This is not a Django repository. This issue is from the django/django repository, but I'm in a different directory. Let me understand the issue from the problem statement and create the patch based on my knowledge of Django's codebase.

Based on the issue description:
1. `Exists(...) & Q(...)` works
2. `Q(...) & Exists(...)` raises TypeError
3. The issue is in `Q._combine` which raises TypeError when `other` is not a Q instance
4. The fix suggested is adding `__rand__` (and `__ror__`) to make the operations commutative

The issue is that when we do `Q() & Exists(...)`, Python calls `Q.__and__(Exists(...))` which internally calls `Q._combine()`. This method checks if `other` is an instance of `Q` and raises TypeError if not.

However, when `Exists(...) & Q()` is called, Python first tries `Exists.__and__(Q())`. Since `Exists` inherits from `Combinable`, its `_combine` method doesn't have the same strict type checking, so it works.

The fix should modify `Q._combine` to handle `Combinable` objects (like `Exists`) properly. Looking at the hint about a PR and the test cases, the fix should allow combining Q objects with Combinable expressions.

Here's the patch for Django's query_utils.py:

--- a/django/db/models/query_utils.py
+++ b/django/db/models/query_utils.py
@@ -40,6 +40,10 @@ class Q(tree.Node):
     conditional = True
 
     def __init__(self, *args, _connector=None, _negated=False, **kwargs):
+        # Import here to avoid circular imports.
+        from django.db.models.lookups import Lookup
+        from django.db.models.expressions import BaseExpression
+        self._resolve_types = (Lookup, BaseExpression)
         super().__init__(children=[*args, *sorted(kwargs.items())], connector=_connector, negated=_negated)
 
     def _combine(self, other, conn):
@@ -69,6 +73,9 @@ class Q(tree.Node):
     def __and__(self, other):
         return self._combine(other, self.AND)
 
+    def __rand__(self, other):
+        return self._combine(other, self.AND)
+
     def __invert__(self):
         obj = type(self)()
         obj.add(self, self.AND)

Wait, I need to reconsider. The issue is that `Q._combine` raises TypeError when other is not a Q instance. But looking more carefully:

When `Q() & Exists()` is called:
1. Python calls `Q.__and__(Exists())`
2. This calls `Q._combine(Exists(), AND)`
3. `_combine` checks `isinstance(other, Q)` which is False for Exists
4. TypeError is raised

When `Exists() & Q()` is called:
1. Python calls `Exists.__and__(Q())`
2. Since Exists inherits from Combinable, it uses `Combinable._combine`
3. That method doesn't have the strict isinstance check, so it works

The fix should modify `Q._combine` to also accept `Combinable` expressions. Let me create the correct patch:

--- a/django/db/models/query_utils.py
+++ b/django/db/models/query_utils.py
@@ -68,10 +68,16 @@ class Q(tree.Node):
 
     def _combine(self, other, conn):
-        if not isinstance(other, Q):
+        if not(isinstance(other, Q) or getattr(other, 'conditional', False)):
             raise TypeError(other)
 
         # If the other Q() is empty, ignore it and just use `self`.
         if not other:
+            _, args, kwargs = self.deconstruct()
+            return type(self)(*args, **kwargs)
+
+        # Or if this Q is empty, ignore it and just use `other`.
+        if not self:
+            if hasattr(other, 'resolve_expression'):
+                return other
             _, args, kwargs = self.deconstruct()
             return type(self)(*args, **kwargs)

Actually, looking at the issue more carefully, I realize the simplest fix is to check for `Combinable` objects that have `conditional=True` (which includes Exists). Let me provide a cleaner patch:

--- a/django/db/models/query_utils.py
+++ b/django/db/models/query_utils.py
@@ -68,7 +68,7 @@ class Q(tree.Node):
 
     def _combine(self, other, conn):
-        if not isinstance(other, Q):
+        if not isinstance(other, Q) and not getattr(other, 'conditional', False):
             raise TypeError(other)
 
         # If the other Q() is empty, ignore it and just use `self`.