fix(reference): preserve observed directories and unreadable links

Continue validating child directories observed before a parent enumeration failure. Reconcile unobserved link targets at the reader using canonical path identity and the nearest failed ancestor, preserving exclusions and cancellation.

Refs: #4013, #4053, #4060

Co-authored-by: XY-code1 <1611761391@qq.com>

src/reference/ReferenceSourceReaderEntries.ts

@@ -134,6 +134,7 @@ export const traverseDirectory = async (
         readFailure,
       ),
     );
+    scheduleObservedDirectories(state, directories);
     return { ok: true, value: undefined };
   }
   const after = await validateDirectory(
@@ -152,6 +153,7 @@ export const traverseDirectory = async (
         "Directory changed while it was read",
       ),
     );
+    scheduleObservedDirectories(state, directories);
     return { ok: true, value: undefined };
   }
   if (current.path !== state.root)
@@ -160,9 +162,16 @@ export const traverseDirectory = async (
       kind: "directory",
       path: pathFromRoot(state.root, current.path),
     });
+  scheduleObservedDirectories(state, directories);
+  return { ok: true, value: undefined };
+};
+
+const scheduleObservedDirectories = (
+  state: TraversalState,
+  directories: PendingDirectory[],
+): void => {
   directories.reverse();
   state.pending.push(...directories);
-  return { ok: true, value: undefined };
 };
 
 const directoryReadFailure = (cause: unknown): string => {
@@ -207,7 +216,10 @@ const processEntry = async (
         ok: false,
         error: failure("io", "Reference source exclusion check failed"),
       };
-    if (excluded.value) return { ok: true, value: undefined };
+    if (excluded.value) {
+      state.exclusions.push({ path, kind: "unknown" });
+      return { ok: true, value: undefined };
+    }
     state.entries.push(entryFailure(path, "unknown", "io", metadata.message));
     return { ok: true, value: undefined };
   }
@@ -228,7 +240,10 @@ const processEntry = async (
         message: "Reference source exclusion check failed",
       },
     };
-  if (excluded.value) return { ok: true, value: undefined };
+  if (excluded.value) {
+    state.exclusions.push({ path, kind });
+    return { ok: true, value: undefined };
+  }
   if (isAborted(state.signal)) return { ok: false, error: cancelled() };
   if (kind === "symlink")
     state.entries.push(