🤖 fix: block background execution for SSH/remote workspaces

Add supportsBackgroundExecution property to Runtime interface to detect
runtime capability. SSH workspaces return clear error message instead of
failing with ENOENT or running on wrong host.

TODO comments added for future SSH support via nohup/setsid.

Author: ethanndickson

src/node/runtime/LocalRuntime.ts

@@ -39,6 +39,9 @@ import { expandTilde } from "./tildeExpansion";
 export class LocalRuntime implements Runtime {
   private readonly srcBaseDir: string;
 
+  /** LocalRuntime supports background execution via detached process groups */
+  readonly supportsBackgroundExecution = true;
+
   constructor(srcBaseDir: string) {
     // Expand tilde to actual home directory path for local file system operations
     this.srcBaseDir = expandTilde(srcBaseDir);

src/node/runtime/Runtime.ts

@@ -364,6 +364,13 @@ export interface Runtime {
    * @returns Result with new workspace path and source branch, or error
    */
   forkWorkspace(params: WorkspaceForkParams): Promise<WorkspaceForkResult>;
+
+  /**
+   * Whether this runtime supports background process execution.
+   * LocalRuntime: true (uses detached process groups)
+   * SSHRuntime: false (TODO: implement via nohup/setsid + file-based output capture)
+   */
+  readonly supportsBackgroundExecution: boolean;
 }
 
 /**

src/node/runtime/SSHRuntime.ts

@@ -71,6 +71,12 @@ export class SSHRuntime implements Runtime {
   private readonly config: SSHRuntimeConfig;
   private readonly controlPath: string;
 
+  /**
+   * SSHRuntime does not yet support background execution.
+   * TODO: Implement via nohup/setsid + file-based output capture on remote host
+   */
+  readonly supportsBackgroundExecution = false;
+
   constructor(config: SSHRuntimeConfig) {
     // Note: srcBaseDir may contain tildes - they will be resolved via resolvePath() before use
     // The WORKSPACE_CREATE IPC handler resolves paths before storing in config

src/node/services/tools/bash.ts

@@ -249,6 +249,16 @@ export const createBashTool: ToolFactory = (config: ToolConfiguration) => {
           };
         }
 
+        // TODO: Add SSH runtime support for background processes (nohup/setsid + file-based output)
+        if (!config.runtime.supportsBackgroundExecution) {
+          return {
+            success: false,
+            error: "Background execution is not yet supported for SSH/remote workspaces",
+            exitCode: -1,
+            wall_duration_ms: 0,
+          };
+        }
+
         if (!config.workspaceId || !config.backgroundProcessManager) {
           return {
             success: false,