Resolve remarks

Author: Gijsreyn

docs/reference/schemas/extension/stdout/discover.md

@@ -29,8 +29,9 @@ extension manifest on the system. DSC expects every JSON Line emitted to stdout
 The output must be a JSON object. The object must define the full path to the discovered manifest.
 If an extension returns JSON that is invalid against this schema, DSC raises an error.
 
-If the extension doesn't discover any manifests, it must return nothing to stdout. An empty output
-indicates no resources were found.
+If the extension doesn't discover any manifests, it must return nothing to stdout and exit with
+code `0`. An empty output with a zero exit code indicates no resources were found. A non-zero exit
+code indicates an error, even if stdout is empty.
 
 ## Required Properties
 
@@ -53,3 +54,11 @@ discovered, the extension must not emit any output to stdout.
 Type:     string
 Required: true
 ```
+
+## Exit codes
+
+The extension must return one of the following exit codes:
+
+- `0` - Success. The extension completed discovery. If no manifests were found, stdout is empty.
+- Non-zero - Error. DSC treats any non-zero exit code as a failure and surfaces the extension's
+  stderr output as an error message.

dsc/tests/dsc_extension_discover.tests.ps1

@@ -156,4 +156,4 @@ Describe 'Discover extension tests' {
             $env:DSC_RESOURCE_PATH = $null
         }
     }
-}
+}

extensions/powershell/powershell.discover.ps1

@@ -119,4 +119,4 @@ function Invoke-DscResourceDiscovery {
     }
 }
 
-Invoke-DscResourceDiscovery
+Invoke-DscResourceDiscovery