docs: add Keep a Changelog for 2.0.0

CHANGELOG.md

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+# Changelog
+
+All notable changes to this project are documented in this file.
+
+The format is based on [Keep a Changelog](https://keepachangelog.com/en/1.1.0/),
+and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0.html).
+
+## [Unreleased]
+
+## [2.0.0] - 2026-09-18
+
+Security modernization. Requires **Node.js 18+**. Vendors **msgpack-c c-7.0.2**.
+GitHub Actions tests Node 18/20/22 on Ubuntu, macOS, and Windows 2022.
+
+### Added
+
+- Fail-closed unpack limits: array/map length ≤ 1,000,000, str/bin/ext ≤ 32 MiB,
+  nesting depth ≤ 512. The bomb `dd ff 00 00 00` throws instead of allocating.
+- Pack recursion cap of 512 (deep input throws instead of SIGSEGV).
+- `Stream` emits `error` on unpack throw and drops the offending buffer.
+- `worker_threads` support (`NAN_MODULE_WORKER_ENABLED`, thread-local sbuffer
+  pool and `bytes_remaining`).
+- TypeScript types (`index.d.ts`).
+- `node:test` suite, c8 + gcov coverage gated at 95%.
+- `SECURITY.md` and `COVERAGE.md`.
+
+### Changed
+
+- `nan` is `^2.23.1` (installs 2.x current).
+- `binding.gyp` no longer pins `-std=c++11`.
+- node-gyp 10+ uses Python 3.
+- Dates pack as ISO-8601 strings (`toISOString()`) at every nesting level.
+- Objects with `toJSON()` use that return value at every nesting level.
+- Numeric own keys are packed instead of dropped.
+- Cycle marks use V8 private symbols so a user key named `_msgpack_stack` is
+  kept.
+- Integral doubles outside uint64/int64 range (for example `1e30`) pack as
+  float64.
+- Map keys are installed with `DefineOwnProperty` so a wire `__proto__` cannot
+  replace the decoded object's prototype.
+- Property reads during pack go through `Nan::TryCatch` (throwing getters and
+  Proxy traps raise a catchable error).
+- `Stream` snapshots `bytes_remaining` and consumes the frame **before**
+  `emit('msg')`, so a listener that unpacks or throws cannot desync or replay.
+- `Stream` emits packed integer `0` and packed `null` as real messages.
+
+### Fixed
+
+- Top-level `Buffer` packs as MessagePack bin, not `Buffer.prototype.toJSON`'s
+  `{type, data}` map (`#49`).
+- sbuffer leak on pack throw (`#25686`).
+- Python msgpack maps with bin8 payloads unpack (`#10`).
+- `Stream` no longer skips packed `0` (`#44`).
+
+### Security
+
+- Unpacker rejects oversized headers before the C decoder allocates.
+- Pack throw paths free or return pooled sbuffers on every exit.
+- msgpack-c c-7.0.2 includes unpacker buffer-expansion overflow checks.
+
+[Unreleased]: https://github.com/msgpack/msgpack-node/compare/e04c9b55f98d64512174d6e859b8294b729659a2...HEAD
+[2.0.0]: https://github.com/msgpack/msgpack-node/commit/e04c9b55f98d64512174d6e859b8294b729659a2