Move the codec to stable Effect 4.0.x (0.2.0)

GitHub: #10

Objective and immutable scope

Move @misofm/codec from Effect release candidates (peer 4.0.0-rc.112 || 4.0.0-rc.115) to stable Effect 4.0.x so misofm/app and @misofm/engine-web-adapter can share one Effect 4.0.4 copy. Release as 0.2.0. Preserve the public API (built dist identical to 0.1.1), the Wasm assets (encoder 90da75c7…, decoder 70caf381…), bounds, cancellation, and backpressure. No source, ABI, or asset change; no adapter, app, or Engine work.

Why: engine-web-adapter@0.5.13 depended on effect@4.0.0-rc.112. When the application shares one Effect 4.0.x copy with the codec (deduplicated install, for example bun's loose peers), the adapter's rc.112 runtime runs a codec Layer built by that copy and fails with Cannot read properties of undefined (reading 'scheduler'). Unit tests did not catch it because they resolve one Effect copy.

Base: origin/main 10abab98191b878482a02c0d8e9a2572c8eb0958 (codec 0.1.1). Branch effect-4.0.4, PR #9. Effect guidance: skills revision 0507930 (references/migration.md, "Effect v4 release candidates to 4.0.x").

Implementation contract

• package.json: version 0.2.0, peer effect >=4.0.3 <4.1, dev dependency effect pinned exactly to 4.0.4 (the codec imports only effect; there is no @effect/* package), CHANGELOG.md in files. Regenerate bun.lock.
• scripts/pack-check.mjs runs the isolated packed-consumer matrix on Effect 4.0.3 and 4.0.4 (Bun, Node, Chromium, Firefox, WebKit) and requires CHANGELOG.md in the tarball.
• CHANGELOG.md records the behaviour audit and the consumer migration note. README and .github/RELEASING.md name the new matrix.
• Historical evidence (docs/evidence/packed-consumers.json, .github/RELEASE_EVIDENCE/003, 006) is not rewritten.

Evidence (candidate, not published)

• Compiles unchanged against 4.0.4; the built .js, .d.ts, and maps are byte-identical to the 0.1.1 output.
• Differential script across {0.1.1, 0.2.0} × {rc.115, 4.0.4}: identical error shapes (message, JSON, Cause.pretty, Schema encoding), encoded FLAC and decoded PCM hashes, exit reasons, source-error identity, interruption while waiting for input, early take, timeout on a stalled source, and encode interruption without late writes. One measured exception: JSON.stringify of a FlacDecodeError whose cause is a SchemaError is now compact (Effect #8895); the only producer is an ABI-violation path (see CHANGELOG.md).
• Local: bun run check (40 pass, 5 native-only skips), pinned-native bun run test:integration (5 pass), bun run build:wasm:verify (both assets reproduce), bun run pack:check on 4.0.3 and 4.0.4. npm install --strict-peer-deps plus npm ls valid on 4.0.4 and 4.0.3; 4.0.0-rc.115 is rejected with ERESOLVE.
• Repro of the original failure and its absence with codec 0.2.0 plus adapter 0.6.0: see the adapter PR Move to stable Effect 4.0.x (0.6.0) engine-web-adapter#130.

Release contract and blockers

Release follows .github/RELEASING.md: merge a reviewed, green PR; run npm-publish.yml on main with mode=publish, the exact 40-character merge SHA, and expected_version=0.2.0; create the v0.2.0 release/tag at that commit; record the run URL, registry integrity, and decoder hash here and in .github/RELEASE_EVIDENCE/010/registry-release.json. Blockers: the adapter PR installs this codec from the throwaway branch effect-4.0.4-ci-dist and must be flipped to the published 0.2.0 after release; delete that branch afterwards. Publication has not been performed.