Include CLI stderr for stdio startup pipe failures

stephentoub · Copilot · stephentoub · commit b35e9f63df49 · 2026-05-05T15:41:19.000-04:00
Co-authored-by: Copilot &lt;223556219+Copilot@users.noreply.github.com&gt;
diff --git a/dotnet/src/Client.cs b/dotnet/src/Client.cs
@@ -1154,6 +1154,17 @@ internal static async Task<T> InvokeRpcAsync<T>(JsonRpc rpc, string method, obje
             }
             throw new IOException($"Communication error with Copilot CLI: {ex.Message}", ex);
         }
+        catch (IOException ex) when (stderrBuffer is not null)
+        {
+            var stderrOutput = await GetStderrOutputAsync(stderrBuffer, stderrReader);
+
+            if (!string.IsNullOrEmpty(stderrOutput))
+            {
+                throw new IOException(FormatCliExitedMessage("CLI process exited unexpectedly.", stderrOutput), ex);
+            }
+
+            throw;
+        }
         catch (RemoteRpcException ex)
         {
             throw new IOException($"Communication error with Copilot CLI: {ex.Message}", ex);

Original file line number	Diff line number	Diff line change
`@@ -1154,6 +1154,17 @@ internal static async Task<T> InvokeRpcAsync<T>(JsonRpc rpc, string method, obje`
`1154`	`1154`	`}`
`1155`	`1155`	`throw new IOException($"Communication error with Copilot CLI: {ex.Message}", ex);`
`1156`	`1156`	`}`
	`1157`	`+ catch (IOException ex) when (stderrBuffer is not null)`
	`1158`	`+ {`
	`1159`	`+ var stderrOutput = await GetStderrOutputAsync(stderrBuffer, stderrReader);`
	`1160`	`+`
	`1161`	`+ if (!string.IsNullOrEmpty(stderrOutput))`
	`1162`	`+ {`
	`1163`	`+ throw new IOException(FormatCliExitedMessage("CLI process exited unexpectedly.", stderrOutput), ex);`
	`1164`	`+ }`
	`1165`	`+`
	`1166`	`+ throw;`
	`1167`	`+ }`
`1157`	`1168`	`catch (RemoteRpcException ex)`
`1158`	`1169`	`{`
`1159`	`1170`	`throw new IOException($"Communication error with Copilot CLI: {ex.Message}", ex);`