feat: brain.auditGraph() — read-only graph-truth audit

- New public API: walks every canonical relationship record, queries the same
  read path applications use (related() with all visibility tiers included),
  and classifies every discrepancy into its failure family: missingFromReads
  (records the read path omits — stale adjacency), danglingEndpoints
  (endpoint entity gone — the partial-delete scar class), readOnlyVerbIds
  (read-path edges with no canonical record — ghosts). Design-hidden
  internal/system edges are counted separately so intentional hiding is never
  misclassified as loss. Counts exact; example lists capped with an explicit
  truncatedExamples flag; loud narration on incoherence; mutates nothing.
- Classification core lives in src/graph/graphAudit.ts behind injected seams
  (canonical walks + the end-to-end read) so the discrepancy logic is testable
  in isolation; brainy wires the seams to storage walks and related().
- getNounIdsWithPagination now refuses an undecodable resume cursor loudly —
  the third and final pagination walk brought under the 8.5.2 cursor contract.
- Types exported: GraphAuditReport, GraphAuditDiscrepancy. Docs: the
  inspection guide gains the audit -> repair -> audit verification ritual.

docs/guides/inspection.md

@@ -166,6 +166,34 @@ brainy inspect diff /data/brain-prod /data/brain-staging
 Sample-based — for a full diff, dump both with `inspect dump` and compare
 the JSONL.
 
+## Auditing graph-read truth
+
+`brain.auditGraph()` (8.6.0+) proves — or disproves — that relationship reads
+return canonical truth on a given brain, without mutating anything. It walks
+every stored relationship record, asks the same read path your application
+uses (`related()`, VFS `readdir`) with every visibility tier included, and
+classifies every discrepancy:
+
+```typescript
+const report = await brain.auditGraph()
+
+report.coherent              // true = related()/readdir can be trusted on this brain
+report.missingFromReadsCount // records the read path omits — stale index
+report.danglingEndpointsCount // relationships whose endpoint entity is gone
+report.readOnlyCount         // read-path edges with NO stored record — ghosts
+report.visibilityHiddenCount // internal/system edges hidden by design (not a fault)
+```
+
+Counts are always exact; the example lists (`missingFromReads`,
+`danglingEndpoints`, `readOnlyVerbIds`) are capped at `maxExamples`
+(default 100) and `truncatedExamples` says so when they are.
+
+Run it after any engine upgrade, restore, or migration. If it reports
+discrepancies, run `brain.repairIndex()` and audit again — a `coherent`
+report after the repair is the verified statement that the heal worked.
+Cost: one relationship-record walk plus one indexed read per distinct
+source entity — safe on a live brain.
+
 ## Repairing a corrupted store
 
 If invariants fail and you suspect index corruption, `inspect repair`