Pull Request Checklist

• Have you added new tests to prevent regressions?
• If a documentation update is necessary, have you opened a PR to the documentation repository?
• Did you update the typescript typings accordingly (if applicable)?
• Does the description below contain a link to an existing issue or a description of the issue you are solving?
• Does the name of your PR follow our conventions?

Description of Changes

Top of the stack, stacked on #18331.

Moves the supported TypeScript range up from 5.5–5.8 to 5.8, 5.9 and 6.0, and builds on 6.0.2.

ConstraintChecking had to be restructured

TypeScript 6.0 rejects ConstraintChecking.DEFERRED and IMMEDIATE as they were written:

src/deferrable.ts(67,19): error TS4094: Property '#constraints' of exported
anonymous class type may not be private or protected.

Both were class expressions passed straight to classToInvokable inside a static property initializer, so the type they produce has no name to refer to, and a private field cannot be described in the emitted declarations without one. They now have named declarations outside the class body, with the static accessors kept as the documented entry points — which preserves both the class names and the descriptions the generated docs point at.

One observable side effect: DEFERRED and IMMEDIATE become static accessors rather than enumerable data properties, so they no longer appear in Object.keys(ConstraintChecking) or a spread of it. Both are still reached the same way.

cls.test.ts also gains an explicit declare id: CreationOptional<number>, which 6.0 needs to infer the model's creation attributes.

This is the one non-mechanical change in the PR, so it is covered by new unit tests in packages/core/test/unit/deferrable.test.ts: accessor identity, name preservation, construction with and without new, frozen constraints, and isEqual (including that DEFERRED and IMMEDIATE are never equal to each other).

Everything else is mechanical

The @ts-ignore comments that newer compilers no longer need are dropped, and the two in the data types test become @ts-expect-error — which is what their own comments said they were waiting to be:

// eslint-disable-next-line @typescript-eslint/prefer-ts-expect-error -- error only appears in TS 5.5+
// @ts-ignore -- intentionally testing invalid input

Ordering

TypeDoc had to reach 0.28 first (#18331); 0.27 refuses to run on TypeScript 6.0 and docs is a required CI job.

Verification

yarn build, yarn test-unit (2220 passing), yarn test-typings across all 13 projects, and yarn docs with no warnings — all on TypeScript 6.0.2.

🤖 Generated with Claude Code

https://claude.ai/code/session_01EgPPfqYYk6PFGbanp5mAFh