feat!: bump json-schema-to-typescript to v16 in generator

[mfal]

Split out of #303, which bumped the rest of the production dependency majors. json-schema-to-typescript was held back because it is the only bump in that batch that changes the generated client output.

⚠️ This cuts a major release

There is one breaking public type change (below), so this is a feat! with a BREAKING CHANGE: footer. lerna-lite will therefore cut a major: the repo is currently on 4.455.x, so merging this releases 5.0.0. If that is not wanted right now, this PR should wait rather than be downgraded to a non-breaking commit type — the type change is real either way.

The (T | null) | null noise is fixed, not shipped

A naive bump produces ~164 insertions / 132 deletions across the two generated types.ts files, ~120 of which are redundant (T | null) | null nestings. Those are not shipped here.

Root cause: v16 adds native support for the OpenAPI 3.0 nullable: true keyword (bcherny/json-schema-to-typescript#755). The local populateNullableTypes helper rewrote { ..., nullable: true } into anyOf: [{ ..., nullable: true }, { type: "null" }] but left the nullable flag on the inner schema, so v16 appended a second | null.

populateNullableTypes is deleted in favour of the upstream implementation. That is strictly more correct, not just tidier:

• The helper was only ever applied to components.schemas (Schemas.ts), so nullable: true on inline schemas under paths was silently discarded. v16 honours it everywhere — this is where every remaining diff line comes from.
• The helper bailed out on $ref schemas; v16 handles nullable next to a $ref too. (No occurrences in the current specs, so no output change from this.)

Evidence that the removal is behaviour-preserving where the helper did apply: regenerating with v16 and no helper leaves the entire components.schemas section byte-identical to the v15 output. The only change in that section is the cosmetic index signature below.

With the fix, the generated diff is 30 lines per file instead of 148.

Classification of every remaining change

Reviewed line by line across both v2/types.ts and v3-next/types.ts (v3-next mirrors v2 exactly).

Widening — safe (request bodies, callers may now also pass null)

Endpoint	Fields
PATCH /v2/stacks/{stackId}	updateSchedule
PATCH /v2/mail-addresses/{mailAddressId}/autoresponder	inline { expiresAt, message, startsAt }
PATCH /v2/contributors/{contributorId}	descriptions, deviatingContractOwner, deviatingSupportInformation
PATCH /v2/contributors/{contributorId}/extensions/{extensionId}	detailedDescriptions, externalFrontends, frontendFragments, webhookUrls
PUT/PATCH project + server storage-space endpoints	notificationThresholdInBytes

Cosmetic — type-equivalent

DomainmigrationDomainNotMigratableValidationError.context:

-          [k: string]: string;
+          [k: string]:
+            | string
+            | MittwaldAPIV2.Components.Schemas.DomainmigrationDomainNotMigratableReason;

From bcherny/json-schema-to-typescript#704 (TS2411 fix — index signatures widened to cover sibling named properties). DomainmigrationDomainNotMigratableReason is a union of string literals and therefore a subtype of string, so the index signature accepts and yields exactly the same set of values. Noisier to read, identical to use.

Narrowing — BREAKING (1 occurrence)

GET /v2/page-insights, 200 response, metrics[]:

-                  score?: number;
+                  score?: number | null;

The spec declares score as {"type": "number", "format": "double", "nullable": true}. v15 dropped that because the field lives in an inline path schema, so the previous type was wrong — the API could always return null here. Under strictNullChecks, consumers reading metrics[].score must now narrow before use. Correct, but breaking, hence the major.

Verification

test:client-generation-clean is not evidence of anything here — it is literally git diff --exit-code, and nothing in CI runs build:client-prod, so generated-output changes are invisible to the PR pipeline. The regeneration was run locally instead; the committed specs under packages/mittwald/spec/ make it deterministic and offline.

• yarn lint ✅
• yarn nx run-many -t build --skip-nx-cache ✅
• yarn nx run-many -t test:compile --skip-nx-cache ✅
• yarn nx run-many -t test --skip-nx-cache ✅
• packages/generator unit tests — 23 passed, 7 suites ✅ (the generator's test target is empty, so test:unit was run explicitly)
• Baseline check before the bump: regenerating on v15 reproduced the committed output exactly, so the diff below is attributable to the bump alone
• Determinism check after the bump: a second build:client-prod reproduced the committed output exactly

The regeneration is a separate commit (feat!: update generated client) so the generated diff is reviewable on its own. Note that this means the first commit is not green in isolation — the generator changes without the matching regeneration — which is inherent to the split.

.yarnrc.yml sets npmMinimalAgeGate: 10080; json-schema-to-typescript@16.0.0 is past the 7-day window and installs cleanly.

🤖 Generated with Claude Code