Typecheck experiment in CI; drop the pre-push hook

[kcarnold]

Moves the experiment/ typecheck from a local git hook into CI, where the work actually happens.

Why

Nothing typechecks experiment/ at PR time:

Workflow	Covers
backend-tests.yml	backend/
frontend-tests.yml	frontend/
mindmap-tests.yml	prototype-mindmap/
build-experiment-image.yml	builds the image — push to main only

The only check experiment/ had was the Husky pre-push hook, and it gates on [ "$remote_ref" = "refs/heads/main" ] — a direct local push to main. Under PR flow that never happens: feature-branch pushes skip the gate, and merges run server-side where no local hook exists. So the hook guards a path the project doesn't use, which is why it hasn't fired in a long time.

build-experiment-image.yml would catch a type error via next build (there's no typescript.ignoreBuildErrors in next.config.ts), but only after the change is on main, and it fails the image push rather than the PR.

Net: a dead guard standing in front of a real gap.

What changed

Added .github/workflows/experiment-tests.yml, mirroring backend-tests.yml — same trigger shape, permissions: contents: read, same step sequence. Runs typecheck plus the Vitest suite on PRs touching experiment/**.

One deviation worth noting: npm test is watch mode in this package (unlike backend, where it's vitest run), so CI calls npm run test:run. Commented inline so it doesn't read as an inconsistency.

Removed .husky/pre-push and the root package.json entries that existed only to install it. grep -rn "husky\|prepare" across the repo found references in no file but the root manifest — the Dockerfile copies only per-app manifests, and the devcontainer's postCreateCommand runs uv sync and cd frontend && npm install, never a root install.

Beyond being inert, the hook had two latent problems if it ever did fire: cd experiment sits inside the while read loop without a subshell, so a multi-ref push would run the second iteration from the wrong directory; and it never installs dependencies, so a stale experiment/node_modules fails confusingly.

Testing

• Ran the exact CI steps locally in experiment/: npm ci, then npm run typecheck (clean) and npm run test:run (20/20 passing in 1 file).
• Parsed all seven workflow files with yaml.safe_load; all valid.
• Compared the new workflow's trigger keys, permissions, working-directory, and step sequence against backend-tests.yml to confirm it matches the house pattern.
• This PR touches .github/workflows/experiment-tests.yml, which is in its own paths filter, so the new workflow runs on this PR and validates itself.

Note for the reviewer

Root package.json and package-lock.json are now near-empty shells — the manifest keeps only name/version/description, and the lockfile has zero dependencies. Deleting both outright would be tidier, and nothing references them, but the sandbox blocked me from removing package.json. If you want them gone: git rm package.json package-lock.json.

Related

Follow-up to the docs cleanup in #618, which noted this gap. That PR adds a CLAUDE.md line documenting the pre-push hook; once both land, that line should come out. Happy to drop it from #618 pre-merge — say the word.

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