🤖 refactor: unify SSH/Docker runtimes and runtime selection

- Extract RemoteRuntime base class (shared exec + file ops)\n- Switch runtime selection UI/state to discriminated union (SSH host / Docker image)\n- Add Docker option to CreationControls and persist last-used host/image\n- Fix remote stdin.close idempotence and SSH tilde expansion edge cases\n\n_Generated with mux_

Author: ammar-agent

docs/system-prompt.mdx

@@ -47,59 +47,59 @@ When the user asks you to remember something:
 /**
  * Build environment context XML block describing the workspace.
  * @param workspacePath - Workspace directory path
- * @param runtimeType - Runtime type: "local", "worktree", "ssh", or "docker"
+ * @param runtimeType - Runtime type (local, worktree, ssh, docker)
  */
-function buildEnvironmentContext(
-  workspacePath: string,
-  runtimeType: "local" | "worktree" | "ssh" | "docker"
-): string {
-  if (runtimeType === "local") {
-    // Local runtime works directly in project directory - may or may not be git
-    return `
-<environment>
-You are working in a directory at ${workspacePath}
-
-- Tools run here automatically
-- You are meant to do your work isolated from the user and other agents
-</environment>
-`;
-  }
-
-  if (runtimeType === "ssh") {
-    // SSH runtime clones the repository on a remote host
-    return `
-<environment>
-You are in a clone of a git repository at ${workspacePath}
-
-- This IS a git repository - run git commands directly (no cd needed)
-- Tools run here automatically
-- You are meant to do your work isolated from the user and other agents
-</environment>
-`;
-  }
-
-  if (runtimeType === "docker") {
-    // Docker runtime runs in an isolated container
-    return `
-<environment>
-You are in a clone of a git repository at ${workspacePath} inside a Docker container
-
-- This IS a git repository - run git commands directly (no cd needed)
-- Tools run here automatically inside the container
-- You are meant to do your work isolated from the user and other agents
-</environment>
-`;
+function buildEnvironmentContext(workspacePath: string, runtimeType: RuntimeMode): string {
+  // Common lines shared across git-based runtimes
+  const gitCommonLines = [
+    "- This IS a git repository - run git commands directly (no cd needed)",
+    "- Tools run here automatically",
+    "- You are meant to do your work isolated from the user and other agents",
+  ];
+
+  let description: string;
+  let lines: string[];
+
+  switch (runtimeType) {
+    case RUNTIME_MODE.LOCAL:
+      // Local runtime works directly in project directory - may or may not be git
+      description = `You are working in a directory at ${workspacePath}`;
+      lines = [
+        "- Tools run here automatically",
+        "- You are meant to do your work isolated from the user and other agents",
+      ];
+      break;
+
+    case RUNTIME_MODE.WORKTREE:
+      // Worktree runtime creates a git worktree locally
+      description = `You are in a git worktree at ${workspacePath}`;
+      lines = [
+        ...gitCommonLines,
+        "- Do not modify or visit other worktrees (especially the main project) without explicit user intent",
+      ];
+      break;
+
+    case RUNTIME_MODE.SSH:
+      // SSH runtime clones the repository on a remote host
+      description = `You are in a clone of a git repository at ${workspacePath}`;
+      lines = gitCommonLines;
+      break;
+
+    case RUNTIME_MODE.DOCKER:
+      // Docker runtime runs in an isolated container
+      description = `You are in a clone of a git repository at ${workspacePath} inside a Docker container`;
+      lines = gitCommonLines;
+      break;
+
+    default:
+      assertNever(runtimeType, `Unknown runtime type: ${String(runtimeType)}`);
   }
 
-  // Worktree runtime creates a git worktree locally
   return `
 <environment>
-You are in a git worktree at ${workspacePath}
+${description}
 
-- This IS a git repository - run git commands directly (no cd needed)
-- Tools run here automatically
-- Do not modify or visit other worktrees (especially the main project) without explicit user intent
-- You are meant to do your work isolated from the user and other agents
+${lines.join("\n")}
 </environment>
 `;
 }

src/browser/components/ChatInput/CreationControls.tsx

@@ -1,10 +1,10 @@
 import React, { useCallback, useEffect } from "react";
-import { RUNTIME_MODE, type RuntimeMode } from "@/common/types/runtime";
+import { RUNTIME_MODE, type RuntimeMode, type ParsedRuntime } from "@/common/types/runtime";
 import { Select } from "../Select";
 import { Loader2, Wand2 } from "lucide-react";
 import { cn } from "@/common/lib/utils";
 import { Tooltip, TooltipTrigger, TooltipContent } from "../ui/tooltip";
-import { SSHIcon, WorktreeIcon, LocalIcon } from "../icons/RuntimeIcons";
+import { SSHIcon, WorktreeIcon, LocalIcon, DockerIcon } from "../icons/RuntimeIcons";
 import { DocsLink } from "../DocsLink";
 import type { WorkspaceNameState } from "@/browser/hooks/useWorkspaceName";
 
@@ -14,12 +14,12 @@ interface CreationControlsProps {
   branchesLoaded: boolean;
   trunkBranch: string;
   onTrunkBranchChange: (branch: string) => void;
-  runtimeMode: RuntimeMode;
+  /** Currently selected runtime (discriminated union: SSH has host, Docker has image) */
+  selectedRuntime: ParsedRuntime;
   defaultRuntimeMode: RuntimeMode;
-  sshHost: string;
-  onRuntimeModeChange: (mode: RuntimeMode) => void;
+  /** Set the currently selected runtime (discriminated union) */
+  onSelectedRuntimeChange: (runtime: ParsedRuntime) => void;
   onSetDefaultRuntime: (mode: RuntimeMode) => void;
-  onSshHostChange: (host: string) => void;
   disabled: boolean;
   /** Project name to display as header */
   projectName: string;
@@ -80,6 +80,17 @@ const RUNTIME_OPTIONS: Array<{
     idleClass:
       "bg-transparent text-muted border-transparent hover:border-[var(--color-runtime-ssh)]/40",
   },
+  {
+    value: RUNTIME_MODE.DOCKER,
+    label: "Docker",
+    description: "Run in Docker container",
+    docsPath: "/runtime/docker",
+    Icon: DockerIcon,
+    activeClass:
+      "bg-[var(--color-runtime-docker)]/20 text-[var(--color-runtime-docker-text)] border-[var(--color-runtime-docker)]/60",
+    idleClass:
+      "bg-transparent text-muted border-transparent hover:border-[var(--color-runtime-docker)]/40",
+  },
 ];
 
 function RuntimeButtonGroup(props: RuntimeButtonGroupProps) {
@@ -153,18 +164,20 @@ export function CreationControls(props: CreationControlsProps) {
   // Don't check until branches have loaded to avoid prematurely switching runtime
   const isNonGitRepo = props.branchesLoaded && props.branches.length === 0;
 
+  // Extract mode from discriminated union for convenience
+  const runtimeMode = props.selectedRuntime.mode;
+
   // Local runtime doesn't need a trunk branch selector (uses project dir as-is)
-  const showTrunkBranchSelector =
-    props.branches.length > 0 && props.runtimeMode !== RUNTIME_MODE.LOCAL;
+  const showTrunkBranchSelector = props.branches.length > 0 && runtimeMode !== RUNTIME_MODE.LOCAL;
 
-  const { runtimeMode, onRuntimeModeChange } = props;
+  const { selectedRuntime, onSelectedRuntimeChange } = props;
 
   // Force local runtime for non-git directories (only after branches loaded)
   useEffect(() => {
-    if (isNonGitRepo && runtimeMode !== RUNTIME_MODE.LOCAL) {
-      onRuntimeModeChange(RUNTIME_MODE.LOCAL);
+    if (isNonGitRepo && selectedRuntime.mode !== RUNTIME_MODE.LOCAL) {
+      onSelectedRuntimeChange({ mode: "local" });
     }
-  }, [isNonGitRepo, runtimeMode, onRuntimeModeChange]);
+  }, [isNonGitRepo, selectedRuntime.mode, onSelectedRuntimeChange]);
 
   const handleNameChange = useCallback(
     (e: React.ChangeEvent<HTMLInputElement>) => {
@@ -263,12 +276,39 @@ export function CreationControls(props: CreationControlsProps) {
         <label className="text-muted-foreground text-xs font-medium">Workspace Type</label>
         <div className="flex flex-wrap items-center gap-3">
           <RuntimeButtonGroup
-            value={props.runtimeMode}
-            onChange={props.onRuntimeModeChange}
+            value={runtimeMode}
+            onChange={(mode) => {
+              // Convert mode to ParsedRuntime with appropriate defaults
+              switch (mode) {
+                case RUNTIME_MODE.SSH:
+                  onSelectedRuntimeChange({
+                    mode: "ssh",
+                    host: selectedRuntime.mode === "ssh" ? selectedRuntime.host : "",
+                  });
+                  break;
+                case RUNTIME_MODE.DOCKER:
+                  onSelectedRuntimeChange({
+                    mode: "docker",
+                    image: selectedRuntime.mode === "docker" ? selectedRuntime.image : "",
+                  });
+                  break;
+                case RUNTIME_MODE.LOCAL:
+                  onSelectedRuntimeChange({ mode: "local" });
+                  break;
+                case RUNTIME_MODE.WORKTREE:
+                default:
+                  onSelectedRuntimeChange({ mode: "worktree" });
+                  break;
+              }
+            }}
             defaultMode={props.defaultRuntimeMode}
             onSetDefault={props.onSetDefaultRuntime}
             disabled={props.disabled}
-            disabledModes={isNonGitRepo ? [RUNTIME_MODE.WORKTREE, RUNTIME_MODE.SSH] : undefined}
+            disabledModes={
+              isNonGitRepo
+                ? [RUNTIME_MODE.WORKTREE, RUNTIME_MODE.SSH, RUNTIME_MODE.DOCKER]
+                : undefined
+            }
           />
 
           {/* Branch selector - shown for worktree/SSH */}
@@ -293,19 +333,34 @@ export function CreationControls(props: CreationControlsProps) {
           )}
 
           {/* SSH Host Input */}
-          {props.runtimeMode === RUNTIME_MODE.SSH && (
+          {selectedRuntime.mode === "ssh" && (
             <div className="flex items-center gap-2">
               <label className="text-muted-foreground text-xs">host</label>
               <input
                 type="text"
-                value={props.sshHost}
-                onChange={(e) => props.onSshHostChange(e.target.value)}
+                value={selectedRuntime.host}
+                onChange={(e) => onSelectedRuntimeChange({ mode: "ssh", host: e.target.value })}
                 placeholder="user@host"
                 disabled={props.disabled}
                 className="bg-bg-dark text-foreground border-border-medium focus:border-accent h-7 w-36 rounded-md border px-2 text-sm focus:outline-none disabled:opacity-50"
               />
             </div>
           )}
+
+          {/* Docker Image Input */}
+          {selectedRuntime.mode === "docker" && (
+            <div className="flex items-center gap-2">
+              <label className="text-muted-foreground text-xs">image</label>
+              <input
+                type="text"
+                value={selectedRuntime.image}
+                onChange={(e) => onSelectedRuntimeChange({ mode: "docker", image: e.target.value })}
+                placeholder="ubuntu:22.04"
+                disabled={props.disabled}
+                className="bg-bg-dark text-foreground border-border-medium focus:border-accent h-7 w-36 rounded-md border px-2 text-sm focus:outline-none disabled:opacity-50"
+              />
+            </div>
+          )}
         </div>
       </div>
     </div>

src/browser/components/ChatInput/index.tsx

@@ -1446,12 +1446,10 @@ const ChatInputInner: React.FC<ChatInputProps> = (props) => {
               branchesLoaded={creationState.branchesLoaded}
               trunkBranch={creationState.trunkBranch}
               onTrunkBranchChange={creationState.setTrunkBranch}
-              runtimeMode={creationState.runtimeMode}
+              selectedRuntime={creationState.selectedRuntime}
               defaultRuntimeMode={creationState.defaultRuntimeMode}
-              sshHost={creationState.sshHost}
-              onRuntimeModeChange={creationState.setRuntimeMode}
+              onSelectedRuntimeChange={creationState.setSelectedRuntime}
               onSetDefaultRuntime={creationState.setDefaultRuntimeMode}
-              onSshHostChange={creationState.setSshHost}
               disabled={isSendInFlight}
               projectName={props.projectName}
               nameState={creationState.nameState}