One stray duplicate row used to fail every tag in a key-value group or none of them,
depending on whether an unrelated key was absent. Duplicated keys are now refused
per key: only that key's tags publish BadConfigurationError and the rest of the group
reads normally. The key-value cap reads up to 2x the distinct keys (+1 to detect
excess), so a few stray duplicates are attributed per key and only a gross excess
(history/events table) fails the whole group. Duplicated-key refusals count as
answered refusals for health. The row-cap, duplicate-key and multi-row warnings now
use the per-plan limiter (m-3); the reader-wide limiter is removed. Unit tests pin
both the all-keys-present and absent-key cases with Good controls; live SQL Server
gate added (23/23).
Refs #744
Claude-Session: https://claude.ai/code/session_01Ub9hGmYLQvn9XETzw7CMsT
Joseph Doherty
c1b9c7ec5c