fix(cliproxy): add session check on delete and atomic settings writes

- Block variant deletion when CLIProxy has active sessions
- Use temp file + rename pattern for atomic settings writes
- Prevents partial writes on crash/interruption

src/cliproxy/services/variant-service.ts

@@ -15,7 +15,7 @@ import { loadOrCreateUnifiedConfig } from '../../config/unified-config-loader';
 import { DEFAULT_BACKEND } from '../platform-detector';
 import { isUnifiedMode } from '../../config/unified-config-loader';
 import { deleteConfigForPort } from '../config-generator';
-import { deleteSessionLockForPort } from '../session-tracker';
+import { hasActiveSessions, deleteSessionLockForPort } from '../session-tracker';
 import { warn } from '../../utils/ui';
 import {
   createSettingsFile,
@@ -154,6 +154,22 @@ export function createVariant(
  */
 export function removeVariant(name: string): VariantOperationResult {
   try {
+    // First check if variant exists and has active sessions
+    const variants = listVariantsFromConfig();
+    const existingVariant = variants[name];
+
+    if (!existingVariant) {
+      return { success: false, error: `Variant '${name}' not found` };
+    }
+
+    // Check for active sessions on this variant's port before deletion
+    if (existingVariant.port && hasActiveSessions(existingVariant.port)) {
+      return {
+        success: false,
+        error: `Cannot delete variant '${name}': CLIProxy is running with active sessions. Stop the session first.`,
+      };
+    }
+
     let variant: VariantConfig | null;
 
     if (isUnifiedMode()) {
@@ -179,11 +195,7 @@ export function removeVariant(name: string): VariantOperationResult {
       }
     }
 
-    if (!variant) {
+    return { success: true, variant: variant ?? undefined };
-      return { success: false, error: `Variant '${name}' not found` };
-    }
-
-    return { success: true, variant };
   } catch (error) {
     return { success: false, error: (error as Error).message };
   }

src/cliproxy/services/variant-settings.ts

@@ -63,10 +63,13 @@ function ensureDir(dir: string): void {
 }
 
 /**
- * Write settings file atomically
+ * Write settings file atomically using temp file + rename.
+ * The renameSync is atomic on POSIX systems, preventing partial writes on crash.
  */
 function writeSettings(filePath: string, settings: SettingsFile): void {
-  fs.writeFileSync(filePath, JSON.stringify(settings, null, 2) + '\n', 'utf8');
+  const tempPath = `${filePath}.tmp.${process.pid}`;
+  fs.writeFileSync(tempPath, JSON.stringify(settings, null, 2) + '\n', 'utf8');
+  fs.renameSync(tempPath, filePath);
 }
 
 /**
@@ -248,7 +251,9 @@ export function updateSettingsModel(settingsPath: string, model: string): void {
       delete (settings.env as unknown as Record<string, string>).ANTHROPIC_MODEL;
     }
 
-    fs.writeFileSync(resolvedPath, JSON.stringify(settings, null, 2) + '\n', 'utf8');
+    const tempPath = `${resolvedPath}.tmp.${process.pid}`;
+    fs.writeFileSync(tempPath, JSON.stringify(settings, null, 2) + '\n', 'utf8');
+    fs.renameSync(tempPath, resolvedPath);
   } catch {
     // Ignore errors - settings file may be invalid
   }