Retire rumcodecs: mark the experiment closed in the README and on npm

[thewtex]

rumcodecs set out to answer one question: could numcodecs.js be reimplemented in Rust/WASM without breaking its API or its byte formats? It could — the interop fixtures decode, the compat suite passes — and that is the whole of what the experiment had to say. This retires it rather than leaving a maintained-looking package that nobody is maintaining.

What changed

README.md — a [!WARNING] callout above the usage docs stating the project is retired, unmaintained, and that numcodecs.js is the replacement. Placement is deliberate: below the codec table or the quick start, the reader has already started integrating. Contributing now says issues and PRs are not being reviewed and that forking under MIT is the way forward, keeping the AGENTS.md and Code of Conduct links. The two CI badges are dropped — they go blank the moment the workflows are disabled or the repo is archived.

package.json — the same message where npm renders it: description prefixed [RETIRED — experiment, unmaintained] (this is what shows in npm search results), retired/deprecated/unmaintained keywords, and a deprecated field. Version bumps 0.1.1 → 0.1.2 because the npm package page only re-renders on publish, so without a new version none of this reaches the registry at all.

test/index.test.ts — a retirement notice block, 7 tests, suite 52 → 59.

Why the tests

The notice lives in two files that drift independently. A routine npm version bump or a docs edit drops one side, and the result is a package that says retired in one place and maintained in the other — which nobody notices until it is published. test/index.test.ts already read package.json to guard export-map drift, so the assertions live alongside that existing check: deprecated non-empty and naming the replacement, description and keywords marked retired, and the README callout present, saying retired, linking the same replacement, and sitting above the quick start.

Each assertion was mutation-tested rather than accepted on green. Stripping the package.json markers fails 4; deleting the callout fails 2; moving it below the quick start fails 1. Two early versions passed under mutation and were rewritten — a whole-file numcodecs.js match (the name appears throughout the prose below) and then a bare-name match inside the callout (it appears in the callout's own first sentence). Both are now one scoped match on the full markdown link.

Implementation detail worth flagging

The callout is delimited by where the blockquote ends, not by a fixed trailing string. Slicing to a literal degrades silently: indexOf returns -1 when the anchor moves, slice(0, -1) then hands back nearly the whole README, and "the link is inside the callout" starts passing on a link nowhere near it — reopening the exact hole the test exists to close. There is a mutation covering that case specifically.

Not done here — needs registry credentials

• npm deprecate "@fideus-labs/rumcodecs@*" "..." is what actually makes npm install print a warning. The deprecated field in package.json is not a substitute — that flag is registry state, and it is also the only way to cover the already-published 0.1.0 and 0.1.1. The field is kept anyway so the intent survives in version control rather than living only as registry state someone has to remember to reapply.
• Publishing 0.1.2 — tagging v0.1.2 triggers .github/workflows/release.yml.

Verification

Full suite 59/59 across 8 files, pnpm check clean (vp check --fix relocated the deprecated key to canonical position). pkg/ was unbuilt in this worktree, so build:wasm:node was run to exercise the WASM-backed suites rather than reporting around them.

coderabbit review could not run — rate_limit, org usage spending cap exceeded, unchanged on retry — so the review was done manually. It caught four defects in the original draft: a comment falsely claiming package.json triggers npm install warnings, the silent-pass slice above, a redundant regex alternation, and a README line asserting the package "is marked deprecated" before npm deprecate had run.

AGENTS.md still describes the project in the present tense and is left unchanged.

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