fix(reference): retain unverified symlink target provenance

Keep the observed target path and failed directory in the unreadable-link diagnostic without promoting either to proven graph identity. Verify the retained path through the importer boundary.

Refs: #4013, #4053

src/reference/ReferenceSourceReader.ts

@@ -147,7 +147,7 @@ export const reconcileUnobservedSymlinkTargets = (
       kind: "symlink",
       path: entry.path,
       code: ancestor.code,
-      message: `Symbolic link target is inside a directory that could not be enumerated: ${ancestor.message}`,
+      message: `Symbolic link target ${JSON.stringify(entry.target)} was not inventoried because directory ${JSON.stringify(ancestor.path)} could not be enumerated: ${ancestor.message}`,
     };
   }
 };

tests/boundary/filesystem/referenceSourceUnreadableDirectories.test.ts

@@ -108,6 +108,7 @@ describe("reference source native unreadable directories", () => {
             kind: "symlink",
             target: null,
             target_state: "unreadable",
+            limitations: [expect.stringContaining('"hidden/target.txt"')],
           }),
         );
       } finally {