feat: record the pin a prose reread confirmed

A prose citation whose text lived under several pins stayed in
read again until the text changed, so fixnes, zesarux and emucorex,
exact at their pins, would have refused every later bump.
prose_written_at names the pin a reader confirmed; it settles the
readings and never overrides a history with one candidate.

scripts/profile_sync.py

@@ -3016,14 +3016,23 @@ def _writing_pairs(
     Each reading lists (repo, writing pin, current pin) per declared
     repository. A repository whose text lived under several pins gives one
     reading per pin; the caller settles them when they all agree.
+
+    `prose_written_at` names the pin a reader confirmed the prose against.
+    Among several candidate pins it is the answer: fixnes's doOpenFDSBIOS
+    citation lived under four pins, exact at the last, and with nothing to
+    record that reading the bump stayed refused for good. It never
+    overrides a history with a single candidate.
     """
     options: list[list] = []
     ambiguous: list[str] = []
+    attested = str(document.get("prose_written_at") or "")
     for pin_field, mode, repo in repos:
         current = _pin_of(document, f"{pin_field}_commit", mode)
         if not current:
             continue
         written = _writing_pins(revisions, intro_sha, f"{pin_field}_commit", mode)
+        if attested in written:
+            written = [attested]
         if len(written) > 1:
             ambiguous.append(f"{pin_field}_commit {' -> '.join(written)}")
         # The current pin among the candidates reads as "no move" (None) for
@@ -3336,7 +3345,7 @@ def _stale_prose_blocks(name: str, path: Path, args: argparse.Namespace) -> bool
     if stale:
         print(
             f"{name}: {len(stale)} prose citation(s) written under an older pin; "
-            "run --realign-prose or read them before the pin moves",
+            "run --realign-prose, or read them and set prose_written_at to the pin they match",
             file=sys.stderr,
         )
     return bool(stale)