fix(hunt): an empty product file no longer fails the source producer on every row of a change

The 150 unread rows were not a checkout failure: the entry-point scan read every product file and one empty
file raised empty_source, which escaped the cached property and failed the source producer on every row of
the change (and re-read the whole tree per row). Empty product files are skipped; the row's own file still
has to be non-empty.

Co-Authored-By: Claude Fable 5.1 <[email protected]>

src/openultrasast/hunt/producers.py

@@ -91,7 +91,13 @@ class Context:
     @cached_property
     def entry_points(self) -> list[mapping.EntryPointRecord]:
         for path in self.product_files:
-            self.read(path)
+            try:
+                self.read(path)
+            except _Absent:
+                # An empty product file elsewhere in the tree is not this row's problem. Before this guard one
+                # such file failed the source producer on every row of the change, and the failure escaped the
+                # cache so every row re-read the whole tree.
+                continue
         return mapping.analyze_entry_points(self.root, [build_file_target(self.root, self.root / path) for path in self.product_files])
 
     @cached_property