The original title is: "Why scheduling tools get availability wrong (and how to fix it)"

Short summary

Grid-based scheduling tools pre-generate fixed time slots, which hides valid availability when calendar events don't align to slot boundaries. A free-window approach instead subtracts busy periods from available hours to surface every valid start time where a requested duration fits. Combining this with cache-first display and confirm-time re-validation prevents double-bookings while keeping page loads fast.

• •Grid-based slot generation hides valid availability when events end mid-slot
• •Free-window computation subtracts busy periods from available intervals to expose all valid start times
• •Cache-first display with confirm-time re-validation prevents stale-cache double-bookings

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