Add connectionStartupTimeout for resilience against Siri ET MQTT broker unavailability

[jessicaKoehnke]

Summary

Adds a connectionStartupTimeout configuration parameter to the SIRI MQTT updater so that OTP can start routing without real-time data when the MQTT broker is unavailable at startup, instead of blocking indefinitely. The MQTT client continues retrying in the background and resumes processing live messages once the broker becomes available.

Issue

No related issue.

Motivation

Previously, if the MQTT broker was unreachable when OTP started, the blocking .join() call in connectAndSubscribeToClient() would hang OTP startup indefinitely with no fallback.

How the code works

The HiveMQ client connection is now initiated non-blocking. At startup, OTP waits up to connectionStartupTimeout (default: 30s) for the broker to connect. If the broker connects in time, normal priming proceeds (retained messages are processed before routing is enabled). If not, OTP logs a warning and marks the updater as primed immediately, allowing routing to start without real-time data. Subscription setup is moved into the onConnect callback so it is correctly re-established on every reconnect, including after a broker restart.

New optional parameter in router-config.json:

{
  "type": "siri-et-mqtt",
  "connectionStartupTimeout": "PT30S"
}

Unit tests

No unit tests were added. The change is primarily a resilience/configuration improvement to the MQTT connection lifecycle. Manual verification was done to confirm OTP starts correctly both when the broker is available and when it is not.

Documentation

• The connectionStartupTimeout parameter is documented inline in SiriETMqttUpdaterConfig.java using OTP's config framework, and the auto-generated SiriMqttUpdater.md table and parameter details section have been updated accordingly.
• The class-level Javadoc on MqttEstimatedTimetableSource was updated to describe the new startup timeout behavior.
• A new OtpVersion.V2_10 enum entry was added to mark the parameter's introduction version.

[codecov]

Codecov Report

❌ Patch coverage is 20.93023% with 34 lines in your changes missing coverage. Please review.
✅ Project coverage is 71.01%. Comparing base (630a126) to head (d17bb6c).
⚠️ Report is 89 commits behind head on dev-2.x.

Files with missing lines	Patch %	Lines
...iri/updater/mqtt/MqttEstimatedTimetableSource.java	0.00%	31 Missing ⚠️
...rip/gtfs/updater/mqtt/MqttGtfsRealtimeUpdater.java	0.00%	2 Missing ⚠️
...siri/updater/mqtt/MqttSiriETUpdaterParameters.java	50.00%	1 Missing ⚠️

Additional details and impacted files

@@              Coverage Diff              @@
##             dev-2.x    #7489      +/-   ##
=============================================
- Coverage      71.39%   71.01%   -0.38%     
+ Complexity     21112    21004     -108     
=============================================
  Files           2344     2352       +8     
  Lines          87167    87294     +127     
  Branches        8633     8637       +4     
=============================================
- Hits           62231    61994     -237     
- Misses         21936    22312     +376     
+ Partials        3000     2988      -12     

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[MaxGosau]

MqttEstimatedTimetableSource could be seperated into multiple classes (e.g. Clientfactory, MetricsConfiguration, Orchestration) but we should do that in a seperate PR, therefore approved.