Sub-builders called after validateServerConfig (prefixV4, prefixV6,
allocation strategy, dns, oidc client secret/path, isSafeServerURL)
each returned the first error. So an operator that fixed one
issue saw the next one only on the next startup.
Lift one *configValidator across the entire LoadServerConfig flow.
validateServerConfigInto(v) populates it; each sub-builder's error
is wrapped in a structured *ConfigError (with the original sentinel
kept on the Cause field, so errors.Is against errOidcMutuallyExclusive,
errServerURLSame/Suffix, ErrNoPrefixConfigured, and
ErrInvalidAllocationStrategy keeps working). v.Err() is checked once,
right before the &Config{} construction.
TestReadConfig/base-domain-in-server-url-err matched the old sentinel
wording; flipped to the new structured Reason. Added
TestLoadServerConfig_CollectsAcrossSubBuilders to lock the wiring:
four sub-builder failures from a single config produce four
*ConfigErrors in the report.
Updates #3227
Kristoffer Dalby
4cad0b564e