diff --git a/nexus/mnemosyne/__pycache__/archive.cpython-311.pyc b/nexus/mnemosyne/__pycache__/archive.cpython-311.pyc
new file mode 100644
index 0000000..aee0d23
Binary files /dev/null and b/nexus/mnemosyne/__pycache__/archive.cpython-311.pyc differ
diff --git a/nexus/mnemosyne/archive.py b/nexus/mnemosyne/archive.py
index 6a13b20..4e65b13 100644
--- a/nexus/mnemosyne/archive.py
+++ b/nexus/mnemosyne/archive.py
@@ -49,8 +49,22 @@ class MnemosyneArchive:
         with open(self.path, "w") as f:
             json.dump(data, f, indent=2)
 
-    def add(self, entry: ArchiveEntry, auto_link: bool = True) -> ArchiveEntry:
-        """Add an entry to the archive. Auto-links to related entries."""
+    def add(self, entry: ArchiveEntry, auto_link: bool = True, skip_dups: bool = False) -> ArchiveEntry:
+        """Add an entry to the archive. Auto-links to related entries.
+
+        Args:
+            entry: The entry to add.
+            auto_link: Whether to automatically compute holographic links.
+            skip_dups: If True, return existing entry instead of adding a duplicate
+                       (same title+content hash).
+
+        Returns:
+            The added (or existing, if skip_dups=True and duplicate found) entry.
+        """
+        if skip_dups:
+            existing = self.find_by_hash(entry.content_hash)
+            if existing:
+                return existing
         self._entries[entry.id] = entry
         if auto_link:
             self.linker.apply_links(entry, list(self._entries.values()))
@@ -581,6 +595,83 @@ class MnemosyneArchive:
         self._save()
         return entry
 
+    def update_entry(
+        self,
+        entry_id: str,
+        title: Optional[str] = None,
+        content: Optional[str] = None,
+        metadata: Optional[dict] = None,
+        re_link: bool = True,
+    ) -> ArchiveEntry:
+        """Update fields on an existing entry.
+
+        Only provided fields are changed. Bumps updated_at and optionally
+        recomputes holographic links (since content changed).
+
+        Args:
+            entry_id: ID of the entry to update.
+            title: New title (None = keep existing).
+            content: New content (None = keep existing).
+            metadata: New metadata dict (None = keep existing, {} to clear).
+            re_link: Whether to recompute holographic links after update.
+
+        Returns:
+            The updated ArchiveEntry.
+
+        Raises:
+            KeyError: If entry_id does not exist.
+        """
+        entry = self._entries.get(entry_id)
+        if entry is None:
+            raise KeyError(entry_id)
+
+        old_hash = entry.content_hash
+
+        if title is not None:
+            entry.title = title
+        if content is not None:
+            entry.content = content
+        if metadata is not None:
+            entry.metadata = metadata
+        entry.touch()
+
+        # Re-link only if content actually changed
+        if re_link and entry.content_hash != old_hash:
+            # Clear existing links to this entry from others
+            for other in self._entries.values():
+                if entry_id in other.links:
+                    other.links.remove(entry_id)
+            entry.links = []
+            # Re-apply
+            self.linker.apply_links(entry, list(self._entries.values()))
+
+        self._save()
+        return entry
+
+    def find_by_hash(self, content_hash: str) -> Optional[ArchiveEntry]:
+        """Find an entry by its content hash (title + content SHA-256).
+
+        Returns the first match, or None if no entry has this hash.
+        """
+        for entry in self._entries.values():
+            if entry.content_hash == content_hash:
+                return entry
+        return None
+
+    def find_duplicates(self) -> list[list[ArchiveEntry]]:
+        """Find groups of entries with identical content hashes.
+
+        Returns a list of groups, where each group is a list of 2+ entries
+        sharing the same title+content. Sorted by group size descending.
+        """
+        hash_groups: dict[str, list[ArchiveEntry]] = {}
+        for entry in self._entries.values():
+            h = entry.content_hash
+            hash_groups.setdefault(h, []).append(entry)
+        dups = [group for group in hash_groups.values() if len(group) > 1]
+        dups.sort(key=lambda g: len(g), reverse=True)
+        return dups
+
     def rebuild_links(self, threshold: Optional[float] = None) -> int:
         """Recompute all links from scratch.