Exports the standard nav functions as vi.fn() and a beforeNavigate that
captures the registered callback. The exported simulateNavigate(href)
helper fires that callback and returns the cancel spy — the whole
capture-and-fire pattern lives in the shared module, not the raw callback.
An embedded beforeEach clears the captured callback and the mock call
histories before every test. Part of #560.
Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>
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