AI leaves garrison when moving away from captured village

[Copilot]

When the AI captures a village, it now splits its army and leaves a 1-soldier garrison behind to build up forces, rather than moving on immediately with the full army and gaining no benefit from the village.

Changes Made

• Garrison creation: Modified executeAI() to split off a 1-soldier garrison when an AI army moves away from an owned village, with safeguards against duplicate garrisons at the same village (checks both existing armies and garrisons created earlier in the same tick).
• Minimum soldier threshold: AI armies garrisoning an owned village now stay put until they accumulate at least 5 soldiers (AI_MIN_SOLDIERS_TO_MOVE), preventing small garrison armies from immediately wandering off and creating trails of 1-soldier armies.
• Army cap: Added a maximum of 5 total AI armies (AI_MAX_ARMIES). Garrison creation is skipped if the cap would be exceeded.
• Tests: Added deterministic tests using getInternalStateForTest() to validate both garrison creation on departure and garrison staying behavior below the soldier threshold.

Testing

• ✅ All 132 unit tests pass
• ✅ CodeQL security scan: 0 alerts

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[dmccoystephenson]

@copilot Unit tests for the backend are failing and the AI is splitting far too often:

[Copilot]

@copilot Unit tests for the backend are failing and the AI is splitting far too often:

<img width="1282" height="932" alt="image" src="https://github.com/user-attachments/assets/716e7214-0a14-4e7a-...

Fixed in ef4e0f1. Two issues addressed:

1. Over-splitting: The garrison army would gain soldiers from village generation, then the AI would assign it a destination on the next tick, triggering another garrison split — repeating every tick. Fixed by checking for an existing friendly army already staying at the village before creating a new garrison.

2. Test failure: The test used hardcoded village at (6,6) which broke after the random map generation merge. Updated to use getInternalStateForTest() for deterministic setup.

All 131 tests pass.

[Copilot]

Pull request overview

This PR updates the AI turn logic so that when an AI army leaves an AI-owned village, it splits off a 1-soldier garrison (while avoiding repeated/duplicate garrison creation at the same village), and adds a deterministic regression test to validate the behavior.

Changes:

• Update executeAI() to create a 1-soldier garrison when an AI army starts moving away from an AI-owned village.
• Prevent garrison over-splitting by skipping garrison creation when a friendly non-moving army is already stationed at that village (including garrisons created earlier in the same tick).
• Add a new deterministic test using getInternalStateForTest() to avoid randomness-related coordinate brittleness.

Reviewed changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated no comments.

File	Description
backend/src/main/java/com/barony/backend/service/GameService.java	Adds AI garrison-splitting logic when moving away from AI-owned villages, with safeguards against duplicate garrisons.
backend/src/test/java/com/barony/backend/service/GameServiceTest.java	Adds a deterministic regression test for AI garrison behavior (and minor whitespace-only adjustments).

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[dmccoystephenson]

@copilot The enemy is still splitting very often, causing trails of 1 man armies to pop up. The AI should decide to garrison at a village until it reaches a particular number of soldiers. Maybe a limit should be placed on how many armies can exist at one time too.

[Copilot]

@copilot The enemy is still splitting very often, causing trails of 1 man armies to pop up. The AI should decide to garrison at a village until it reaches a particular number of soldiers. Maybe a limi...

Fixed in dacfe1f. Two changes:

1. Minimum soldier threshold (AI_MIN_SOLDIERS_TO_MOVE = 5): AI armies sitting on owned villages now stay put until they've accumulated at least 5 soldiers. This prevents the pattern where a 1-soldier garrison gains a soldier from village generation, immediately gets sent somewhere, and spawns another garrison.

2. Army cap (AI_MAX_ARMIES = 5): No new garrisons are created if the AI already has 5 armies total.

All 132 tests pass including a new test verifying that small garrisons stay at their village.