[FEATURE] #879 - Unit and integration tests for multi-agent execution modes

[stephanj]

Parent Issue

Part of #879 — Support Multi-Agent Execution Modes Per Task

Task

Comprehensive test coverage for the multi-agent execution feature.

Test Cases

TaskExecutionMode Config Tests

• Enum serializes/deserializes to task YAML correctly
• Per-task override takes precedence over global default
• Missing field defaults to null (falls back to global)
• Global default persists across settings changes

AgentRole & Context Builder Tests

• Implementer context includes full task spec + write instructions
• Reviewer context includes diff + acceptance criteria + verdict format
• Validator context includes test/lint instructions
• Revision context includes review comments from previous cycle
• ChatMessageContext carries role and previous phase output correctly

MultiAgentPhaseManager Tests

• SINGLE mode: one phase, immediate completion
• IMPLEMENTER_REVIEWER: two phases (implement → review), APPROVE → complete
• IMPLEMENTER_REVIEWER: REQUEST_CHANGES → revision → re-review cycle
• IMPLEMENTER_REVIEWER: max revisions exhausted → task marked for manual review
• VERIFY_ONLY: skips implementation, runs validation only
• Phase failure propagates correctly to runner

DiffCaptureService Tests

• Baseline captured correctly (git rev-parse HEAD)
• Diff captured between baseline and working tree
• Changed files list matches actual modifications
• Large diff truncated with summary
• Non-git project fallback works

ReviewVerdictParser Tests

• Structured APPROVE verdict parsed correctly
• Structured REQUEST_CHANGES with comments parsed correctly
• Fallback heuristic detects "approve" keyword
• Fallback heuristic detects "changes needed" / "reject" keywords
• Malformed output defaults to REQUEST_CHANGES (conservative)
• Empty output handled gracefully

Role-Based CLI Dispatch Tests

• Different tools selected for implementer vs. reviewer
• Default: same tool for all roles
• Tool config correctly passed to each phase execution

Files to Create

• src/test/java/com/devoxx/genie/service/spec/MultiAgentPhaseManagerTest.java (new)
• src/test/java/com/devoxx/genie/service/spec/DiffCaptureServiceTest.java (new)
• src/test/java/com/devoxx/genie/service/spec/ReviewVerdictParserTest.java (new)
• src/test/java/com/devoxx/genie/service/spec/AgentRoleContextTest.java (new)

Dependencies

• Requires: All other [FEATURE] Support Multi-Agent Execution Modes Per Task #879 sub-tasks

Acceptance Criteria

• All test cases above pass
• No flaky tests
• Existing tests unaffected
• SINGLE mode regression tests confirm zero behavior change