fix(8.0): accept application-supplied entity ids, not just UUIDs

Sharding required a 32-hex UUID and threw "Invalid UUID format" on every
non-UUID id, even though add()'s own docs show `id: "user-12345"` and the u64
id-mapper happily assigns ints to any string. So custom ids mapped fine in
memory then threw on save — breaking documented usage and any 7.x consumer
using friendly ids (`'user-123'`, slugs, emails) on upgrade.

getShardId() (renamed from getShardIdFromUuid) now buckets UUID-format ids by
their first byte (on-disk layout unchanged, so existing data never moves) and
hashes any other id via FNV-1a into the same 256-bucket space. The hash is part
of the on-disk contract and must not change. Verbs stay Brainy-generated UUIDs
by contract; only custom noun ids take the hash path.

Adds getShardId unit coverage: dual scheme, determinism, even distribution
across buckets, and the empty-id guard.

src/storage/baseStorage.ts

@@ -25,7 +25,7 @@ import {
   NOUN_TYPE_COUNT,
   VERB_TYPE_COUNT
 } from '../types/graphTypes.js'
-import { getShardIdFromUuid } from './sharding.js'
+import { getShardId } from './sharding.js'
 import { BlobStorage, type BlobStoreAdapter } from './blobStorage.js'
 import { unwrapBinaryData } from './binaryDataCodec.js'
 import { prodLog } from '../utils/logger.js'
@@ -161,7 +161,7 @@ function isSingletonSystemKey(key: string): boolean {
  * No type parameter needed - direct O(1) lookup by ID
  */
 function getNounVectorPath(id: string): string {
-  const shard = getShardIdFromUuid(id)
+  const shard = getShardId(id)
   return `entities/nouns/${shard}/${id}/vectors.json`
 }
 
@@ -170,7 +170,7 @@ function getNounVectorPath(id: string): string {
  * No type parameter needed - direct O(1) lookup by ID
  */
 function getNounMetadataPath(id: string): string {
-  const shard = getShardIdFromUuid(id)
+  const shard = getShardId(id)
   return `entities/nouns/${shard}/${id}/metadata.json`
 }
 
@@ -179,7 +179,7 @@ function getNounMetadataPath(id: string): string {
  * No type parameter needed - direct O(1) lookup by ID
  */
 function getVerbVectorPath(id: string): string {
-  const shard = getShardIdFromUuid(id)
+  const shard = getShardId(id)
   return `entities/verbs/${shard}/${id}/vectors.json`
 }
 
@@ -188,7 +188,7 @@ function getVerbVectorPath(id: string): string {
  * No type parameter needed - direct O(1) lookup by ID
  */
 function getVerbMetadataPath(id: string): string {
-  const shard = getShardIdFromUuid(id)
+  const shard = getShardId(id)
   return `entities/verbs/${shard}/${id}/metadata.json`
 }
 
@@ -392,7 +392,7 @@ export abstract class BaseStorage extends BaseStorageAdapter {
     }
 
     // Valid entity UUID - apply sharding
-    const shardId = getShardIdFromUuid(id)
+    const shardId = getShardId(id)
 
     if (context === 'noun-metadata') {
       return {

src/storage/sharding.ts

@@ -1,55 +1,77 @@
 /**
- * Unified UUID-based sharding for all storage adapters
+ * Unified id-based sharding for all storage adapters.
  *
- * Uses first 2 hex characters of UUID for consistent, predictable sharding
- * that scales from hundreds to millions of entities without configuration.
+ * Maps any entity id to one of 256 buckets (00-ff) for consistent, predictable
+ * on-disk layout that scales from hundreds to millions of entities with no
+ * configuration.
  *
  * Sharding characteristics:
  * - 256 buckets (00-ff)
- * - Deterministic (same UUID always maps to same shard)
+ * - Deterministic (the same id always maps to the same shard)
  * - No configuration required
- * - Works across all storage types (filesystem, S3, GCS, memory)
+ * - Works across the filesystem and memory adapters
  * - Efficient for list operations and pagination
+ *
+ * Two id shapes are supported, by design:
+ * - **UUID-format ids** (32 hex chars) shard by their first byte. This is the
+ *   original scheme, kept byte-for-byte so existing on-disk layouts never move.
+ * - **Application ids** (`'user-123'`, slugs, emails — anything else) shard by a
+ *   stable FNV-1a hash. Requiring callers to mint UUIDs would break the
+ *   documented `add({ id: '…' })` contract; a shard is only a bucket, so any
+ *   deterministic, well-distributed mapping is correct.
+ *
+ * The hash is part of the on-disk contract: **never change it** — doing so would
+ * relocate every application-id record.
  */
 
 /**
- * Extract shard ID from UUID
+ * 32-bit FNV-1a hash of a string, returned as a 2-hex-char shard bucket (00-ff).
+ * Deterministic and uniformly distributed across the 256 buckets.
  *
- * Uses first 2 hex characters of the UUID as the shard ID.
- * This provides 256 evenly-distributed buckets (00-ff).
+ * @param value - The string to hash (an entity id that is not UUID-format).
+ * @returns A 2-character hex shard id.
+ */
+function hashToShardId(value: string): string {
+  let hash = 0x811c9dc5 // FNV offset basis
+  for (let i = 0; i < value.length; i++) {
+    hash ^= value.charCodeAt(i)
+    hash = Math.imul(hash, 0x01000193) // FNV prime
+  }
+  return ((hash >>> 0) & 0xff).toString(16).padStart(2, '0')
+}
+
+/**
+ * Resolve the shard bucket (00-ff) for an entity id.
  *
- * @param uuid - UUID string (with or without hyphens)
- * @returns 2-character hex shard ID (00-ff)
+ * UUID-format ids (32 hex chars, with or without hyphens) shard by their first
+ * byte — preserving the original on-disk layout. Any other id is hashed (FNV-1a)
+ * into the same 256-bucket space, so application-supplied ids like `'user-123'`
+ * work without forcing callers to mint UUIDs.
+ *
+ * @param id - The entity id (UUID-format or any application string).
+ * @returns A 2-character hex shard id (00-ff).
+ * @throws If `id` is empty.
  *
  * @example
  * ```typescript
- * getShardIdFromUuid('ab123456-1234-5678-9abc-def012345678') // returns 'ab'
- * getShardIdFromUuid('cd987654-4321-8765-cba9-fed543210987') // returns 'cd'
- * getShardIdFromUuid('00000000-0000-0000-0000-000000000000') // returns '00'
+ * getShardId('ab123456-1234-5678-9abc-def012345678') // 'ab' (UUID first byte)
+ * getShardId('user-12345')                            // FNV-1a hash bucket
  * ```
  */
-export function getShardIdFromUuid(uuid: string): string {
-  if (!uuid) {
-    throw new Error('UUID is required for sharding')
+export function getShardId(id: string): string {
+  if (!id) {
+    throw new Error('id is required for sharding')
   }
 
-  // Remove hyphens and convert to lowercase
-  const normalized = uuid.toLowerCase().replace(/-/g, '')
-
-  // Validate UUID format (32 hex characters)
-  if (normalized.length !== 32) {
-    throw new Error(`Invalid UUID format: ${uuid} (expected 32 hex chars, got ${normalized.length})`)
+  // UUID-format ids (32 hex chars) keep the original first-byte bucketing so
+  // existing on-disk data is never relocated.
+  const normalized = id.toLowerCase().replace(/-/g, '')
+  if (/^[0-9a-f]{32}$/.test(normalized)) {
+    return normalized.substring(0, 2)
   }
 
-  // Extract first 2 characters
-  const shardId = normalized.substring(0, 2)
-
-  // Validate hex format
-  if (!/^[0-9a-f]{2}$/.test(shardId)) {
-    throw new Error(`Invalid UUID prefix: ${shardId} (expected 2 hex chars)`)
-  }
-
-  return shardId
+  // Any other id (application keys, slugs, emails) is hashed into a bucket.
+  return hashToShardId(id)
 }
 
 /**