## Summary
Projects that configure their own `metricExporters` or `metricReaders`
in `trigger.config.ts` were losing task metrics on nearly every run, and
seeing an unexplained `Failed to flush tracingSDK` alongside
`OTLPExporterError: Bad Request` in their run logs. Spans and logs kept
working, so the runs otherwise looked healthy.
## Root cause and fix
Every configured exporter gets its own `PeriodicExportingMetricReader`,
and `meterProvider.forceFlush()` fans out across all readers with
`Promise.all`, so two collections can land on the same millisecond.
`@opentelemetry/host-metrics` divides by the elapsed interval to compute
`process.cpu.utilization`
([common.ts](https://github.com/open-telemetry/opentelemetry-js-contrib/blob/main/packages/host-metrics/src/stats/common.ts)),
so a zero interval yields `0/0`. `JSON.stringify(NaN)` is `null`, and a
collector rejects `"asDouble": null` with a 400 that drops the
**entire** request, not just the offending point.
`flush()` and `shutdown()` now walk the metric readers one at a time, so
collections can no longer share a timestamp. Each reader is isolated, so
one failing reader cannot skip the readers behind it, and every failure
is logged with the reader that produced it. The first error is still
rethrown, so callers see failures exactly as before.
As a second layer, non-finite data points are dropped just before our
own export, so a metric that divides by zero cannot take the rest of the
batch with it. Exporters and readers supplied through
`trigger.config.ts` are untouched by that filter and still receive raw
data.
The trade-off is that configured exporters now flush after the built-in
one rather than alongside it, so flush latency is the sum rather than
the max.
An internal test package's dependency on core was replaced with a local
helper, because core now needs that package in `devDependencies` and the
two together formed a workspace cycle.
## Verification
Tested against a real collector in a container: a batch containing a
`NaN` reading is rejected with a 400 without the fix and accepted with
it, and a single flush is asserted to collect from one reader at a time.
nicktrn
fa7eea39d8