fix: use exact issue-number boundary in own-branch adoption (#442)

Replace substring issue-marker matching with a numeric word-boundary
regex so issue-42 adoption is not false-blocked by unrelated issue-420
branches. Add regression tests for the #42 vs #420 collision.

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

tests/test_issue_lock_adoption.py

@@ -25,6 +25,16 @@ class TestAssessOwnBranchAdoption(unittest.TestCase):
         )
         self.assertEqual(result["outcome"], ADOPT)
         self.assertTrue(result["adopt"])
+        self.assertFalse(result["block"])
+        self.assertEqual(result["matched_branch"], REQ)
+        self.assertEqual(result["matched_head_sha"], "934688a")
+
+    def test_exact_own_branch_adopted_when_sha_missing(self):
+        result = assess_own_branch_adoption(
+            issue_number=420, requested_branch=REQ, existing_branches=[REQ]
+        )
+        self.assertEqual(result["outcome"], ADOPT)
+        self.assertIsNone(result["matched_head_sha"])
 
     def test_different_branch_same_issue_blocks(self):
         result = assess_own_branch_adoption(
@@ -34,6 +44,20 @@ class TestAssessOwnBranchAdoption(unittest.TestCase):
         )
         self.assertEqual(result["outcome"], BLOCK_COMPETING)
         self.assertTrue(result["block"])
+        self.assertFalse(result["adopt"])
+        self.assertIn("feat/issue-420-other-work", result["competing_branches"])
+        self.assertIn("fail closed", result["reason"])
+
+    def test_own_branch_plus_competing_branch_blocks(self):
+        # Ambiguous ownership: fail closed even though the exact branch exists.
+        result = assess_own_branch_adoption(
+            issue_number=420,
+            requested_branch=REQ,
+            existing_branches=[{"name": REQ}, {"name": "feat/issue-420-rogue"}],
+        )
+        self.assertEqual(result["outcome"], BLOCK_COMPETING)
+        self.assertTrue(result["block"])
+        self.assertEqual(result["competing_branches"], ["feat/issue-420-rogue"])
 
     def test_no_matching_branch_is_normal_path(self):
         result = assess_own_branch_adoption(
@@ -42,10 +66,44 @@ class TestAssessOwnBranchAdoption(unittest.TestCase):
             existing_branches=[{"name": "feat/issue-999-unrelated"}],
         )
         self.assertEqual(result["outcome"], NO_MATCH)
+        self.assertFalse(result["block"])
+        self.assertFalse(result["adopt"])
+
+    def test_empty_branch_list_is_normal_path(self):
+        result = assess_own_branch_adoption(
+            issue_number=420, requested_branch=REQ, existing_branches=[]
+        )
+        self.assertEqual(result["outcome"], NO_MATCH)
+
+    def test_higher_issue_number_branch_does_not_block_lower_issue_adoption(self):
+        # issue-420 must not be treated as competing work for issue #42.
+        own_branch = "feat/issue-42-widget"
+        result = assess_own_branch_adoption(
+            issue_number=42,
+            requested_branch=own_branch,
+            existing_branches=[
+                {"name": own_branch, "commit_sha": "abc1234"},
+                {"name": "feat/issue-420-server-code-parity"},
+            ],
+        )
+        self.assertEqual(result["outcome"], ADOPT)
+        self.assertTrue(result["adopt"])
+        self.assertFalse(result["block"])
+        self.assertEqual(result["matched_branch"], own_branch)
+
+    def test_unrelated_higher_number_branch_is_ignored_without_own_branch(self):
+        result = assess_own_branch_adoption(
+            issue_number=42,
+            requested_branch="feat/issue-42-thing",
+            existing_branches=[{"name": "feat/issue-420-server-code-parity"}],
+        )
+        self.assertEqual(result["outcome"], NO_MATCH)
+        self.assertFalse(result["block"])
+        self.assertFalse(result["adopt"])
 
 
 class TestBuildAdoptionProof(unittest.TestCase):
-    def test_proof_has_required_fields(self):
+    def test_proof_has_all_required_fields(self):
         assessment = assess_own_branch_adoption(
             issue_number=420,
             requested_branch=REQ,
@@ -60,8 +118,20 @@ class TestBuildAdoptionProof(unittest.TestCase):
             lock_file_path="/tmp/example-lock.json",
             lock_file_status="written",
         )
+        for key in (
+            "issue_number",
+            "branch_name",
+            "branch_head_commit",
+            "adoption_reason",
+            "no_existing_pr_proof",
+            "no_competing_live_lock_proof",
+            "lock_file_path",
+            "lock_file_status",
+        ):
+            self.assertIn(key, proof)
         self.assertEqual(proof["branch_head_commit"], "934688a")
         self.assertTrue(proof["no_existing_pr_proof"])
+        self.assertTrue(proof["no_competing_live_lock_proof"])
 
 
 if __name__ == "__main__":