Remove exists() from Runtime interface, use shared utility

Per review feedback, the Runtime interface should be minimal. The
exists() method can be implemented as a utility function using stat().

Changes:
- Remove exists() from Runtime interface
- Remove implementations from LocalRuntime and SSHRuntime
- Create fileExists() utility in src/utils/runtime/fileExists.ts
- Update file_edit_insert.ts to use the utility function

This keeps the Runtime interface minimal while providing the same
functionality through a shared utility.

Author: ammar-agent

src/runtime/LocalRuntime.ts

@@ -214,13 +214,4 @@ export class LocalRuntime implements Runtime {
       );
     }
   }
-
-  async exists(path: string): Promise<boolean> {
-    try {
-      await fs.access(path);
-      return true;
-    } catch {
-      return false;
-    }
-  }
 }

src/runtime/Runtime.ts

@@ -85,13 +85,6 @@ export interface Runtime {
    * @throws RuntimeError if path does not exist or cannot be accessed
    */
   stat(path: string): Promise<FileStat>;
-
-  /**
-   * Check if path exists
-   * @param path Absolute or relative path to check
-   * @returns True if path exists, false otherwise
-   */
-  exists(path: string): Promise<boolean>;
 }
 
 /**

src/runtime/SSHRuntime.ts

@@ -332,18 +332,4 @@ export class SSHRuntime implements Runtime {
       });
     });
   }
-
-  async exists(path: string): Promise<boolean> {
-    await this.ensureConnected();
-
-    if (!this.sftpClient) {
-      throw new RuntimeErrorClass("SFTP client not connected", "network");
-    }
-
-    return new Promise((resolve) => {
-      this.sftpClient!.stat(path, (err) => {
-        resolve(!err);
-      });
-    });
-  }
 }

src/services/tools/file_edit_insert.ts

@@ -6,6 +6,7 @@ import { TOOL_DEFINITIONS } from "@/utils/tools/toolDefinitions";
 import { validatePathInCwd, WRITE_DENIED_PREFIX } from "./fileCommon";
 import { executeFileEditOperation } from "./file_edit_operation";
 import { RuntimeError } from "@/runtime/Runtime";
+import { fileExists } from "@/utils/runtime/fileExists";
 
 /**
  * File edit insert tool factory for AI assistant
@@ -43,9 +44,9 @@ export const createFileEditInsertTool: ToolFactory = (config: ToolConfiguration)
           : path.resolve(config.cwd, file_path);
 
         // Check if file exists using runtime
-        const fileExists = await config.runtime.exists(resolvedPath);
+        const exists = await fileExists(config.runtime, resolvedPath);
 
-        if (!fileExists) {
+        if (!exists) {
           if (!create) {
             return {
               success: false,

src/utils/runtime/fileExists.ts

@@ -0,0 +1,16 @@
+import type { Runtime } from "@/runtime/Runtime";
+
+/**
+ * Check if a path exists using runtime.stat()
+ * @param runtime Runtime instance to use
+ * @param path Path to check
+ * @returns True if path exists, false otherwise
+ */
+export async function fileExists(runtime: Runtime, path: string): Promise<boolean> {
+  try {
+    await runtime.stat(path);
+    return true;
+  } catch {
+    return false;
+  }
+}