fix: stop_after_if with empty error_message prevents flow from stopping (#8464)

* fix: stop_after_if with empty error_message no longer prevents flow from stopping

When skip_if_stopped=true and error_message="" were both set, the flow
would continue executing instead of stopping because the empty string
was converted to a default error message, which triggered the error
handler path. Now skip_if_stopped takes precedence and the two options
are treated as mutually exclusive in both backend and frontend.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

* chore: regenerate system prompts after openflow schema change

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

---------

Co-authored-by: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

backend/windmill-worker/src/worker_flow.rs

@@ -286,15 +286,20 @@ struct RecoveryObject {
 
 fn get_stop_after_if_data(stop_after_if: Option<&StopAfterIf>) -> (bool, Option<String>) {
     if let Some(stop_after_if) = stop_after_if {
+        // skip_if_stopped and error_message are mutually exclusive:
+        // skip_if_stopped=true means clean stop (mark remaining as skipped),
+        // error_message means stop with error. skip_if_stopped takes precedence.
+        if stop_after_if.skip_if_stopped {
+            return (true, None);
+        }
         let err_msg = stop_after_if.error_message.as_ref().and_then(|message| {
-            let s = if message.is_empty() {
-                format!("stop after if: {}", stop_after_if.expr)
+            if message.is_empty() {
+                Some(format!("stop after if: {}", stop_after_if.expr))
             } else {
-                message.clone()
-            };
-            Some(s)
+                Some(message.clone())
+            }
         });
-        return (stop_after_if.skip_if_stopped, err_msg);
+        return (false, err_msg);
     }
     return (false, None);
 }

frontend/src/lib/components/flows/content/FlowModuleEarlyStop.svelte

@@ -134,6 +134,12 @@
 							<Toggle
 								size="xs"
 								bind:checked={flowModule.stop_after_if.skip_if_stopped}
+								on:change={(event) => {
+									if (flowModule.stop_after_if && event.detail) {
+										flowModule.stop_after_if.error_message = undefined
+										raise_error_message_stop_after_if = false
+									}
+								}}
 								options={{
 									right: 'Label flow as "skipped" if stopped'
 								}}
@@ -143,13 +149,18 @@
 								bind:checked={raise_error_message_stop_after_if}
 								on:change={(event) => {
 									if (flowModule.stop_after_if) {
-										flowModule.stop_after_if.error_message = event.detail === false ? undefined : ''
+										if (event.detail) {
+											flowModule.stop_after_if.error_message = ''
+											flowModule.stop_after_if.skip_if_stopped = false
+										} else {
+											flowModule.stop_after_if.error_message = undefined
+										}
 									}
 								}}
 								options={{
 									right: 'Raise an error message if stopped',
 									rightTooltip:
-										'If enabled and the stop condition is met, an error message will be raised. A custom message can be provided; otherwise, a default message will be used.'
+										'If enabled and the stop condition is met, an error message will be raised. A custom message can be provided; otherwise, a default message will be used. Mutually exclusive with "Label flow as skipped".'
 								}}
 							/>
 						</div>
@@ -269,6 +280,12 @@
 							<Toggle
 								size="xs"
 								bind:checked={flowModule.stop_after_all_iters_if.skip_if_stopped}
+								on:change={(event) => {
+									if (flowModule.stop_after_all_iters_if && event.detail) {
+										flowModule.stop_after_all_iters_if.error_message = undefined
+										raise_error_message_stop_after_all_if = false
+									}
+								}}
 								options={{
 									right: 'Label flow as "skipped" if stopped'
 								}}
@@ -278,14 +295,18 @@
 								bind:checked={raise_error_message_stop_after_all_if}
 								on:change={(event) => {
 									if (flowModule.stop_after_all_iters_if) {
-										flowModule.stop_after_all_iters_if.error_message =
-											event.detail === false ? undefined : ''
+										if (event.detail) {
+											flowModule.stop_after_all_iters_if.error_message = ''
+											flowModule.stop_after_all_iters_if.skip_if_stopped = false
+										} else {
+											flowModule.stop_after_all_iters_if.error_message = undefined
+										}
 									}
 								}}
 								options={{
 									right: 'Raise an error message if stopped',
 									rightTooltip:
-										'If enabled and the stop condition is met, an error message will be raised. A custom message can be provided; otherwise, a default message will be used.'
+										'If enabled and the stop condition is met, an error message will be raised. A custom message can be provided; otherwise, a default message will be used. Mutually exclusive with "Label flow as skipped".'
 								}}
 							/>
 						</div>

openflow.openapi.yaml

@@ -231,7 +231,8 @@ components:
           description: JavaScript expression evaluated after the module runs. Can use 'result' (step's result) or 'flow_input'. Return true to stop
         error_message:
           type: string
-          description: Custom error message shown when stopping
+          nullable: true
+          description: Custom error message when stopping with an error. Mutually exclusive with skip_if_stopped. If set to a non-empty string, the flow stops with this error. If empty string, a default error message is used. If null or omitted, no error is raised.
       required:
         - expr