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fix(ws): keep watched pairs as metric labels, bound only the unknown ones - #426
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…ones #401 closed the cardinality hole in ws_clients_total / ws_messages_sent_total / ws_messages_dropped_total by folding every pair-specific subscription into `other`. That is safe — no client-supplied string can mint a series — but it also costs all per-pair visibility: {pair="other"} and {pair="*"} together are barely more than one number, so "which pair actually has subscribers" stops being answerable. config.pairs is operator-defined and fixed for the life of the process, which makes it a bounded label domain. A subscription to a watched pair now keeps its own label; everything else still collapses into `other`. The safety property is unchanged: the whole unbounded space is one series. The test environment configures no pairs, so the test stubs one — without that the watched-pair branch is unreachable and the assertion would pass for the wrong reason. Claude-Session: https://claude.ai/code/session_01USgemLt4Rnz4SGB1Srf3GB
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Follow-up to #401, which I merged. That PR closed the cardinality hole correctly — after it, no client-supplied string could mint a Prometheus series — but it folded every pair-specific subscription into
other, which also removed all per-pair visibility.{pair="other"}and{pair="*"}together are barely more than one number, so "which pair actually has subscribers" stopped being answerable on the dashboard.config.pairsis operator-defined and fixed for the lifetime of the process, which makes it a bounded label domain. So:otherThe safety property is unchanged: the entire unbounded space is exactly one series.
On the test
The test environment configures no pairs at all, so
config.pairsis empty and the watched-pair branch would never execute — the assertion would have passed for the wrong reason. The test stubs a single watched pair throughvi.mock('../config')withimportOriginal, becausefanout.tsreadsconfig.pairsonce at module load.src/__tests__/fanout.test.ts: 8 passed.tsc --noEmitclean.Credit for the original fix and the metric-label test harness goes to @Jossy-ossy in #401 — this only refines the label domain.
https://claude.ai/code/session_01USgemLt4Rnz4SGB1Srf3GB