fix(openclaw): replace json-five serializer to prevent panic on empty collections

json-five 0.3.1 panics when pretty-printing nested empty maps/arrays.
Switch value_to_rt_value() to serde_json::to_string_pretty() which
produces valid JSON5 output without the panic. Add regression test for
removing the last provider (empty providers map).

src-tauri/src/openclaw_config.rs

@@ -8,7 +8,6 @@ use crate::error::AppError;
 use crate::settings::{effective_backup_retain_count, get_openclaw_override_dir};
 use chrono::Local;
 use indexmap::IndexMap;
-use json_five::parser::{FormatConfiguration, TrailingComma};
 use json_five::rt::parser::{
     from_str as rt_from_str, JSONKeyValuePair as RtJSONKeyValuePair,
     JSONObjectContext as RtJSONObjectContext, JSONText as RtJSONText, JSONValue as RtJSONValue,
@@ -490,11 +489,11 @@ fn derive_entry_separator(leading_ws: &str) -> String {
 }
 
 fn value_to_rt_value(value: &Value, parent_indent: &str) -> Result<RtJSONValue, AppError> {
-    let source = json_five::to_string_formatted(
-        value,
-        FormatConfiguration::with_indent(2, TrailingComma::NONE),
-    )
-    .map_err(|e| AppError::Config(format!("Failed to serialize JSON5 section: {e}")))?;
+    // `json-five` 0.3.1 can panic when pretty-printing nested empty maps/arrays.
+    // Serialize with `serde_json` instead; the resulting JSON is valid JSON5 and
+    // can still be parsed back into the round-trip AST we use for insertion.
+    let source = serde_json::to_string_pretty(value)
+        .map_err(|e| AppError::Config(format!("Failed to serialize JSON section: {e}")))?;
 
     let adjusted = reindent_json5_block(&source, parent_indent);
     let text = rt_from_str(&adjusted).map_err(|e| {
@@ -1051,4 +1050,37 @@ mod tests {
             assert!(err.to_string().contains("OpenClaw config changed on disk"));
         });
     }
+
+    #[test]
+    fn remove_last_provider_writes_empty_providers_without_panic() {
+        let source = r#"{
+  models: {
+    mode: 'merge',
+    providers: {
+      '1-copy': {
+        api: 'anthropic-messages',
+      },
+    },
+  },
+}
+"#;
+
+        with_test_paths(source, |_| {
+            let outcome = remove_provider("1-copy").unwrap();
+            assert!(outcome.backup_path.is_some());
+
+            let config = read_openclaw_config().unwrap();
+            let providers = config
+                .get("models")
+                .and_then(|models| models.get("providers"))
+                .and_then(Value::as_object)
+                .cloned()
+                .unwrap_or_default();
+
+            assert!(providers.is_empty());
+
+            let written = fs::read_to_string(get_openclaw_config_path()).unwrap();
+            assert!(written.contains("\"providers\": {}"));
+        });
+    }
 }