test(8.0): get() resolves null for absent custom ids instead of throwing

Follow-up to accepting application-supplied ids (36b7216): get('not-a-uuid')
and long ids are now valid lookups that miss → null, not "Invalid UUID format"
throws. Empty / null / undefined still throw (structurally invalid input).
Aligns the unit suite with the accept-any-id behaviour; the v5.1.0 "stricter
UUID validation" rule these cases encoded is superseded.

tests/unit/brainy/get.test.ts

@@ -159,19 +159,18 @@ describe('Brainy.get()', () => {
     })
 
     it('should handle invalid ID formats gracefully', async () => {
-      // v5.1.0: Invalid formats now throw errors instead of returning null
-      const invalidIds = [
-        '',            // Empty string
-        'not-a-uuid',  // Invalid format
-        '12345',       // Too short
+      // 8.0: any non-empty string is a valid custom id (sharding hashes it), so
+      // a lookup that misses resolves to null — there is no "invalid format".
+      const missingIds = [
+        'not-a-uuid', // valid custom id, simply absent
+        '12345'       // valid custom id, simply absent
       ]
-
-      // Act & Assert - expect errors for invalid formats
-      for (const invalidId of invalidIds) {
-        await expect(brain.get(invalidId)).rejects.toThrow()
+      for (const id of missingIds) {
+        await expect(brain.get(id)).resolves.toBeNull()
       }
 
-      // Null/undefined should also throw
+      // Structurally-invalid input (empty / null / undefined) still throws.
+      await expect(brain.get('')).rejects.toThrow()
       await expect(brain.get(null as any)).rejects.toThrow()
       await expect(brain.get(undefined as any)).rejects.toThrow()
     })
@@ -215,11 +214,9 @@ describe('Brainy.get()', () => {
   
   describe('edge cases', () => {
     it('should handle very long IDs', async () => {
-      // v5.1.0: Stricter UUID validation - invalid IDs throw errors
+      // 8.0: a long string is a valid custom id; a miss resolves to null.
       const longId = 'x'.repeat(1000)
-
-      // Expect error for invalid UUID format
-      await expect(brain.get(longId)).rejects.toThrow('Invalid UUID format')
+      await expect(brain.get(longId)).resolves.toBeNull()
     })
     
     it('should handle special characters in IDs', async () => {