- readClaimId: URLSearchParams.get returns '' for ?claim=, not null.
Normalize to null so the contract matches the JSDoc and consumers
can treat empty as absent.
- Tests: regression for ?claim= → null; open/close preserves other
query params (?foo=bar survives open/close unchanged).
- Tighten pushStateMock/replaceStateMock typing to vi.fn<() => void>()
per code-review nit (drops the verbose ReturnType<typeof vi.fn>).