feat(8.0): reserved-field enforcement — reservedFieldPolicy defaults to throw

An untyped (JS) caller that smuggles a Brainy-reserved field (confidence,
weight, subtype, visibility, service, createdBy, noun/verb, data, createdAt,
updatedAt, _rev) inside a write-path metadata bag previously got a silent
remap-or-drop — a class of bug where confidence-evolution writes no-oped for
weeks before being caught on read-back. 8.0 closes this with no silent failures.

- New BrainyConfig.reservedFieldPolicy: 'throw' | 'warn' | 'remap' (default 'throw').
  'throw' rejects the write naming every offending key + its correct write path;
  'warn' remaps with a one-shot per-key warning; 'remap' is the legacy silent path.
- Central enforceReservedPolicy gate wired into all four remap methods (add,
  update, relate, updateRelation) so live calls AND their transact()/with()
  mirrors honor it. Single-source reservedWritePath guidance shared by throw+warn.
- 'warn' now warns for EVERY reserved key (closes the gap where only
  system-managed fields warned). Dead warnDropped* helpers removed.
- Import pipeline migrated to route reserved values (confidence/weight/subtype)
  through dedicated params and strip reserved keys from extractor/customMetadata
  bags via the canonical split*MetadataRecord helpers — imports no longer trip
  the default throw.
- Tests: new reservedFieldPolicy matrix (throw/warn/remap across every write
  path + transact); remap-correctness suite reframed as opt-in 'remap'; shared
  test-factory no longer emits reserved keys in custom metadata.

src/neural/neuralImport.ts

@@ -7,6 +7,7 @@
 
 import { Brainy } from '../brainy.js'
 import { NounType, VerbType } from '../types/graphTypes.js'
+import { splitNounMetadataRecord, splitVerbMetadataRecord } from '../types/reservedFields.js'
 import * as fs from '../universal/fs.js'
 import * as path from '../universal/path.js'
 // @ts-ignore
@@ -802,9 +803,12 @@ export class NeuralImport {
           data: this.extractMainText(entity.originalData),
           type: entity.nounType as NounType,
           subtype: entity.subtype ?? options.defaultSubtype ?? 'extracted',
+          // `confidence` is a reserved field — dedicated param, not metadata
+          // (8.0 reservedFieldPolicy defaults to 'throw').
+          confidence: entity.confidence,
           metadata: {
-            ...entity.originalData,
-            confidence: entity.confidence,
+            // Strip any reserved keys the source data smuggled into the bag.
+            ...splitNounMetadataRecord(entity.originalData).custom,
             id: entity.suggestedId
           }
         })
@@ -821,7 +825,8 @@ export class NeuralImport {
           confidence: relationship.confidence, // reserved field — dedicated param, not metadata
           metadata: {
             context: relationship.context,
-            ...relationship.metadata
+            // Strip any reserved keys smuggled into the edge metadata bag.
+            ...splitVerbMetadataRecord(relationship.metadata).custom
           }
         })
       }