Don't collapse pure-DC pool on brief negative-grid transients (#359) … #672

Job	Run time
lint	15s
validate (3.12)	34s
validate (3.10)	44s
validate (3.11)	1m 0s
validate (3.13)	43s
build (linux/arm/v7, base-linux-arm-v7) / build	1m 11s
build-addon (linux/arm64, addon-linux-arm64) / build	48s
build-addon (linux/amd64, addon-linux-amd64) / build	55s
build (linux/arm64, base-linux-arm64) / build	1m 30s
build (linux/amd64, base-linux-amd64) / build	35s
merge-addon / merge	17s
merge / merge	24s
	8m 56s

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