fix: a truncated tree does not prove a file gone

When the forge truncates the HEAD tree, the rename search cannot see every path, yet a bare filename it did not find was reported GONE. eden's fs_paths.h and path_util.cpp exist under src/common/fs/. Such a citation is now AMBIGUOUS with the reason, as the realign path already says unclear and never absent.

scripts/profile_sync.py

@@ -873,6 +873,12 @@ def _written_against_head(part: RefPart, head_lines: list[str] | None) -> bool:
     )
 
 
+# What the rename search answers when a tree it needed came back truncated:
+# a file missing from a partial listing may still exist, so absence is not
+# established. eden's fs_paths.h and path_util.cpp were reported GONE.
+TREE_TRUNCATED = "(HEAD tree truncated by the forge)"
+
+
 def anchor_part(
     part: RefPart,
     fetch: Callable[[str, str, int | None, Sequence[str]], list[str] | None],
@@ -906,6 +912,13 @@ def anchor_part(
     if head_lines is None:
         moved, candidates = rename_getter(part.path)
         if moved is None:
+            if candidates == [TREE_TRUNCATED]:
+                return PartResult(
+                    part, "AMBIGUOUS", None, None, None, [],
+                    "absent from a HEAD tree the forge truncated: "
+                    "the file may still exist",
+                    slug, url,
+                )
             if candidates:
                 return PartResult(
                     part,
@@ -1579,6 +1592,7 @@ def build_report(
 
     owners: dict[tuple[str, int | None], tuple[RepoView, str]] = {}
     context: dict[str, object] = {}
+    truncated_trees: set[str] = set()
     pin_trees: dict[str, list[str] | None] = {}
 
     def _locate(
@@ -1745,6 +1759,8 @@ def build_report(
                 view.repo, view.head, cache_dir, offline
             )
             context[key] = (comparison, tree)
+            if truncated:
+                truncated_trees.add(key)
             if truncated and tree:
                 print(
                     f"{name}: {key} HEAD tree truncated by the forge, "
@@ -1772,6 +1788,8 @@ def build_report(
             # across repositories turns a resolvable path into an ambiguous one.
             if view is owner:
                 candidates = near
+        if not candidates and any(v.repo.slug in truncated_trees for v in ordered):
+            return None, [TREE_TRUNCATED]
         return None, candidates
 
     # Pin trees before HEAD trees, each read only when reached.

tests/test_profile_sync.py

@@ -1245,6 +1245,19 @@ class TestBuildReport(unittest.TestCase):
         self.assertEqual(statuses, ["UNCHECKED"])
         self.assertIn("refused", report.entries[0].parts[0].reason)
 
+    def test_a_truncated_head_tree_is_not_an_absence(self):
+        """git.eden-emu.dev truncates the HEAD tree: fs_paths.h, cited bare,
+        was reported GONE though it lives under src/common/fs/."""
+        self.files[("pinsha", "fs_paths.h")] = ["x", "hit"]
+        profile_sync.upstream.list_tree = (
+            lambda repo, sha, cache_dir, offline=False: (["other.c"], True)
+        )
+        with contextlib.redirect_stderr(io.StringIO()):
+            report = build_report("test", self._profile(["fs_paths.h:2"]), self.dir)
+        part = report.entries[0].parts[0]
+        self.assertEqual(part.status, "AMBIGUOUS")
+        self.assertIn("truncated", part.reason)
+
     def test_counts_by_status(self):
         self.files[("pinsha", "a.c")] = ["x", "hit", "y"]
         self.files[("headsha", "a.c")] = ["pad", "x", "hit", "y"]