothing.
  All three now throw; the two legacy tests that pinned the silent
  no-op as 'graceful' now pin the refusal.
- find() where keys accept both spellings: a metadata.-prefixed key
  falls back to its flattened spelling when the prefixed one is not
  indexed (metadata is flattened at index time). A literal nested custom
  key named metadata still wins when indexed as spelled.

Five regression pins in aggregate-reserved-fields.test.ts (4 of 5 vary
red on the unfixed code).

tests/integration/aggregate-reserved-fields.test.ts

@@ -0,0 +1,169 @@
+/**
+ * @module tests/integration/aggregate-reserved-fields
+ * @description One field-resolution law across the whole aggregation + query
+ * surface (SELF-AGGREGATE-DELETE-DRIFT). Laws:
+ * (1) aggregates grouped by a RESERVED field (subtype) decrement on delete —
+ *     the delete-side entity view carries every reserved field, so the
+ *     decrement finds its group (counts must never drift from ground truth);
+ * (2) same for update: moving an entity between reserved-field groups
+ *     decrements the old group and increments the new one (no double-count);
+ * (3) aggregation source.where on a reserved field (subtype) FILTERS instead
+ *     of silently matching nothing;
+ * (4) removeMany refuses empty/invalid selectors loudly (bare array, empty
+ *     object, ids: []) instead of resolving as a silent no-op;
+ * (5) find() accepts both where spellings: flattened (entry.title) and
+ *     storage-shaped (metadata.entry.title) resolve to the same rows.
+ */
+import { describe, it, expect, beforeEach, afterEach } from 'vitest'
+import { Brainy } from '../../src/brainy.js'
+import { NounType } from '../../src/types/graphTypes.js'
+
+const stubEmbedding = async (text: string): Promise<number[]> => {
+  const hash = text.split('').reduce((acc, char) => acc + char.charCodeAt(0), 0)
+  return new Array(384).fill(0).map((_, i) => Math.sin(hash + i))
+}
+
+describe('aggregation + query field-resolution law', () => {
+  let brain: Brainy
+
+  beforeEach(async () => {
+    brain = new Brainy({
+      requireSubtype: false,
+      storage: { type: 'memory' as const },
+      embeddingFunction: stubEmbedding
+    })
+    await brain.init()
+  })
+
+  afterEach(async () => {
+    await brain.close()
+  })
+
+  it('reserved-field groupBy decrements on delete (the drift bug)', async () => {
+    brain.defineAggregate({
+      name: 'by_subtype',
+      source: { type: NounType.Document },
+      groupBy: ['subtype'],
+      metrics: { count: { op: 'count' } }
+    })
+
+    const ids: string[] = []
+    for (let i = 0; i < 5; i++) {
+      ids.push(
+        await brain.add({
+          data: `doc-${i}`,
+          type: NounType.Document,
+          subtype: 'note',
+          metadata: { team: 'alpha' }
+        })
+      )
+    }
+    let groups = await brain.queryAggregate('by_subtype')
+    expect(groups).toHaveLength(1)
+    expect(groups[0].groupKey).toEqual({ subtype: 'note' })
+    expect(groups[0].metrics.count).toBe(5)
+
+    await brain.remove(ids[0])
+    await brain.flush()
+
+    groups = await brain.queryAggregate('by_subtype')
+    expect(groups[0].metrics.count).toBe(4)
+    const live = await brain.find({ type: NounType.Document, limit: 100 })
+    expect(groups[0].metrics.count).toBe(live.length)
+  })
+
+  it('reserved-field groupBy moves between groups on update (no double-count)', async () => {
+    brain.defineAggregate({
+      name: 'by_subtype',
+      source: { type: NounType.Document },
+      groupBy: ['subtype'],
+      metrics: { count: { op: 'count' } }
+    })
+    const id = await brain.add({
+      data: 'doc-move',
+      type: NounType.Document,
+      subtype: 'draft'
+    })
+    await brain.update({ id, subtype: 'published' })
+
+    const groups = await brain.queryAggregate('by_subtype')
+    const byKey = Object.fromEntries(
+      groups.map((g) => [String(g.groupKey.subtype), g.metrics.count])
+    )
+    expect(byKey['published']).toBe(1)
+    // The old group must be gone or zero — never still counting the entity.
+    expect(byKey['draft'] ?? 0).toBe(0)
+  })
+
+  it('source.where on a reserved field filters instead of matching nothing', async () => {
+    brain.defineAggregate({
+      name: 'notes_only',
+      source: { type: NounType.Document, where: { subtype: 'note' } },
+      groupBy: ['team'],
+      metrics: { count: { op: 'count' } }
+    })
+    await brain.add({
+      data: 'n1',
+      type: NounType.Document,
+      subtype: 'note',
+      metadata: { team: 'alpha' }
+    })
+    await brain.add({
+      data: 'd1',
+      type: NounType.Document,
+      subtype: 'draft',
+      metadata: { team: 'alpha' }
+    })
+
+    const groups = await brain.queryAggregate('notes_only')
+    expect(groups).toHaveLength(1)
+    expect(groups[0].metrics.count).toBe(1) // the note, never the draft
+  })
+
+  it('removeMany refuses empty/invalid selectors loudly', async () => {
+    const id = await brain.add({ data: 'keep-me', type: NounType.Document })
+
+    // Bare array passed positionally — the classic silent no-op.
+    await expect(
+      brain.removeMany([id] as unknown as Parameters<typeof brain.removeMany>[0])
+    ).rejects.toThrow(/bare array/)
+    // Empty selector object.
+    await expect(
+      brain.removeMany({} as Parameters<typeof brain.removeMany>[0])
+    ).rejects.toThrow(/requires a selector/)
+    // Explicit empty id list.
+    await expect(brain.removeMany({ ids: [] })).rejects.toThrow(/ids: \[\]/)
+
+    // Nothing was deleted by any of the refused calls.
+    expect(await brain.get(id)).toBeTruthy()
+  })
+
+  it('find() accepts both flattened and metadata.-prefixed where spellings', async () => {
+    await brain.add({
+      data: 'nested-doc',
+      type: NounType.Document,
+      metadata: { entry: { title: 'T1' }, classifier: { contextHints: { vfsPath: '/n/a.md' } } }
+    })
+    await brain.flush()
+
+    const flat = await brain.find({
+      type: NounType.Document,
+      where: { 'entry.title': 'T1' },
+      limit: 10
+    })
+    const prefixed = await brain.find({
+      type: NounType.Document,
+      where: { 'metadata.entry.title': 'T1' },
+      limit: 10
+    })
+    const deepPrefixed = await brain.find({
+      type: NounType.Document,
+      where: { 'metadata.classifier.contextHints.vfsPath': '/n/a.md' },
+      limit: 10
+    })
+    expect(flat).toHaveLength(1)
+    expect(prefixed).toHaveLength(1)
+    expect(prefixed[0].id).toBe(flat[0].id)
+    expect(deepPrefixed).toHaveLength(1)
+  })
+})