Add the plumbing that lets a checker receive (at evaluation, report
rendering, and metrics extraction) observations produced by other
checkers on DiscoveryEntry records it originally published.
Surface changes:
- RelatedObservation struct: one downstream observation, tagged with
the producing CheckerID and the Ref matching the DiscoveryEntry
it covers.
- ObservationGetter gains GetRelated(ctx, key), so rules can opt in
to cross-checker composition. mapObservationGetter (remote
/evaluate path) returns empty; the host owns lineage resolution.
- ReportContext interface: Data() + Related(key). Reporters consume
it instead of a raw json.RawMessage, which collapses the former
legacy/Ctx duplicate and gives one uniform signature:
GetHTMLReport(ctx ReportContext) (string, error)
ExtractMetrics(ctx ReportContext, t time.Time) ([]CheckMetric, error)
- NewReportContext(data, related) and StaticReportContext(data) build
fixed-payload contexts for entry points without an ObservationContext.
- ExternalReportRequest gains a Related map so the host can ship
pre-composed lineage to a remote checker over /report. The SDK's
/report handler threads it through to the reporter via
NewReportContext, closing the wire gap that previously forced
remote reports to a StaticReportContext with no related data.
Tests cover the Related map round-trip end-to-end via a peeking provider.
Adds HealthResponse carrying inflight count, total requests, 1/5/15-min
EWMA load averages, uptime, and NumCPU so a scheduler can pick the least
busy worker. A background sampler updates the load averages every 5s,
stopped by a new idempotent Close method. Work endpoints (/collect,
/evaluate, /report) are wrapped with a trackWork middleware; /health
and /definition are excluded so polling traffic does not pollute the
signal.
Errors from provider.Collect() and json.Marshal were returned with HTTP
200, making failures invisible to monitoring, proxies, and clients that
check status codes. Return 500 Internal Server Error so HTTP-level
tooling can detect failures without parsing the response body.
