Computes three signed metrics per window from the underlying
        forensic windows analysis:
          - slip_velocity_days_per_day: completion shift / window
            duration (positive = slipping, negative = recovering).
            MIXED DAY-TYPES — numerator is the WORKING-day completion
            shift, denominator is CALENDAR days between data dates, so
            the value is working-days-of-slip per calendar-day-elapsed,
            NOT a dimensionless rate. The honest-named alias
            ``slip_velocity_workdays_per_calendar_day`` (identical
            value), a per-row ``velocity_units`` string, and the
            top-level ``basis`` field make this explicit. Quote
            ``basis`` in any expert report.
          - slip_acceleration: velocity[n] - velocity[n-1] (positive
            = slip rate increasing, negative = decelerating/recovery)
          - half_period_estimated_slip_days: shift / 2 (forensic
            "where were we at the midpoint" centroid estimate), in
            WORKING days

        Cumulative aggregates ``mean_velocity_days_per_day`` (and its
        honest alias ``mean_velocity_workdays_per_calendar_day``),
        ``max_velocity_window``, accelerating/decelerating/recovery
        window counts.

        Honest caveats embedded in the response (mandatory for expert
        reports): midpoint estimates are probabilistic centroids, not
        observed events; velocity is per-window average, not
        instantaneous; acceleration is a finite difference, not a true
        second derivative.

        Built on top of AACE RP 29R-03 §3.3 windows analysis. Use this
        tool when you want a slip-rate trend line on top of the same
        per-window math ``forensic_windows_analysis`` already computes.

        Args:
            schedules: chronologically ordered list of dicts — the SAME
                shape ``forensic_windows_analysis`` accepts. Each dict
                carries ``label`` (optional) and EXACTLY ONE of
                ``xer_content`` or ``xer_path``. Preferred input for
                hosted/remote clients.
            xer_paths: legacy chronologically ordered list of server-side
                XER paths.
            xer_contents: legacy chronologically ordered list of XER text
                contents (alternative for hosted/remote use).
            Supply EXACTLY ONE of schedules / xer_paths / xer_contents
            (at least 2 entries).

        Returns:
            {
              "rows": [{window_label, period_start, period_end,
                        window_duration_days, shift_days, shift_workdays,
                        shift_calendar_days,
                        slip_velocity_days_per_day,
                        slip_velocity_workdays_per_calendar_day,
                        velocity_units, slip_acceleration,
                        acceleration_units, midpoint_estimate_date,
                        half_period_estimated_slip_days,
                        half_period_estimated_slip_workdays,
                        half_period_units}, ...],
              "cumulative": {mean_velocity_days_per_day,
                             mean_velocity_workdays_per_calendar_day,
                             velocity_units, max_velocity_window,
                             accelerating_windows,
                             decelerating_windows,
                             recovery_windows},
              "units": "working-days of slip per calendar-day elapsed",
              "basis": "<numerator/denominator day-type disclosure>",
              "standard": "AACE RP 29R-03 §3.3 (Windows Analysis)",
              "caveat": "..."
            }