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Owner-scoped usage meter read.

Reuses the metering primitives: used_in_window already SUMs abs(amount) = per-rotor COMPUTE units (a 4-rotor static counts 4), so the meter inherits compute-unit accounting. The tier is resolved via entitlement_for (default-down: a forged/unknown tier → free, never pro), never a raw dict lookup of the request-supplied tier.

resets_at is the ROLLING window's next age-out instant — the oldest in-window debit's created_at + the window length. With no in-window debit there is nothing pending to age out, so resets_at = now. It is NEVER since + window (which equals now for every request because since = now - window).