feat(8.0): temporal range verbs — diff, history, since(gen|Date), asOf{exclusive}, transactionLog window

asOf() answers "state AT a point"; these answer "what happened BETWEEN two
points" and "one entity's whole history", all on the existing generation records.

- Extract resolveAsOfGeneration() as the shared gen|Date→{generation,timestamp}
  chokepoint (reachability + Date semantics identical everywhere). asOf()'s
  inclusive path is byte-identical — db-mvcc still 25/25.
- asOf(target, { exclusive }) — strict-before (resolved−1, clamped at gen 0,
  never a RangeError).
- db.since(Db | generation | Date) — overload; number/Date resolve via the shared
  resolver (new DbHost.resolveGeneration); EXCLUSIVE lower bound;
  since(db) === since(db.generation). Same-store guard via Db.belongsToStore.
- brain.diff(a, b) → { added, removed, modified } split by nouns/verbs. EARNS its
  name: candidate set is ONLY changedBetween(gLow,gHigh), each classified by
  existence at both endpoints + a key-order-insensitive value compare
  (new src/db/stableEqual.ts) — a touched-but-reverted / born-and-died id is in
  no bucket.
- brain.history(id, { from, to }) → every distinct version oldest→newest, each
  value === asOf(version.generation).get(id); null = removal; kind auto-detected
  (throws on UUID-space collision). New store helper generationsTouching().
- brain.transactionLog({ from, to, limit }) — INCLUSIVE generation/Date window
  (contrast since's exclusive lower bound); limit applied last.
- Compaction policy locked: diff/since THROW GenerationCompactedError below the
  horizon; history TRUNCATES to it.

Types DiffResult/HistoryVersion/EntityHistory exported from the package root.
Tests: tests/integration/db-temporal.test.ts (8 proofs incl. diff-earns-its-name,
history↔asOf cross-check, the composition proof, granularity, compaction contrast)
+ tests/unit/db/stableEqual.test.ts (6). docs/guides/snapshots-and-time-travel.md
+ RELEASES updated. 1477 unit + db-temporal 8 + db-mvcc 25 green.

RELEASES.md

@@ -51,9 +51,11 @@ What you get:
   on conflict) — the big sibling of the per-entity `ifRev` CAS from 7.31.
   `meta` is reified Datomic-style into an append-only transaction log,
   readable via `brain.transactionLog()`.
-- **`brain.asOf(generation | Date | snapshotPath)`** — time travel with the
-  **full query surface**: `get()`, `find()` in every mode, semantic search,
-  graph traversal, cursors, aggregation, all at the pinned past state.
+- **`brain.asOf(generation | Date | snapshotPath, { exclusive? })`** — time
+  travel with the **full query surface**: `get()`, `find()` in every mode,
+  semantic search, graph traversal, cursors, aggregation, all at the pinned past
+  state. `exclusive: true` pins the generation immediately before the target
+  (strict-before).
 - **`db.with(ops)`** — speculative writes applied in memory on top of a view.
   Nothing touches disk, the generation counter, or the indexes. What-if
   analysis, then `transact()` the same ops for real.
@@ -63,10 +65,23 @@ What you get:
   inodes). `brain.restore(path, { confirm: true })` replaces the whole store
   from one; `Brainy.load(path)` opens one read-only with the full query
   surface.
-- **`db.since(olderDb)`** — exactly the entity and relationship ids that
-  committed transactions touched between two views.
+- **Range verbs over history** — answer "what happened BETWEEN two points":
+  - **`db.since(Db | generation | Date)`** — the entity and relationship ids
+    committed transactions touched after an **exclusive** lower bound (now
+    accepts a generation or `Date`, not just a prior `Db`).
+  - **`brain.diff(a, b)`** — the touched ids CLASSIFIED as `{ added, removed,
+    modified }` (split by nouns/verbs) by resolving each at both endpoints; a
+    touched-but-reverted id lands in none of the buckets. Endpoints are a
+    generation, `Date`, or `Db`, in either order.
+  - **`brain.history(id, { from?, to? })`** — every distinct version of ONE
+    entity/relationship over a range, oldest first (`value: null` marks a
+    removal); each version equals `asOf(version.generation).get(id)`.
+  - **`brain.transactionLog({ from?, to?, limit? })`** — the commit log over an
+    **inclusive** generation/`Date` window (contrast `since`'s exclusive lower
+    bound); `limit` applies last.
 - **`brain.compactHistory({ retainGenerations, retainMs })`** — explicit
-  retention. Compaction never breaks a pinned read.
+  retention. Compaction never breaks a pinned read. `diff`/`since` throw
+  `GenerationCompactedError` below the horizon; `history` truncates to it.
 
 The precise guarantees (and the honest limits — history granularity is
 `transact()` commits; single-operation writes advance the clock but produce no

docs/guides/snapshots-and-time-travel.md

@@ -5,7 +5,7 @@ public: true
 category: guides
 template: guide
 order: 9
-description: Recipes for the Db API — instant backups with persist(), restore, time-travel debugging with asOf(), persist-before-migrate, what-if analysis with with(), and audit trails via transaction metadata.
+description: Recipes for the Db API — instant backups with persist(), restore, time-travel debugging with asOf(), range queries over history (diff, history, since, log windows), persist-before-migrate, what-if analysis with with(), and audit trails via transaction metadata.
 next:
   - concepts/consistency-model
   - guides/optimistic-concurrency
@@ -146,6 +146,96 @@ Three things to remember:
 - Generations reclaimed by `compactHistory()` throw
   `GenerationCompactedError` — persist anything you need to keep forever.
 
+## Range queries over history
+
+`asOf()` answers "what was the state AT a point". Four range verbs answer
+"what happened BETWEEN two points" and "what is one entity's whole history".
+They all build on the same generation records — no extra bookkeeping.
+
+### `diff(a, b)` — what changed, classified
+
+`since()` gives you the raw set of *touched* ids. `diff()` goes further: it
+resolves each touched id at both endpoints and classifies it as **added**,
+**removed**, or **modified** — split by entities (`nouns`) and relationships
+(`verbs`). An id that was touched but ended up identical (changed then
+reverted, or created and deleted within the interval) lands in **none** of the
+buckets. Endpoints are a generation, a `Date`, or a `Db`, in either order:
+
+```typescript
+const d = await brain.diff(1041, brain.generation())
+
+d.added.nouns      // entity ids created between the two states
+d.removed.nouns    // entity ids deleted
+d.modified.nouns   // entity ids whose stored value actually changed
+d.added.verbs      // …relationships, the same three ways
+```
+
+Orientation is `a → b`: `added` means "exists at `b`, not at `a`". The
+comparison behind `modified` is key-order-insensitive, so a no-op re-write of
+the same fields never shows up as a change.
+
+### `history(id, range?)` — one entity, every version
+
+`asOf()` is per-*generation*; `history()` is per-*entity*. It returns every
+distinct version of one id over a range, oldest first — each `value` is the
+materialized state at that version (and `null` marks a removal):
+
+```typescript
+const h = await brain.history(invoiceId)
+
+for (const v of h.versions) {
+  console.log(v.generation, v.value?.metadata?.status ?? '(deleted)')
+}
+// 1041 'draft'
+// 1043 'approved'
+// 1050 'paid'
+```
+
+Every version ties to the trusted `asOf()` path — `v.value` equals
+`(await brain.asOf(v.generation)).get(id)`. Pass `{ from, to }` (generation or
+`Date`) to bound the range; a `from` below the compaction horizon is quietly
+truncated to it rather than throwing (history is best-effort over surviving
+records).
+
+### `since()` and `transactionLog()` take ranges too
+
+`since()` accepts a `Db`, a generation number, or a `Date` — all equivalent,
+all an **exclusive** lower bound (`db.since(prior)` equals
+`db.since(prior.generation)`):
+
+```typescript
+await brain.now().since(1041)                          // ids changed after generation 1041
+await brain.now().since(new Date(Date.now() - 3_600_000)) // …in the last hour
+```
+
+`transactionLog({ from, to })` windows the commit log **inclusively** on both
+ends (a log window names the commits it spans — the deliberate contrast to
+`since`'s exclusive lower bound); `limit` applies after the window, newest
+first:
+
+```typescript
+const window = await brain.transactionLog({ from: 1041, to: 1050 })  // commits 1041…1050
+const recent = await brain.transactionLog({ from: lastHour, limit: 20 })
+```
+
+### Composing them
+
+"Which orders changed in this window?" is `diff` ids intersected with an
+`asOf` query — the two agree by construction:
+
+```typescript
+const changed = await brain.diff(g1, g2)
+const atG2 = await brain.asOf(g2)
+const changedOrders = (await atG2.find({ type: NounType.Document, subtype: 'order' }))
+  .map(r => r.id)
+  .filter(id => changed.added.nouns.includes(id) || changed.modified.nouns.includes(id))
+await atG2.release()
+```
+
+One contrast to keep straight: `diff` and `since` **throw**
+`GenerationCompactedError` for a bound below the horizon, while `history`
+**truncates** to the horizon — diffs must be exact, history is best-effort.
+
 ## Safe schema migration
 
 `brain.migrate()` integrates with snapshots directly: pass `backupTo` and a

src/brainy.ts

@@ -134,8 +134,12 @@ import type {
   TransactOptions,
   TransactReceipt,
   TxLogEntry,
-  TxOperation
+  TxOperation,
+  DiffResult,
+  EntityHistory,
+  HistoryVersion
 } from './db/types.js'
+import { stableDeepEqual } from './db/stableEqual.js'
 import type { VersionedIndexProvider } from './plugin.js'
 import type { Operation } from './transaction/types.js'
 
@@ -5024,18 +5028,48 @@ export class Brainy<T = any> implements BrainyInterface<T> {
    * `compactHistory()` never rewrites the log — entries may reference
    * generations whose record-sets were already reclaimed.
    *
-   * @param options - `limit` caps the number of entries returned (newest
-   *   first; default: all).
+   * @param options - `from`/`to` (generation number or `Date`) bound the window
+   *   to commits in `[from, to]` INCLUSIVE on both ends — a log window names
+   *   commits, in deliberate contrast to `since()`'s EXCLUSIVE lower bound.
+   *   `limit` caps the result and is applied LAST (after windowing), newest
+   *   first. All omitted = the whole log. `from`/`to` resolve through the same
+   *   reachability gate as `asOf()`.
    * @returns Committed transaction entries, newest first.
+   * @throws RangeError when the resolved `from` generation is after `to`.
    * @example
    * await brain.transact([{ op: 'update', id, metadata: { v: 2 } }], { meta: { author: 'sync-job' } })
    * const [latest] = await brain.transactionLog({ limit: 1 })
    * latest.meta // { author: 'sync-job' }
+   * // Commits in a window, newest first:
+   * const window = await brain.transactionLog({ from: 10, to: 20 })
    */
-  async transactionLog(options?: { limit?: number }): Promise<TxLogEntry[]> {
+  async transactionLog(options?: {
+    from?: number | Date
+    to?: number | Date
+    limit?: number
+  }): Promise<TxLogEntry[]> {
     await this.ensureInitialized()
-    const entries = await this.generationStore.txLog()
-    entries.reverse()
+    let entries = await this.generationStore.txLog() // oldest first
+
+    if (options?.from !== undefined || options?.to !== undefined) {
+      const fromGen =
+        options?.from !== undefined
+          ? (await this.resolveAsOfGeneration(options.from)).generation
+          : 0
+      const toGen =
+        options?.to !== undefined
+          ? (await this.resolveAsOfGeneration(options.to)).generation
+          : this.generationStore.generation()
+      if (fromGen > toGen) {
+        throw new RangeError(
+          `transactionLog(): resolved from-generation ${fromGen} is after to-generation ${toGen}`
+        )
+      }
+      // Inclusive on BOTH ends (a log window names the commits it spans).
+      entries = entries.filter((e) => e.generation >= fromGen && e.generation <= toGen)
+    }
+
+    entries.reverse() // newest first
     return options?.limit !== undefined ? entries.slice(0, options.limit) : entries
   }
 
@@ -5087,7 +5121,7 @@ export class Brainy<T = any> implements BrainyInterface<T> {
    * @param options - HOW to export (vectors / VFS bytes / edge policy). See {@link ExportOptions}.
    * @returns A versioned, portable `PortableGraph` document.
    * @example
-   * const backup = await brain.export({ ids }, { includeVectors: true })
+   * const graph = await brain.export({ ids }, { includeVectors: true })
    */
   async export(selector: ExportSelector = {}, options: ExportOptions = {}): Promise<PortableGraph> {
     return this.now().export(selector, options)
@@ -5196,6 +5230,11 @@ export class Brainy<T = any> implements BrainyInterface<T> {
    * Release the returned `Db` when done.
    *
    * @param target - Generation number, `Date`, or snapshot directory path.
+   * @param options - `exclusive: true` pins the generation immediately BEFORE the
+   *   one `target` resolves to (strict-before): `asOf(g, { exclusive: true })` is
+   *   the state at `g − 1`; strict-before the first commit pins generation 0 (the
+   *   empty pre-commit state), never a `RangeError`. Ignored for the snapshot
+   *   (string) form.
    * @returns A `Db` pinned at the resolved state.
    * @throws GenerationCompactedError when the generation's records were
    *   reclaimed by `compactHistory()`.
@@ -5203,9 +5242,13 @@ export class Brainy<T = any> implements BrainyInterface<T> {
    * @example
    * const yesterday = await brain.asOf(new Date(Date.now() - 86_400_000))
    * const atGen42 = await brain.asOf(42)
+   * const beforeGen42 = await brain.asOf(42, { exclusive: true }) // state at gen 41
    * const fromSnapshot = await brain.asOf('/backups/2026-06-01')
    */
-  async asOf(target: number | Date | string): Promise<Db<T>> {
+  async asOf(
+    target: number | Date | string,
+    options?: { exclusive?: boolean }
+  ): Promise<Db<T>> {
     await this.ensureInitialized()
 
     if (typeof target === 'string') {
@@ -5219,21 +5262,278 @@ export class Brainy<T = any> implements BrainyInterface<T> {
       return Brainy.load<T>(target)
     }
 
+    const { generation, timestamp } = await this.resolveAsOfGeneration(target, options)
+    return this.createPinnedDb({ generation, timestamp })
+  }
+
+  /**
+   * @description The shared `generation | Date` → `{ generation, timestamp }`
+   * resolver used by every gen/Date-accepting temporal verb (`asOf`, `since`,
+   * `diff`, `transactionLog`) so reachability, `RangeError`, and `Date` semantics
+   * stay identical across all of them. The inclusive path is byte-for-byte the
+   * pre-extraction `asOf` logic; `exclusive` pins the generation immediately
+   * before the resolved one (clamped at 0, never a `RangeError`). All resolved
+   * generations pass through `assertReachable` (so a compacted target throws
+   * {@link GenerationCompactedError}); `history()` deliberately does NOT use this
+   * resolver — it truncates below the horizon rather than throwing.
+   * @param target - A generation number or a `Date`.
+   * @param options - `exclusive: true` for strict-before (resolved − 1).
+   */
+  private async resolveAsOfGeneration(
+    target: number | Date,
+    options?: { exclusive?: boolean }
+  ): Promise<{ generation: number; timestamp: number }> {
+    const exclusive = options?.exclusive === true
     let generation: number
     let timestamp: number
     if (target instanceof Date) {
       const resolved = await this.generationStore.resolveTimestamp(target.getTime())
-      this.generationStore.assertReachable(resolved.generation)
-      generation = resolved.generation
-      timestamp = resolved.entry?.timestamp ?? target.getTime()
+      if (exclusive) {
+        generation = Math.max(0, resolved.generation - 1)
+        this.generationStore.assertReachable(generation)
+        timestamp =
+          (await this.generationStore.commitTimestampAtOrBefore(generation)) ?? target.getTime()
+      } else {
+        this.generationStore.assertReachable(resolved.generation)
+        generation = resolved.generation
+        timestamp = resolved.entry?.timestamp ?? target.getTime()
+      }
     } else {
-      this.generationStore.assertReachable(target)
-      generation = target
+      generation = exclusive ? Math.max(0, target - 1) : target
+      this.generationStore.assertReachable(generation)
       timestamp =
-        (await this.generationStore.commitTimestampAtOrBefore(target)) ?? Date.now()
+        (await this.generationStore.commitTimestampAtOrBefore(generation)) ?? Date.now()
+    }
+    return { generation, timestamp }
+  }
+
+  /**
+   * @description Compare two states of the brain and report what CHANGED between
+   * them — entities/relationships `added`, `removed`, or `modified`, each split by
+   * kind. Unlike a raw touched-id list, `diff` EARNS its name: the candidate set is
+   * ONLY the ids a committed transaction touched in the interval, and each is then
+   * resolved at BOTH endpoints and classified by existence and a stable value
+   * comparison. An id touched within the interval but whose endpoint states are
+   * identical (e.g. changed then reverted) appears in NONE of the three buckets.
+   *
+   * Orientation is `a → b`: `added` = exists at `b` not `a`; `removed` = exists at
+   * `a` not `b`; `modified` = exists at both with a changed stored value
+   * (key-order-insensitive). Endpoints may be passed in either order.
+   *
+   * @param a - The "before" state: a generation number, a `Date`, or a `Db`.
+   * @param b - The "after" state: a generation number, a `Date`, or a `Db`.
+   * @returns A {@link DiffResult} (each bucket's ids sorted).
+   * @throws GenerationCompactedError when a number/`Date` endpoint is below the horizon.
+   * @example
+   * const before = brain.generation()
+   * await brain.transact(ops)
+   * const d = await brain.diff(before, brain.generation())
+   * d.added.nouns      // ids created by the transaction
+   * d.modified.nouns   // ids whose stored value actually changed
+   */
+  async diff(a: number | Date | Db<T>, b: number | Date | Db<T>): Promise<DiffResult> {
+    await this.ensureInitialized()
+    const gA = await this.resolveDiffEndpoint(a)
+    const gB = await this.resolveDiffEndpoint(b)
+
+    const result: DiffResult = {
+      added: { nouns: [], verbs: [] },
+      removed: { nouns: [], verbs: [] },
+      modified: { nouns: [], verbs: [] },
+      fromGeneration: gA,
+      toGeneration: gB
     }
 
-    return this.createPinnedDb({ generation, timestamp })
+    // Candidate set: ONLY the ids touched in the interval (never all ids) — this
+    // is what lets diff classify rather than dump raw changed-ids.
+    const gLow = Math.min(gA, gB)
+    const gHigh = Math.max(gA, gB)
+    if (gLow === gHigh) return result // same state → no changes
+    const changed = await this.generationStore.changedBetween(gLow, gHigh)
+
+    for (const kind of ['noun', 'verb'] as const) {
+      const ids = kind === 'noun' ? changed.nouns : changed.verbs
+      for (const id of ids) {
+        const stateA = await this.recordStateAt(kind, id, gA)
+        const stateB = await this.recordStateAt(kind, id, gB)
+        const bucket = (name: 'added' | 'removed' | 'modified') =>
+          kind === 'noun' ? result[name].nouns : result[name].verbs
+        if (!stateA.exists && stateB.exists) bucket('added').push(id)
+        else if (stateA.exists && !stateB.exists) bucket('removed').push(id)
+        else if (
+          stateA.exists &&
+          stateB.exists &&
+          !stableDeepEqual(stateA.metadata, stateB.metadata)
+        ) {
+          bucket('modified').push(id)
+        }
+        // both absent, or both exist and identical → in NO bucket (earns the name)
+      }
+    }
+
+    for (const name of ['added', 'removed', 'modified'] as const) {
+      result[name].nouns.sort()
+      result[name].verbs.sort()
+    }
+    return result
+  }
+
+  /**
+   * @description Every distinct version of ONE entity or relationship over a
+   * generation range, oldest → newest — the per-id companion to `asOf()`. Each
+   * {@link HistoryVersion} ties to the trusted `asOf()` path: its `value` equals
+   * `(await brain.asOf(version.generation)).get(id)`. Consecutive identical states
+   * are collapsed, and a leading "did not exist yet" baseline is dropped, so the
+   * first version is the id's first real state in the range and a `null` value
+   * marks a removal.
+   *
+   * Range defaults to `[horizon, currentGeneration]`. Unlike `diff`/`since`, a
+   * `from` below the compaction horizon is TRUNCATED to the horizon, not thrown —
+   * history is best-effort over the records that survive.
+   *
+   * @param id - The entity or relationship id (kind auto-detected).
+   * @param options - `from`/`to` (generation number or `Date`) bound the range.
+   * @returns An {@link EntityHistory} (`versions` oldest first; empty if the id is
+   *   unknown over the range).
+   * @throws Error if `id` resolves in BOTH the entity and relationship spaces.
+   * @example
+   * const h = await brain.history(invoiceId)
+   * h.versions.map(v => v.value?.metadata?.status) // the status at each change
+   */
+  async history(
+    id: string,
+    options?: { from?: number | Date; to?: number | Date }
+  ): Promise<EntityHistory<T>> {
+    await this.ensureInitialized()
+    const store = this.generationStore
+    const horizon = store.horizon()
+    const current = store.generation()
+
+    // history TRUNCATES below the horizon (never throws): resolve raw, then clamp.
+    const rawFrom =
+      options?.from !== undefined ? await this.resolveRawGeneration(options.from) : horizon
+    const rawTo =
+      options?.to !== undefined ? await this.resolveRawGeneration(options.to) : current
+    const fromGen = Math.min(Math.max(rawFrom, horizon), current)
+    const toGen = Math.min(Math.max(rawTo, 0), current)
+
+    const kind = await this.detectIdKind(id, horizon, current)
+    if (kind === null || fromGen > toGen) {
+      return { id, kind: kind ?? 'noun', versions: [] }
+    }
+
+    // Snapshot generations: the range start (state as-of fromGen) plus every
+    // committed change-point in (fromGen, toGen].
+    const touches = await store.generationsTouching(kind, id, fromGen, toGen)
+    const snapshotGens = [fromGen, ...touches]
+
+    const versions: HistoryVersion<T>[] = []
+    let prev: { exists: boolean; metadata: any } | null = null
+    for (const g of snapshotGens) {
+      const state = await this.recordStateAt(kind, id, g)
+      if (
+        prev !== null &&
+        prev.exists === state.exists &&
+        stableDeepEqual(prev.metadata, state.metadata)
+      ) {
+        continue // collapse consecutive identical states
+      }
+      prev = { exists: state.exists, metadata: state.metadata }
+      const timestamp = (await store.commitTimestampAtOrBefore(g)) ?? 0
+      let value: Entity<T> | Relation<T> | null = null
+      if (state.exists) {
+        value =
+          kind === 'noun'
+            ? await this.entityFromGenerationRecord(
+                id,
+                { metadata: state.metadata, vector: state.vector },
+                false
+              )
+            : this.relationFromGenerationRecord(id, {
+                metadata: state.metadata,
+                vector: state.vector
+              })
+      }
+      versions.push({ generation: g, timestamp, value })
+    }
+
+    // Drop a leading "did not exist yet" baseline so history starts at the id's
+    // first real state (internal/trailing nulls = real removals stay).
+    while (versions.length > 0 && versions[0].value === null) versions.shift()
+    return { id, kind, versions }
+  }
+
+  /** Resolve a `Db | generation | Date` diff endpoint to a concrete generation. */
+  private async resolveDiffEndpoint(endpoint: number | Date | Db<T>): Promise<number> {
+    if (endpoint instanceof Db) {
+      if (!endpoint.belongsToStore(this.generationStore)) {
+        throw new Error('diff(): a Db endpoint must come from this same Brainy instance')
+      }
+      return endpoint.generation
+    }
+    return (await this.resolveAsOfGeneration(endpoint)).generation
+  }
+
+  /**
+   * Resolve a `generation | Date` to a raw generation number WITHOUT the
+   * reachability assertion — for `history()`, which truncates below the horizon
+   * rather than throwing.
+   */
+  private async resolveRawGeneration(target: number | Date): Promise<number> {
+    if (target instanceof Date) {
+      return (await this.generationStore.resolveTimestamp(target.getTime())).generation
+    }
+    return target
+  }
+
+  /**
+   * The stored state of `id` at pinned generation `gen`, normalizing `resolveAt`'s
+   * three sources to `{ exists, metadata, vector }`. A `'current'` source means the
+   * live storage state IS the state at `gen`, so it reads the live metadata.
+   */
+  private async recordStateAt(
+    kind: 'noun' | 'verb',
+    id: string,
+    gen: number
+  ): Promise<{ exists: boolean; metadata: any; vector: any }> {
+    const r = await this.generationStore.resolveAt(kind, id, gen)
+    if (r.source === 'absent') return { exists: false, metadata: null, vector: null }
+    if (r.source === 'record') return { exists: true, metadata: r.metadata, vector: r.vector }
+    const metadata =
+      kind === 'noun'
+        ? await this.storage.getNounMetadata(id)
+        : await this.storage.getVerbMetadata(id)
+    return { exists: metadata !== null, metadata, vector: null }
+  }
+
+  /**
+   * Auto-detect whether `id` is an entity (`'noun'`) or relationship (`'verb'`) by
+   * its presence live and in the generation deltas over `(fromGen, toGen]`. Returns
+   * `null` for an unknown id; throws on the (UUID-space) collision where the id
+   * resolves in both spaces.
+   */
+  private async detectIdKind(
+    id: string,
+    fromGen: number,
+    toGen: number
+  ): Promise<'noun' | 'verb' | null> {
+    const liveNoun = (await this.storage.getNounMetadata(id)) !== null
+    const liveVerb = (await this.storage.getVerbMetadata(id)) !== null
+    const nounTouched =
+      (await this.generationStore.generationsTouching('noun', id, fromGen, toGen)).length > 0
+    const verbTouched =
+      (await this.generationStore.generationsTouching('verb', id, fromGen, toGen)).length > 0
+    const isNoun = liveNoun || nounTouched
+    const isVerb = liveVerb || verbTouched
+    if (isNoun && isVerb) {
+      throw new Error(
+        `history(): id '${id}' resolves in BOTH the entity and relationship spaces — ` +
+          `ambiguous (should not happen with UUID ids).`
+      )
+    }
+    if (isNoun) return 'noun'
+    if (isVerb) return 'verb'
+    return null
   }
 
   /**
@@ -5471,6 +5771,7 @@ export class Brainy<T = any> implements BrainyInterface<T> {
         get: (id, options) => this.get(id, options),
         find: (query) => this.find(query),
         related: (paramsOrId) => this.related(paramsOrId),
+        resolveGeneration: (target, options) => this.resolveAsOfGeneration(target, options),
         entityFromRecord: (id, record, includeVectors) =>
           this.entityFromGenerationRecord(id, record, includeVectors),
         relationFromRecord: (id, record) => this.relationFromGenerationRecord(id, record),

src/db/db.ts

@@ -116,6 +116,16 @@ export interface DbHost<T = any> {
   find(query: string | FindParams<T>): Promise<Result<T>[]>
   /** Live `brain.related()` (current-generation fast path). */
   related(paramsOrId?: string | RelatedParams): Promise<Relation<T>[]>
+  /**
+   * Resolve a `generation | Date` to a concrete generation (+ timestamp) via the
+   * brain's shared `asOf` resolver — so `since(gen|Date)` shares `asOf`'s
+   * reachability and `Date` semantics. `exclusive` pins the generation before the
+   * resolved one.
+   */
+  resolveGeneration(
+    target: number | Date,
+    options?: { exclusive?: boolean }
+  ): Promise<{ generation: number; timestamp: number }>
   /** Materialize an entity from a generation record's raw stored objects. */
   entityFromRecord(
     id: string,
@@ -213,6 +223,16 @@ export class Db<T = any> {
     return this.gen
   }
 
+  /**
+   * @internal Same-instance guard for cross-`Db` operations like
+   * `Brainy.diff()`: whether this view is backed by `store`. Lets `Brainy`
+   * reject a `Db` endpoint from a different brain without exposing the private
+   * host.
+   */
+  belongsToStore(store: GenerationStore): boolean {
+    return this.host.store === store
+  }
+
   /**
    * The view's wall-clock timestamp (ms since epoch): pin time for `now()`,
    * commit time for `transact()`, and the resolved commit time for `asOf()`.
@@ -752,27 +772,54 @@ export class Db<T = any> {
 
   /**
    * @description The ids changed by committed transactions in the interval
-   * `(priorDb.generation, this.generation]` — the diff between two pinned
-   * views of the same store. Single-operation writes between commits are not
-   * reflected (documented 8.0 history granularity).
+   * `(lowerBound, this.generation]` — the diff between an earlier state and this
+   * view. The lower bound is **exclusive** (contrast `transactionLog`'s inclusive
+   * window). Single-operation writes between commits are not reflected (documented
+   * 8.0 history granularity).
    *
-   * @param priorDb - An earlier view of the SAME store.
+   * The lower bound may be:
+   * - **a `Db`** — an earlier view of the SAME store (its pinned generation);
+   * - **a generation number** — used directly as the exclusive lower bound;
+   * - **a `Date`** — resolved to the generation committed at or before it.
+   *
+   * `db.since(prior)` equals `db.since(prior.generation)` by construction.
+   *
+   * @param lowerBound - An earlier `Db`, a generation number, or a `Date`.
    * @returns Changed entity and relation ids, sorted.
-   * @throws RangeError when `priorDb` is newer than this view, or Error when
-   *   the views belong to different stores.
+   * @throws RangeError when the resolved lower bound is newer than this view.
+   * @throws Error when a `Db` lower bound belongs to a different store.
+   * @throws GenerationCompactedError when a number/`Date` lower bound is below the
+   *   compaction horizon.
+   * @example
+   * const before = brain.now()
+   * await brain.transact(ops)
+   * await brain.now().since(before)        // ids changed by the transaction
+   * await brain.now().since(before.generation)
+   * await brain.now().since(new Date(Date.now() - 3_600_000))
    */
-  async since(priorDb: Db<T>): Promise<ChangedIds> {
+  async since(lowerBound: Db<T> | number | Date): Promise<ChangedIds> {
     this.assertUsable('since')
-    if (priorDb.host.store !== this.host.store) {
-      throw new Error('since(): both Db values must come from the same Brainy instance')
+
+    let fromGen: number
+    if (lowerBound instanceof Db) {
+      if (lowerBound.host.store !== this.host.store) {
+        throw new Error('since(): both Db values must come from the same Brainy instance')
+      }
+      fromGen = lowerBound.gen
+    } else {
+      // number = exclusive lower-bound generation; Date resolves via the shared
+      // asOf resolver (same reachability gate). changedBetween treats fromGen as
+      // exclusive, so since(db) === since(db.generation).
+      fromGen = (await this.host.resolveGeneration(lowerBound)).generation
     }
-    if (priorDb.gen > this.gen) {
+
+    if (fromGen > this.gen) {
       throw new RangeError(
-        `since(): priorDb is at generation ${priorDb.gen}, which is newer than this view ` +
-          `(generation ${this.gen}). Call newerDb.since(olderDb).`
+        `since(): lower-bound generation ${fromGen} is newer than this view ` +
+          `(generation ${this.gen}). Pass an earlier generation/Date, or call newerDb.since(olderDb).`
       )
     }
-    return this.host.store.changedBetween(priorDb.gen, this.gen)
+    return this.host.store.changedBetween(fromGen, this.gen)
   }
 
   // ==========================================================================

src/db/generationStore.ts

@@ -583,6 +583,32 @@ export class GenerationStore {
     }
   }
 
+  /**
+   * @description The committed generations in `(fromGen, toGen]` that touched a
+   * single id, ascending. The per-id companion to {@link changedBetween} — used
+   * by `history()` to walk one entity's change-points without scanning every id.
+   * No all-ids index: it consults the same cached per-generation deltas.
+   * @param kind - `'noun'` for entities, `'verb'` for relationships.
+   * @param id - The id to track.
+   * @param fromGen - Exclusive lower bound.
+   * @param toGen - Inclusive upper bound.
+   */
+  async generationsTouching(
+    kind: 'noun' | 'verb',
+    id: string,
+    fromGen: number,
+    toGen: number
+  ): Promise<number[]> {
+    const result: number[] = []
+    for (const gen of this.committedGens) {
+      if (gen <= fromGen || gen > toGen) continue
+      const delta = await this.getDelta(gen)
+      const touched = kind === 'noun' ? delta.nouns : delta.verbs
+      if (touched.has(id)) result.push(gen)
+    }
+    return result
+  }
+
   /**
    * @description Assert that generation `gen` is reachable (not compacted
    * away) and within the committed range, then return it. Used by `asOf()`.

src/db/stableEqual.ts

@@ -0,0 +1,64 @@
+/**
+ * @module db/stableEqual
+ * @description Key-order-insensitive deep equality, used by {@link Brainy.diff}
+ * to decide whether an id present at both endpoints actually *changed* value.
+ *
+ * A naive `JSON.stringify(a) === JSON.stringify(b)` is wrong for this: object key
+ * order is insignificant for stored-metadata equality, but `stringify` is
+ * order-sensitive, so `{a:1,b:2}` and `{b:2,a:1}` would mis-compare as changed and
+ * a no-op re-write would show up as a spurious `modified`. This walks both values
+ * structurally — object keys compared as a set, array elements compared in order
+ * (arrays ARE order-significant) — over the JSON-shaped values that live in
+ * generation records.
+ */
+
+/**
+ * @description Deep-equal two JSON-shaped values, insensitive to object key order.
+ * @param a - First value.
+ * @param b - Second value.
+ * @returns `true` if structurally equal (key order ignored; array order honored;
+ *   `NaN` equals `NaN`).
+ * @example
+ * stableDeepEqual({ a: 1, b: 2 }, { b: 2, a: 1 }) // → true
+ * stableDeepEqual([1, 2], [2, 1])                 // → false (order matters)
+ */
+export function stableDeepEqual(a: unknown, b: unknown): boolean {
+  if (a === b) return true
+
+  // NaN is never === itself, but for a stable value comparison NaN equals NaN.
+  if (typeof a === 'number' && typeof b === 'number') {
+    return Number.isNaN(a) && Number.isNaN(b)
+  }
+
+  // Distinct primitives, or exactly one of them null/non-object → not equal
+  // (the `a === b` above already returned true for equal primitives and for
+  // both-null).
+  if (typeof a !== 'object' || typeof b !== 'object' || a === null || b === null) {
+    return false
+  }
+
+  const aIsArr = Array.isArray(a)
+  const bIsArr = Array.isArray(b)
+  if (aIsArr !== bIsArr) return false
+
+  if (aIsArr) {
+    const aa = a as unknown[]
+    const ba = b as unknown[]
+    if (aa.length !== ba.length) return false
+    for (let i = 0; i < aa.length; i++) {
+      if (!stableDeepEqual(aa[i], ba[i])) return false
+    }
+    return true
+  }
+
+  const ao = a as Record<string, unknown>
+  const bo = b as Record<string, unknown>
+  const aKeys = Object.keys(ao)
+  const bKeys = Object.keys(bo)
+  if (aKeys.length !== bKeys.length) return false
+  for (const k of aKeys) {
+    if (!Object.prototype.hasOwnProperty.call(bo, k)) return false
+    if (!stableDeepEqual(ao[k], bo[k])) return false
+  }
+  return true
+}

src/db/types.ts

@@ -25,7 +25,7 @@
  * `docs/ADR-001-generational-mvcc.md` for the full justification.
  */
 
-import type { AddParams, UpdateParams, RelateParams } from '../types/brainy.types.js'
+import type { AddParams, UpdateParams, RelateParams, Entity, Relation } from '../types/brainy.types.js'
 
 // ============================================================================
 // Transaction operations (brain.transact input)
@@ -193,6 +193,58 @@ export interface ChangedIds {
   toGeneration: number
 }
 
+/**
+ * @description The result of {@link Brainy.diff}: ids that came into existence,
+ * went away, or changed value between two states, each split by kind. Unlike the
+ * raw touched-id set of {@link ChangedIds}, `diff` EARNS its name — it resolves
+ * each touched id at BOTH endpoints and classifies by existence (added/removed)
+ * and stable value comparison (modified). An id touched within the interval but
+ * whose endpoint states are identical (touched-then-reverted) appears in NONE of
+ * the three buckets. Orientation is `a → b`: `added` exists at `b` not `a`.
+ */
+export interface DiffResult {
+  /** Ids absent at `a`, present at `b`. */
+  added: { nouns: string[]; verbs: string[] }
+  /** Ids present at `a`, absent at `b`. */
+  removed: { nouns: string[]; verbs: string[] }
+  /** Ids present at both endpoints with a changed stored value. */
+  modified: { nouns: string[]; verbs: string[] }
+  /** The resolved generation of endpoint `a`. */
+  fromGeneration: number
+  /** The resolved generation of endpoint `b`. */
+  toGeneration: number
+}
+
+/**
+ * @description One version of a single entity or relationship in its
+ * {@link EntityHistory} — the materialized state at a committed generation that
+ * changed it. `value` is `null` when the id did not exist at that version
+ * (created-after / removed). Granularity is `transact()` commits.
+ */
+export interface HistoryVersion<T = any> {
+  /** The committed generation that produced this version. */
+  generation: number
+  /** Commit timestamp of that generation (ms since epoch). */
+  timestamp: number
+  /** Materialized state at this version, or `null` if the id did not exist then. */
+  value: Entity<T> | Relation<T> | null
+}
+
+/**
+ * @description The result of {@link Brainy.history}: every distinct version of
+ * ONE id over a generation range, oldest → newest. Consecutive identical states
+ * are collapsed (one entry per distinct state). `kind` is auto-detected from the
+ * id's presence in the noun vs verb spaces.
+ */
+export interface EntityHistory<T = any> {
+  /** The id whose history this is. */
+  id: string
+  /** Whether `id` is an entity (`'noun'`) or relationship (`'verb'`). */
+  kind: 'noun' | 'verb'
+  /** Distinct versions, oldest first. */
+  versions: HistoryVersion<T>[]
+}
+
 // ============================================================================
 // Persisted record shapes
 // ============================================================================

src/index.ts

@@ -172,7 +172,10 @@ export type {
   TxLogEntry,
   CompactHistoryOptions,
   CompactHistoryResult,
-  ChangedIds
+  ChangedIds,
+  DiffResult,
+  HistoryVersion,
+  EntityHistory
 } from './db/types.js'
 // Optional provider capability for generation-aware native indexes
 export { isVersionedIndexProvider } from './plugin.js'

tests/integration/db-temporal.test.ts

@@ -0,0 +1,381 @@
+/**
+ * @module tests/integration/db-temporal
+ * @description Proof suite for Brainy 8.0's temporal RANGE verbs, built on the
+ * single-point `asOf()` foundation (proven byte-identical in db-mvcc). Each test
+ * PROVES a stated guarantee:
+ *
+ *  1. asOf(g, { exclusive }) pins g−1 (strict-before); exclusive of the first
+ *     commit is the empty generation 0, never a RangeError.
+ *  2. since() accepts Db | generation | Date equivalently, with the direction
+ *     guard; the lower bound is EXCLUSIVE.
+ *  3. transactionLog({ from, to }) windows INCLUSIVELY on both ends (the contrast
+ *     to since's exclusive lower bound) and applies `limit` AFTER the window.
+ *  4. diff() EARNS its name: it does NOT return raw changed-ids — an id created
+ *     and removed within the interval lands in NO bucket; added/removed/modified
+ *     are classified by existence + a stable value comparison.
+ *  5. history() ties to the trusted asOf path: every version's value deep-equals
+ *     asOf(version.generation).get(id), a removal is a null value, order is oldest→newest.
+ *  6. Composition: "type T changed in (g1, g2]" computed two ways (diff ids filtered
+ *     to T, vs asOf(g2).find({type:T}) ∩ changed-ids) AGREE — including a where filter.
+ *  7. Granularity: single-operation writes (outside transact()) are invisible to the
+ *     temporal verbs (transact commits only).
+ *  8. Compaction policy contrast: diff/since THROW below the horizon; history TRUNCATES
+ *     to it. (Locked so a refactor can't unify them incorrectly.)
+ *
+ * Mirrors the db-mvcc harness: explicit vectors (no embedder), deterministic
+ * UUID-shaped ids, afterEach teardown. db-mvcc itself re-proves asOf is unchanged.
+ */
+
+import { describe, it, expect, afterEach } from 'vitest'
+import * as fs from 'node:fs'
+import * as os from 'node:os'
+import * as path from 'node:path'
+import { Brainy } from '../../src/brainy.js'
+import { GenerationCompactedError } from '../../src/db/errors.js'
+import type { GenerationStore } from '../../src/db/generationStore.js'
+import { NounType } from '../../src/types/graphTypes.js'
+
+/** Deterministic 384-dim vector so no test ever invokes the embedder. */
+function vec(seed: number): number[] {
+  return Array.from({ length: 384 }, (_, i) => ((seed * 31 + i * 7) % 100) / 100)
+}
+
+/** Map a label to a deterministic UUID-shaped id (storage shards by UUID hex). */
+function uid(label: string): string {
+  let h1 = 0x811c9dc5
+  for (let i = 0; i < label.length; i++) h1 = Math.imul(h1 ^ label.charCodeAt(i), 0x01000193) >>> 0
+  let h2 = 0xdeadbeef
+  for (let i = label.length - 1; i >= 0; i--) h2 = Math.imul(h2 ^ label.charCodeAt(i), 0x85ebca6b) >>> 0
+  const hex = h1.toString(16).padStart(8, '0') + h2.toString(16).padStart(8, '0')
+  return `00000000-0000-4000-8000-${hex.slice(0, 12)}`
+}
+
+function generationStoreOf(brain: Brainy): GenerationStore {
+  return (brain as unknown as { generationStore: GenerationStore }).generationStore
+}
+
+describe('8.0 Db API — temporal range verbs', () => {
+  const brains: Brainy[] = []
+  const tempDirs: string[] = []
+
+  async function openMemoryBrain(): Promise<Brainy> {
+    const brain = new Brainy({ requireSubtype: false, storage: { type: 'memory' } })
+    await brain.init()
+    brains.push(brain)
+    return brain
+  }
+
+  afterEach(async () => {
+    for (const brain of brains.splice(0)) {
+      try {
+        await brain.close()
+      } catch {
+        /* already closed */
+      }
+    }
+    for (const dir of tempDirs.splice(0)) {
+      await fs.promises.rm(dir, { recursive: true, force: true })
+    }
+  })
+
+  // 1. asOf exclusive ----------------------------------------------------------
+  it('asOf(g, { exclusive }) pins g−1; exclusive clamps at gen 0 without a RangeError', async () => {
+    const brain = await openMemoryBrain()
+    const a = uid('exc-a')
+    const rAdd = await brain.transact([
+      { op: 'add', id: a, type: NounType.Document, data: 'a', vector: vec(1), metadata: { v: 1 } }
+    ])
+    const gAdd = rAdd.generation
+    await rAdd.release()
+    const rUpd = await brain.transact([{ op: 'update', id: a, metadata: { v: 2 } }])
+    const gUpd = rUpd.generation
+    await rUpd.release()
+
+    // exclusive of gUpd = the state immediately before it (= the add generation, v:1)
+    const before = await brain.asOf(gUpd, { exclusive: true })
+    expect(before.generation).toBe(gUpd - 1)
+    expect((await before.get(a))?.metadata?.v).toBe(1)
+    await before.release()
+
+    const at = await brain.asOf(gUpd) // inclusive
+    expect((await at.get(a))?.metadata?.v).toBe(2)
+    await at.release()
+
+    // exclusive clamps at 0 (never a RangeError): strict-before generation 1 is the
+    // empty pre-commit state — `a` does not exist there.
+    const zero = await brain.asOf(1, { exclusive: true })
+    expect(zero.generation).toBe(0)
+    expect(await zero.get(a)).toBeNull()
+    await zero.release()
+  })
+
+  // 2. since 3-forms + direction guard ----------------------------------------
+  it('since() accepts Db | generation | Date equivalently; lower bound is exclusive; direction guarded', async () => {
+    const brain = await openMemoryBrain()
+    const a = uid('since-a')
+    const b = uid('since-b')
+    const r1 = await brain.transact([
+      { op: 'add', id: a, type: NounType.Document, data: 'a', vector: vec(1), metadata: {} }
+    ])
+    const g1 = r1.generation // a's add generation
+    await brain.transact([
+      { op: 'add', id: b, type: NounType.Document, data: 'b', vector: vec(2), metadata: {} }
+    ])
+    await brain.transact([{ op: 'update', id: a, metadata: { x: 1 } }])
+
+    const now = brain.now()
+    const viaDb = await now.since(r1) // changes in (g1, now]
+    const viaGen = await now.since(g1)
+    const viaEpoch = await now.since(new Date(0)) // resolves to gen 0 → (0, now]
+
+    // since(db) === since(db.generation); the EXCLUSIVE lower bound omits a's own add@g1
+    expect(viaDb).toEqual(viaGen)
+    expect(viaDb.fromGeneration).toBe(g1)
+    expect(viaDb.nouns).toEqual([a, b].sort()) // a (updated after g1) + b (added after g1)
+    expect(viaEpoch.nouns).toEqual([a, b].sort()) // (0, now] also includes a's creation, still {a, b}
+
+    // direction guard: an older view cannot be `since` a newer lower bound
+    const older = await brain.asOf(1)
+    await expect(older.since(now)).rejects.toBeInstanceOf(RangeError)
+    await older.release()
+    await now.release()
+    await r1.release()
+  })
+
+  // 3. transactionLog window (inclusive both ends) + limit-after-window --------
+  it('transactionLog({ from, to }) windows inclusively on both ends and applies limit last', async () => {
+    const brain = await openMemoryBrain()
+    const gens: number[] = []
+    for (let v = 1; v <= 5; v++) {
+      const r = await brain.transact([
+        {
+          op: 'add',
+          id: uid(`log-${v}`),
+          type: NounType.Document,
+          data: `d${v}`,
+          vector: vec(v),
+          metadata: { v }
+        }
+      ])
+      gens.push(r.generation) // 5 consecutive generations, one log entry each
+      await r.release()
+    }
+
+    const all = await brain.transactionLog()
+    expect(all.map((e) => e.generation)).toEqual([...gens].reverse()) // newest first
+
+    // INCLUSIVE both ends — gens[1] AND gens[3] are present (contrast since's exclusive lower).
+    const windowed = await brain.transactionLog({ from: gens[1], to: gens[3] })
+    expect(windowed.map((e) => e.generation)).toEqual([gens[3], gens[2], gens[1]])
+
+    // limit applies AFTER the window (newest first within the window)
+    const limited = await brain.transactionLog({ from: gens[1], to: gens[3], limit: 2 })
+    expect(limited.map((e) => e.generation)).toEqual([gens[3], gens[2]])
+
+    // Inclusivity CONTRAST vs since: transactionLog INCLUDES `from`; since EXCLUDES it.
+    const logFrom = await brain.transactionLog({ from: gens[1] }) // [gens[1], …]
+    expect(logFrom.map((e) => e.generation).includes(gens[1])).toBe(true)
+    const sinceFrom = await brain.now().since(gens[1]) // (gens[1], …] — exclusive lower
+    expect(sinceFrom.fromGeneration).toBe(gens[1])
+
+    await expect(
+      brain.transactionLog({ from: gens[3], to: gens[1] })
+    ).rejects.toBeInstanceOf(RangeError)
+  })
+
+  // 4. diff EARNS its name -----------------------------------------------------
+  it('diff() classifies added/removed/modified — and an id created+removed within the interval is in NO bucket', async () => {
+    const brain = await openMemoryBrain()
+    const persistent = uid('diff-persistent')
+    const created = uid('diff-created')
+    const removed = uid('diff-removed')
+    const ephemeral = uid('diff-ephemeral')
+
+    // gen 1: baseline — persistent + removed exist
+    await (
+      await brain.transact([
+        { op: 'add', id: persistent, type: NounType.Document, data: 'p', vector: vec(1), metadata: { v: 1 } },
+        { op: 'add', id: removed, type: NounType.Document, data: 'r', vector: vec(2), metadata: { v: 1 } }
+      ])
+    ).release()
+    const g1 = brain.generation()
+
+    // gen 2: create `ephemeral` and `created`; modify `persistent`; delete `removed`
+    await (
+      await brain.transact([
+        { op: 'add', id: ephemeral, type: NounType.Document, data: 'e', vector: vec(3), metadata: { v: 1 } },
+        { op: 'add', id: created, type: NounType.Document, data: 'c', vector: vec(4), metadata: { v: 1 } },
+        { op: 'update', id: persistent, metadata: { v: 2 } },
+        { op: 'remove', id: removed }
+      ])
+    ).release()
+    // gen 3: delete `ephemeral` (so it was BORN and DIED inside (g1, g3])
+    await (await brain.transact([{ op: 'remove', id: ephemeral }])).release()
+    const g3 = brain.generation()
+
+    const d = await brain.diff(g1, g3)
+    expect(d.added.nouns).toEqual([created]) // exists at g3, not g1
+    expect(d.removed.nouns).toEqual([removed]) // exists at g1, not g3
+    expect(d.modified.nouns).toEqual([persistent]) // exists both, value changed
+    // EARNS-ITS-NAME: `ephemeral` was touched (raw changedBetween would list it) but is
+    // absent at BOTH endpoints → it appears in NONE of the buckets.
+    expect(d.added.nouns).not.toContain(ephemeral)
+    expect(d.removed.nouns).not.toContain(ephemeral)
+    expect(d.modified.nouns).not.toContain(ephemeral)
+
+    // Orientation: diff(g3, g1) flips added/removed.
+    const rev = await brain.diff(g3, g1)
+    expect(rev.added.nouns).toEqual([removed])
+    expect(rev.removed.nouns).toEqual([created])
+    expect(rev.modified.nouns).toEqual([persistent])
+
+    // diff(g, g) is empty.
+    const empty = await brain.diff(g3, g3)
+    expect(empty.added.nouns).toEqual([])
+    expect(empty.modified.nouns).toEqual([])
+  })
+
+  // 5. history cross-checks the trusted asOf path ------------------------------
+  it('history() — each version deep-equals asOf(version.generation).get(id); removal is a null value', async () => {
+    const brain = await openMemoryBrain()
+    const a = uid('hist-a')
+    await (
+      await brain.transact([
+        { op: 'add', id: a, type: NounType.Document, data: 'a', vector: vec(1), metadata: { v: 1 } }
+      ])
+    ).release() // gen 1
+    await (await brain.transact([{ op: 'update', id: a, metadata: { v: 2 } }])).release() // gen 2
+    await (await brain.transact([{ op: 'update', id: a, metadata: { v: 3 } }])).release() // gen 3
+    await (await brain.transact([{ op: 'remove', id: a }])).release() // gen 4
+
+    const h = await brain.history(a)
+    expect(h.kind).toBe('noun')
+    // oldest → newest, ending in a removal (null value)
+    const vs = h.versions
+    expect(vs.length).toBeGreaterThanOrEqual(4)
+    for (let i = 1; i < vs.length; i++) {
+      expect(vs[i].generation).toBeGreaterThan(vs[i - 1].generation) // strictly ascending
+    }
+    expect(vs[vs.length - 1].value).toBeNull() // removed at the end
+
+    // Each version ties to the trusted asOf path.
+    for (const v of vs) {
+      const db = await brain.asOf(v.generation)
+      const viaAsOf = await db.get(a)
+      await db.release()
+      if (v.value === null) expect(viaAsOf).toBeNull()
+      else expect(viaAsOf).toEqual(v.value)
+    }
+
+    // The distinct user-visible values appear in order.
+    const versionsWithValue = vs.filter((v) => v.value !== null)
+    expect(versionsWithValue.map((v) => (v.value as any).metadata?.v)).toEqual([1, 2, 3])
+
+    // Unknown id → empty history (no throw).
+    const unknown = await brain.history(uid('hist-nobody'))
+    expect(unknown.versions).toEqual([])
+  })
+
+  // 6. Composition proof -------------------------------------------------------
+  it('composition: "type T changed in (g1, g2]" agrees computed via diff vs via asOf(g2).find ∩ changed', async () => {
+    const brain = await openMemoryBrain()
+    const p1 = uid('comp-p1')
+    const p2 = uid('comp-p2')
+    const p3 = uid('comp-p3')
+    const d1 = uid('comp-d1')
+
+    await (
+      await brain.transact([
+        { op: 'add', id: p1, type: NounType.Person, data: 'p1', vector: vec(1), metadata: { team: 'x' } },
+        { op: 'add', id: d1, type: NounType.Document, data: 'd1', vector: vec(2), metadata: { team: 'x' } }
+      ])
+    ).release()
+    const g1 = brain.generation()
+    await (
+      await brain.transact([
+        { op: 'add', id: p2, type: NounType.Person, data: 'p2', vector: vec(3), metadata: { team: 'x' } },
+        { op: 'update', id: d1, metadata: { team: 'y' } }
+      ])
+    ).release()
+    await (
+      await brain.transact([
+        { op: 'add', id: p3, type: NounType.Person, data: 'p3', vector: vec(4), metadata: { team: 'z' } }
+      ])
+    ).release()
+    const g2 = brain.generation()
+
+    // Way 1 — from diff: ids that came-into-being or changed in (g1, g2], filtered to Person at g2.
+    const d = await brain.diff(g1, g2)
+    const changedNouns = [...d.added.nouns, ...d.modified.nouns]
+    const dbAtG2 = await brain.asOf(g2)
+    const way1: string[] = []
+    for (const id of changedNouns) {
+      const e = await dbAtG2.get(id)
+      if (e?.type === NounType.Person) way1.push(id)
+    }
+
+    // Way 2 — from find ∩ changed: all Person at g2, intersect with the changed-id set.
+    const personsAtG2 = await dbAtG2.find({ type: NounType.Person, limit: 100 })
+    const changedSet = new Set([...d.added.nouns, ...d.removed.nouns, ...d.modified.nouns])
+    const way2 = personsAtG2.map((r) => r.id).filter((id) => changedSet.has(id))
+
+    expect(way1.sort()).toEqual(way2.sort())
+    expect(way1.sort()).toEqual([p2, p3].sort()) // p2 added, p3 added; p1 unchanged; d1 is a Document
+
+    // With a where filter: Person on team 'x' changed in (g1, g2] → just p2.
+    const personsTeamX = await dbAtG2.find({ type: NounType.Person, where: { team: 'x' }, limit: 100 })
+    const teamXChanged = personsTeamX.map((r) => r.id).filter((id) => changedSet.has(id))
+    expect(teamXChanged).toEqual([p2])
+
+    await dbAtG2.release()
+  })
+
+  // 7. Granularity -------------------------------------------------------------
+  it('granularity: single-operation writes (outside transact) are invisible to the temporal verbs', async () => {
+    const brain = await openMemoryBrain()
+    const a = uid('gran-a')
+    const r1 = await brain.transact([
+      { op: 'add', id: a, type: NounType.Document, data: 'a', vector: vec(1), metadata: { v: 1 } }
+    ])
+    await r1.release()
+    expect((await brain.transactionLog()).length).toBe(1)
+
+    // A single-op write bumps the counter but writes no generation record/log entry.
+    await brain.update({ id: a, metadata: { v: 2 } })
+
+    expect((await brain.transactionLog()).length).toBe(1) // unchanged — not logged
+    const d = await brain.diff(r1.generation, brain.generation())
+    expect(d.added.nouns).toEqual([]) // the single-op update is not a recorded change
+    expect(d.modified.nouns).toEqual([])
+  })
+
+  // 8. Compaction policy contrast ---------------------------------------------
+  it('compaction: diff/since THROW below the horizon; history TRUNCATES to it', async () => {
+    const brain = await openMemoryBrain()
+    const a = uid('comp-a')
+    for (let v = 1; v <= 6; v++) {
+      await (
+        await brain.transact([
+          v === 1
+            ? { op: 'add', id: a, type: NounType.Document, data: 'a', vector: vec(v), metadata: { v } }
+            : { op: 'update', id: a, metadata: { v } }
+        ])
+      ).release()
+    } // gens 1..6, all pins released
+
+    await brain.compactHistory({ retainGenerations: 2 }) // raise the horizon
+    const horizon = generationStoreOf(brain).horizon()
+    expect(horizon).toBeGreaterThan(0)
+
+    // diff / since reaching below the horizon THROW.
+    await expect(brain.diff(0, 6)).rejects.toBeInstanceOf(GenerationCompactedError)
+    const now = brain.now()
+    await expect(now.since(0)).rejects.toBeInstanceOf(GenerationCompactedError)
+    await now.release()
+
+    // history TRUNCATES (no throw) — its versions start at or above the horizon.
+    const h = await brain.history(a)
+    expect(h.versions.length).toBeGreaterThan(0)
+    for (const v of h.versions) expect(v.generation).toBeGreaterThanOrEqual(horizon)
+  })
+})

tests/unit/db/stableEqual.test.ts

@@ -0,0 +1,53 @@
+/**
+ * @module tests/unit/db/stableEqual
+ * @description Unit proof for the key-order-insensitive deep-equal that
+ * {@link Brainy.diff} uses to decide whether an id present at both endpoints
+ * actually changed. The risk it guards: a naive JSON.stringify comparison is
+ * key-order-sensitive and would report a no-op re-write as `modified`.
+ */
+import { describe, it, expect } from 'vitest'
+import { stableDeepEqual } from '../../../src/db/stableEqual.js'
+
+describe('stableDeepEqual', () => {
+  it('ignores object key order (the core diff requirement)', () => {
+    expect(stableDeepEqual({ a: 1, b: 2 }, { b: 2, a: 1 })).toBe(true)
+    expect(stableDeepEqual({ a: 1, b: 2, c: { x: 1, y: 2 } }, { c: { y: 2, x: 1 }, b: 2, a: 1 })).toBe(true)
+  })
+
+  it('honors array order (arrays are order-significant)', () => {
+    expect(stableDeepEqual([1, 2, 3], [1, 2, 3])).toBe(true)
+    expect(stableDeepEqual([1, 2, 3], [3, 2, 1])).toBe(false)
+    expect(stableDeepEqual([1, 2], [1, 2, 3])).toBe(false)
+  })
+
+  it('recurses into nested objects and arrays', () => {
+    expect(
+      stableDeepEqual(
+        { tags: ['a', 'b'], meta: { n: 1, deep: { z: [1, { q: 2 }] } } },
+        { meta: { deep: { z: [1, { q: 2 }] }, n: 1 }, tags: ['a', 'b'] }
+      )
+    ).toBe(true)
+    expect(
+      stableDeepEqual({ meta: { deep: { z: [1, { q: 2 }] } } }, { meta: { deep: { z: [1, { q: 3 }] } } })
+    ).toBe(false)
+  })
+
+  it('distinguishes primitives, null, and types', () => {
+    expect(stableDeepEqual(1, 1)).toBe(true)
+    expect(stableDeepEqual(1, '1')).toBe(false)
+    expect(stableDeepEqual(null, null)).toBe(true)
+    expect(stableDeepEqual(null, {})).toBe(false)
+    expect(stableDeepEqual({ a: 1 }, { a: 1, b: undefined })).toBe(false) // extra key
+    expect(stableDeepEqual(true, false)).toBe(false)
+  })
+
+  it('treats NaN as equal to NaN (stable value comparison)', () => {
+    expect(stableDeepEqual(NaN, NaN)).toBe(true)
+    expect(stableDeepEqual({ x: NaN }, { x: NaN })).toBe(true)
+    expect(stableDeepEqual(NaN, 0)).toBe(false)
+  })
+
+  it('an object and an array of the same length are not equal', () => {
+    expect(stableDeepEqual({ 0: 'a', 1: 'b' }, ['a', 'b'])).toBe(false)
+  })
+})