diff --git a/nexus/mnemosyne/__pycache__/entry.cpython-311.pyc b/nexus/mnemosyne/__pycache__/entry.cpython-311.pyc
new file mode 100644
index 0000000..8e12425
Binary files /dev/null and b/nexus/mnemosyne/__pycache__/entry.cpython-311.pyc differ
diff --git a/nexus/mnemosyne/entry.py b/nexus/mnemosyne/entry.py
index a9e4be4..bcfc67d 100644
--- a/nexus/mnemosyne/entry.py
+++ b/nexus/mnemosyne/entry.py
@@ -6,6 +6,7 @@ with metadata, content, and links to related entries.
 
 from __future__ import annotations
 
+import hashlib
 from dataclasses import dataclass, field
 from datetime import datetime, timezone
 from typing import Optional
@@ -24,8 +25,19 @@ class ArchiveEntry:
     topics: list[str] = field(default_factory=list)
     metadata: dict = field(default_factory=dict)
     created_at: str = field(default_factory=lambda: datetime.now(timezone.utc).isoformat())
+    updated_at: str = field(default_factory=lambda: datetime.now(timezone.utc).isoformat())
     links: list[str] = field(default_factory=list)  # IDs of related entries
 
+    @property
+    def content_hash(self) -> str:
+        """SHA-256 hash of title + content for dedup detection."""
+        raw = f"{self.title}\x00{self.content}".encode()
+        return hashlib.sha256(raw).hexdigest()
+
+    def touch(self):
+        """Bump updated_at to now."""
+        self.updated_at = datetime.now(timezone.utc).isoformat()
+
     def to_dict(self) -> dict:
         return {
             "id": self.id,
@@ -36,9 +48,16 @@ class ArchiveEntry:
             "topics": self.topics,
             "metadata": self.metadata,
             "created_at": self.created_at,
+            "updated_at": self.updated_at,
             "links": self.links,
+            "content_hash": self.content_hash,
         }
 
     @classmethod
     def from_dict(cls, data: dict) -> ArchiveEntry:
-        return cls(**{k: v for k, v in data.items() if k in cls.__dataclass_fields__})
+        # Strip non-field keys (like content_hash which is computed)
+        filtered = {k: v for k, v in data.items() if k in cls.__dataclass_fields__}
+        # Backfill updated_at for legacy entries that lack it
+        if "updated_at" not in filtered:
+            filtered["updated_at"] = filtered.get("created_at", datetime.now(timezone.utc).isoformat())
+        return cls(**filtered)