/claim #71

Summary

• add focused Vitest coverage for the Clerk plugin constructor, table bootstrap, webhook handling, and session authentication paths
• mock svix and jose so the tests exercise the plugin behavior without external Clerk services or real JWT keys
• cover user/session webhook writes, invalid instance rejection, session verification bypasses, missing DB sessions, and DB lookup failures

Verification

• COREPACK_ENABLE_PROJECT_SPEC=0 corepack pnpm exec prettier --check plugins/clerk/index.test.ts
• COREPACK_ENABLE_PROJECT_SPEC=0 corepack pnpm vitest plugins/clerk/index.test.ts --run
• git diff --check
• COREPACK_ENABLE_PROJECT_SPEC=0 corepack pnpm exec tsc --noEmit --pretty false still reports existing repository type errors in plugins/cdc, src/cache, src/do, and src/operation; no errors mention plugins/clerk/index.test.ts
• COREPACK_ENABLE_PROJECT_SPEC=0 corepack pnpm vitest --run still reports the existing 4 RLS failures in src/rls/index.test.ts; the new Clerk test file passes in the full run

Notes

This is a non-overlapping coverage slice for #71, separate from the Stripe and WebSocket plugin test PRs I submitted earlier.