fix(mcp): accept strict-descendant dead-session recovery (Closes #768)

Permit fail-closed recovery when a clean local head is a strict
descendant of the recorded PR/remote head, with server-side ancestry
proof. Propagate recovery evidence through commit, push, and PR
duplicate gates so an owning PR is not re-blocked as competing work.

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

tests/test_issue_755_owning_pr_recovery.py

@@ -73,12 +73,21 @@ def owning_pr(number=OWNING_PR, ref=BRANCH, sha=HEAD, issue=ISSUE):
 def sanctioned_token(
     issue_number=ISSUE, pr_number=OWNING_PR, branch=BRANCH, head=HEAD
 ):
-    """The evidence shape the server derives from a granted recovery."""
+    """The evidence shape the server derives from a granted recovery.
+
+    #768 extends the token with recorded/accepted heads and the head relation
+    so a strict-descendant recovery can still exempt the owning PR after the
+    remediation commit lands. Exact-head recovery (#753/#755) reports equal
+    heads under the same shape.
+    """
     return {
         "issue_number": issue_number,
         "pr_number": pr_number,
         "branch_name": branch,
         "head_sha": head,
+        "recorded_head": head,
+        "accepted_head": head,
+        "head_relation": issue_lock_recovery.HEAD_RELATION_EQUAL,
     }