docs(8.0): RELEASES — portable export/import (BackupData v1) + distinctCount any-type section

RELEASES.md

@@ -80,6 +80,47 @@ historical records) are documented in:
 - [docs/ADR-001-generational-mvcc.md](docs/ADR-001-generational-mvcc.md) — the
   design record: persisted layout, commit protocol, crash recovery, proof table
 
+### Portable export & import (BackupData v1)
+
+A portable, versioned graph format that serializes part or all of a brain to a
+single JSON document and restores it — the cross-environment, cross-version
+(7.x↔8.0), partial-or-whole companion to the native `persist()` snapshot.
+
+```ts
+// Export is a method on the immutable Db, so it composes with now()/asOf()/with()
+const backup = await brain.export({ collection: id }, { includeVectors: true })
+await otherBrain.import(backup, { onConflict: 'merge' })  // dedup-by-id
+
+;(await brain.asOf(gen)).export(sel)        // time-travel export
+brain.now().with(ops).export(sel)           // what-if export
+```
+
+- **`brain.export(selector?, options?)` / `db.export(...)`** → a versioned
+  `BackupData` document. Selectors reuse `find()`'s grammar: `{ ids }`,
+  `{ collection }` (alias `memberOf`, transitive `Contains`),
+  `{ connected: { from, depth } }`, `{ vfsPath }`, predicate
+  (`{ type, subtype, where, service }`), or the whole brain (omit) — and they
+  compose. Options: `includeVectors`, `includeContent` (VFS file bytes),
+  `includeSystem`, `edges: 'induced' | 'incident' | 'none'`.
+- **`brain.import(backup, options?)`** is polymorphic: a `BackupData` document is
+  restored as **one atomic transaction** (`onConflict: 'merge' | 'replace' | 'skip'`,
+  `reembed: 'auto' | 'never'`, `remapIds` for cloning); a file/buffer routes to the
+  existing CSV/PDF/Excel/JSON ingestion. No migration for ingestion callers.
+- **`validateBackup(data)`** — dry-run structural/version/endpoint check before import.
+- **Format** (`format:'brainy-backup'`, `formatVersion: 1`) is identical on 7.x
+  (7.32.0) and 8.0; standard fields (`subtype`/`visibility`/`data`/…) are top-level,
+  `metadata` is custom-only. Current-state (no generation history — that lives in
+  `persist()`). Types exported from the package root.
+- Guide: [docs/guides/export-and-import.md](docs/guides/export-and-import.md).
+
+### Aggregation: distinctCount over any value type
+
+`distinctCount` now counts distinct values of **any** type (strings, booleans,
+numbers) — previously it silently returned `0` for non-numeric fields, missing its
+primary use (distinct categories / users / tags). `percentile` (with `p`; median =
+`p: 0.5`), `stddev`, and `variance` are exact and delete-safe alongside the
+write-time `sum`/`count`/`avg`/`min`/`max`.
+
 ### Removed surfaces and their replacements
 
 | Removed in 8.0 | Replacement |