feat(clean-release): complete and verify backend test suite (33 passing tests)

- Relocated and standardized tests for clean_release subsystem into __tests__ sub-packages.
- Implemented missing unit tests for preparation_service, audit_service, and stages.
- Enhanced API contract tests for candidate preparation and compliance reporting.
- Updated 023-clean-repo-enterprise coverage matrix with final verification results.
- Fixed relative import issues and model validation mismatches during test migration.

backend/src/models/__tests__/test_clean_release.py

@@ -0,0 +1,149 @@
+# [DEF:__tests__/test_clean_release:Module]
+# @RELATION: VERIFIES -> ../clean_release.py
+# @PURPOSE: Contract testing for Clean Release models
+# [/DEF:__tests__/test_clean_release:Module]
+
+import pytest
+from datetime import datetime
+from pydantic import ValidationError
+from src.models.clean_release import (
+    ReleaseCandidate, 
+    ReleaseCandidateStatus, 
+    ProfileType, 
+    CleanProfilePolicy, 
+    DistributionManifest,
+    ManifestItem,
+    ManifestSummary,
+    ClassificationType,
+    ComplianceCheckRun,
+    CheckFinalStatus,
+    CheckStageResult,
+    CheckStageName,
+    CheckStageStatus,
+    ComplianceReport,
+    ExecutionMode
+)
+
+# @TEST_FIXTURE: valid_enterprise_candidate
+@pytest.fixture
+def valid_candidate_data():
+    return {
+        "candidate_id": "RC-001",
+        "version": "1.0.0",
+        "profile": ProfileType.ENTERPRISE_CLEAN,
+        "created_at": datetime.now(),
+        "created_by": "admin",
+        "source_snapshot_ref": "v1.0.0-snapshot"
+    }
+
+def test_release_candidate_valid(valid_candidate_data):
+    rc = ReleaseCandidate(**valid_candidate_data)
+    assert rc.candidate_id == "RC-001"
+    assert rc.status == ReleaseCandidateStatus.DRAFT
+
+def test_release_candidate_empty_id(valid_candidate_data):
+    valid_candidate_data["candidate_id"] = "  "
+    with pytest.raises(ValueError, match="candidate_id must be non-empty"):
+        ReleaseCandidate(**valid_candidate_data)
+
+# @TEST_FIXTURE: valid_enterprise_policy
+@pytest.fixture
+def valid_policy_data():
+    return {
+        "policy_id": "POL-001",
+        "policy_version": "1",
+        "active": True,
+        "prohibited_artifact_categories": ["test-data"],
+        "required_system_categories": ["core"],
+        "internal_source_registry_ref": "REG-1",
+        "effective_from": datetime.now(),
+        "profile": ProfileType.ENTERPRISE_CLEAN
+    }
+
+# @TEST_INVARIANT: policy_purity
+def test_enterprise_policy_valid(valid_policy_data):
+    policy = CleanProfilePolicy(**valid_policy_data)
+    assert policy.external_source_forbidden is True
+
+# @TEST_EDGE: enterprise_policy_missing_prohibited
+def test_enterprise_policy_missing_prohibited(valid_policy_data):
+    valid_policy_data["prohibited_artifact_categories"] = []
+    with pytest.raises(ValueError, match="enterprise-clean policy requires prohibited_artifact_categories"):
+        CleanProfilePolicy(**valid_policy_data)
+
+# @TEST_EDGE: enterprise_policy_external_allowed
+def test_enterprise_policy_external_allowed(valid_policy_data):
+    valid_policy_data["external_source_forbidden"] = False
+    with pytest.raises(ValueError, match="enterprise-clean policy requires external_source_forbidden=true"):
+        CleanProfilePolicy(**valid_policy_data)
+
+# @TEST_INVARIANT: manifest_consistency
+# @TEST_EDGE: manifest_count_mismatch
+def test_manifest_count_mismatch():
+    summary = ManifestSummary(included_count=1, excluded_count=0, prohibited_detected_count=0)
+    item = ManifestItem(path="p", category="c", classification=ClassificationType.ALLOWED, reason="r")
+    
+    # Valid
+    DistributionManifest(
+        manifest_id="m1", candidate_id="rc1", policy_id="p1", 
+        generated_at=datetime.now(), generated_by="u", items=[item], 
+        summary=summary, deterministic_hash="h"
+    )
+    
+    # Invalid count
+    summary.included_count = 2
+    with pytest.raises(ValueError, match="manifest summary counts must match items size"):
+        DistributionManifest(
+            manifest_id="m1", candidate_id="rc1", policy_id="p1", 
+            generated_at=datetime.now(), generated_by="u", items=[item], 
+            summary=summary, deterministic_hash="h"
+        )
+
+# @TEST_INVARIANT: run_integrity
+# @TEST_EDGE: compliant_run_stage_fail
+def test_compliant_run_validation():
+    base_run = {
+        "check_run_id": "run1",
+        "candidate_id": "rc1",
+        "policy_id": "p1",
+        "started_at": datetime.now(),
+        "triggered_by": "u",
+        "execution_mode": ExecutionMode.TUI,
+        "final_status": CheckFinalStatus.COMPLIANT,
+        "checks": [
+            CheckStageResult(stage=CheckStageName.DATA_PURITY, status=CheckStageStatus.PASS),
+            CheckStageResult(stage=CheckStageName.INTERNAL_SOURCES_ONLY, status=CheckStageStatus.PASS),
+            CheckStageResult(stage=CheckStageName.NO_EXTERNAL_ENDPOINTS, status=CheckStageStatus.PASS),
+            CheckStageResult(stage=CheckStageName.MANIFEST_CONSISTENCY, status=CheckStageStatus.PASS),
+        ]
+    }
+    # Valid
+    ComplianceCheckRun(**base_run)
+    
+    # One stage fails -> cannot be COMPLIANT
+    base_run["checks"][0].status = CheckStageStatus.FAIL
+    with pytest.raises(ValueError, match="compliant run requires PASS on all mandatory stages"):
+        ComplianceCheckRun(**base_run)
+        
+    # Missing stage -> cannot be COMPLIANT
+    base_run["checks"] = base_run["checks"][1:]
+    with pytest.raises(ValueError, match="compliant run requires all mandatory stages"):
+        ComplianceCheckRun(**base_run)
+
+def test_report_validation():
+    # Valid blocked report
+    ComplianceReport(
+        report_id="rep1", check_run_id="run1", candidate_id="rc1",
+        generated_at=datetime.now(), final_status=CheckFinalStatus.BLOCKED,
+        operator_summary="Blocked", structured_payload_ref="ref",
+        violations_count=2, blocking_violations_count=2
+    )
+    
+    # BLOCKED with 0 blocking violations
+    with pytest.raises(ValueError, match="blocked report requires blocking violations"):
+        ComplianceReport(
+            report_id="rep1", check_run_id="run1", candidate_id="rc1",
+            generated_at=datetime.now(), final_status=CheckFinalStatus.BLOCKED,
+            operator_summary="Blocked", structured_payload_ref="ref",
+            violations_count=2, blocking_violations_count=0
+        )