Another approach.

.github/workflows/ci.yml

@@ -91,11 +91,13 @@ jobs:
 
       # On Windows, a non-blocking pipe might respond (when emulating Unix-y
       # API) with ENOSPC to indicate buffer full. Trial doesn't handle this
-      # well. So, we pipe the output through cat to make buffer handling someone
+      # well. So, we pipe the output through pipethrough that will hopefully be
-      # else's problem.
+      # able to do the right thing by using Windows APIs.
       - name: Run tox for corresponding Python version
         if: ${{ contains(matrix.os, 'windows') }}
-        run: python -m tox | cat
+        run: |
+          pip install twisted
+          python -m tox | python misc/windows-enospc/passthrough.py
 
       - name: Upload eliot.log
         uses: actions/upload-artifact@v3

misc/windows-enospc/passthrough.py

@@ -0,0 +1,38 @@
+"""
+Writing to non-blocking pipe can result in ENOSPC when using Unix APIs on
+Windows.  So, this program passes through data from stdin to stdout, using
+Windows APIs instead of Unix-y APIs.
+"""
+
+import sys
+
+from twisted.internet.stdio import StandardIO
+from twisted.internet import reactor
+from twisted.internet.protocol import Protocol
+from twisted.internet.interfaces import IHalfCloseableProtocol
+from twisted.internet.error import ReactorNotRunning
+from zope.interface import implementer
+
+@implementer(IHalfCloseableProtocol)
+class Passthrough(Protocol):
+    def readConnectionLost(self):
+        self.transport.loseConnection()
+
+    def writeConnectionLost(self):
+        try:
+            reactor.stop()
+        except ReactorNotRunning:
+            pass
+
+    def dataReceived(self, data):
+        self.transport.write(data)
+
+    def connectionLost(self, reason):
+        try:
+            reactor.stop()
+        except ReactorNotRunning:
+            pass
+
+
+std = StandardIO(Passthrough())
+reactor.run()