feat: align claim/lock gates with branches-only worktrees (#275)

Allow issue lock from base-equivalent branches/ worktrees instead of
requiring the literal master/main branch name. Runtime preflight and
mark_issue/lock_issue now inspect the declared active task workspace so
dirty control-checkout state does not block clean task worktrees.

Closes #275

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

tests/test_issue_lock_worktree.py

@@ -36,7 +36,32 @@ class TestIssueLockWorktreeAssessment(unittest.TestCase):
             porcelain_status="",
         )
         self.assertFalse(result["proven"])
-        self.assertIn("issue lock must be taken from base branch", result["reasons"][0])
+        self.assertIn("base-equivalence could not be proven", result["reasons"][0])
+
+    def test_base_equivalent_feature_branch_passes(self):
+        result = issue_lock_worktree.assess_issue_lock_worktree(
+            worktree_path="/repo/branches/issue-275",
+            current_branch="feat/issue-275-claim-lock-branches-worktree",
+            porcelain_status="",
+            base_equivalent=True,
+            inspected_git_root="/repo/branches/issue-275",
+            base_branch="origin/master",
+        )
+        self.assertTrue(result["proven"])
+        self.assertFalse(result["block"])
+        self.assertEqual(result["base_branch"], "origin/master")
+
+    def test_non_base_equivalent_branch_fails(self):
+        result = issue_lock_worktree.assess_issue_lock_worktree(
+            worktree_path="/repo/branches/issue-275",
+            current_branch="feat/issue-275-claim-lock-branches-worktree",
+            porcelain_status="",
+            base_equivalent=False,
+            inspected_git_root="/repo/branches/issue-275",
+            base_branch=None,
+        )
+        self.assertFalse(result["proven"])
+        self.assertIn("must be base-equivalent", result["reasons"][0])
 
     def test_untracked_files_do_not_block(self):
         result = issue_lock_worktree.assess_issue_lock_worktree(
@@ -96,4 +121,4 @@ class TestPrWorktreeMatch(unittest.TestCase):
 
 
 if __name__ == "__main__":
-    unittest.main()
+    unittest.main()