feat: non-destructive branch recovery after lost issue locks (Closes #440)

Implements the #420 recovery umbrella: keyed persistent issue locks with
own-branch adoption, structured branch ownership parsing, create_pr lock
resolution after MCP restart, and workflow docs forbidding destructive
branch deletion as the default recovery path.

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

issue_lock_adoption.py

@@ -14,6 +14,8 @@ this module additionally records whether they passed for proof purposes.
 
 from __future__ import annotations
 
+import issue_branch_ownership
+
 ADOPT = "adopt_existing_branch"
 BLOCK_COMPETING = "block_competing_branch"
 NO_MATCH = "no_matching_branch"
@@ -40,13 +42,12 @@ def assess_own_branch_adoption(
     existing_branches,
 ) -> dict:
     """Decide whether an existing matching branch is adoptable."""
-    marker = f"issue-{issue_number}"
     requested = (requested_branch or "").strip()
 
     matches: list[tuple[str, str | None]] = []
     for entry in existing_branches or []:
         name = _branch_name(entry).strip()
-        if marker in name:
+        if issue_branch_ownership.branch_tracks_issue(name, issue_number):
             matches.append((name, _branch_sha(entry)))
 
     competing = sorted({name for name, _ in matches if name != requested})