implements a check to do not define at runtime a value on an Map<String,String> undefined key for a BUILD_AND_RUNTIME_FIXED config

[dcdh]

Description

Currently it is possible to define on a Map<String,String> config used in BUILD_AND_RUNTIME_FIXED a value on an undefined key.
When it is done on a know property a message is displayed enlightening the fact that it is not possible.

Sample reproducer:

1. git clone https://github.com/dcdh/code-with-quarkus-config.git
2. ./build.sh
3. ./run.sh

You will see this message at application startup

sample-1  | 2026-03-14 21:14:25,935 WARN  [io.quarkus.runtime.configuration.ConfigRecorder] (main) Build time property cannot be changed at runtime:
sample-1  |  - config.properties.inside is set to 'redefined' but it is build time fixed to 'inside'. Did you change the property config.properties.inside after building the application?
sample-1  |  - config.property is set to 'redefined' but it is build time fixed to 'inside'. Did you change the property config.property after building the application?
sample-1  | 2026-03-14 21:14:25,935 INFO  [org.acme.MyConfigService] (main) inside
sample-1  | 2026-03-14 21:14:25,935 INFO  [org.acme.MyConfigService] (main) inside=inside
sample-1  | 2026-03-14 21:14:25,935 INFO  [org.acme.MyConfigService] (main) other=redefined

The config is defined this way

@ConfigMapping(prefix = "config")
@ConfigRoot(phase = ConfigPhase.BUILD_AND_RUN_TIME_FIXED)
public interface MyConfig {

    /**
     * property
     */
    String property();

    /**
     * properties
     */
    Map<String, String> properties();
}

The docker-compose used to launch the application is defined this way to overload the values

services:
  sample:
    image: sample/code-with-quarkus-config-sample:1.0.0-SNAPSHOT
    environment:
      - CONFIG_PROPERTY=redefined
      - CONFIG_PROPERTIES_INSIDE=redefined
      - CONFIG_PROPERTIES_OTHER=redefined

other which is an undefined key in application.properties is defined. Other are not overloaded.

Implementation ideas

It should impact the io.quarkus.runtime.configuration.ConfigRecorder

[quarkus-bot]

/cc @edeandrea (container-image), @geoand (container-image)

[dcdh]

/cc @radcortez