chore(ci): add dead-code and unused-export detection to CI (closes #297)

[Cyber-Mitch]

closes #297

No CI step detected unused exports or dead code, so it accumulated silently over time. Adds knip as a dead-code/unused-export gate, wired into the existing PR-gate workflow.

Tool selection — knip, not the two the issue also named

• ts-prune — rejected. Effectively unmaintained upstream, and has no Next.js App Router awareness: every page.tsx/layout.tsx/route.ts default export, plus metadata/generateStaticParams, would need hand-maintained entry config it barely supports. On a 104-file App Router codebase that's a false-positive storm, not a usable gate.
• eslint-plugin-unused-imports — rejected as the answer to this specific issue. It only finds unused imports/variables within a file — it does not detect cross-file unused exports, which is literally the issue title. ESLint here already reports unused vars; this plugin wouldn't add the capability actually being asked for.
• knip — chosen. Built-in Next.js plugin correctly resolves App Router's implicit entry points — verified empirically, not assumed: 0 page/layout/route false positives across all 104 .ts/.tsx files. Reads the repo's one path alias (@/* → ./src/*) from tsconfig.json automatically, with zero manual config. Single-package repo means none of knip's monorepo configuration curve applies. Covers unused exports, unused exported types, and unused dependencies in one pass — actively maintained (v6.33.0).

Scope discipline — a detection gate, not a cleanup PR

First zero-config run: 36 findings (2 unused deps, 1 unused devDep, 24 unused exports, 9 unused exported types, 0 unused files). That's too many to verify-and-delete safely inside a "wire in the detector" PR — several are genuinely ambiguous (framework re-export idioms, a config gap producing a false positive, and an 11-symbol block in src/lib/error-handler.ts that looks like a complete module built ahead of use, which needs real investigation before anyone decides it's safe to remove).

Decision: scoped-ignore baseline. All 36 pre-existing findings are individually grandfathered in knip.ts with per-file comments naming each symbol, so future contributors know exactly why they're allowlisted rather than wondering. Zero code deleted or modified — this PR is the gate, not the cleanup.

The one real config gap was fixed properly, not ignored around

e2e/mocks/freighter.ts initially flagged as an unreferenced file — but that's a config gap, not a real dead-code finding: this repo has two Playwright configs (root playwright.config.ts for ./tests, e2e/playwright.config.ts for ./e2e), and knip's Playwright plugin only auto-detects one. Fixed by pointing the plugin at both config files, rather than ignoring the false positive — this keeps future dead code under e2e/ and tests/ genuinely catchable, instead of permanently blind to that directory.

Proof the gate actually works — a canary, not just a clean run

A clean pnpm run deadcode exit-0 against the current tree doesn't prove the gate would catch anything new — it could just as easily mean the tool is misconfigured to find nothing. Verified instead: added a stray export const __x = 42 in a new src/lib/ file → pnpm run deadcode correctly failed (Unused files (1), exit 1). Removed after confirming. The gate demonstrably fails the build on a genuine new finding.

Changed files

.github/workflows/e2e.yml | 3 + (new step, after "Dependency vulnerability audit")
knip.ts | 92 + (new config: Next.js + Vitest + dual-Playwright plugins, plus the commented 36-item allowlist)
package.json | 2 + (deadcode script, knip devDependency)
pnpm-lock.yaml | 551 +- (knip + transitive deps only — no existing package's pinned version changed or removed)

CI step (.github/workflows/e2e.yml), placed as a cheap static check before the expensive build/Lighthouse/Playwright steps:

- name: Dead code and unused exports
  run: pnpm run deadcode

Verification

Check	Result
pnpm run typecheck	✅
pnpm run lint	✅ (pre-existing warnings only)
pnpm run build	✅
pnpm run audit:high	✅
pnpm run bundle:budget	✅ (723.0/780.0 KiB)
pnpm run deadcode	✅ clean; canary-verified to fail on genuine new findings

"How to test" — satisfied

• package.json now has a dead-code detection tool configured — knip@^6.33.0, deadcode script, knip.ts config
• CI has a step for unused export detection — .github/workflows/e2e.yml → "Dead code and unused exports"

Follow-up cleanup — a precise checklist, not a vague pointer

Every one of the 36 baseline findings, individually, so whoever picks this up doesn't need to re-run knip and re-derive the list:

Unused dependencies (3)

• @chakra-ui/next-js — not imported anywhere in src/
• @stellar/stellar-base — transitively provided by @stellar/stellar-sdk; no direct import
• autoprefixer (devDep) — Tailwind v3 leftover; Tailwind v4 (@tailwindcss/postcss) autoprefixes internally

src/lib/error-handler.ts — highest-value investigation (11 findings): RPCError, ContractError, ValidationError, ErrorLogger, ErrorHandler, withErrorHandler, useErrorHandler, retryWithBackoff, enum ErrorType, interface AppError. Looks like a complete error-handling module built ahead of use — needs a dynamic-import / planned-feature check before anyone removes it.

Everything else, by file:

• src/lib/soroban.ts (5) — buildUnlockAssetsTransaction, parseSimulationError, LeaderboardRow, BoostConfig, ContractCallOptions
• src/lib/backend.ts (3) — getAirdrop, listAirdropRecipients, Recipient
• src/hooks/useSorobanQuery.ts (3) — useLockAssets, useOptimisticUpdate, useTransactionStates
• src/i18n/routing.ts (5) — Link, redirect, usePathname, useRouter, Locale — next-intl idiom; either wire up consumers or drop the re-exports
• src/hooks/useSorobanEvents.ts (1) — classifyGetEventsError
• src/lib/feeBumpGuard.ts (1) — SPONSORABLE_FUNCTIONS
• src/types/farm.ts (1) — toStroops
• src/config/index.ts (1) — StellarNetworkPreset
• src/hooks/useToast.tsx (1) — NotificationType
• src/components/ErrorBoundary/ErrorBoundary.tsx (1) — ErrorBoundarySection
• e2e/mocks/freighter.ts (1) — injectFreighterMock: trivial fix, just drop the export keyword (only used within its own file)

Also unrelated, worth its own small issue: 15 pre-existing vitest failures (matchMedia is not a function, a jsdom/Chakra environment gap) — vitest isn't run in CI today, so this has been invisible. Needs a window.matchMedia polyfill in the vitest setup.

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