Previously `TraefikLabelBuilder` hardcoded `tls.certresolver=default` on
every router. That assumes a resolver literally named `default` exists
in the Traefik static config — true for ACME-backed installs, false for
dev/local installs that use a file-based TLS store. Traefik logs
"Router uses a nonexistent certificate resolver" for the bogus resolver
on every managed app, and any future attempt to define a differently-
named real resolver would silently skip these routers.
Server-wide setting via `CAMELEER_SERVER_RUNTIME_CERTRESOLVER` (empty by
default) flows through `ConfigMerger.GlobalRuntimeDefaults.certResolver`
into `ResolvedContainerConfig.certResolver`. When blank the
`tls.certresolver` label is omitted entirely; `tls=true` is still
emitted so Traefik serves the default TLS-store cert. When set, the
label is emitted with the configured resolver name.
Not per-app/per-env configurable: there is one Traefik per server
instance and one resolver config; app-level override would only let
users break their own routers.
TDD: TraefikLabelBuilderTest gains 3 cases (resolver set, null, blank).
Full unit suite 211/0/0.
Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>
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