fix(review): upgrade old default items of anchored files, tag anchored results (#390)

A pending default item recorded before the saver anchor no longer
shortcuts the rescan when only the anchor resolves the file: the
anchored item supersedes it. Apply accepts a resolved re-resolution only
when it is tagged as the saver anchor's, the anchored pair must carry a
positive text to choose, and limited anchored evidence still counts as a
choice. TESTING.md describes the ruling.

py/api/review.py

@@ -730,8 +730,8 @@ def _candidate_still_offered(resolution: dict, choice: str) -> bool:
     that rewords the top-level reason or reorders candidates leaves a
     pending item applicable.
     """
-    if isinstance(resolution, dict) and resolution.get("state") == "resolved":
-        # The bytes now name one pair (the saver anchor, #390): only it.
+    if isinstance(resolution, dict) and resolution.get("anchor") == "saver":
+        # Only the saver anchor resolves the bytes (#390): its pair alone.
         resolution = {"state": "ambiguous", "candidates": [resolution]}
     if not isinstance(resolution, dict) or resolution.get("state") != "ambiguous":
         return False