Tasks 3.4-3.6 of the overview-dashboard plan.
Polling (3.4/3.5):
- OverviewPollerService: one timer at the fastest configured cadence, each
target polled when its own interval is due, fan-out per sweep, no retries
(the next tick is the retry, so damping stays the only place that decides
whether a failure is worth showing).
- OverviewSnapshotStore: atomic swap of a complete immutable graph plus a
change event. Pages read it and never probe — the cache-first requirement.
- LeaderResolver: per-group leader from akka-cluster data, with the
split-brain flag scoped to members that are actually answering, so an
ordinary failover is not misread as a disagreement.
UI (3.6): ThemeShell + StatusPill/TechCard composition against the mockup;
instance cards carry the status stripe (dashed for Unreachable), the check
detail list and the raw ready/active signal line.
Two defects found by verification rather than by review:
- The active tier answers with a status code and an EMPTY body, but the client
demanded parseable JSON on every probe — so a healthy pair rendered as
"role unknown" instead of Active/Standby. Split into ProbeAsync (ready tier,
body is the payload) and ProbeStatusAsync (active tier, code is the answer).
Caught by a live smoke run against two fake health endpoints; the poller
tests now serve an empty body so they hold the fix.
- SweepAsync published even when cancellation was already requested, leaving a
half-probed registry as the store's final state on shutdown. It now checks
the token itself rather than relying on the transport to throw.
Also: app.UseAntiforgery() is required despite the anonymous-by-design
pipeline — AddRazorComponents stamps antiforgery metadata unconditionally and
the endpoint middleware hard-fails without it (every page was 500). Chosen
over DisableAntiforgery() so a future form is protected by default.
147 tests, 0 warnings. Live-verified end to end against fake endpoints:
Up/Unreachable/Active/Standby, leader chip, cluster-data line, KPI counts.
Joseph Doherty