diff --git a/README.md b/README.md
index 57920f2..646292e 100644
--- a/README.md
+++ b/README.md
@@ -38,17 +38,18 @@ Full Self Coding (FSC) is a sophisticated framework designed to automate softwar
 
 ### Execution Modes
 
-FSC supports two execution modes — choose based on your environment:
+FSC runs agents as native processes by default. Docker is an optional isolation mode, not a requirement.
 
 | Mode | Isolation | Overhead | Best For |
 |------|-----------|----------|----------|
-| **Docker** | Full container isolation | ~200MB/agent | Production, untrusted code |
-| **bare** (WorktreeExecutor) | Git worktree | ~0 | Development, testing, resource-constrained servers |
+| **worktree** (default) | One native git worktree per task, agent runs as a normal process | ~0 | Everyday use, many parallel agents |
+| **bare** | Fresh git clone + spawned process | disk only | When worktrees are not suitable |
+| **docker** (optional) | Full container isolation | ~200MB/agent | Untrusted code |
 
-Configure via `.fsc/config.json`:
+Select with `--mode`, the `FSC_EXECUTION_MODE` environment variable, or `.fsc/config.json`:
 ```json
 {
-  "executionMode": "bare"
+  "executionMode": "worktree"
 }
 ```
 
diff --git a/packages/cli/src/index.ts b/packages/cli/src/index.ts
index 54fdcde..5c651a7 100755
--- a/packages/cli/src/index.ts
+++ b/packages/cli/src/index.ts
@@ -142,7 +142,7 @@ export function createCLI(): Command {
     .command('run')
     .description('Run the full self-coding analysis and task execution')
     .option('-c, --config <path>', 'Path to configuration file')
-    .option('--mode <mode>', 'Execution mode (docker|bare|worktree)', 'bare')
+    .option('--mode <mode>', 'Execution mode: worktree (native git worktree), bare, or docker (optional)', 'worktree')
     .action(async (options) => {
       try {
         // If config option is provided, add it to process.argv for the main function to pick up
diff --git a/packages/core/src/config.ts b/packages/core/src/config.ts
index 462679a..7c3783b 100644
--- a/packages/core/src/config.ts
+++ b/packages/core/src/config.ts
@@ -143,8 +143,9 @@ export interface Config {
     customizedMessage?: string;
 
     /**
-     * Execution mode: 'docker' (container isolation) or 'bare' (git clone + Bun.spawn)
-     * @default 'docker'
+     * Execution mode: 'worktree' (native git worktree, default), 'bare' (git clone + Bun.spawn)
+     * or 'docker' (container isolation, optional)
+     * @default 'worktree'
      */
     executionMode?: ExecutionMode;
 
@@ -222,7 +223,7 @@ export interface Config {
 export const DEFAULT_CONFIG: Config = {
     agentType: SWEAgentType.CLAUDE_CODE,
     maxDockerContainers: 10,
-    executionMode: 'docker',
+    executionMode: 'worktree',
     dockerImageRef: 'node:latest',
     maxParallelDockerContainers: 10,
     dockerTimeoutSeconds: 300000,
@@ -233,7 +234,7 @@ export const DEFAULT_CONFIG: Config = {
     workStyle: WorkStyle.DEFAULT,
     codingStyleLevel: 0,
     // Harness defaults
-    harnessMode: 'docker',
+    harnessMode: 'local',
     maxParallelAgents: 1,
     progressDir: './',
     enableProgrammaticToolCalling: false,
diff --git a/packages/core/src/configReader.ts b/packages/core/src/configReader.ts
index ab6b96a..47c9417 100644
--- a/packages/core/src/configReader.ts
+++ b/packages/core/src/configReader.ts
@@ -362,6 +362,14 @@ export class ConfigReader {
 
         const configWithEnv = { ...baseConfig };
 
+        const mode = process.env.FSC_EXECUTION_MODE;
+        if (mode !== undefined) {
+            if (mode !== 'worktree' && mode !== 'bare' && mode !== 'docker') {
+                throw new Error(`FSC_EXECUTION_MODE must be worktree, bare or docker (got "${mode}")`);
+            }
+            configWithEnv.executionMode = mode;
+        }
+
         // Apply environment variable overrides
         for (const [envVar, configKey] of Object.entries(envMappings)) {
             const envValue = process.env[envVar];
diff --git a/packages/core/src/taskExecutor.ts b/packages/core/src/taskExecutor.ts
index 7594f9e..05b6e80 100644
--- a/packages/core/src/taskExecutor.ts
+++ b/packages/core/src/taskExecutor.ts
@@ -194,10 +194,12 @@ export class BareWorkspaceExecutor extends TaskExecutor {
 
 // ─── 工厂函数 ───
 
-export type ExecutionMode = "docker" | "bare";
+/** worktree = native git worktree per task (default); bare = clone + spawn; docker = container isolation (optional). */
+export type ExecutionMode = "worktree" | "bare" | "docker";
 
 export function createTaskExecutor(mode: ExecutionMode): TaskExecutor {
-	if (mode === "bare") {
+	if (mode !== "docker") {
+		// "worktree" is scheduled by TaskSolverManager.startWorktreeMode; per-task fallback is native too.
 		return new BareWorkspaceExecutor();
 	}
 	// Docker mode: 动态导入原 DockerInstance 并包装为 TaskExecutor
diff --git a/packages/core/src/taskSolver.ts b/packages/core/src/taskSolver.ts
index 7eeda06..71219f0 100644
--- a/packages/core/src/taskSolver.ts
+++ b/packages/core/src/taskSolver.ts
@@ -28,7 +28,7 @@ export class TaskSolver {
         this.agentType = agentType;
         this.gitURL = gitURL;
         this.referenceContext = referenceContext || "";
-        this.executor = createTaskExecutor(config.executionMode || 'docker');
+        this.executor = createTaskExecutor(config.executionMode || 'worktree');
         this.containerName = "";
     }
 
diff --git a/packages/core/src/taskSolverManager.ts b/packages/core/src/taskSolverManager.ts
index 49ba7b3..793ce5a 100644
--- a/packages/core/src/taskSolverManager.ts
+++ b/packages/core/src/taskSolverManager.ts
@@ -63,7 +63,7 @@ export class TaskSolverManager {
 
     async start() {
         // Worktree mode: bypass Docker/bare scheduler
-        if ((this.config as any).executionMode === 'worktree') {
+        if (this.config.executionMode === 'worktree') {
             await this.startWorktreeMode();
             return;
         }
diff --git a/packages/core/test/configReaderSupplementary.test.ts b/packages/core/test/configReaderSupplementary.test.ts
index 0d188d8..c58839d 100644
--- a/packages/core/test/configReaderSupplementary.test.ts
+++ b/packages/core/test/configReaderSupplementary.test.ts
@@ -178,4 +178,25 @@ describe('ConfigReader with Supplementary Configuration', () => {
         expect(config.maxDockerContainers).toBe(10); // From default config
         expect(config.customizedWorkStyle).toBe(undefined); // Should not have supplementary config values
     });
-});
\ No newline at end of file
+});
+describe("executionMode", () => {
+  test("defaults to the native worktree mode", async () => {
+    const { DEFAULT_CONFIG } = await import("../src/config");
+    expect(DEFAULT_CONFIG.executionMode).toBe("worktree");
+    expect(DEFAULT_CONFIG.harnessMode).toBe("local");
+  });
+
+  test("FSC_EXECUTION_MODE overrides the config and is validated", async () => {
+    const { readConfigWithEnv } = await import("../src/configReader");
+    const prev = process.env.FSC_EXECUTION_MODE;
+    try {
+      process.env.FSC_EXECUTION_MODE = "docker";
+      expect(readConfigWithEnv().executionMode).toBe("docker");
+      process.env.FSC_EXECUTION_MODE = "nope";
+      expect(() => readConfigWithEnv()).toThrow(/FSC_EXECUTION_MODE/);
+    } finally {
+      if (prev === undefined) delete process.env.FSC_EXECUTION_MODE;
+      else process.env.FSC_EXECUTION_MODE = prev;
+    }
+  });
+});