test(8.0): asOf() error-path spot-checks + find() triple-composition correctness + scale-bench harness

- db-mvcc proof 9: asOf(-1|1.5|future) → RangeError, bad snapshot path → descriptive
  error, use-after-release() throws on get/find/related (Y.15 error-path coverage).
- find-triple-composition: proves vector ∩ metadata ∩ graph returns exactly the
  entity satisfying all three and excludes those failing any one (decoys, wrong category).
- find-composition-scale.js: parameterized latency harness (vector/metadata/graph/
  vector+metadata/triple) with non-empty asserts; precomputed vectors, no model load.

tests/integration/db-mvcc.test.ts

@@ -1155,4 +1155,33 @@ describe('8.0 Db API — generational MVCC', () => {
     await second.release()
     await third.release()
   })
+
+  // ==========================================================================
+  // 9. asOf() / released-Db error paths (Y.15 spot-checks)
+  // ==========================================================================
+  it('proof 9 — asOf() rejects out-of-range targets and a released Db throws on every read', async () => {
+    const brain = await openMemoryBrain()
+    await (
+      await brain.transact([
+        { op: 'add', id: uid('asof-err'), type: NounType.Document, data: 'x', metadata: { v: 1 } }
+      ])
+    ).release()
+    const current = brain.generation()
+
+    // Negative, non-integer, and future generations are honest RangeErrors —
+    // never a silent clamp to a neighbouring generation.
+    await expect(brain.asOf(-1)).rejects.toThrow(RangeError)
+    await expect(brain.asOf(1.5)).rejects.toThrow(RangeError)
+    await expect(brain.asOf(current + 999)).rejects.toThrow(RangeError)
+
+    // A string that is not a snapshot directory is a descriptive error, not a crash.
+    await expect(brain.asOf('/no/such/snapshot/dir')).rejects.toThrow(/not a snapshot directory/)
+
+    // Use-after-release is rejected on every read method, naming the released generation.
+    const db = brain.now()
+    await db.release()
+    await expect(db.get(uid('asof-err'))).rejects.toThrow(/released Db/)
+    await expect(db.find({ where: { v: 1 } })).rejects.toThrow(/released Db/)
+    await expect(db.related(uid('asof-err'))).rejects.toThrow(/released Db/)
+  })
 })