diff --git a/packages/cli-workflow/__tests__/commands.test.ts b/packages/cli-workflow/__tests__/commands.test.ts
index 6ce819d..cd5b85e 100644
--- a/packages/cli-workflow/__tests__/commands.test.ts
+++ b/packages/cli-workflow/__tests__/commands.test.ts
@@ -35,9 +35,9 @@ describe("cli workflow commands", () => {
       bundlePath,
       `import fs from "node:fs";
 
-export default async function* () {
+export default async function* (input) {
   fs.existsSync(".");
-  yield { role: "noop", content: "ok", meta: { done: true } };
+  yield { role: "noop", content: input.prompt, meta: { done: true } };
   return { returnCode: 0, summary: "done" };
 }
 `,
@@ -81,7 +81,7 @@ export default async function* () {
     const bundlePath = join(storageRoot, "bad.esm.js");
     await writeFile(
       bundlePath,
-      'import x from "./local";\nexport default async function* run() { return { returnCode: 0, summary: "" }; }\n',
+      'import x from "./local";\nexport default async function* (input) { return { returnCode: 0, summary: input.prompt }; }\n',
       "utf8",
     );
     const r = await cmdAdd(storageRoot, "solve-issue", bundlePath);
diff --git a/packages/cli-workflow/__tests__/thread-cli.test.ts b/packages/cli-workflow/__tests__/thread-cli.test.ts
index 3fa147e..664fc41 100644
--- a/packages/cli-workflow/__tests__/thread-cli.test.ts
+++ b/packages/cli-workflow/__tests__/thread-cli.test.ts
@@ -13,16 +13,16 @@ import { cmdThreadRemove, cmdThreadShow } from "../src/cmd-thread.js";
 import { cmdThreads } from "../src/cmd-threads.js";
 import { pathExists } from "../src/fs-utils.js";
 
-const fastBundleSource = `export default async function* () {
-  yield { role: "planner", content: "plan", meta: { plan: "x" } };
+const fastBundleSource = `export default async function* (input) {
+  yield { role: "planner", content: "plan", meta: { plan: input.prompt } };
   yield { role: "coder", content: "code", meta: { diff: "y" } };
   return { returnCode: 0, summary: "done" };
 }
 `;
 
-const slowPlannerBundleSource = `export default async function* () {
+const slowPlannerBundleSource = `export default async function* (input) {
   await new Promise((r) => setTimeout(r, 400));
-  yield { role: "planner", content: "plan", meta: { plan: "x" } };
+  yield { role: "planner", content: "plan", meta: { plan: input.prompt } };
   yield { role: "coder", content: "code", meta: { diff: "y" } };
   return { returnCode: 0, summary: "done" };
 }
@@ -30,9 +30,9 @@ const slowPlannerBundleSource = `export default async function* () {
 
 const cliEntryPath = fileURLToPath(new URL("../src/cli.ts", import.meta.url));
 
-const abortablePlannerBundleSource = `export default async function* () {
+const abortablePlannerBundleSource = `export default async function* (input) {
   await new Promise((r) => setTimeout(r, 600));
-  yield { role: "planner", content: "plan", meta: { plan: "x" } };
+  yield { role: "planner", content: "plan", meta: { plan: input.prompt } };
   yield { role: "coder", content: "code", meta: { diff: "y" } };
   return { returnCode: 0, summary: "done" };
 }
diff --git a/packages/workflow/__tests__/bundle-validator.test.ts b/packages/workflow/__tests__/bundle-validator.test.ts
index f9b6afa..9d9c6bc 100644
--- a/packages/workflow/__tests__/bundle-validator.test.ts
+++ b/packages/workflow/__tests__/bundle-validator.test.ts
@@ -6,9 +6,9 @@ describe("validateWorkflowBundle", () => {
   test("accepts minimal valid builtin-only bundle", () => {
     const source = `import fs from "node:fs";
 
-export default async function* run() {
+export default async function* (input) {
   fs.existsSync(".");
-  return { returnCode: 0, summary: "ok" };
+  return { returnCode: 0, summary: input.prompt };
 }
 `;
     const r = validateWorkflowBundle({ filePath: "/tmp/w.esm.js", source });
@@ -18,7 +18,8 @@ export default async function* run() {
   test("rejects wrong filename suffix", () => {
     const r = validateWorkflowBundle({
       filePath: "/tmp/w.js",
-      source: "export default async function* run() { return { returnCode: 0, summary: '' }; }\n",
+      source:
+        "export default async function* (input) { return { returnCode: 0, summary: input.prompt }; }\n",
     });
     expect(r.ok).toBe(false);
   });
@@ -49,7 +50,7 @@ export default async function* run() {
     const r = validateWorkflowBundle({
       filePath: "/tmp/w.esm.js",
       source:
-        'import x from "some-package";\nexport default async function* run() { return { returnCode: 0, summary: "" }; }\n',
+        'import x from "some-package";\nexport default async function* (input) { return { returnCode: 0, summary: input.prompt }; }\n',
     });
     expect(r.ok).toBe(false);
   });
@@ -58,7 +59,7 @@ export default async function* run() {
     const r = validateWorkflowBundle({
       filePath: "/tmp/w.esm.js",
       source:
-        'export default async function* run() { await import("fs"); return { returnCode: 0, summary: "" }; }\n',
+        'export default async function* (input) { await import("fs"); return { returnCode: 0, summary: input.prompt }; }\n',
     });
     expect(r.ok).toBe(false);
     if (!r.ok) {
@@ -70,7 +71,7 @@ export default async function* run() {
     const r = validateWorkflowBundle({
       filePath: "/tmp/w.esm.js",
       source:
-        'export default async function* run() { require("fs"); return { returnCode: 0, summary: "" }; }\n',
+        'export default async function* (input) { require("fs"); return { returnCode: 0, summary: input.prompt }; }\n',
     });
     expect(r.ok).toBe(false);
   });
diff --git a/packages/workflow/__tests__/engine.test.ts b/packages/workflow/__tests__/engine.test.ts
index 6ec61fa..af2da5d 100644
--- a/packages/workflow/__tests__/engine.test.ts
+++ b/packages/workflow/__tests__/engine.test.ts
@@ -51,7 +51,7 @@ describe("executeThread", () => {
       const result = await executeThread(
         demoWorkflow,
         "demo-flow",
-        "Fix the login redirect bug in #3",
+        { prompt: "Fix the login redirect bug in #3", steps: [] },
         { isDryRun: false, maxRounds: 5, signal: ac.signal },
         { threadId, hash, dataJsonlPath: dataPath, infoJsonlPath: infoPath },
         logger,
@@ -103,6 +103,53 @@ describe("executeThread", () => {
     }
   });
 
+  test("pre-filled ThreadInput.steps skips roles already present", async () => {
+    const root = await mkdtemp(join(tmpdir(), "wf-engine-fork-"));
+    try {
+      const threadId = "01KQXKW18CT8G75T53R8F4G7YG";
+      const hash = "C9NMV6V2TQT81";
+      const dataPath = join(root, "logs", hash, `${threadId}.data.jsonl`);
+      const infoPath = join(root, "logs", hash, `${threadId}.info.jsonl`);
+      await mkdir(join(root, "logs", hash), { recursive: true });
+
+      const logger = createLogger({ sink: { kind: "file", path: infoPath } });
+      const ac = new AbortController();
+
+      const result = await executeThread(
+        demoWorkflow,
+        "demo-flow",
+        {
+          prompt: "continue from planner",
+          steps: [
+            {
+              role: "planner",
+              content: "plan-body",
+              meta: { plan: "do-it", files: ["a.ts"] },
+            },
+          ],
+        },
+        { isDryRun: false, maxRounds: 5, signal: ac.signal },
+        { threadId, hash, dataJsonlPath: dataPath, infoJsonlPath: infoPath },
+        logger,
+      );
+
+      expect(result.returnCode).toBe(0);
+
+      const dataText = await readFile(dataPath, "utf8");
+      const lines = dataText
+        .trim()
+        .split("\n")
+        .filter((l) => l !== "");
+      expect(lines.length).toBe(2);
+
+      const role1 = JSON.parse(lines[1] ?? "{}") as Record<string, unknown>;
+      expect(role1.role).toBe("coder");
+      expect(role1.content).toBe("code-body");
+    } finally {
+      await rm(root, { recursive: true, force: true });
+    }
+  });
+
   test("respects maxRounds=0 (start record only)", async () => {
     const root = await mkdtemp(join(tmpdir(), "wf-engine-max0-"));
     try {
@@ -118,7 +165,7 @@ describe("executeThread", () => {
       const result = await executeThread(
         demoWorkflow,
         "demo-flow",
-        "hello",
+        { prompt: "hello", steps: [] },
         { isDryRun: false, maxRounds: 0, signal: ac.signal },
         { threadId, hash, dataJsonlPath: dataPath, infoJsonlPath: infoPath },
         logger,
diff --git a/packages/workflow/__tests__/hash.test.ts b/packages/workflow/__tests__/hash.test.ts
index dca18e8..23cbdd4 100644
--- a/packages/workflow/__tests__/hash.test.ts
+++ b/packages/workflow/__tests__/hash.test.ts
@@ -17,7 +17,7 @@ describe("hashWorkflowBundleBytes", () => {
   test("stable for identical content", () => {
     const encoder = new TextEncoder();
     const data = encoder.encode(
-      "export default async function* run() { return { returnCode: 0, summary: '' }; }\n",
+      "export default async function* (input) { return { returnCode: 0, summary: input.prompt }; }\n",
     );
     expect(hashWorkflowBundleBytes(data)).toBe(hashWorkflowBundleBytes(data));
   });
diff --git a/packages/workflow/__tests__/worker.test.ts b/packages/workflow/__tests__/worker.test.ts
index 599b97c..74e5c9b 100644
--- a/packages/workflow/__tests__/worker.test.ts
+++ b/packages/workflow/__tests__/worker.test.ts
@@ -7,8 +7,8 @@ import { join } from "node:path";
 
 import { getWorkerHostScriptPath } from "../src/worker-entry-path.js";
 
-const bundleSource = `export default async function* () {
-  yield { role: "planner", content: "p", meta: { plan: "x" } };
+const bundleSource = `export default async function* (input) {
+  yield { role: "planner", content: "p", meta: { plan: input.prompt } };
   yield { role: "coder", content: "c", meta: { diff: "y" } };
   return { returnCode: 0, summary: "completed: moderator returned END" };
 }
diff --git a/packages/workflow/src/create-role-moderator.ts b/packages/workflow/src/create-role-moderator.ts
index b36db96..abb2f11 100644
--- a/packages/workflow/src/create-role-moderator.ts
+++ b/packages/workflow/src/create-role-moderator.ts
@@ -1,9 +1,11 @@
 import {
   END,
   type RoleMeta,
+  type RoleOutput,
   type RoleStep,
   START,
   type ThreadContext,
+  type ThreadInput,
   type WorkflowDefinition,
   type WorkflowFn,
   type WorkflowFnOptions,
@@ -24,18 +26,24 @@ export function createRoleModerator<M extends RoleMeta>(
   def: Pick<WorkflowDefinition<M>, "roles" | "moderator">,
 ): WorkflowFn {
   return async function* roleModeratorWorkflow(
-    prompt: string,
+    input: ThreadInput,
     options: WorkflowFnOptions,
   ): AsyncGenerator<RoleOutput, WorkflowResult> {
     const nowMs = Date.now();
     const start: ThreadContext<M>["start"] = {
       role: START,
-      content: prompt,
-      meta: { maxRounds: options.maxRounds, threadId: options.threadId },
+      content: input.prompt,
+      meta: { maxRounds: options.maxRounds },
       timestamp: nowMs,
     };
 
-    let steps: RoleStep<M>[] = [];
+    const baseTs = Date.now();
+    let steps: RoleStep<M>[] = input.steps.map((out, i) => ({
+      role: out.role,
+      content: out.content,
+      meta: out.meta,
+      timestamp: baseTs + i,
+    })) as RoleStep<M>[];
 
     while (true) {
       if (steps.length >= options.maxRounds) {
@@ -46,7 +54,6 @@ export function createRoleModerator<M extends RoleMeta>(
       }
 
       const ctx: ThreadContext<M> = {
-        threadId: options.threadId,
         start,
         steps,
       };
diff --git a/packages/workflow/src/engine.ts b/packages/workflow/src/engine.ts
index 68de1f3..0d145f0 100644
--- a/packages/workflow/src/engine.ts
+++ b/packages/workflow/src/engine.ts
@@ -2,7 +2,7 @@ import { appendFile, mkdir } from "node:fs/promises";
 import { dirname } from "node:path";
 
 import type { LogFn } from "./logger.js";
-import type { WorkflowFn, WorkflowResult } from "./types.js";
+import type { ThreadInput, WorkflowFn, WorkflowResult } from "./types.js";
 
 export type ExecuteThreadIo = {
   threadId: string;
@@ -29,7 +29,7 @@ async function appendDataLine(path: string, record: unknown): Promise<void> {
 export async function executeThread(
   fn: WorkflowFn,
   workflowName: string,
-  prompt: string,
+  input: ThreadInput,
   options: ExecuteThreadOptions,
   io: ExecuteThreadIo,
   logger: LogFn,
@@ -43,7 +43,7 @@ export async function executeThread(
     hash: io.hash,
     threadId: io.threadId,
     parameters: {
-      prompt,
+      prompt: input.prompt,
       options: {
         isDryRun: options.isDryRun,
         maxRounds: options.maxRounds,
@@ -64,10 +64,9 @@ export async function executeThread(
     };
   }
 
-  const gen = fn(prompt, {
+  const gen = fn(input, {
     isDryRun: options.isDryRun,
     maxRounds: options.maxRounds,
-    threadId: io.threadId,
   });
 
   let written = 0;
diff --git a/packages/workflow/src/index.ts b/packages/workflow/src/index.ts
index a7c33cf..79fc6b5 100644
--- a/packages/workflow/src/index.ts
+++ b/packages/workflow/src/index.ts
@@ -47,6 +47,7 @@ export {
   START,
   type StartStep,
   type ThreadContext,
+  type ThreadInput,
   type WorkflowDefinition,
   type WorkflowFn,
   type WorkflowFnOptions,
diff --git a/packages/workflow/src/types.ts b/packages/workflow/src/types.ts
index 37e1b5f..f4dfd9b 100644
--- a/packages/workflow/src/types.ts
+++ b/packages/workflow/src/types.ts
@@ -18,16 +18,21 @@ export type WorkflowResult = {
   summary: string;
 };
 
+/** Input to a workflow — prompt plus optional historical steps for fork/resume. */
+export type ThreadInput = {
+  prompt: string;
+  steps: RoleOutput[];
+};
+
 /** Options passed to a workflow bundle's default-export function (engine-provided). */
 export type WorkflowFnOptions = {
   isDryRun: boolean;
   maxRounds: number;
-  threadId: string;
 };
 
 /** Bundle contract — default export is a function returning an AsyncGenerator. */
 export type WorkflowFn = (
-  prompt: string,
+  input: ThreadInput,
   options: WorkflowFnOptions,
 ) => AsyncGenerator<RoleOutput, WorkflowResult>;
 
@@ -41,7 +46,7 @@ export type RoleResult<Meta extends Record<string, unknown>> = {
 export type StartStep = {
   role: typeof START;
   content: string;
-  meta: { maxRounds: number; threadId: string };
+  meta: { maxRounds: number };
   timestamp: number;
 };
 
@@ -52,7 +57,6 @@ export type RoleStep<M extends RoleMeta> = {
 
 /** Thread-scoped context passed to roles and moderator. */
 export type ThreadContext<M extends RoleMeta = RoleMeta> = {
-  threadId: string;
   start: StartStep;
   steps: RoleStep<M>[];
 };
diff --git a/packages/workflow/src/worker.ts b/packages/workflow/src/worker.ts
index 1e7f60b..a0b7520 100644
--- a/packages/workflow/src/worker.ts
+++ b/packages/workflow/src/worker.ts
@@ -228,7 +228,7 @@ async function main(): Promise<void> {
       await executeThread(
         workflowFn,
         cmd.workflowName,
-        cmd.prompt,
+        { prompt: cmd.prompt, steps: [] },
         { ...cmd.options, signal: ac.signal },
         io,
         logger,