Add application warmup feature to run routing queries during startup

[vpaturet]

Summary

Add a configurable application warmup feature that runs transit routing queries in a background
thread during OTP startup. This warms up the application — JIT compilation, GraphQL schema caches,
routing data structures, and other lazily initialized components — before production traffic arrives.

How it works

When the warmup section is present in router-config.json, a daemon thread sends sequential
GraphQL trip queries through the configured API (TransModel or GTFS), exercising the full request
stack: GraphQL parsing, data fetchers, Raptor + A* routing, itinerary filtering, and response
serialization. The thread starts after Raptor transit data is created and stops when all updaters
are primed (health endpoint returns UP) or after a maximum of 20 queries.

Queries alternate between depart-at/arrive-by and cycle through access/egress mode combinations
(walk, car-to-park). Query parameters are passed as GraphQL variables rather than string
interpolation, matching how production clients call the API.

Configuration example

"warmup": {
  "api": "transmodel",
  "from": { "lat": 59.9139, "lon": 10.7522 },
  "to": { "lat": 59.95, "lon": 10.76 }
}

Design

• WarmupConfig — config parsing (final class, Api enum implements DocumentedEnum, version V2_10)
• WarmupWorker — background thread that orchestrates warmup queries with max query limit, completion summary (count, failures, elapsed time), and top-level Throwable catch
• WarmupQueryExecutor — strategy interface returning success/failure boolean
• TransmodelWarmupQueryExecutor / GtfsWarmupQueryExecutor — cache schema, context, and (for GTFS) the GraphQL instance at construction time; use GraphQL variables for query parameters; both use immutable Map.of/Map.ofEntries for variables
• Package: standalone.configure.warmup (startup lifecycle, not HTTP infrastructure)

Safety

• Null guard for @Nullable GraphQL schema (warns if API feature is disabled)
• Top-level catch (Throwable) ensures the warmup thread never dies silently
• GraphQL errors logged at WARN for operator visibility
• Exception stack traces logged at DEBUG
• Warmup thread launch and skip both logged at INFO
• Daemon thread — killed on JVM shutdown

Unit tests

• WarmupConfigTest — tests config parsing (absent section, coordinate parsing, API enum parsing)
• WarmupQueryValidationTest — validates both static query constants against the actual GraphQL schemas at build time

Documentation

• RouterConfiguration.md regenerated with the new warmup section
• package.md documents the warmup subpackage lifecycle and design

[codecov]

Codecov Report

❌ Patch coverage is 22.28261% with 143 lines in your changes missing coverage. Please review.
✅ Project coverage is 71.19%. Comparing base (96ca627) to head (c989cf2).

Files with missing lines	Patch %	Lines
...nner/standalone/configure/warmup/WarmupWorker.java	0.00%	70 Missing ⚠️
...onfigure/warmup/TransmodelWarmupQueryExecutor.java	0.00%	35 Missing ⚠️
...lone/configure/warmup/GtfsWarmupQueryExecutor.java	0.00%	32 Missing ⚠️
...ner/standalone/configure/ConstructApplication.java	0.00%	4 Missing ⚠️
...pentripplanner/standalone/config/RouterConfig.java	50.00%	1 Missing ⚠️
...r/standalone/config/routerconfig/WarmupConfig.java	97.56%	1 Missing ⚠️

Additional details and impacted files

@@              Coverage Diff              @@
##             dev-2.x    #7509      +/-   ##
=============================================
- Coverage      71.29%   71.19%   -0.11%     
- Complexity     21217    21222       +5     
=============================================
  Files           2365     2369       +4     
  Lines          87770    87954     +184     
  Branches        8686     8698      +12     
=============================================
+ Hits           62574    62615      +41     
- Misses         22183    22327     +144     
+ Partials        3013     3012       -1     

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[vpaturet]

@flaktack have you put in place a similar feature for your OTP deployments?