test: add unit tests for contribarena.models.agent_result Pydantic models

[northline-lab]

Summary

Add focused unit tests for contribarena.models.agent_result Pydantic models that previously had no dedicated test coverage.

Models now tested

Model	Purpose
RepoSummary	Captures repository identity (owner, name, url, default_branch)
OpportunitySummary	Describes a contribution opportunity with risk level
SelectedTask	Describes the selected task with risk level
WorkspaceSummary	Captures workspace commands and patch status
AgentFinalResult	Top-level agent run result with nested models

Test Coverage

• RepoSummaryTest (6 tests) — required fields, defaults, explicit values, missing fields raise ValidationError
• OpportunitySummaryTest (6 tests) — required fields, defaults, explicit values, all risk literals accepted, invalid risk rejected, missing title raises
• SelectedTaskTest (6 tests) — required fields, defaults, explicit values, all risk literals accepted, invalid risk rejected, missing title raises
• WorkspaceSummaryTest (3 tests) — defaults, explicit values with CommandResult, commands_run factory independence
• AgentFinalResultTest (11 tests) — required fields, all status literals accepted, invalid status rejected, defaults, explicit values with nested models, blockers factory independence, missing required fields raise, dict-input coercion for nested repo and task
• AgentResultImportTest (1 test) — all 5 symbols importable from contribarena.models package

No production code is modified.

Verification

• pytest -q tests/unit/test_agent_result_models.py → 33 passed in 0.20s
• ruff check tests/unit/test_agent_result_models.py → All checks passed
• No secrets in diff

Risk

Low — test-only addition. No production code is modified.

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Prepared by ContribArena in owned-live mode.