refactor(core): split client into base config and extended client

[matthewvolk]

Summary

• Extracts shared BigCommerce client configuration into a new framework-agnostic core/client/base.ts module
• Updates core/next.config.ts to import baseClient from ./client/base instead of client from the barrel ./client
• Updates core/client/index.ts to spread baseClientConfig instead of duplicating config fields

Motivation

In Next.js 16, core/client/index.ts statically imports next/headers, next/navigation, and next-intl/server. When next.config.ts imports this module, those imports poison the process-wide AsyncLocalStorage context, causing "workUnitAsyncStorage" invariant errors at runtime.

This is Approach B from CATALYST-1808. Compared to the dynamic-imports approach in PR #2905 (Approach A), this approach:

• Avoids runtime overhead of dynamic import() on every request
• Keeps all Next.js-dependent hooks in index.ts exactly as-is
• Is a smaller, more surgical change (new file + two edits)

Test plan

• pnpm tsc --noEmit in core/ — no new type errors
• pnpm build — Next.js config resolution works without AsyncLocalStorage errors
• Grep confirms next.config.ts no longer imports from ./client barrel
• All 30+ consumer files importing from ~/client continue working unchanged

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Latest commit: 9a80d1d

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Project	Deployment	Actions	Updated (UTC)
catalyst	Building	Preview, Comment	Mar 3, 2026 6:40pm

[github-actions]

Bundle Size Report

Comparing against baseline from 8b5fee6 (2026-03-03).

No bundle size changes detected.

[matthewvolk]

Closing in favor of #2905