fix(author-lock): dead-session recovery cross-session PR base-sync (Closes #872)

issue_lock_worktree.py

@@ -150,23 +150,14 @@ def read_merge_sync_provenance(
     *,
     prior_head_sha: str | None,
     synced_head_sha: str | None,
+    remote: str | None = None,
 ) -> dict:
-    """Observe whether ``synced_head_sha`` is a sanctioned merge-based branch sync
-    that advanced the PR branch past ``prior_head_sha`` (#871).
+    """Observe whether ``synced_head_sha`` is a sanctioned merge-sync of a base
+    into the branch above ``prior_head_sha`` (#871/#872).
 
-    ``gitea_update_pr_branch_by_merge`` advances a PR branch by merging the base
-    branch *into* the branch (``POST /pulls/{n}/update?style=merge``). The result
-    is a merge commit ``M`` on the branch whose **first** parent is the prior
-    branch head and whose second parent is the base tip. When the owning session
-    then dies without the durable lock's recorded head being refreshed, the local
-    worktree still sits at ``prior_head_sha`` while the live PR head is ``M``.
-
-    Recovering that drift safely requires proving the remote head is *exactly*
-    such a merge-sync — not a rewrite, rebase, force-push, or an unrelated
-    commit. This is that server-side observation. It reports facts only; the
-    disposition lives in ``issue_lock_recovery``. Every field is read from git in
-    the declared worktree — nothing is supplied by, or reachable from, an MCP
-    caller (#871).
+    Reports server-derived git facts only; the recovery disposition lives in
+    ``issue_lock_recovery``. All comparisons are executed locally in the
+    declared worktree -- nothing is taken from caller parameters.
 
     Provenance is proven only when ALL hold:
 
@@ -183,6 +174,7 @@ def read_merge_sync_provenance(
     path = (worktree_path or "").strip()
     prior = (prior_head_sha or "").strip()
     synced = (synced_head_sha or "").strip()
+    target_remote = (remote or "").strip() or None
     result: dict = {
         "prior_head_sha": prior or None,
         "synced_head_sha": synced or None,
@@ -235,6 +227,23 @@ def read_merge_sync_provenance(
     try:
         result["prior_present"] = _present(prior)
         result["synced_present"] = _present(synced)
+        if not result["synced_present"] and path and os.path.isdir(path):
+            if target_remote:
+                subprocess.run(
+                    ["git", "-C", path, "fetch", target_remote, "--quiet"],
+                    capture_output=True,
+                    text=True,
+                    check=False,
+                )
+                result["synced_present"] = _present(synced)
+            if not result["synced_present"]:
+                subprocess.run(
+                    ["git", "-C", path, "fetch", "--quiet"],
+                    capture_output=True,
+                    text=True,
+                    check=False,
+                )
+                result["synced_present"] = _present(synced)
     except OSError as exc:  # git unavailable — fail closed, never assume
         result["reasons"].append(f"merge-sync provenance probe could not run: {exc}")
         return result