diff --git a/scripts/src/workdir-normalize.test.ts b/scripts/src/workdir-normalize.test.ts
new file mode 100644
index 00000000..17c5e3ce
--- /dev/null
+++ b/scripts/src/workdir-normalize.test.ts
@@ -0,0 +1,76 @@
+import { describe, expect, test } from "bun:test";
+
+const WORKDIR_MAX_LENGTH = 512;
+
+function normalizeWorkdirPath(value: unknown, providerId: string): string {
+  const raw = typeof value === "string" ? value.trim() : "";
+  if (raw.length === 0) throw new Error("workdir path is required");
+  if (raw.length > WORKDIR_MAX_LENGTH) throw new Error(`workdir path must be ${WORKDIR_MAX_LENGTH} characters or fewer`);
+  if (raw.includes("\u0000")) throw new Error("workdir path contains an invalid character");
+  if (raw.startsWith("/")) return raw.replace(/\/+$/u, "") || "/";
+  const base = providerId === "main-server" ? "/workspace" : "/home/ubuntu";
+  return `${base.replace(/\/+$/u, "")}/${raw}`.replace(/\/+$/u, "") || "/";
+}
+
+function normalizeWorkdirProviderId(value: string): string {
+  const trimmed = value.trim();
+  if (trimmed.length === 0) return "main-server";
+  return trimmed;
+}
+
+describe("workdir path normalization contract", () => {
+  test("absolute paths are preserved as-is", () => {
+    expect(normalizeWorkdirPath("/workspace/met_nonlinear", "D601")).toBe("/workspace/met_nonlinear");
+    expect(normalizeWorkdirPath("/home/ubuntu/big-paper3", "D518")).toBe("/home/ubuntu/big-paper3");
+  });
+
+test("relative paths are prefixed with provider default workdir", () => {
+    expect(normalizeWorkdirPath("met_nonlinear", "D601")).toBe("/home/ubuntu/met_nonlinear");
+    expect(normalizeWorkdirPath("met_nonlinear", "D518")).toBe("/home/ubuntu/met_nonlinear");
+    expect(normalizeWorkdirPath("met_nonlinear", "main-server")).toBe("/workspace/met_nonlinear");
+  });
+
+  test("D518 and D601 both use /home/ubuntu as base", () => {
+    expect(normalizeWorkdirPath("big_paper", "D518")).toBe("/home/ubuntu/big_paper");
+    expect(normalizeWorkdirPath("big_paper", "D601")).toBe("/home/ubuntu/big_paper");
+  });
+
+  test("trailing slashes are stripped", () => {
+    expect(normalizeWorkdirPath("/workspace/met_nonlinear///", "D601")).toBe("/workspace/met_nonlinear");
+  });
+
+  test("empty string throws", () => {
+    expect(() => normalizeWorkdirPath("", "D601")).toThrow("workdir path is required");
+  });
+
+  test("null character throws", () => {
+    expect(() => normalizeWorkdirPath("/workspace/test\u0000bad", "D601")).toThrow("workdir path contains an invalid character");
+  });
+
+  test("paths exceeding max length throw", () => {
+    const longPath = "/" + "a".repeat(WORKDIR_MAX_LENGTH);
+    expect(() => normalizeWorkdirPath(longPath, "D601")).toThrow(`workdir path must be ${WORKDIR_MAX_LENGTH} characters or fewer`);
+  });
+
+  test("root path normalizes to /", () => {
+    expect(normalizeWorkdirPath("/", "D601")).toBe("/");
+  });
+
+  test("D518 provider maps to /home/ubuntu", () => {
+    expect(normalizeWorkdirPath("big_paper", "D518")).toBe("/home/ubuntu/big_paper");
+    expect(normalizeWorkdirPath("/mnt/d/work/big_paper", "D518")).toBe("/mnt/d/work/big_paper");
+  });
+});
+
+describe("workdir provider normalization contract", () => {
+  test("empty providerId defaults to main-server", () => {
+    expect(normalizeWorkdirProviderId("")).toBe("main-server");
+    expect(normalizeWorkdirProviderId("   ")).toBe("main-server");
+  });
+
+  test("valid providerIds are preserved", () => {
+    expect(normalizeWorkdirProviderId("D518")).toBe("D518");
+    expect(normalizeWorkdirProviderId("D601")).toBe("D601");
+    expect(normalizeWorkdirProviderId("main-server")).toBe("main-server");
+  });
+});
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