feat: support React 19

[rfgamaral]

Overview

Widens the React peer range to ^18.0.0 || ^19.0.0 and moves the development environment to React 19.

Today @doist/typist peers on React 18 only, which blocks consumers from even trying React 19: npm fails to resolve. @doist/reactist already allows both (>=18.0.0 <20.0.0), so Typist is the remaining gate. Both todoist-web and comms-web are still on React 18.3.1, so nothing changes for them right now.

Typist barely touches React — a single forwardRef component and a handful of hooks, with Tiptap handling the editor integration, and @tiptap/react already supports 17, 18, and 19. The built output is byte-for-byte identical whether it is compiled against React 18 or 19 types.

Since development now happens on React 19, a React 18 Compatibility job installs React 18 over the top of a normal install and runs the same type checking and test suite against it. That keeps the oldest supported version covered without aliased packages, extra configs, or duplicated scripts. When React 18 support is eventually dropped, deleting that job is the only cleanup needed. The job restores the shared node_modules cache but never saves it, so the downgraded tree cannot leak into the other jobs.

Replaces #1325, which bumped the same dependencies but left React 18 untested, and would not have published the widened range from a chore commit.

PR Checklist

• Pull request title follows the Conventional Commits Specification

Test plan

• Observe that CI is green, which covers static analysis, tests, and the build on React 19, plus type checking and tests on React 18
• Open the Netlify preview Storybook and confirm the editor stories behave as expected under React 19

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[doistbot]

Widens the React peer range to ^18.0.0 || ^19.0.0, moves the dev environment to React 19, and adds a well-constructed restore-only-cache CI job to keep React 18 type-checking and tests covered.

Few things worth tightening:

• Pin the compatibility job's React 18 packages to the actual minimum versions (e.g. react@18.0.0, react-dom@18.0.0) — bare @18 specs resolve to the latest 18 release, so 18.0.x consumers go untested despite the job's stated purpose.
• After the single React 18 install, run type checking and tests concurrently with run-p check:types test to shorten the job's wall-clock time.

I also included a few optional follow-up notes in the details below.

Optional follow-up note (1)

• .github/workflows/check-ci-validation.yml:161: check:types has noEmit and the test script does not depend on it, so these two validations can run concurrently after the single React 18 install. Running them with run-p check:types test would shorten the compatibility job's wall-clock time without duplicating setup work.

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[rfgamaral]

On the optional note about running the two validations concurrently with `run-p check:types test`: skipping it. Type checking takes ~0.5s and the tests ~1.4s, against a job whose runtime is dominated by the install, so the gain is under a second. Not worth interleaving the output and making failures harder to read.

[doist-release-bot]

🎉 This PR is included in version 16.1.0 🎉

The release is available on:

• npm package (@latest dist-tag)
• GitHub release

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