chore: Upgrade to TypeScript 6.0.3 and API Extractor 7.x

[bc-0dp]

What/Why?

Upgrade the SDK from TypeScript 5.8 to 6.0.3 (via a 5.9 checkpoint), ahead of the eventual TypeScript 7 (native) move. TS 6.0 is a transitional release; its breaking changes are handled here. Also migrates the declaration rollup from @microsoft/api-extractor 6.3.0 (bundled TS 3.1) to 7.58.9.

Key changes:

• tsconfig.base.json: "ignoreDeprecations": "6.0" (silences baseUrl, moduleResolution node10, and target es5 pending the TS 7 migration) and "types": ["*"] to restore the pre-6.0 automatic @types global inclusion.
• ts-loader now uses an explicit configFile with onlyCompileBundledFiles, so the webpack build type-checks only bundled files, not the whole repo (TS 6.0 defaults strict: true and types: []).
• build-dts passes --rootDir .. (TS 6.0 no longer infers rootDir for the multi-package emit) and strips api-extractor 7.x export { } markers, so consumers keep importing the SDK's bare-declared types, matching the long-standing published .d.ts shape.
• Migrated 6 api-extractor configs and the auto-export generator to the 7.x schema.
• .npmrc legacy-peer-deps=true works around @bigcommerce/eslint-config's stale optional typescript peer (^4 || ^5); added @bigcommerce/eslint-plugin as a direct devDep so ESLint resolves it.

Reviewer note: the docs/ diff includes api-extractor 7.x numeric disambiguation renames (e.g. Omit.md becomes Omit_2.md, PaymentProviderCustomerType becomes PaymentProviderCustomer_2). Content is unchanged; only the internal collision labels differ.

Rollout/Rollback

Tooling and build-config change only. No runtime feature flags, experiments, or migrations. The published JS bundles are behavior-equivalent (Babel still targets the existing browserslist); only the .d.ts structure and build config change. Rollback is a straight revert of this branch.

Testing

• SDK, all green under TS 6.0.3: lint (52 projects), test (core 2478 tests plus 51 other projects), build, bundle-dts, docs (587 files), build-cdn.
• Consumer (checkout-js): typecheck output is byte-identical to the published-SDK baseline (214 pre-existing errors on its master, 0 new). TS2459 "declared locally but not exported" count is 0, confirming the export { } strip. build passes; the test suite reports 1324 pass with 2 pre-existing failures unrelated to the SDK.
• Sandbox UAT: full checkout flow works end to end (cart, payment, order placement, order confirmation) against the TS6 build.

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Note

Medium Risk
Published .d.ts shape and the declaration rollup pipeline change with a major TypeScript and API Extractor jump; runtime JS is unchanged but downstream typecheck compatibility is the main regression surface.

Overview
Upgrades the monorepo toolchain from TypeScript ~5.8 to 6.0.3 and @microsoft/api-extractor from 6.3 to 7.58.9, with lockfile and devDependency updates (@bigcommerce/eslint-plugin, api-extractor’s Rushstack stack).

TypeScript 6 compatibility: tsconfig.base.json adds ignoreDeprecations: "6.0" and types: ["*"] so global @types behavior matches pre-6.0. Webpack ts-loader now points at tsconfig.base.json with onlyCompileBundledFiles: true so bundles are type-checked without pulling the whole repo under TS 6 defaults.

Declaration build: build-dts uses tsc --rootDir .. for multi-package emits, rolls up .d.ts via API Extractor 7 (mainEntryPointFilePath, untrimmedFilePath, overrideTsconfig, suppressed extractor messages), and strips api-extractor 7 export { } lines so published typings stay consumer-friendly. The same pattern applies to core, hosted-form-v2, and auto-export–generated integration configs.

npm: .npmrc sets legacy-peer-deps=true until @bigcommerce/eslint-config declares a TypeScript 6 peer range.

^{Reviewed by Cursor Bugbot for commit 1774427. Bugbot is set up for automated code reviews on this repo. Configure here.}

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Cursor Bugbot has reviewed your changes and found 1 potential issue.

^{Reviewed by Cursor Bugbot for commit 1774427. Configure here.}

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Missing wait before declaration strip

Medium Severity

The new perl step that strips export { } lines runs as the next Nx command while both api-extractor processes are still backgrounded (&) with no trailing wait. The strip (and following rm -rf ../../temp) can run before rollups finish, yielding incomplete .d.ts files or deleting temp while extractors still read it.

 

^{Reviewed by Cursor Bugbot for commit 1774427. Configure here.}