Add @polyvariant/smithy-ts-runtime: out-of-the-box transports

[kubukoz]

Closes the README TODO: the Transport / StreamTransport implementations had to be written by hand in every consuming project — a near-identical fetch wrapper each time, plus a hand-rolled ndjson read loop wherever streaming was used. This publishes that as @polyvariant/smithy-ts-runtime.

What ships

fetchTransport implements both halves of the generated contract from one object:

const transport = fetchTransport({ baseUrl: '/api' })
const directory = new DirectoryClient(transport)
const feed = new FeedClient(transport, transport)   // streaming ops

• Unary — baseUrl joining, query building (dropping undefined), lowercased response headers, empty/non-JSON body tolerance.
• Streaming — ndjson and binary framing in both directions, lazy in both (one line deframed per pull, so a long-lived stream never buffers). A streamed request body uses duplex: 'half' where the platform supports it and buffers where it doesn't.
• Non-2xx is returned, not thrown — the generated client needs the status and body to dispatch declared errors: [...]. 401 is the exception; pass your generated error class via unauthenticated to keep existing instanceof checks working.
• Middleware — chain / around / mapRequest / withHeaders / tap, plus interceptorStack for handlers registered and removed after construction (what a React effect needs).
• Framing primitives (encodeNdjson, decodeNdjson, …) are exported for transports this package doesn't ship.

The package is zero-dependency and ESM-only.

Type compatibility is checked, not assumed

The library declares its own structural copies of the transport types and imports nothing from generated code, so generated.ts stays self-contained. typecheck/src/runtimeUsage.ts drives the real generated clients with the library's transport, so if the codegen changes the contract and the library isn't updated, it stops compiling.

Build

TypeScript moves into a pnpm workspace (runtime/ + typecheck/). nix flake check now builds and unit-tests the library (39 node:test cases covering framing round-trips, chunk-split multi-byte characters, laziness, the transport against a fetch double, and middleware ordering) before typechecking the generated sample. pnpm check runs the same without nix.

Publishing

.github/workflows/npm-publish.yml publishes on a v* tag, so one tag ships both halves at the same version. The tag is the only source of version truth — runtime/package.json keeps a placeholder 0.0.0 the workflow overwrites, so there's no version to bump by hand. It runs the full check before publishing, and uses npm provenance.

Hand-written rather than folded into ci.yml, since that file is generated by sbt-typelevel and CI fails if it drifts.

Needs an NPM_TOKEN secret with publish rights on the @polyvariant scope before the first tag.

Verification

nix flake check passes: library build + typecheck + 39 tests, then the generated-sample typecheck including the compatibility file. Package packs cleanly with no @types/node leakage into the published .d.ts.

🤖 Generated with Claude Code