Serve a hand-written Prometheus text-exposition document at a
configurable path, defaulting to /metrics. The plugin is stdlib-only
under Yaegi, so this cannot use a client library.
Add MetricsConfig: Enabled gates the route, Path overrides it,
AllowedCIDRs lets an unauthenticated caller scrape from a trusted
source address, and ModelLabel opts into a per-(provider,model)
breakdown that defaults off to avoid a series-count explosion.
Reuse the existing admin bearer-token auth path instead of adding a
second credential check. Reuse the batched, chunked reads GET
/admin/api/overview and GET /admin/api/usage already use, so a scrape
costs no extra store round trip.
Expose request, token, and cost counters per scope, provider attempt
and failure counters, a provider-health gauge from the discovery
circuit breaker, and a budget-consumed-ratio gauge per limited scope
for Prometheus alerting. Add a rate-limit-rejection counter in
limits.go: this is the one number with no existing accounting to read
back, so checkAndCount now increments a small in-process,
per-process-lifetime counter on every violation.
Escape every label value for backslash, double quote, and newline. An
unescaped quote in a label value, such as a discovered model id, makes
the whole scrape unparseable, and Prometheus reports an unparseable
scrape as the target being down rather than as one bad line.
Cover the auth gate matrix, exposition structure (TYPE per family,
counters ending _total, no duplicate series), label escaping
round-trips, the model-label opt-in, and counters reflecting real
seeded usage rather than zeros.
