feat(season): restart the lobby into a seasonal world during its window

[TheMeinerLP]

Summary

A season is its own world, built by the build team as worlds/<name>/ with a map file. The lobby restarts into that world while the season window is active.

• Config in avaje-config: seasons.<id>.{world,from,to,enabled} and seasons.zone (default Europe/Berlin).
• New column features/season, cloudnet variant only. The local variant excludes it because nothing there would restart the lobby.

How it works

• The world is chosen at startup via LobbyWorldChoice (in core), resolved by ServiceLoader in PlatformBeans.
• Every 1200 ticks and after each disconnect, the column compares the started world with the desired one. If they differ, a restart is marked pending (logged once). The lobby stops via MinecraftServer.stopCleanly() only when nobody is online, and CloudNet restarts it.
• Season end and the enabled kill switch use the same path.
• Invalid config aborts startup. Invalid live config only warns, so it cannot cause a restart loop.

Why this shape

• Supersedes feat: run seasons from configuration (Stage 4) #225, which decorated the running world through an undo stack. It depended on FeatureGate/Togglz/stages from feat: gate features by kill switch, release stage and time window (Stage 3) #216/feat: show build servers to the team in the navigator (Stage 5) #219, which only landed in branch docs/lobby-season-spec, never in main.
• Restart instead of live switch: no undo, and no moving players between instances.
• ServiceLoader instead of an Avaje bean: a spike showed a bean from the column is always empty when runtime builds MapProvider (the column requires runtime beans). A separate module would force column-to-column imports.

Trade-offs

• No upper bound on waiting: a busy or AFK lobby delays the season. Operators can use /stop.
• More than one LobbyWorldChoice aborts startup.

Out of scope (later changes)

Navigator icons, chat prefix, block/display/sound effects, stages/preview, /season list, player notice, local variant.

Tests

MapPoolTest, LobbyWorldResolutionTest, SeasonCalendarTest, SeasonConfigReaderTest, RestartPolicyTest, SeasonModuleTest (Cyano Env, injected Clock, env.tick()), SeasonWorldChoiceTest, VariantStartTest (both variants), SeasonLobbyWorldTest, SeasonRestartWiringTest (real BeanScope), SeasonMapFileNameTest. ./gradlew build is green.

Not tested: a real CloudNet restart cycle.

OpenSpec

Change: openspec/changes/seasonal-lobby-world

https://claude.ai/code/session_01A7aAe2E6wAEbi6jjnyPTWH

[github-actions]

Test results

  255 files    255 suites   17m 14s ⏱️
  425 tests   424 ✅ 1 💤 0 ❌
1 275 runs  1 272 ✅ 3 💤 0 ❌

Results for commit 2c68de8.