DRU-484: Schedule usage polls with idle backoff

[czpython]

Usage snapshots stop updating when no Usage page is open. Add core.refresh_usage with a fixed five-minute schedule so connected subscriptions update without a browser.

UsageScrape.is_due() polls first-time subscriptions and subscriptions with a completed call after the last scrape. A completed call takes priority over an exhausted snapshot. Otherwise, an exhausted window waits for its earliest reset. A window reset makes one poll due.

Unchanged quota values increase the interval through 5, 10, 20, 40, and 60 minutes. One interval table sets the history limit and delay. The quota property compares the error tag, five-hour percentage, and weekly percentages in provider order. Only changed quota values restart the interval. Manual refresh retains its 60-second floor.

The task reloads each subscription before a poll. Session expiry and revocation during a tick do not break later polls. The schedule is a code constant, consistent with the current @task contract. No schema or frontend changes are required.

Validation

• uv run ruff check backend and uv run ruff format --check backend passed.
• uv run pytest backend/ passed: 1,744 tests.
• The focused usage run passed: 55 tests across scheduling, provider polls, and usage routes.
• Backend and frontend CI passed. The documentation preview passed. Frontend checks ran in CI for this revision.
• Tests used mocked provider endpoints. No live provider or deployment checks ran.

Closes DRU-484.

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Project	Status	Preview	Updated
druks	🟢 Ready	View Preview	Sep 8, 2026, 7:05 PM

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