docs: measured performance envelopes v1 (per-op p50/p95 at 1k and 10k, pure-JS floor)

First edition of the per-release performance-envelope contract: every
number measured against the built dist on stated hardware, never
projected. Sub-0.1ms get/related (adjacency O(degree), scale-flat),
1-9ms indexed metadata finds, ~178ms semantic (query embedding
dominates), ~167ms durability-priced single-op writes flat across
scale, 8-45ms steady-state flush independent of history backlog
(the 8.9.0 change). Two weak spots stated honestly: addMany commits
per-item today (batched chunk commits belong to the unified-commit
roadmap), and pure-JS warm open grows with corpus (4.9s at 10k) —
the native accelerator's reason to exist. Refresh rule: any release
touching a measured path re-measures in the same release.

RELEASES.md

@@ -8,8 +8,53 @@ Full auto-generated changelog: `CHANGELOG.md` · Releases: https://github.com/so
 - Debugging data, query, or storage behaviour
 - A new Brainy feature is available that you want to adopt
 
+## Removed APIs — 7.x → 8.x (the complete ledger)
+
+Every public API removed at the 8.0 major, with its sanctioned replacement. If your code
+still calls a left-column name on 8.x it throws (or the config key is rejected) — the
+replacement is always a one-line change. (Standing contract from 8.9.0 forward: removals
+happen only at majors, after ≥1 minor of loud runtime deprecation naming the replacement.)
+
+| Removed (7.x) | Replacement (8.x) |
+|---|---|
+| `brain.search(query, k)` | `find({ query })` — semantic; `find({ query, searchMode })` for hybrid |
+| `brain.getRelations({...})` | `related(id, opts)` for adjacency; `find({ connected: {...} })` for scoped traversal |
+| `brain.neural()` clustering | `find({ vector })` + aggregation `GROUP BY` |
+| `Db.search()` | `db.find({ vector })` |
+| Pre-8.0 storage path aliases (`directory`, `basePath`, …) | one `storage.path` key (old aliases throw) |
+| Reserved keys inside `metadata` bags (silently remapped in 7.x) | top-level params (`subtype`, `visibility`, `confidence`, `weight`, …) — reserved-in-bag throws |
+| 7.x COW branches layout (`branches/main/`) | generational MVCC (`asOf()`, `now()`, `db.persist(path)`) — on-disk migration is automatic at first 8.x open |
+
+The fork/snapshot family (`brain.snapshot()`, `createSnapshot()`, `restoreSnapshot()`)
+is sometimes cited as a 7.x removal — those methods never existed on 7.x; the 8.0 Db API
+(`asOf`/`persist`/`restore({confirm})`) is their first real implementation.
+
 ---
 
+## v8.9.0 — 2026-07-19 (flush is durability-only: history maintenance moves to close())
+
+The write path stops paying maintenance costs — the last structural piece of the
+flush-storm class (a production deployment measured single writes blocked 25–191s behind
+history reclaim running inline on flush under memory pressure):
+
+- **`flush()` never compacts history.** It persists the current window's deltas and
+  nothing else — its cost no longer depends on history backlog or retention mode, in any
+  configuration. **`close()` is the auto-compaction site** (time-bounded per pass, ~5s;
+  an early stop is a consistent prefix and the next pass resumes).
+- **`compactHistory()` gains `timeBudgetMs`** — bound your own maintenance windows; the
+  same resumable-prefix guarantee applies.
+- **The documented trade**: a long-lived writer that never closes accumulates history
+  until its next explicit `compactHistory()`. Predictable writes, explicit maintenance.
+  If you run bounded retention on an always-on service, schedule a periodic
+  `compactHistory({ ...caps, timeBudgetMs })` in your maintenance window.
+- **New public doc: `docs/performance-envelopes.md`** — measured per-op envelopes
+  (p50/p95 at stated scales, hardware, and backend, with the measuring script cited).
+  Refresh rule going forward: any release touching a measured path re-runs that op's
+  benchmark and updates the envelope in the same release.
+- **New in this file: the Removed APIs 7.x→8.x table** (top of this document) — every
+  removal with its sanctioned replacement, one place, per the engine-currency contract.
+  Standing from here: removals only at majors, after ≥1 minor of loud runtime deprecation.
+
 ## v8.8.2 — 2026-07-19 (one field-resolution law: reserved-field aggregates stop drifting)
 
 Four fixes from a consumer conformance audit, all rooted in the same disease — two field-resolution