fix: generate tsc-safe TypeScript for parameters and payloads presets

[ALagoni97]

Note for reviewers: the payloads/headers fix (#373, defects 3 & 4) is implemented here as a post-processing preset because @asyncapi/modelina@6.0.0-next.11 is an external published package with no patch tooling in this repo. These two defects could alternatively be solved upstream in Modelina's MarshalFunction/UnmarshalFunction (lib/.../generators/typescript/presets/utils/) instead — that would be a separate repo and release. The preset keeps the fix self-contained and testable here.

Problem

Generation reports zero errors, but the generated .ts does not compile. A downstream publish pipeline runs npm i && npm run build && npm publish; the tsc build step exits non-zero and nothing publishes. These are silent-at-generation, fatal-at-build defects.

Fixes four independent template defects across two presets, tracked upstream as #372 (parameters) and #373 (payloads).

Defects & fixes

parameters preset — #372 (src/codegen/inputs/openapi/generators/parameters.ts)

1. Query serializer/deserializer used the raw spec name as the property accessor. Fields are constrained to camelCase (skip) but the code emitted this.Skip → TS2551 Property 'Skip' does not exist. Introduced a ParameterConfig carrying both name (original wire key) and propertyName (constrained accessor), plus a buildConstrainedNameMap() helper. Every this.* accessor now uses the constrained name; every wire key (params.append('Skip'), params.has(...), URL placeholders, extractPathParameters switch cases) keeps the original casing. The path serializer already behaved correctly; this makes serialize, deserialize, fromUrl, and extractPathParameters consistent.
2. deserializeUrl was only generated when the class had query params, but fromUrl() always calls it. A path-only parameters class failed with TS2551 Property 'deserializeUrl' does not exist. deserializeUrl is now always emitted (a harmless no-op when there are no query params).

payloads / headers presets — #373 (new src/codegen/modelina/presets/marshalling.ts)

These defects originate in Modelina's TS_COMMON_PRESET marshalling. Modelina is an external published package with no patch tooling in this repo, so the fix is a small post-processing preset (createMarshallingFixPreset) that runs immediately after TS_COMMON_PRESET. Each replacement is derived from the model, so it targets exactly the affected property line and leaves everything else untouched.

3. Unconditional null fallback for non-nullable date-time in unmarshal(). instance.created = obj["created"] == null ? null : new Date(...) yields Date | null where the field is declared Date → TS2322. The null branch is dropped for required, non-nullable date fields.
4. Nullable array guarded only by !== undefined in marshal(), then iterated. null slips past the guard into for (const item of this.signers) → TS2531 Object is possibly 'null'. An explicit !== null guard is added.

Wired into both payloads.ts and headers.ts, which share the same marshalling setup.

Verification

• Both minimal reproductions regenerated through this CLI and compiled with tsc --strict — clean.
• The full safepay-v2 client (203 generated files) compiles clean under strict tsc (ignoring ajv/ajv-formats resolution noise that resolves after npm i).
• Added regression tests: parameters.spec.ts ([Bug]: TypeScript parameters preset emits non-compiling code (query-param casing + missing deserializeUrl for path-only params) #372) and payload.spec.ts ([Bug]: TypeScript payloads preset emits non-compiling code (non-nullable date-time null fallback + nullable-array marshal) #373), asserting the exact fixed output from inline specs.
• Full suite: 49 suites / 627 tests pass, 74 snapshots. The only snapshot delta is the intended deserializeUrl no-op added to path-only classes; no payload snapshots changed.
• lint and typecheck:test clean.

Closes #372
Closes #373

🤖 Generated with Claude Code

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