build: replace tsup with tsdown

[Rel1cx]

What kind of change does this PR introduce?

• Bugfix
• Feature
• Docs
• Test
• New Binding issue #___
• Code style update
• Refactor
• Build-related changes
• Other, please describe:

Does this PR introduce a breaking change?

• Yes, and the changes were approved in issue #___
• No

Checklist

• When resolving issues, they are referenced in the PR's title (e.g fix: remove a typo, closes #___, #___)
• I have added a convincing reason for adding this feature, if necessary

Other information

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Project	Deployment	Preview	Comments	Updated (UTC)
eslint-react	Ready	Preview	Comment	Sep 1, 2025 6:10pm

[Copilot]

Pull Request Overview

This PR replaces the tsup build tool with tsdown across the entire monorepo. The migration involves updating configuration files, package dependencies, and build scripts to use the new build tool while maintaining similar configuration options.

• Replace tsup with tsdown as the TypeScript build tool
• Update all package.json files to use tsdown dependency instead of tsup
• Migrate configuration files from tsup.config.ts to tsdown.config.ts with appropriate API changes

Reviewed Changes

Copilot reviewed 42 out of 45 changed files in this pull request and generated no comments.

Show a summary per file

File	Description
packages/utilities/var/tsup.config.ts	Removed old tsup configuration file
packages/utilities/var/tsdown.config.ts	Added new tsdown configuration file
packages/utilities/var/package.json	Updated build script and dependency from tsup to tsdown
packages/utilities/kit/tsdown.config.ts	Updated import and removed splitting option
packages/utilities/kit/package.json	Updated build script and dependency
packages/utilities/eff/tsdown.config.ts	Updated import and removed splitting option
packages/utilities/eff/package.json	Updated build script and dependency
packages/utilities/ast/tsup.config.ts	Removed old tsup configuration file
packages/utilities/ast/tsdown.config.ts	Added new tsdown configuration file
packages/utilities/ast/package.json	Updated build script and dependency
packages/shared/tsup.config.ts	Removed old tsup configuration file
packages/shared/tsdown.config.ts	Added new tsdown configuration file
packages/shared/package.json	Updated build script and dependency
packages/plugins/eslint-plugin/tsup.config.ts	Removed old tsup configuration file
packages/plugins/eslint-plugin/tsdown.config.ts	Added new tsdown configuration file
packages/plugins/eslint-plugin/package.json	Updated build script and dependency
packages/plugins/eslint-plugin-react-x/tsup.config.ts	Removed old tsup configuration file
packages/plugins/eslint-plugin-react-x/tsdown.config.ts	Added new tsdown configuration file
packages/plugins/eslint-plugin-react-x/package.json	Updated build script and dependency
packages/plugins/eslint-plugin-react-web-api/tsup.config.ts	Removed old tsup configuration file
packages/plugins/eslint-plugin-react-web-api/tsdown.config.ts	Added new tsdown configuration file
packages/plugins/eslint-plugin-react-web-api/package.json	Updated build script and dependency
packages/plugins/eslint-plugin-react-naming-convention/tsup.config.ts	Removed old tsup configuration file
packages/plugins/eslint-plugin-react-naming-convention/tsdown.config.ts	Added new tsdown configuration file
packages/plugins/eslint-plugin-react-naming-convention/package.json	Updated build script and dependency
packages/plugins/eslint-plugin-react-hooks-extra/tsdown.config.ts	Updated import and removed splitting option
packages/plugins/eslint-plugin-react-hooks-extra/package.json	Updated build script and dependency
packages/plugins/eslint-plugin-react-dom/tsdown.config.ts	Updated import and removed splitting option
packages/plugins/eslint-plugin-react-dom/package.json	Updated build script and dependency
packages/plugins/eslint-plugin-react-debug/tsdown.config.ts	Updated import and removed splitting option
packages/plugins/eslint-plugin-react-debug/package.json	Updated build script and dependency
packages/core/tsdown.config.ts	Updated import and removed splitting option
packages/core/package.json	Updated build script and dependency
package.json	Updated root dependencies to include tsdown and remove tsup
.pkgs/eslint-plugin-local/tsdown.config.ts	Updated import and removed splitting option
.pkgs/eslint-plugin-local/package.json	Updated build script and dependency

Files not reviewed (1)

• pnpm-lock.yaml: Language not supported

Comments suppressed due to low confidence (2)

packages/utilities/var/tsdown.config.ts:1

• The splitting option has been removed from the new configuration but was present in the original tsup config. This inconsistency across packages could lead to different build behaviors. Consider documenting why this option was removed or ensuring consistency across all migrated configs.

import type { Options } from "tsdown";

packages/utilities/kit/tsdown.config.ts:1

• The splitting option is being removed from existing configurations during the migration. This represents a behavioral change from the original tsup configuration and should be documented or reviewed to ensure it's intentional.

import type { Options } from "tsdown";

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[socket-security]

Review the following changes in direct dependencies. Learn more about Socket for GitHub.

Diff	Package	Supply Chain Security	Vulnerability	Quality	Maintenance	License
	@​stylistic/​eslint-plugin@​5.2.3 ⏵ 5.3.1	-6			+3
	@​effect/​platform-node@​0.96.0 ⏵ 0.96.1				+2
	effect@​3.17.9 ⏵ 3.17.10				+2

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