docs: add CHANGELOG.md

CHANGELOG.md

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+# Changelog
+
+Notable changes to the TORPC reference implementation: the codec published as
+[`@w3tech.io/torpc-decoder`](https://www.npmjs.com/package/@w3tech.io/torpc-decoder), the transform
+rule library under [`packages/torpc-toevm-rules/`](./packages/torpc-toevm-rules/), and the benchmark
+harness under [`bench/`](./bench/).
+
+The format follows [Keep a Changelog](https://keepachangelog.com/en/1.1.0/). Version headings are
+npm releases of the codec, the only published package here, dated to the day that version was
+published. Repository changes that no release carries yet sit under Unreleased. The specification
+this code implements versions separately, in [w3tech/torpc](https://github.com/w3tech/torpc).
+
+## Unreleased
+
+### Changed
+
+- The decoder publish workflow authenticates with npm trusted publishing over OIDC and requests
+  provenance, so releases after 0.1.0 carry a provenance attestation. 0.1.0 was published before
+  this landed and carries none.
+
+## [0.1.0] - 2026-08-25
+
+First npm release of the reference codec, `@w3tech.io/torpc-decoder`, under Apache-2.0. Its
+normative reference is EVM RPC Compression v1 (Draft) in the specification repository.
+
+### Added
+
+- Bidirectional mapper between standard EVM JSON-RPC responses and the TORPC compact form:
+  `forward(method, response)` and `backward(method, response)`. Structural only — it reshapes what
+  it is given and resolves no ABIs, so producing decoded `{event, args}` and `{function, args}`
+  shapes remains the server's job. Forward renames fields, converts hex to decimal, strips padding
+  from indexed topics, drops the service fields and applies EIP-55; where a log or transaction
+  already carries provider-decoded fields it collapses to the decoded shape.
+- Coverage of 23 methods across 8 mappers: the hex-integer group, transaction and receipt, logs,
+  block, uncle, block receipts and fee history.
+- A conformance adapter, [`codec/scripts/conformance-adapter.ts`](./codec/scripts/conformance-adapter.ts),
+  which drives the specification repository's golden vectors against this mapper. The published
+  suite is a single-case scaffold, so a green run means "this case holds", not conformance.
+- The package ships built JavaScript with type declarations rather than the TypeScript in
+  `codec/src`: Node does not strip types inside `node_modules`, so a `.ts` entry point cannot be
+  imported. Inside a checkout the sources are still imported directly, with no build step.
+- CI across the workspace — typecheck, tests, lint and the publishable build — and a dispatch-only
+  publish workflow that installs the packed tarball into a throwaway project and imports it before
+  anything is released.
+
+## 2026-08-13
+
+### Added
+
+- Repository published, Apache-2.0 throughout, as one pnpm workspace with one lockfile:
+  [`codec/`](./codec/) (the mapper), [`packages/torpc-toevm-rules/`](./packages/torpc-toevm-rules/)
+  (the individual transform rules the mapper composes: hex stripping, hex to decimal, service-field
+  dropping), and [`bench/`](./bench/) (the benchmark harness).
+- The benchmark harness and its results: token efficiency and retrieval accuracy over captured
+  Ethereum mainnet responses rather than synthetic data, with the methodology and the known
+  measurement limits in [`bench/README.md`](./bench/README.md).
+- The published live run,
+  [`bench/results/live-token-savings-2026-07-17.md`](./bench/results/live-token-savings-2026-07-17.md):
+  21 methods across 25 Ethereum mainnet blocks against a live endpoint, counted with `o200k_base`
+  over the full HTTP response body. Token-weighted reduction against raw is 35.3% at T1 and 48.4%
+  at T2, with per-method figures in the document.