fix: resolve a bare cited name at the pin first

A ref citing a bare filename, the way prose does, was matched against the
HEAD tree alone. A file that moved since the pin then resolved to its
HEAD path, which does not exist at the pin, and the ref reported GONE
with "pin revision missing": it failed for the one reason it never
should, its own success at HEAD.

The pin tree is searched first, HEAD stays the fallback, and the rename
search carries the pin path forward as it does for any written path.
This is what the resolver already documents for prefixed and suffixed
paths; the bare-name branch was the one that did not follow it.

linapple cites Memory.cpp, src/Memory.cpp at its pin and
src/apple2/Memory.cpp today. Its refs now name where the code went
instead of reporting it missing.

scripts/profile_sync.py

@@ -1230,6 +1230,7 @@ def build_report(
 
     owners: dict[tuple[str, int | None], tuple[RepoView, str]] = {}
     context: dict[str, object] = {}
+    pin_trees: dict[str, list[str] | None] = {}
 
     def _locate(
         path: str, start: int | None = None, tokens: tuple = ()
@@ -1251,20 +1252,27 @@ def build_report(
         if tail and any(head == v.repo.name for v in views):
             candidates.append(tail)
         if "/" not in path:
-            # A bare filename, the way prose cites files. The HEAD tree of
-            # each repository resolves it when exactly one path carries it.
+            # A bare filename, the way prose cites files. Resolved against the
+            # pin before HEAD: the ref was written at the pin, and a file that
+            # moved since would otherwise be resolved to a HEAD path that does
+            # not exist at the pin, reporting GONE for the one reason it never
+            # should. The rename search then carries the pin path to HEAD.
             for view in views:
-                _, tree = _context_for(view)
-                matches = [
-                    p for p in tree or []
-                    if posixpath.basename(p) == path
-                ]
-                if len(matches) > 1:
-                    matches = narrow_by_cited(matches, cited_dirs)
-                # A few survivors are told apart by the cited line below: a
-                # 266-line Windows configure.ac cannot carry line 754.
-                if len(matches) <= 4:
-                    candidates.extend(m for m in matches if m not in candidates)
+                for tree in (_pin_tree_for(view), _context_for(view)[1]):
+                    matches = [
+                        p for p in tree or []
+                        if posixpath.basename(p) == path
+                    ]
+                    if len(matches) > 1:
+                        matches = narrow_by_cited(matches, cited_dirs)
+                    # A few survivors are told apart by the cited line below: a
+                    # 266-line Windows configure.ac cannot carry line 754.
+                    if len(matches) <= 4:
+                        candidates.extend(
+                            m for m in matches if m not in candidates
+                        )
+                    if matches:
+                        break
         elif not any(
             upstream.fetch_file(v.repo, sha, path, cache_dir, offline) is not None
             for v in views for sha in (v.pin, v.head)
@@ -1339,6 +1347,14 @@ def build_report(
             owners[key] = _locate(path, start, tokens)
         return owners[key]
 
+    def _pin_tree_for(view: RepoView):
+        """Tree at the revision the refs were written against, memoised."""
+        key = view.repo.slug
+        if key not in pin_trees:
+            tree, _ = upstream.list_tree(view.repo, view.pin, cache_dir, offline)
+            pin_trees[key] = tree
+        return pin_trees[key]
+
     def _context_for(view: RepoView):
         key = view.repo.slug
         if key not in context: