Message credits for Clip AI. Each host-key message (brief or chat turn) now
spends one credit against a per-user allowance — 30 messages / 3h by default
(overridable via AI_CREDIT_LIMIT / AI_CREDIT_WINDOW_HOURS). The window is a
fixed rolling window that resets on the first request after it elapses. When the
allowance is exhausted the AI route returns 429 with a friendly "resets in
Xh Ym" message and a nudge to add your own key.
Usage meter in AI settings (Settings → Clip AI) — a progress bar showing
used / limit, remaining, and when it resets. Turns amber near the cap and red
when reached. Users on their own key see "Unlimited on your key" instead.
Storage + atomic windowed increment in public.ai_usage /
public.consume_ai_credit (migration 20260708000100_ai_usage.sql); read-only
snapshot at GET /api/ai/usage. Metering fails open — a DB hiccup never
blocks a message.
Changed
ResolvedAIConfig carries an ownKey flag so the route can tell host-key usage
(metered) from bring-your-own-key usage (unmetered — billed to the user's
provider).
