fix(open-api): correctness fixes for ts-client multipart/cookies/response types and composite parameter types

[nx-plugin-for-aws]

Reason for this change

Reviewing the generated TypeScript client against a variety of OpenAPI specs — petstore v3, an Error-schema / oneOf spec, a multipart-upload spec, an edge spec with reserved keywords and readOnly fields, a streaming spec, and finally a real FastAPI service — surfaced five correctness bugs that either produce invalid TypeScript or silently break at runtime. Each is a small, localised fix and each gets a regression test.

Description of changes

1. type: object with no additionalProperties emitted invalid TypeScript. The template rendered [key: string]: <link.typescriptType>; unconditionally, and the empty typescriptType produced [key: string]: ; — a tsc syntax error. Fall back to unknown so the emitted code stays valid.

2. multipart/form-data bodies were sent with a boundary-less Content-Type. The generator pre-set Content-Type: multipart/form-data before fetch() had a chance to compute the boundary from the FormData body; servers cannot parse the resulting request because RFC 7578 requires the boundary= parameter. Skip the assignment for multipart bodies so the runtime populates a correct header.

3. Cookie parameters were silently dropped. in: cookie parameters were typed on the request input but never serialised onto the wire — the user thought they were sending a session cookie and the server never saw it. Serialise them into a percent-encoded Cookie: header (both node-side and cross-origin browser callers need this explicitly).

4. Multi-media-type request bodies produced a comma-joined Content-Type. Content-Type: 'application/json,application/xml,application/x-www-form-urlencoded' is wire-incorrect — servers parse the header as a single value. Pick one wire type (preferring application/json / +json variants, falling back to the first entry).

5. Composite parameter schemas were never hoisted. FastAPI / Pydantic v2 encode Optional[T] parameters inline as {anyOf: [T, {type: 'null'}], title: '<name>'}. The existing hoisting pass walked request/response JSON schemas into components.schemas but didn't walk parameters[].schema, so hey-api-openapi synthesised an anonymous composite type named from the title (e.g. XClient, Session, Tag) but never emitted a declaration. Every FastAPI-generated client then failed to compile with Cannot find name 'XClient' / '"Session" is not defined'. The fix extends the hoister to walk parameter schemas too; once hoisted, the existing primitive-inlining path produces the correct string | null etc. — no lossy rewrite.

Also in the shared codegen data: normalise hey-api's in: 'formData' to in: 'body' so downstream consumers see a single body kind.

Description of how you validated changes

• Regression tests for each scenario land alongside the existing content-type, additional-properties and fast-api spec files.
• Full suite passes: 1731 tests, lint, build, all smoke tests (incl. Windows).
• End-to-end sanity with tsx against a mock fetch: petstore (7 tests), complex (4 tests, including 409 error via renamed _Error), advanced (multipart → auto-boundary, Blob octet-stream, cookies, deprecated, allOf) — all green after the fix.
• Integration tests against real servers (FastAPI, tRPC-via-trpc-to-openapi, Smithy): 29 py-client + 29 ts-client tests pass. SigV4-signed FastAPI calls through a mock API Gateway IAM proxy — 6 py + 6 ts — confirm the middleware hooks work against the IAM-auth flow.

Issue # (if applicable)

Follow-up to the review in #586.

Checklist

• My code adheres to the CONTRIBUTING GUIDE and DESIGN GUIDELINES

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By submitting this pull request, I confirm that my contribution is made under the terms of the Apache-2.0 license

[codecov-commenter]

Codecov Report

❌ Patch coverage is 90.90909% with 1 line in your changes missing coverage. Please review.
✅ Project coverage is 89.10%. Comparing base (34760f8) to head (1ab5629).
⚠️ Report is 1 commits behind head on main.

Files with missing lines	Patch %	Lines
packages/nx-plugin/src/open-api/utils/normalise.ts	88.88%	0 Missing and 1 partial ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #613      +/-   ##
==========================================
+ Coverage   89.07%   89.10%   +0.03%     
==========================================
  Files         107      107              
  Lines        3477     3487      +10     
  Branches      757      760       +3     
==========================================
+ Hits         3097     3107      +10     
  Misses        176      176              
  Partials      204      204              

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