feat: require conflict proof for skipped non-mergeable PRs (Closes #322)

Add assess_non_mergeable_skip_proof to validate reviewer reports document
head SHA, mergeability result, conflict proof command, conflicting files,
and head-change status for each skipped non-mergeable PR, or classify
MERGEABILITY_UNVERIFIED when proof cannot be retrieved.

Co-Authored-By: Claude Opus 4.8 (1M context) <[email protected]>

tests/test_llm_workflow_split.py

@@ -121,4 +121,10 @@ def test_start_issue_template_references_work_issue_workflow():
 def test_create_issue_final_report_verifier_exported():
     from review_proofs import assess_create_issue_final_report
 
-    assert callable(assess_create_issue_final_report)
+    assert callable(assess_create_issue_final_report)
+
+
+def test_non_mergeable_skip_verifier_exported():
+    from review_proofs import assess_non_mergeable_skip_proof
+
+    assert callable(assess_non_mergeable_skip_proof)

tests/test_reviewer_mergeability_skip.py

@@ -0,0 +1,150 @@
+"""Tests for non-mergeable skip conflict-proof verifier (#322)."""
+import sys
+import unittest
+from pathlib import Path
+
+sys.path.insert(0, str(Path(__file__).resolve().parent.parent))
+
+from reviewer_mergeability_skip import assess_non_mergeable_skip_proof  # noqa: E402
+
+HEAD_A = "0fdc8f582026b72a229d59a172c0a63ac4aaeaf9"
+HEAD_B = "1111111111111111111111111111111111111111"
+
+
+def _good_skip_report(pr_number: int, head: str, files: str = "review_proofs.py") -> str:
+    return "\n".join([
+        f"Skipped PR #{pr_number} (non-mergeable).",
+        f"- PR number: #{pr_number}",
+        f"- Current head SHA: {head}",
+        "- Mergeability result: false",
+        "- Conflict proof command: git merge-tree $(git merge-base prgs/master prgs/feat) prgs/master prgs/feat",
+        f"- Conflicting files: {files}",
+        "- Head unchanged since prior blocker",
+        "- Blocking category: merge conflict",
+    ])
+
+
+class TestNonMergeableSkipProof(unittest.TestCase):
+    def test_no_skips_passes(self):
+        report = "Selected PR #203 for review. No earlier PRs skipped."
+        result = assess_non_mergeable_skip_proof(report, skipped_prs=[])
+        self.assertTrue(result["proven"])
+        self.assertFalse(result["block"])
+
+    def test_documented_non_mergeable_skip_passes(self):
+        report = _good_skip_report(282, HEAD_A)
+        result = assess_non_mergeable_skip_proof(
+            report,
+            skipped_prs=[{
+                "pr_number": 282,
+                "mergeable": False,
+                "head_sha": HEAD_A,
+                "mergeability_verified": True,
+                "conflicting_files": ["review_proofs.py"],
+                "head_changed_since_prior_blocker": False,
+            }],
+        )
+        self.assertTrue(result["proven"])
+
+    def test_skip_without_conflict_proof_blocks(self):
+        report = "\n".join([
+            "Skipped PR #284 because it was not mergeable.",
+            f"Head SHA: {HEAD_B}",
+        ])
+        result = assess_non_mergeable_skip_proof(
+            report,
+            skipped_prs=[{
+                "pr_number": 284,
+                "mergeable": False,
+                "head_sha": HEAD_B,
+                "mergeability_verified": True,
+            }],
+        )
+        self.assertFalse(result["proven"])
+        self.assertTrue(result["block"])
+        self.assertTrue(any("conflict proof" in r for r in result["reasons"]))
+
+    def test_missing_head_sha_blocks(self):
+        report = _good_skip_report(282, HEAD_A).replace(HEAD_A, "")
+        result = assess_non_mergeable_skip_proof(
+            report,
+            skipped_prs=[{
+                "pr_number": 282,
+                "mergeable": False,
+                "head_sha": HEAD_A,
+                "mergeability_verified": True,
+            }],
+        )
+        self.assertFalse(result["proven"])
+
+    def test_mergeability_unverified_classification_passes(self):
+        report = "\n".join([
+            "Skipped PR #282.",
+            "Classification: MERGEABILITY_UNVERIFIED",
+            "Conflict proof could not be retrieved in this session.",
+        ])
+        result = assess_non_mergeable_skip_proof(
+            report,
+            skipped_prs=[{
+                "pr_number": 282,
+                "mergeable": False,
+                "mergeability_verified": False,
+            }],
+        )
+        self.assertTrue(result["proven"])
+
+    def test_unverified_without_classification_blocks(self):
+        report = "Skipped PR #282 due to conflicts."
+        result = assess_non_mergeable_skip_proof(
+            report,
+            skipped_prs=[{
+                "pr_number": 282,
+                "mergeable": False,
+                "mergeability_verified": False,
+            }],
+        )
+        self.assertFalse(result["proven"])
+        self.assertTrue(any("MERGEABILITY_UNVERIFIED" in r for r in result["reasons"]))
+
+    def test_non_mergeable_without_file_details_still_passes_with_command(self):
+        report = _good_skip_report(284, HEAD_B, files="not available")
+        result = assess_non_mergeable_skip_proof(
+            report,
+            skipped_prs=[{
+                "pr_number": 284,
+                "mergeable": False,
+                "head_sha": HEAD_B,
+                "mergeability_verified": True,
+                "conflicting_files": [],
+            }],
+        )
+        self.assertTrue(result["proven"])
+
+    def test_stale_head_requires_head_change_field(self):
+        report = _good_skip_report(282, HEAD_A).replace(
+            "- Head unchanged since prior blocker",
+            "",
+        )
+        result = assess_non_mergeable_skip_proof(
+            report,
+            skipped_prs=[{
+                "pr_number": 282,
+                "mergeable": False,
+                "head_sha": HEAD_A,
+                "mergeability_verified": True,
+                "head_changed_since_prior_blocker": True,
+            }],
+        )
+        self.assertFalse(result["proven"])
+        self.assertTrue(any("head-changed" in r for r in result["reasons"]))
+
+
+class TestExport(unittest.TestCase):
+    def test_review_proofs_reexport(self):
+        from review_proofs import assess_non_mergeable_skip_proof as exported
+
+        self.assertTrue(callable(exported))
+
+
+if __name__ == "__main__":
+    unittest.main()