Enable battalion diversity quest generation (PR 3/3) (#5838)

* Enable battalion diversity quest generation (PR 3/3)

Adds quest creation logic for BattalionDiversityQuest to QuestCreationUtils.

Quest availability:
- Only if province currently has 1-2 battalion types
- This encourages players to diversify their army composition

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

* Clarify PR dependency structure in quest docs

PR 2 (client) and PR 3 (generation) both depend on PR 1 (types),
but are independent of each other. They can be developed in parallel
and merged in either order after PR 1.

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

---------

Co-authored-by: Claude Opus 4.5 <noreply@anthropic.com>

docs/ADDING_NEW_QUESTS.md

@@ -12,7 +12,14 @@ When adding new quest types, use a three-PR strategy to ensure clients never see
 
 3. **PR 3 - Quest Generation (Server)**: Add the actual quest creation logic to `QuestCreationUtils.scala`.
 
-This order ensures that when the server starts generating the new quest type, all clients already know how to display it.
+**PR Dependencies:**
+```
+PR 1 (types)
+  ├── PR 2 (client)
+  └── PR 3 (generation)
+```
+
+PR 2 and PR 3 both depend on PR 1, but are independent of each other. They can be developed in parallel after PR 1 is merged, and merged in either order. The key constraint is that PR 3 should not be deployed before PR 2, so clients understand the quest type before the server starts generating it.
 
 ## Files to Modify
 

src/main/scala/net/eagle0/eagle/library/util/quest_creation/QuestCreationUtils.scala

@@ -32,6 +32,7 @@ import net.eagle0.eagle.model.state.quest.{
   AllianceQuest,
   AlmsAcrossRealmQuest,
   AlmsToProvinceQuest,
+  BattalionDiversityQuest,
   DefeatFactionQuest,
   DevelopProvincesQuest,
   DismissSpecificVassalQuest,
@@ -130,7 +131,8 @@ object QuestCreationUtils {
         QuestCreatorFrom(suppressRiotByForceQuests),
         QuestCreatorFrom(fightBeastsAloneQuests),
         developProvincesQuests,
-        mobilizeProvincesQuests
+        mobilizeProvincesQuests,
+        battalionDiversityQuests
       )
     ) {
       case (questCreator, fr) =>
@@ -770,4 +772,23 @@ object QuestCreationUtils {
     }
     end if
   }
+
+  private def battalionDiversityQuests(
+      province: ProvinceT,
+      @unused allProvinces: Vector[ProvinceT],
+      @unused factions: Vector[FactionT],
+      battalions: Vector[BattalionT],
+      functionalRandom: FunctionalRandom
+  ): RandomState[Vector[Quest]] = {
+    // Only available if province currently has 1-2 battalion types
+    val currentBattalionTypes = province.battalionIds
+      .flatMap(bid => battalions.find(_.id == bid))
+      .map(_.typeId)
+      .distinct
+      .size
+
+    if currentBattalionTypes >= 1 && currentBattalionTypes <= 2 then
+      RandomState(Vector(BattalionDiversityQuest), functionalRandom)
+    else RandomState(Vector(), functionalRandom)
+  }
 }