🤖 test: run DockerRuntime against existing ssh fixture container

Removes the extra DockerRuntime container fixture and instead runs DockerRuntime integration cases by docker-exec'ing into the already-running SSH fixture container. This avoids additional container startup/teardown overhead in CI while still exercising DockerRuntime behavior.

Author: ammar-agent

tests/runtime/runtime.test.ts

@@ -24,11 +24,6 @@ import {
   stopSSHServer,
   type SSHServerConfig,
 } from "./test-fixtures/ssh-fixture";
-import {
-  startDockerRuntimeContainer,
-  stopDockerRuntimeContainer,
-  type DockerRuntimeTestConfig,
-} from "./test-fixtures/docker-fixture";
 import { createTestRuntime, TestWorkspace, type RuntimeType } from "./test-fixtures/test-helpers";
 import { execBuffered, readFileString, writeFileString } from "@/node/utils/runtime/helpers";
 import type { Runtime } from "@/node/runtime/Runtime";
@@ -40,9 +35,6 @@ const describeIntegration = shouldRunIntegrationTests() ? describe : describe.sk
 // SSH server config (shared across all tests)
 let sshConfig: SSHServerConfig | undefined;
 
-// DockerRuntime container config (shared across all tests)
-let dockerConfig: DockerRuntimeTestConfig | undefined;
-
 describeIntegration("Runtime integration tests", () => {
   beforeAll(async () => {
     // Check if Docker is available (required for SSH tests)
@@ -56,18 +48,9 @@ describeIntegration("Runtime integration tests", () => {
     console.log("Starting SSH server container...");
     sshConfig = await startSSHServer();
     console.log(`SSH server ready on port ${sshConfig.port}`);
-
-    console.log("Starting DockerRuntime test container...");
-    dockerConfig = await startDockerRuntimeContainer();
-    console.log(`DockerRuntime container ready: ${dockerConfig.containerName}`);
   }, 120000); // 120s timeout for Docker build/start operations
 
   afterAll(async () => {
-    if (dockerConfig) {
-      console.log("Stopping DockerRuntime test container...");
-      await stopDockerRuntimeContainer(dockerConfig);
-    }
-
     if (sshConfig) {
       console.log("Stopping SSH server container...");
       await stopSSHServer(sshConfig);
@@ -95,7 +78,14 @@ describeIntegration("Runtime integration tests", () => {
       // time budget. Keep the Docker coverage focused on the core Runtime contract.
       const describeNonDocker = type === "docker" ? describe.skip : describe;
       const createRuntime = (): Runtime =>
-        createTestRuntime(type, getBaseWorkdir(), sshConfig, dockerConfig);
+        createTestRuntime(
+          type,
+          getBaseWorkdir(),
+          sshConfig,
+          type === "docker"
+            ? { image: "mux-ssh-test", containerName: sshConfig!.containerId }
+            : undefined
+        );
 
       describe("exec() - Command execution", () => {
         test.concurrent("captures stdout and stderr separately", async () => {

tests/runtime/test-fixtures/docker-fixture.ts

@@ -9,14 +9,18 @@ import * as path from "path";
 import type { Runtime } from "@/node/runtime/Runtime";
 import { WorktreeRuntime } from "@/node/runtime/WorktreeRuntime";
 import { DockerRuntime } from "@/node/runtime/DockerRuntime";
-import type { DockerRuntimeTestConfig } from "./docker-fixture";
 import { SSHRuntime } from "@/node/runtime/SSHRuntime";
 import type { SSHServerConfig } from "./ssh-fixture";
 
 /**
  * Runtime type for test matrix
  * Note: "local" here means worktree runtime (isolated git worktrees), not project-dir runtime
  */
+
+export interface DockerRuntimeTestConfig {
+  image: string;
+  containerName: string;
+}
 export type RuntimeType = "local" | "ssh" | "docker";
 
 /**