fix(openapi-typescript-helpers): preserve tuple types in Readable/Writable

[panwauu]

Changes

Fixes #2632 — Readable<T> and Writable<T> in openapi-typescript-helpers collapse tuple types (e.g. [string, string][] becomes string[][]).

The array branch T extends (infer E)[] ? Readable<E>[] matches tuples since tuples extend arrays, but infer E extracts the union of all element types, losing positional information. This affects all responses in openapi-fetch 0.17.0 because Readable<T> is applied unconditionally in FetchResponse — even when --read-write-markers is not enabled.

Replaced with T extends readonly any[] ? { [K in keyof T]: Readable<T[K]> } which uses TypeScript's mapped type special-casing for tuples to preserve tuple structure. Applied the same fix to Writable<T>.

Before:

Readable<[string, string][]>  →  string[][]

After:

Readable<[string, string][]>  →  [string, string][]

How to Review

The change is in packages/openapi-typescript-helpers/src/index.ts — one line each in Readable<T> and Writable<T>.

I was not able to create a adequate test due to limited experience with typescript generics and no experience in the repo itself. I could only verify very basically by adding a line after the Readable definition:

type test = Readable<[string, string]>

The type for test should now be [string, string] where it was string[] before

Checklist

• Unit tests updated
• docs/ updated (if necessary)
• pnpm run update:examples run (only applicable for openapi-typescript)

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🦋 Changeset detected

Latest commit: ad696ac

The changes in this PR will be included in the next version bump.

This PR includes changesets to release 3 packages

Name	Type
openapi-typescript-helpers	Patch
openapi-fetch	Patch
openapi-react-query	Patch

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[gzm0]

Nice! Implementation looks good. Just one optional comment that might allow simplification.

Could you add some tests for this? I think either of the following would probably work:

• Add to read-write-test.ts: fast but not super clean.
• Create tests for openapi-typescript-helpers: nicer, but a bit more work.

[gzm0]

Suggested change

	: T extends object
	: T extends object | readonly any[]

Would that work as well? Then we could have one less branch (same below).

IIUC the mapped type for object "just" recursively resolved $Read / $Write in keys, that behavior doesn't bother us.