diff --git a/packages/cli/src/pipeline/validation.ts b/packages/cli/src/pipeline/validation.ts
index 87512d2..642dfc4 100644
--- a/packages/cli/src/pipeline/validation.ts
+++ b/packages/cli/src/pipeline/validation.ts
@@ -125,6 +125,21 @@ function collectPipelineSemanticIssues(
         `semantic: step "${stepLabel}" timeout must be a positive number of seconds or duration string`,
       );
     }
+
+    // `script/js` executes its `code` as host JavaScript. Require it to be a
+    // literal string in the pipeline definition: code sourced from another step
+    // ($from) or any expression is rejected, so untrusted/model-generated text
+    // can never become the body of the executed function.
+    if (step.type === "script/js") {
+      const code = isRecord(step.input) ? step.input.code : undefined;
+      if (typeof code !== "string") {
+        issues.push(
+          `semantic: step "${stepLabel}" (script/js) requires a literal string "code"; ` +
+            `code sourced from another step ($from) or an expression is not allowed, ` +
+            `since it would execute untrusted text as host code`,
+        );
+      }
+    }
   }
 
   // Check dependency references
diff --git a/packages/cli/tests/index.test.ts b/packages/cli/tests/index.test.ts
index 507a100..f6853c0 100644
--- a/packages/cli/tests/index.test.ts
+++ b/packages/cli/tests/index.test.ts
@@ -1,6 +1,9 @@
 import { expect, test } from "vite-plus/test";
 import { createStepDispatcher } from "../src/pipeline/dispatcher.ts";
 import { executePipeline } from "../src/pipeline/executor.ts";
+import { collectPipelineIssues } from "../src/pipeline/validation.ts";
+import { getByJsonPointer } from "../src/pipeline/schema.ts";
+import { normalizeConcurrency } from "../src/pipeline/scheduler.ts";
 import { WORKFLOW_VERSION, type PipelineDefinition } from "../src/pipeline/types.ts";
 
 test("cli package skeleton", () => {
@@ -34,3 +37,73 @@ test("pipeline execution can use an isolated step dispatcher", async () => {
     hasSignal: true,
   });
 });
+
+test("dry-run never executes $js expressions (preview must not run code)", async () => {
+  const dispatcher = createStepDispatcher();
+  dispatcher.registerStep("test/echo", (input) => ({ data: input }));
+  const flag = "__bailian_dryrun_should_not_run__";
+  delete (globalThis as Record<string, unknown>)[flag];
+
+  const pipeline: PipelineDefinition = {
+    version: WORKFLOW_VERSION,
+    steps: [
+      {
+        id: "s1",
+        type: "test/echo",
+        input: { probe: { $js: `(globalThis[${JSON.stringify(flag)}] = true), 1` } },
+      },
+    ],
+  };
+
+  const report = await executePipeline(pipeline, {}, { stepDispatcher: dispatcher, dryRun: true });
+  expect(report.status).toBe("planned");
+  expect((globalThis as Record<string, unknown>)[flag]).toBeUndefined();
+});
+
+test("script/js rejects non-literal code sourced from another step ($from)", () => {
+  const dispatcher = createStepDispatcher();
+  dispatcher.registerStep("test/echo", (input) => ({ data: input }));
+  dispatcher.registerStep("script/js", () => ({ data: {} }));
+
+  const pipeline: PipelineDefinition = {
+    version: WORKFLOW_VERSION,
+    steps: [
+      { id: "gen", type: "test/echo", input: { message: "x" } },
+      {
+        id: "run",
+        type: "script/js",
+        input: { code: { $from: "gen", path: "/data/message" } as never },
+      },
+    ],
+  };
+
+  const issues = collectPipelineIssues(pipeline, dispatcher);
+  expect(issues.some((issue) => issue.includes('literal string "code"'))).toBe(true);
+});
+
+test("script/js accepts a literal string code", () => {
+  const dispatcher = createStepDispatcher();
+  dispatcher.registerStep("script/js", () => ({ data: {} }));
+
+  const pipeline: PipelineDefinition = {
+    version: WORKFLOW_VERSION,
+    steps: [{ id: "run", type: "script/js", input: { code: "return 1" } }],
+  };
+
+  expect(collectPipelineIssues(pipeline, dispatcher)).toEqual([]);
+});
+
+test("getByJsonPointer refuses prototype keys and inherited properties", () => {
+  const obj = { a: { b: 1 } };
+  expect(getByJsonPointer(obj, "/a/b")).toBe(1);
+  expect(getByJsonPointer(obj, "/__proto__")).toBeUndefined();
+  expect(getByJsonPointer(obj, "/constructor")).toBeUndefined();
+  expect(getByJsonPointer(obj, "/a/constructor/constructor")).toBeUndefined();
+  expect(getByJsonPointer(obj, "/toString")).toBeUndefined();
+});
+
+test("normalizeConcurrency clamps to a safe maximum", () => {
+  expect(normalizeConcurrency(undefined)).toBe(1);
+  expect(normalizeConcurrency(4)).toBe(4);
+  expect(normalizeConcurrency(100000)).toBe(64);
+});