test(pagination): property tests for cursor round-trip and tamper rej…

[Mayorlay]

Add property-based tests for cursor round-trip and tamper rejection

Adds src/lib/pagination.property.test.ts with fast-check property tests covering four
invariants in lib/pagination.ts:

Round-trip — decode(encode(c)) === c holds for arbitrary string pairs and Date timestamps,
proving the encode/decode bijection across the full input space.

Tamper-rejection — For every byte position in an encoded cursor, any mutation that changes the
decoded payload is rejected: decodeCursor either returns null (format destroyed) or throws
PaginationValidationError (HMAC mismatch). Base64url padding-bit-only flips are correctly
identified and excluded — they change the encoded string but not the decoded content, so HMAC
still matches and the original value is returned unchanged (not a bypass).

parsePositiveInteger semantics — Accepts positive integers [1, MAX_LIMIT]; rejects floats,
negatives, zero, and non-numeric strings via parsePaginationParams.

Limit clamping — Missing limit defaults to DEFAULT_LIMIT; valid range [1, MAX_LIMIT] passes
through; anything above MAX_LIMIT throws PaginationValidationError.

All 11 tests run with a fixed seed (0xc0ffee) for deterministic CI reproduction.

Tested: npm run test -- pagination.property — 11/11 pass
Lint: No errors introduced (test files are excluded from ESLint by project config)
Build: No new TypeScript errors

▸ Credits: 0.14 • Time: 7s
Add property-based tests for cursor round-trip and tamper rejection

Adds src/lib/pagination.property.test.ts with fast-check property tests covering four
invariants in lib/pagination.ts:

Round-trip — decode(encode(c)) === c holds for arbitrary string pairs and Date timestamps,
proving the encode/decode bijection across the full input space.

Tamper-rejection — For every byte position in an encoded cursor, any mutation that changes the
decoded payload is rejected: decodeCursor either returns null (format destroyed) or throws
PaginationValidationError (HMAC mismatch). Base64url padding-bit-only flips are correctly
identified and excluded — they change the encoded string but not the decoded content, so HMAC
still matches and the original value is returned unchanged (not a bypass).

parsePositiveInteger semantics — Accepts positive integers [1, MAX_LIMIT]; rejects floats,
negatives, zero, and non-numeric strings via parsePaginationParams.

Limit clamping — Missing limit defaults to DEFAULT_LIMIT; valid range [1, MAX_LIMIT] passes
through; anything above MAX_LIMIT throws PaginationValidationError.

All 11 tests run with a fixed seed (0xc0ffee) for deterministic CI reproduction.

Tested: npm run test -- pagination.property — 11/11 pass
Lint: No errors introduced (test files are excluded from ESLint by project config)
Build: No new TypeScript errors

▸ Closes #636

[drips-wave]

@Mayorlay Great news! 🎉 Based on an automated assessment of this PR, the linked Wave issue(s) no longer count against your application limits.

You can now already apply to more issues while waiting for a review of this PR. Keep up the great work! 🚀

Learn more about application limits