Improve lint & format speed: ship --cache, skip single top-level ESLint config #2384

Context

Task: would a single top-level ESLint config improve lint/format speed?

Short answer: No. The dominant, zero-risk win is --cache (~10x incremental). Collapsing to one top-level config is a modest cold-only win (~2x) that costs per-package isolation and widens lint scope.

How lint runs today

• One shared config @cpn-console/eslint-config (flat config over @antfu/eslint-config) consumed by 17 eslint.config.* files.
• pnpm -r run lint spawns ~15 separate eslint ./ processes; each re-imports the shared config, reloading Node + plugins + typescript-eslint parser. That startup/parser cost — not config-file count — is what we pay for.
• 14/17 configs are byte-identical bare wrappers. Only 3 diverge:
  • root: ignores apps/packages/plugins (so lint:root is effectively inert for repo source)
  • harbor: ignores src/api/Api.ts
  • client: 2 rule overrides
• No --cache flag anywhere.

Measurements (Node 24.12, ESLint 10.5, antfu 8.2)

Recommendation (in priority order)

1. Ship --cache — DO. Zero-risk, ~10x incremental warm, works under either layout. Adds --cache to the lint/format scripts and ignores .eslintcache.
   • Implementation is already prepared in worktree branch wt/t_2fb40277 (17 files, +34/-31, uncommitted, pending review → PR).
   • Verified: cold pnpm lint 18.98s, warm 8.91s (~2.1x re-run), exit 0; 14 per-package .eslintcache produced.
2. Do NOT collapse to one top-level config. ~2x cold win only; kills per-package lint isolation; surfaces ~40 currently-unlinted root-level violations (pnpm-workspace.yaml, README.md, commitlint.config.cjs, docker/*.yml, every package.json). Revisit only if per-package isolation is explicitly unwanted.
3. Secondary follow-ups (optional):
   • Fix or delete the dead lint:root scope (root config ignores the whole monorepo source).
   • Resolve doc/config drift: AGENTS.md claims server-nestjs uses Prettier, but its eslint.config.mjs does not enable it.

Acceptance

• --cache merged and .eslintcache gitignored
• Single top-level config explicitly decided against (this issue) — no action
• (optional) dead lint:root + Prettier drift resolved in follow-up