GET /api/v1/health re-ran all 14 health checks on every request, 4 of
which shell out to ffmpeg/ffprobe via CliWrap — so each poll spawned ~4
subprocesses. The existing HealthCheckSummary cache was write-only.
Cache the full result list for 30s inside HealthCheckService keyed on a
new "healthcheck.results" entry; a non-forced call returns it on a hit,
skipping the checks and the (subscriber-less) summary publish. Add a
`bool forceRefresh` first parameter to IHealthCheckService.PerformHealthChecks:
the API poll path reads the cache, while startup (RunHealthChecksService)
and the troubleshooting support bundle force a fresh run.
Refresh surface: GET /api/v1/health gains an optional `[FromQuery] bool
refresh` (additive, follows the ?deep= exemplar); the SPA "Refresh health"
button calls /api/v1/health?refresh=true, the initial/poll load does not.
Tests: HealthCheckService cache-hit vs force-bypass (mutually opposing,
non-vacuous), handler+controller refresh-flag threading, SPA refresh URL.
Docs: decisions.md 2026-07-19 (#431), api-conventions §2; regenerated v1.json.
fixes#431
Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>