diff --git a/src/tool_execution.py b/src/tool_execution.py
index e0a04d2..c4294a6 100644
--- a/src/tool_execution.py
+++ b/src/tool_execution.py
@@ -651,15 +651,15 @@ async def execute_tool_block(
     elif tool == "create_document":
         title = content.split("\n")[0].strip()[:60]
         desc = f"create_document: {title}"
-        result = await do_create_document(content, session_id=session_id)
+        result = await do_create_document(content, session_id=session_id, owner=owner)
     elif tool == "update_document":
         desc = f"update_document: {content.split(chr(10))[0][:60]}"
-        result = await do_update_document(content)
+        result = await do_update_document(content, owner=owner)
     elif tool == "edit_document":
-        result = await do_edit_document(content)
+        result = await do_edit_document(content, owner=owner)
         desc = f"edit_document: {result.get('title', '')}"
     elif tool == "suggest_document":
-        result = await do_suggest_document(content)
+        result = await do_suggest_document(content, owner=owner)
         desc = f"suggest_document: {result.get('count', 0)} suggestions"
     elif tool == "search_chats":
         query = content.split("\n")[0].strip()
diff --git a/src/tool_implementations.py b/src/tool_implementations.py
index 1e9032f..40d17be 100644
--- a/src/tool_implementations.py
+++ b/src/tool_implementations.py
@@ -88,6 +88,28 @@ def get_active_document():
     return _active_document_id
 
 
+def _owned_document_query(query, Document, owner: Optional[str]):
+    if owner is None:
+        return query.filter(False)
+    return query.filter(Document.owner == owner)
+
+
+def _get_owned_document(db, Document, doc_id: str, owner: Optional[str], active_only: bool = False):
+    q = db.query(Document).filter(Document.id == doc_id)
+    if active_only:
+        q = q.filter(Document.is_active == True)
+    q = _owned_document_query(q, Document, owner)
+    return q.first()
+
+
+def _most_recent_owned_document(db, Document, owner: Optional[str], active_only: bool = False):
+    q = db.query(Document)
+    if active_only:
+        q = q.filter(Document.is_active == True)
+    q = _owned_document_query(q, Document, owner)
+    return q.order_by(Document.updated_at.desc()).first()
+
+
 # ---------------------------------------------------------------------------
 # Document tools — create/update/edit/suggest living documents
 # ---------------------------------------------------------------------------
@@ -171,7 +193,7 @@ def _coerce_email_document_content(existing: str, incoming: str) -> str:
     return header.rstrip() + "\n---\n" + body
 
 
-async def do_create_document(content_block: str, session_id: Optional[str] = None) -> Dict:
+async def do_create_document(content_block: str, session_id: Optional[str] = None, owner: Optional[str] = None) -> Dict:
     """Create a new document. Supports two formats:
       1) Line-based: line 1 = title, line 2 (optional) = language, rest = content
       2) XML-like tags: <title>...</title><language>...</language><content>...</content>
@@ -240,6 +262,8 @@ async def do_create_document(content_block: str, session_id: Optional[str] = Non
         # Inherit ownership from the chat session so the doc survives that
         # session later being deleted (session_id → NULL).
         _sess = db.query(DbSession).filter(DbSession.id == session_id).first()
+        if owner is not None and (not _sess or _sess.owner != owner):
+            return {"error": "Cannot create document in another user's session"}
         _owner = _sess.owner if _sess else None
 
         doc = Document(
@@ -286,7 +310,7 @@ async def do_create_document(content_block: str, session_id: Optional[str] = Non
         db.close()
 
 
-async def do_update_document(content: str, doc_id: Optional[str] = None) -> Dict:
+async def do_update_document(content: str, doc_id: Optional[str] = None, owner: Optional[str] = None) -> Dict:
     """Update an existing document. Content = full new document text."""
     import uuid
     from src.database import SessionLocal, Document, DocumentVersion
@@ -297,9 +321,9 @@ async def do_update_document(content: str, doc_id: Optional[str] = None) -> Dict
     try:
         doc = None
         if target_id:
-            doc = db.query(Document).filter(Document.id == target_id).first()
+            doc = _get_owned_document(db, Document, target_id, owner)
         if not doc:
-            doc = db.query(Document).order_by(Document.updated_at.desc()).first()
+            doc = _most_recent_owned_document(db, Document, owner)
             if doc:
                 target_id = doc.id
                 set_active_document(target_id)
@@ -350,7 +374,7 @@ def parse_edit_blocks(content: str) -> list:
     return edits
 
 
-async def do_edit_document(content: str, doc_id: Optional[str] = None) -> Dict:
+async def do_edit_document(content: str, doc_id: Optional[str] = None, owner: Optional[str] = None) -> Dict:
     """Apply targeted FIND/REPLACE edits to an existing document."""
     import uuid
     from src.database import SessionLocal, Document, DocumentVersion
@@ -365,11 +389,11 @@ async def do_edit_document(content: str, doc_id: Optional[str] = None) -> Dict:
     try:
         doc = None
         if target_id:
-            doc = db.query(Document).filter(Document.id == target_id).first()
+            doc = _get_owned_document(db, Document, target_id, owner)
         if not doc:
             # Fallback: most recently updated document. Avoids "no active doc" errors
             # after server restart or when the agent loses track of which doc to edit.
-            doc = db.query(Document).order_by(Document.updated_at.desc()).first()
+            doc = _most_recent_owned_document(db, Document, owner)
             if doc:
                 target_id = doc.id
                 set_active_document(target_id)
@@ -458,7 +482,7 @@ def parse_suggest_blocks(content: str) -> list:
     return suggestions
 
 
-async def do_suggest_document(content: str, doc_id: str = None) -> Dict:
+async def do_suggest_document(content: str, doc_id: str = None, owner: Optional[str] = None) -> Dict:
     """Create inline suggestions for the active document WITHOUT modifying it."""
     from src.database import SessionLocal, Document
 
@@ -472,7 +496,7 @@ async def do_suggest_document(content: str, doc_id: str = None) -> Dict:
 
     db = SessionLocal()
     try:
-        doc = db.query(Document).filter(Document.id == target_id).first()
+        doc = _get_owned_document(db, Document, target_id, owner)
         if not doc:
             return {"error": f"Document {target_id} not found"}
 
@@ -1368,6 +1392,7 @@ async def do_manage_documents(content: str, owner: Optional[str] = None) -> Dict
     try:
         if action == "list":
             q = db.query(Document).filter(Document.is_active == True)
+            q = _owned_document_query(q, Document, owner)
             if args.get("search"):
                 q = q.filter(Document.title.ilike(f"%{args['search']}%"))
             if args.get("language"):
@@ -1398,7 +1423,7 @@ async def do_manage_documents(content: str, owner: Optional[str] = None) -> Dict
             doc_id = args.get("document_id") or args.get("id") or args.get("uid")
             if not doc_id:
                 return {"error": "Need document_id (use action=list to find one)", "exit_code": 1}
-            doc = db.query(Document).filter(Document.id == doc_id, Document.is_active == True).first()
+            doc = _get_owned_document(db, Document, doc_id, owner, active_only=True)
             if not doc:
                 return {"error": f"Document '{doc_id}' not found", "exit_code": 1}
             body = doc.current_content or ""
@@ -1423,10 +1448,10 @@ async def do_manage_documents(content: str, owner: Optional[str] = None) -> Dict
             doc_id = args.get("document_id") or args.get("id") or args.get("uid") or _active_document_id
             doc = None
             if doc_id:
-                doc = db.query(Document).filter(Document.id == doc_id).first()
+                doc = _get_owned_document(db, Document, doc_id, owner)
             if not doc:
                 # Fallback: most recently updated doc (likely what the user means)
-                doc = db.query(Document).filter(Document.is_active == True).order_by(Document.updated_at.desc()).first()
+                doc = _most_recent_owned_document(db, Document, owner, active_only=True)
             if not doc:
                 return {"error": "No document to delete", "exit_code": 1}
             title = doc.title
diff --git a/tests/test_document_tool_owner_scope.py b/tests/test_document_tool_owner_scope.py
new file mode 100644
index 0000000..be5f3f0
--- /dev/null
+++ b/tests/test_document_tool_owner_scope.py
@@ -0,0 +1,150 @@
+import asyncio
+import sys
+import types
+
+from src import tool_implementations as tools
+
+
+class _Column:
+    def __init__(self, name):
+        self.name = name
+
+    def __eq__(self, value):
+        return (self.name, "eq", value)
+
+    def desc(self):
+        return (self.name, "desc")
+
+    def ilike(self, value):
+        return (self.name, "ilike", value)
+
+
+class _Document:
+    id = _Column("id")
+    owner = _Column("owner")
+    is_active = _Column("is_active")
+    title = _Column("title")
+    language = _Column("language")
+    updated_at = _Column("updated_at")
+
+
+class _Query:
+    def __init__(self, docs=None, first_doc=None):
+        self.filters = []
+        self.docs = docs or []
+        self.first_doc = first_doc
+
+    def filter(self, *clauses):
+        self.filters.extend(clauses)
+        return self
+
+    def order_by(self, *args):
+        return self
+
+    def limit(self, *args):
+        return self
+
+    def all(self):
+        return self.docs
+
+    def first(self):
+        return self.first_doc
+
+
+class _Db:
+    def __init__(self, query):
+        self.query_obj = query
+
+    def query(self, *args):
+        return self.query_obj
+
+    def close(self):
+        pass
+
+
+def _install_database_stub(monkeypatch, module_name, query):
+    db = _Db(query)
+    db_mod = types.ModuleType(module_name)
+    db_mod.SessionLocal = lambda: db
+    db_mod.Document = _Document
+    db_mod.DocumentVersion = object
+    db_mod.Session = object
+    monkeypatch.setitem(sys.modules, module_name, db_mod)
+    return db
+
+
+def test_owned_document_query_rejects_missing_owner():
+    query = _Query()
+
+    assert tools._owned_document_query(query, _Document, None) is query
+    assert False in query.filters
+
+
+def test_owned_document_query_filters_to_owner():
+    query = _Query()
+
+    assert tools._owned_document_query(query, _Document, "alice") is query
+    assert ("owner", "eq", "alice") in query.filters
+
+
+def test_manage_documents_list_filters_to_calling_owner(monkeypatch):
+    query = _Query()
+    _install_database_stub(monkeypatch, "core.database", query)
+
+    result = asyncio.run(tools.do_manage_documents('{"action":"list"}', owner="alice"))
+
+    assert result["documents"] == []
+    assert ("owner", "eq", "alice") in query.filters
+
+
+def test_manage_documents_read_filters_to_calling_owner(monkeypatch):
+    query = _Query()
+    _install_database_stub(monkeypatch, "core.database", query)
+
+    result = asyncio.run(
+        tools.do_manage_documents('{"action":"read","document_id":"doc-bob"}', owner="alice")
+    )
+
+    assert result["exit_code"] == 1
+    assert ("id", "eq", "doc-bob") in query.filters
+    assert ("owner", "eq", "alice") in query.filters
+
+
+def test_update_document_active_id_filters_to_calling_owner(monkeypatch):
+    query = _Query()
+    _install_database_stub(monkeypatch, "src.database", query)
+    tools.set_active_document("doc-bob")
+    try:
+        result = asyncio.run(tools.do_update_document("new content", owner="alice"))
+    finally:
+        tools.set_active_document(None)
+
+    assert result["error"] == "No documents exist to update"
+    assert ("id", "eq", "doc-bob") in query.filters
+    assert ("owner", "eq", "alice") in query.filters
+
+
+def test_suggest_document_active_id_filters_to_calling_owner(monkeypatch):
+    query = _Query()
+    _install_database_stub(monkeypatch, "src.database", query)
+    tools.set_active_document("doc-bob")
+    try:
+        result = asyncio.run(tools.do_suggest_document(
+            "<<<FIND>>>\nold\n<<<SUGGEST>>>\nnew\n<<<REASON>>>\nbetter\n<<<END>>>",
+            owner="alice",
+        ))
+    finally:
+        tools.set_active_document(None)
+
+    assert result["error"] == "Document doc-bob not found"
+    assert ("id", "eq", "doc-bob") in query.filters
+    assert ("owner", "eq", "alice") in query.filters
+
+
+def test_document_tool_dispatch_forwards_owner():
+    source = open("src/tool_execution.py", encoding="utf-8").read()
+
+    assert "do_create_document(content, session_id=session_id, owner=owner)" in source
+    assert "do_update_document(content, owner=owner)" in source
+    assert "do_edit_document(content, owner=owner)" in source
+    assert "do_suggest_document(content, owner=owner)" in source