docs(changelog): introduce CHANGELOG; note merge + cherry-pick in README

CHANGELOG.md captures the v2.2.0 additions (git_merge, git_cherry_pick,
batch_commit push: "after") alongside condensed historical entries back
to 1.0.0, so consumers have a single chronological reference without
scraping release pages. README one-liner updated to include the new
mutating tools.

Author: AlbinoGeek

CHANGELOG.md

@@ -0,0 +1,48 @@
+# Changelog
+
+All notable changes to `@rethunk/mcp-multi-root-git` are documented here. Format loosely follows [Keep a Changelog](https://keepachangelog.com); the project uses [Semantic Versioning](https://semver.org).
+
+## [2.2.0] — 2026-04-17
+
+Mutating git operations: merge, cherry-pick, and optional push-after for `batch_commit`.
+
+### Added
+
+- **`git_merge`** tool — merge one or more source branches into a destination. Default strategy `auto` cascades fast-forward → rebase → merge-commit per source, preferring linear history. Refuses on dirty tree; stops on first conflict with structured path report. Optional `deleteMergedBranches` / `deleteMergedWorktrees` cascade cleanup, always skipping protected names (`main`, `master`, `dev`, `develop`, `stable`, `trunk`, `prod`, `production`, `release*`, `hotfix*`).
+- **`git_cherry_pick`** tool — play commits from one or more sources onto a destination. Sources may be SHAs, `A..B` ranges, or branch names (expanded to `onto..<branch>`, oldest-first). Uses `--empty=drop` so patch-equivalent re-applies add nothing. Refuses on dirty tree; stops on first conflict, aborting cleanly. Same protected-name cleanup flags as `git_merge`.
+- **`batch_commit`** `push: "after"` — push the current branch to its upstream once every commit in the batch lands. Omitted by default; no behavior change for existing callers.
+
+### Changed
+
+- **Internal** — shared ref/branch helpers extracted to a common module; merge/cherry-pick/batch-commit implementations now reuse the same dirty-tree guards, protected-name checks, and upstream detection.
+- **Tooling** — Biome upgraded to 2.4.11; dev dependency refresh.
+
+### Documentation
+
+- `docs/mcp-tools.md` — `git_merge` and `git_cherry_pick` sections with parameters, JSON shape, and error codes; `batch_commit` `push: "after"` option documented.
+
+## [2.1.0] — prior
+
+- Added `git_log` — path-filtered, time-windowed log across workspace roots.
+- Added `git_diff_summary` — structured, token-efficient diff viewer with per-file truncation and default exclusions (lock files, `dist`, vendor).
+- Added `batch_commit` — sequential multi-commit tool. Mutating, not idempotent.
+- Test harness: fake-server duck-type lets unit tests drive the full FastMCP execute path without a live transport.
+
+## [2.0.1] — prior
+
+- Bug fixes and internal cleanup; no public tool-surface change.
+
+## [2.0.0] — prior
+
+- **Breaking:** JSON response envelope removed. `MCP_JSON_FORMAT_VERSION` now `"2"`; payloads are minified, and optional fields are omitted when empty / `null` / `false` (consumers test for presence, not equality to `null`).
+- Initial preset file schema (`.rethunk/git-mcp-presets.json`) with wrapped and legacy-map layouts.
+
+## [1.0.0] — prior
+
+- Initial release: `git_status`, `git_inventory`, `git_parity`, `list_presets`.
+
+[2.2.0]: https://github.com/Rethunk-AI/mcp-multi-root-git/releases/tag/v2.2.0
+[2.1.0]: https://github.com/Rethunk-AI/mcp-multi-root-git/releases/tag/v2.1.0
+[2.0.1]: https://github.com/Rethunk-AI/mcp-multi-root-git/releases/tag/v2.0.1
+[2.0.0]: https://github.com/Rethunk-AI/mcp-multi-root-git/releases/tag/v2.0.0
+[1.0.0]: https://github.com/Rethunk-AI/mcp-multi-root-git/releases/tag/v1.0.0

README.md

@@ -4,7 +4,7 @@
 [![npm version](https://img.shields.io/npm/v/%40rethunk%2Fmcp-multi-root-git.svg)](https://www.npmjs.com/package/@rethunk/mcp-multi-root-git)
 [![License: MIT](https://img.shields.io/badge/license-MIT-blue.svg)](LICENSE)
 
-**git** tools over MCP: read-only status, multi-root inventory, `HEAD` parity, presets, structured diff viewer, and batch commit. **Install and MCP client wiring:** **[docs/install.md](docs/install.md)** only — do not duplicate those steps elsewhere.
+**git** tools over MCP: read-only status, multi-root inventory, `HEAD` parity, presets, structured diff viewer, batch commit, merge, and cherry-pick. **Install and MCP client wiring:** **[docs/install.md](docs/install.md)** only — do not duplicate those steps elsewhere.
 
 **Repository:** [github.com/Rethunk-AI/mcp-multi-root-git](https://github.com/Rethunk-AI/mcp-multi-root-git) · **npmjs (manual releases):** [`@rethunk/mcp-multi-root-git`](https://www.npmjs.com/package/@rethunk/mcp-multi-root-git) · **GitHub Packages (CI on each tag):** [`@rethunk-ai/mcp-multi-root-git`](https://github.com/Rethunk-AI/mcp-multi-root-git/packages) — see [docs/install.md](docs/install.md) and [HUMANS.md](HUMANS.md) Publishing.