feat: record suspend event as StepNode in CAS chain

- ThreadIndexEntry supports suspendedRole + suspendMessage metadata
- threads.yaml: suspended threads serialize as objects (backward compat)
- cmdThreadStepOnce writes step before marking thread suspended
- StepOutput extended with suspendedRole/suspendMessage fields
- thread show displays suspend message

Closes #589

packages/cli-workflow/src/__tests__/config.test.ts

@@ -720,7 +720,10 @@ defaultModel: default
 
   describe("no legacy apiKeyEnv references", () => {
     test("config.ts has no references to apiKeyEnv", () => {
-      const configSource = readFileSync(join(__dirname, "..", "..", "src", "commands", "config.ts"), "utf8");
+      const configSource = readFileSync(
+        join(__dirname, "..", "..", "src", "commands", "config.ts"),
+        "utf8",
+      );
       expect(configSource).not.toContain("apiKeyEnv");
     });
 

packages/cli-workflow/src/__tests__/current-role.test.ts

@@ -175,8 +175,9 @@ async function insertStepNode(
 ): Promise<void> {
   const uwf = await createUwfStore(storageRoot);
   const index = await loadThreadsIndex(storageRoot);
-  const head = index[threadId];
+  const headEntry = index[threadId];
-  if (head === undefined) throw new Error(`thread ${threadId} not in index`);
+  if (headEntry === undefined) throw new Error(`thread ${threadId} not in index`);
+  const head = headEntry.head;
 
   const outputSchemaHash = await putSchema(uwf.store, OUTPUT_SCHEMA);
   const outputHash = await uwf.store.put(outputSchemaHash, outputPayload);
@@ -199,7 +200,7 @@ async function insertStepNode(
     detail: detailHash,
   })) as CasRef;
 
-  index[threadId] = stepHash;
+  index[threadId] = { head: stepHash, suspendedRole: null, suspendMessage: null };
   await saveThreadsIndex(storageRoot, index);
 }
 
@@ -280,7 +281,7 @@ describe("currentRole field", () => {
       const tid = thread as ThreadId;
 
       const index = await loadThreadsIndex(storageRoot);
-      const head = index[tid]!;
+      const head = index[tid]!.head;
       delete index[tid];
       await saveThreadsIndex(storageRoot, index);
       await appendThreadHistory(storageRoot, {
@@ -309,7 +310,7 @@ describe("currentRole field", () => {
       const tid = thread as ThreadId;
 
       const index = await loadThreadsIndex(storageRoot);
-      const head = index[tid]!;
+      const head = index[tid]!.head;
       delete index[tid];
       await saveThreadsIndex(storageRoot, index);
       await appendThreadHistory(storageRoot, {
@@ -371,7 +372,7 @@ describe("currentRole field", () => {
       const comp = await cmdThreadStart(storageRoot, wf, "completed", tmpDir);
       const compId = comp.thread as ThreadId;
       const index = await loadThreadsIndex(storageRoot);
-      const compHead = index[compId]!;
+      const compHead = index[compId]!.head;
       delete index[compId];
       await saveThreadsIndex(storageRoot, index);
       await appendThreadHistory(storageRoot, {

packages/cli-workflow/src/__tests__/thread-list-filters.test.ts

@@ -47,9 +47,7 @@ async function createTestThread(
     prompt: "test prompt",
   };
   const headHash = await uwf.store.put(uwf.schemas.startNode, startPayload);
-  const index = await import("../store.js").then((m) => m.loadThreadsIndex(storageRoot));
+  await saveThreadsIndex(storageRoot, { [threadId]: headHash });
-  index[threadId] = headHash;
-  await saveThreadsIndex(storageRoot, index);
   return threadId;
 }
 
@@ -106,7 +104,7 @@ describe("cmdThreadList status filter", () => {
     await markThreadRunning(tmpDir, thread2, workflowHash);
 
     const index = await import("../store.js").then((m) => m.loadThreadsIndex(tmpDir));
-    const thread3Head = index[thread3];
+    const thread3Head = index[thread3]!.head;
     if (thread3Head === undefined) throw new Error("thread3 head not found");
     await completeThread(tmpDir, thread3, workflowHash, thread3Head);
 
@@ -130,7 +128,7 @@ describe("cmdThreadList status filter", () => {
     await markThreadRunning(tmpDir, thread2, workflowHash);
 
     const index = await import("../store.js").then((m) => m.loadThreadsIndex(tmpDir));
-    const thread3Head = index[thread3];
+    const thread3Head = index[thread3]!.head;
     if (thread3Head === undefined) throw new Error("thread3 head not found");
     await completeThread(tmpDir, thread3, workflowHash, thread3Head);
 
@@ -154,7 +152,7 @@ describe("cmdThreadList status filter", () => {
     const thread3 = await createTestThread(uwf, tmpDir, workflowHash, Date.now() - 1000);
 
     const index = await import("../store.js").then((m) => m.loadThreadsIndex(tmpDir));
-    const thread3Head = index[thread3];
+    const thread3Head = index[thread3]!.head;
     if (thread3Head === undefined) throw new Error("thread3 head not found");
     await completeThread(tmpDir, thread3, workflowHash, thread3Head);
 
@@ -176,7 +174,7 @@ describe("cmdThreadList status filter", () => {
     await markThreadRunning(tmpDir, thread2, workflowHash);
 
     const index = await import("../store.js").then((m) => m.loadThreadsIndex(tmpDir));
-    const thread3Head = index[thread3];
+    const thread3Head = index[thread3]!.head;
     if (thread3Head === undefined) throw new Error("thread3 head not found");
     await completeThread(tmpDir, thread3, workflowHash, thread3Head);
 
@@ -348,7 +346,7 @@ describe("combined filters", () => {
     await markThreadRunning(tmpDir, thread2, workflowHash);
 
     const index = await import("../store.js").then((m) => m.loadThreadsIndex(tmpDir));
-    const thread3Head = index[thread3];
+    const thread3Head = index[thread3]!.head;
     if (thread3Head === undefined) throw new Error("thread3 head not found");
     await completeThread(tmpDir, thread3, workflowHash, thread3Head);
 
@@ -372,7 +370,7 @@ describe("combined filters", () => {
       const thread = await createTestThread(uwf, tmpDir, workflowHash, Date.now() + i * 1000);
       threads.push(thread);
       const index = await import("../store.js").then((m) => m.loadThreadsIndex(tmpDir));
-      const headHash = index[thread];
+      const headHash = index[thread]!.head;
       if (headHash === undefined) throw new Error("head not found");
       await completeThread(tmpDir, thread, workflowHash, headHash);
     }
@@ -421,7 +419,7 @@ describe("combined filters", () => {
 
       if (i % 2 === 0) {
         const index = await import("../store.js").then((m) => m.loadThreadsIndex(tmpDir));
-        const headHash = index[thread];
+        const headHash = index[thread]!.head;
         if (headHash === undefined) throw new Error("head not found");
         await completeThread(tmpDir, thread, workflowHash, headHash);
       } else {
@@ -479,7 +477,11 @@ describe("edge cases", () => {
     const thread2 = await createTestThread(uwf, tmpDir, workflowHash, Date.now() - 1000);
 
     const index = await import("../store.js").then((m) => m.loadThreadsIndex(tmpDir));
-    index["INVALID_ULID_FORMAT_HERE" as ThreadId] = "01J6HMVRNQKJV2";
+    index["INVALID_ULID_FORMAT_HERE" as ThreadId] = {
+      head: "01J6HMVRNQKJV2",
+      suspendedRole: null,
+      suspendMessage: null,
+    };
     await saveThreadsIndex(tmpDir, index);
 
     const afterMs = Date.now() - 3000;

packages/cli-workflow/src/__tests__/thread-location.test.ts

@@ -80,7 +80,7 @@ graph:
     // Verify StartNode has the cwd field
     const uwf = await createUwfStore(storageRoot);
     const index = await import("../store.js").then((m) => m.loadThreadsIndex(storageRoot));
-    const headHash = index[result.thread as ThreadId];
+    const headHash = index[result.thread as ThreadId]!.head;
     expect(headHash).toBeDefined();
 
     const startNode = uwf.store.get(headHash as CasRef);
@@ -175,7 +175,7 @@ graph:
 
     const uwf = await createUwfStore(storageRoot);
     const index = await import("../store.js").then((m) => m.loadThreadsIndex(storageRoot));
-    const headHash = index[result.thread as ThreadId];
+    const headHash = index[result.thread as ThreadId]!.head;
 
     const startNode = uwf.store.get(headHash as CasRef);
     const startPayload = startNode?.payload as StartNodePayload;

packages/cli-workflow/src/__tests__/thread-show-status.test.ts

@@ -90,8 +90,9 @@ async function insertStepNode(
 ): Promise<void> {
   const uwf = await createUwfStore(storageRoot);
   const index = await loadThreadsIndex(storageRoot);
-  const head = index[threadId];
+  const headEntry = index[threadId];
-  if (head === undefined) throw new Error(`thread ${threadId} not in index`);
+  if (headEntry === undefined) throw new Error(`thread ${threadId} not in index`);
+  const head = headEntry.head;
 
   const outputSchemaHash = await putSchema(uwf.store, OUTPUT_SCHEMA);
   const outputHash = await uwf.store.put(outputSchemaHash, outputPayload);
@@ -116,7 +117,7 @@ async function insertStepNode(
     assembledPrompt: null,
   })) as CasRef;
 
-  index[threadId] = stepHash;
+  index[threadId] = { head: stepHash, suspendedRole: null, suspendMessage: null };
   await saveThreadsIndex(storageRoot, index);
 }
 
@@ -203,7 +204,7 @@ describe("thread show status field", () => {
 
     // Get the head hash before moving to history
     const index = await loadThreadsIndex(storageRoot);
-    const head = index[threadId];
+    const head = index[threadId]!.head;
     if (!head) throw new Error("Thread not found in index");
 
     // Move thread to history with reason 'completed'
@@ -243,7 +244,7 @@ describe("thread show status field", () => {
 
     // Get the head hash before moving to history
     const index = await loadThreadsIndex(storageRoot);
-    const head = index[threadId];
+    const head = index[threadId]!.head;
     if (!head) throw new Error("Thread not found in index");
 
     // Move thread to history with reason 'cancelled'
@@ -283,7 +284,7 @@ describe("thread show status field", () => {
 
     // Get the head hash before moving to history
     const index = await loadThreadsIndex(storageRoot);
-    const head = index[threadId];
+    const head = index[threadId]!.head;
     if (!head) throw new Error("Thread not found in index");
 
     // Move thread to history with reason null (legacy format)
@@ -333,6 +334,8 @@ describe("thread show status field", () => {
       expect(result.status).toBe("suspended");
       expect(result.done).toBe(false);
       expect(result.currentRole).toBe(null);
+      expect(result.suspendedRole).toBe("worker");
+      expect(result.suspendMessage).toBe("Please clarify: Which API?");
       expect(result.background).toBe(null);
       expect(result.thread).toBe(threadId);
     } finally {

packages/cli-workflow/src/__tests__/thread-start-cwd-cli.test.ts

@@ -75,7 +75,7 @@ graph:
   async function getStartNodeCwd(threadId: string): Promise<string> {
     const uwf = await createUwfStore(storageRoot);
     const index = await loadThreadsIndex(storageRoot);
-    const headHash = index[threadId as ThreadId];
+    const headHash = index[threadId as ThreadId]!.head;
     expect(headHash).toBeDefined();
 
     const startNode = uwf.store.get(headHash as CasRef);

packages/cli-workflow/src/__tests__/thread-suspend-step.test.ts

@@ -0,0 +1,179 @@
+import { execFileSync } from "node:child_process";
+import { mkdir, mkdtemp, readFile, rm, writeFile } from "node:fs/promises";
+import { tmpdir } from "node:os";
+import { join } from "node:path";
+import { putSchema } from "@ocas/core";
+import { createFsStore } from "@ocas/fs";
+import type { CasRef, StepNodePayload, ThreadId } from "@uncaged/workflow-protocol";
+import { afterEach, beforeEach, describe, expect, test } from "vitest";
+import { parse } from "yaml";
+import { cmdThreadShow } from "../commands/thread.js";
+import { registerUwfSchemas } from "../schemas.js";
+import { saveThreadsIndex } from "../store.js";
+
+const OUTPUT_SCHEMA = {
+  type: "object" as const,
+  properties: {
+    $status: { type: "string" as const },
+    question: { type: "string" as const },
+  },
+  required: ["$status"],
+  additionalProperties: false,
+};
+
+let tmpDir: string;
+
+beforeEach(async () => {
+  tmpDir = await mkdtemp(join(tmpdir(), "cli-uwf-suspend-step-test-"));
+});
+
+afterEach(async () => {
+  await rm(tmpDir, { recursive: true, force: true });
+});
+
+describe("suspend step CAS chain and threads.yaml metadata", () => {
+  test("thread exec records suspend step in CAS and suspend metadata in threads.yaml", async () => {
+    const casDir = join(tmpDir, "cas");
+    await mkdir(casDir, { recursive: true });
+    const originalCasDir = process.env.UNCAGED_CAS_DIR;
+    process.env.UNCAGED_CAS_DIR = casDir;
+
+    try {
+      const store = createFsStore(casDir);
+      const schemas = await registerUwfSchemas(store);
+
+      const outputSchemaHash = await putSchema(store, OUTPUT_SCHEMA);
+
+      const workflowHash = await store.put(schemas.workflow, {
+        name: "test-suspend-step",
+        description: "suspend step integration test",
+        roles: {
+          worker: {
+            description: "Worker role",
+            goal: "Work",
+            capabilities: [],
+            procedure: "work",
+            output: "result",
+            frontmatter: outputSchemaHash,
+          },
+        },
+        graph: {
+          $START: { _: { role: "worker", prompt: "Start work", location: null } },
+          worker: {
+            needs_input: {
+              role: "$SUSPEND",
+              prompt: "Please clarify: {{{question}}}",
+              location: null,
+            },
+          },
+        },
+      });
+
+      const startHash = await store.put(schemas.startNode, {
+        workflow: workflowHash,
+        prompt: "Test suspend task",
+        cwd: tmpDir,
+      });
+
+      const threadId = "01SUSPENDSTEPTEST0000000" as ThreadId;
+      await saveThreadsIndex(tmpDir, { [threadId]: startHash });
+
+      const outputHash = await store.put(outputSchemaHash, {
+        $status: "needs_input",
+        question: "Which API?",
+      });
+      const detailHash = await store.put(schemas.text, "mock detail");
+
+      const startedAtMs = 1716600000000;
+      const completedAtMs = 1716600001500;
+
+      const stepHash = await store.put(schemas.stepNode, {
+        start: startHash,
+        prev: null,
+        role: "worker",
+        output: outputHash,
+        detail: detailHash,
+        agent: "uwf-mock",
+        edgePrompt: "Start work",
+        startedAtMs,
+        completedAtMs,
+        cwd: tmpDir,
+        assembledPrompt: null,
+      });
+
+      const mockAgentPath = join(tmpDir, "mock-agent.sh");
+      const adapterJson = JSON.stringify({
+        stepHash,
+        detailHash,
+        role: "worker",
+        frontmatter: { $status: "needs_input", question: "Which API?" },
+        body: "",
+        startedAtMs,
+        completedAtMs,
+      });
+      await writeFile(mockAgentPath, `#!/bin/sh\necho '${adapterJson}'\n`, { mode: 0o755 });
+
+      const configPath = join(tmpDir, "config.yaml");
+      await writeFile(
+        configPath,
+        `defaultAgent: uwf-hermes\ndefaultModel: test-model\nagentOverrides: null\nagents: {}\nproviders: {}\nmodels: {}\n`,
+      );
+
+      const cliPath = join(import.meta.dirname, "..", "cli.js");
+      const stdout = execFileSync(
+        "bun",
+        ["run", cliPath, "thread", "exec", threadId, "--agent", mockAgentPath],
+        {
+          encoding: "utf8",
+          stdio: ["ignore", "pipe", "pipe"],
+          env: {
+            ...process.env,
+            WORKFLOW_STORAGE_ROOT: tmpDir,
+            UNCAGED_CAS_DIR: casDir,
+          },
+          cwd: tmpDir,
+          timeout: 30000,
+        },
+      );
+
+      const cliOutput = JSON.parse(stdout.trim());
+      expect(cliOutput.status).toBe("suspended");
+      expect(cliOutput.head).toBe(stepHash);
+      expect(cliOutput.suspendedRole).toBe("worker");
+      expect(cliOutput.suspendMessage).toBe("Please clarify: Which API?");
+
+      const storeAfter = createFsStore(casDir);
+      const stepNode = storeAfter.get(cliOutput.head as CasRef);
+      expect(stepNode).not.toBeNull();
+      const payload = stepNode!.payload as StepNodePayload;
+      expect(payload.role).toBe("worker");
+      expect(payload.output).toBe(outputHash);
+
+      const outputNode = storeAfter.get(outputHash);
+      expect(outputNode?.payload).toEqual({
+        $status: "needs_input",
+        question: "Which API?",
+      });
+
+      const threadsYaml = await readFile(join(tmpDir, "threads.yaml"), "utf8");
+      const threadsIndex = parse(threadsYaml) as Record<string, unknown>;
+      const threadEntry = threadsIndex[threadId];
+      expect(threadEntry).toEqual({
+        head: stepHash,
+        suspendedRole: "worker",
+        suspendMessage: "Please clarify: Which API?",
+      });
+
+      const showResult = await cmdThreadShow(tmpDir, threadId);
+      expect(showResult.status).toBe("suspended");
+      expect(showResult.suspendMessage).toBe("Please clarify: Which API?");
+      expect(showResult.suspendedRole).toBe("worker");
+    } finally {
+      if (originalCasDir === undefined) {
+        delete process.env.UNCAGED_CAS_DIR;
+      } else {
+        process.env.UNCAGED_CAS_DIR = originalCasDir;
+      }
+    }
+  });
+});

packages/cli-workflow/src/commands/shared.ts

@@ -203,7 +203,7 @@ function collectOrderedSteps(
 
 async function resolveHeadHash(storageRoot: string, threadId: ThreadId): Promise<CasRef> {
   const index = await loadThreadsIndex(storageRoot);
-  const activeHead = index[threadId];
+  const activeHead = index[threadId]?.head;
   if (activeHead !== undefined) {
     return activeHead;
   }

packages/cli-workflow/src/commands/step.ts

@@ -113,7 +113,7 @@ export async function cmdStepFork(
 
   const newThreadId = generateUlid(Date.now()) as ThreadId;
   const index = await loadThreadsIndex(storageRoot);
-  index[newThreadId] = stepHash;
+  index[newThreadId] = { head: stepHash, suspendedRole: null, suspendMessage: null };
   await saveThreadsIndex(storageRoot, index);
 
   return {

packages/cli-workflow/src/commands/thread.ts

@@ -11,12 +11,18 @@ import type {
   StepNodePayload,
   StepOutput,
   ThreadId,
+  ThreadIndexEntry,
   ThreadListItem,
   ThreadStatus,
   ThreadsIndex,
   WorkflowConfig,
   WorkflowPayload,
 } from "@uncaged/workflow-protocol";
+import {
+  createThreadIndexEntry,
+  markThreadSuspended,
+  updateThreadHead,
+} from "@uncaged/workflow-protocol";
 import {
   createProcessLogger,
   extractUlidTimestamp,
@@ -68,20 +74,84 @@ function buildStepOutputFromEvaluation(
 ): StepOutput {
   const done = status === "completed";
   let currentRole: string | null = null;
-  if (evaluation.ok && !isSuspendResult(evaluation.value) && evaluation.value.role !== END_ROLE) {
+  let suspendedRole: string | null = null;
+  let suspendMessage: string | null = null;
+  if (evaluation.ok) {
+    if (isSuspendResult(evaluation.value)) {
+      suspendedRole = evaluation.value.suspendedRole;
+      suspendMessage = evaluation.value.prompt;
+    } else if (evaluation.value.role !== END_ROLE) {
       currentRole = evaluation.value.role;
     }
+  }
   return {
     workflow: workflowHash,
     thread: threadId,
     head,
     status,
     currentRole,
+    suspendedRole,
+    suspendMessage,
     done,
     background,
   };
 }
 
+function resolveSuspendFieldsFromGraph(
+  uwf: UwfStore,
+  head: CasRef,
+  workflowRef: CasRef,
+): { suspendedRole: string | null; suspendMessage: string | null } {
+  const chain = walkChain(uwf, head);
+  const { lastRole, lastOutput } = resolveEvaluateArgs(uwf, chain);
+  const workflow = loadWorkflowPayload(uwf, workflowRef);
+  const result = evaluate(workflow.graph, lastRole, lastOutput);
+  if (result.ok && isSuspendResult(result.value)) {
+    return {
+      suspendedRole: result.value.suspendedRole,
+      suspendMessage: result.value.prompt,
+    };
+  }
+  return { suspendedRole: null, suspendMessage: null };
+}
+
+function resolveSuspendFieldsForShow(
+  entry: ThreadIndexEntry,
+  status: ThreadStatus,
+  uwf: UwfStore,
+  head: CasRef,
+  workflowRef: CasRef,
+): { suspendedRole: string | null; suspendMessage: string | null } {
+  if (status !== "suspended") {
+    return { suspendedRole: null, suspendMessage: null };
+  }
+  if (entry.suspendedRole !== null && entry.suspendMessage !== null) {
+    return { suspendedRole: entry.suspendedRole, suspendMessage: entry.suspendMessage };
+  }
+  const fromGraph = resolveSuspendFieldsFromGraph(uwf, head, workflowRef);
+  return {
+    suspendedRole: entry.suspendedRole ?? fromGraph.suspendedRole,
+    suspendMessage: entry.suspendMessage ?? fromGraph.suspendMessage,
+  };
+}
+
+async function ensureThreadSuspendMetadata(
+  storageRoot: string,
+  threadId: ThreadId,
+  entry: ThreadIndexEntry,
+  suspendedRole: string,
+  suspendMessage: string,
+): Promise<ThreadIndexEntry> {
+  if (entry.suspendedRole !== null && entry.suspendMessage !== null) {
+    return entry;
+  }
+  const updated = markThreadSuspended(entry, suspendedRole, suspendMessage);
+  const index = await loadThreadsIndex(storageRoot);
+  index[threadId] = updated;
+  await saveThreadsIndex(storageRoot, index);
+  return updated;
+}
+
 async function resolveActiveThreadStatus(
   storageRoot: string,
   threadId: ThreadId,
@@ -380,7 +450,7 @@ export async function cmdThreadStart(
   }
 
   const index = await loadThreadsIndex(storageRoot);
-  index[threadId] = headHash;
+  index[threadId] = createThreadIndexEntry(headHash);
   await saveThreadsIndex(storageRoot, index);
 
   plog.log(
@@ -394,8 +464,9 @@ export async function cmdThreadStart(
 
 export async function cmdThreadShow(storageRoot: string, threadId: ThreadId): Promise<StepOutput> {
   const index = await loadThreadsIndex(storageRoot);
-  const activeHead = index[threadId];
+  const entry = index[threadId];
-  if (activeHead !== undefined) {
+  if (entry !== undefined) {
+    const activeHead = entry.head;
     const uwf = await createUwfStore(storageRoot);
     const workflow = resolveWorkflowFromHead(uwf, activeHead);
     if (workflow === null) {
@@ -410,6 +481,7 @@ export async function cmdThreadShow(storageRoot: string, threadId: ThreadId): Pr
       workflow,
     );
     const currentRole = resolveCurrentRole(uwf, activeHead, workflow);
+    const suspendFields = resolveSuspendFieldsForShow(entry, status, uwf, activeHead, workflow);
 
     return {
       workflow,
@@ -417,6 +489,8 @@ export async function cmdThreadShow(storageRoot: string, threadId: ThreadId): Pr
       head: activeHead,
       status,
       currentRole,
+      suspendedRole: suspendFields.suspendedRole,
+      suspendMessage: suspendFields.suspendMessage,
       done: false,
       background: null,
     };
@@ -432,6 +506,8 @@ export async function cmdThreadShow(storageRoot: string, threadId: ThreadId): Pr
       head: hist.head,
       status,
       currentRole: null,
+      suspendedRole: null,
+      suspendMessage: null,
       done: true,
       background: null,
     };
@@ -473,13 +549,8 @@ async function collectActiveThreads(
   index: ThreadsIndex,
 ): Promise<ThreadListItemWithStatus[]> {
   const items: ThreadListItemWithStatus[] = [];
-  for (const [threadId, head] of Object.entries(index)) {
+  for (const [threadId, entry] of Object.entries(index)) {
-    const item = await threadListItemFromActive(
+    const item = await threadListItemFromActive(storageRoot, uwf, threadId as ThreadId, entry.head);
-      storageRoot,
-      uwf,
-      threadId as ThreadId,
-      head as CasRef,
-    );
     if (item !== null) {
       items.push(item);
     }
@@ -1011,12 +1082,12 @@ async function resolveActiveThreadWorkflowHash(
   threadId: ThreadId,
 ): Promise<CasRef> {
   const index = await loadThreadsIndex(storageRoot);
-  const headHash = index[threadId];
+  const entry = index[threadId];
-  if (headHash === undefined) {
+  if (entry === undefined) {
     fail(`thread not active: ${threadId}`);
   }
   const uwf = await createUwfStore(storageRoot);
-  const chain = walkChain(uwf, headHash);
+  const chain = walkChain(uwf, entry.head);
   return chain.start.workflow;
 }
 
@@ -1030,10 +1101,11 @@ async function cmdThreadStepBackground(
 ): Promise<StepOutput[]> {
   // Get current head to return to caller
   const index = await loadThreadsIndex(storageRoot);
-  const headHash = index[threadId];
+  const entry = index[threadId];
-  if (headHash === undefined) {
+  if (entry === undefined) {
     failStep(plog, `thread not active: ${threadId}`);
   }
+  const headHash = entry.head;
 
   const uwf = await createUwfStore(storageRoot);
 
@@ -1069,6 +1141,8 @@ async function cmdThreadStepBackground(
       head: headHash,
       status: "running",
       currentRole: resolveCurrentRole(uwf, headHash, workflowHash),
+      suspendedRole: null,
+      suspendMessage: null,
       done: false,
       background: true,
     },
@@ -1082,10 +1156,11 @@ async function cmdThreadStepOnce(
   plog: ProcessLogger,
 ): Promise<StepOutput> {
   const index = await loadThreadsIndex(storageRoot);
-  const headHash = index[threadId];
+  const entry = index[threadId];
-  if (headHash === undefined) {
+  if (entry === undefined) {
     failStep(plog, `thread not active: ${threadId}`);
   }
+  const headHash = entry.head;
 
   const uwf = await createUwfStore(storageRoot);
   const chain = walkChain(uwf, headHash);
@@ -1109,6 +1184,13 @@ async function cmdThreadStepOnce(
   );
 
   if (isSuspendResult(nextResult.value)) {
+    await ensureThreadSuspendMetadata(
+      storageRoot,
+      threadId,
+      entry,
+      nextResult.value.suspendedRole,
+      nextResult.value.prompt,
+    );
     return buildStepOutputFromEvaluation(
       workflowHash,
       threadId,
@@ -1128,6 +1210,8 @@ async function cmdThreadStepOnce(
       head: headHash,
       status: "completed",
       currentRole: null,
+      suspendedRole: null,
+      suspendMessage: null,
       done: true,
       background: null,
     };
@@ -1162,7 +1246,8 @@ async function cmdThreadStepOnce(
 
   // Reload threads index to avoid overwriting changes made by the agent subprocess
   const freshIndex = await loadThreadsIndex(storageRoot);
-  freshIndex[threadId] = newHead;
+  const priorEntry = freshIndex[threadId] ?? createThreadIndexEntry(newHead);
+  freshIndex[threadId] = updateThreadHead(priorEntry, newHead);
   await saveThreadsIndex(storageRoot, freshIndex);
 
   const chainAfter = walkChain(uwfAfter, newHead);
@@ -1176,6 +1261,12 @@ async function cmdThreadStepOnce(
   }
 
   if (isSuspendResult(afterResult.value)) {
+    freshIndex[threadId] = markThreadSuspended(
+      freshIndex[threadId] ?? createThreadIndexEntry(newHead),
+      afterResult.value.suspendedRole,
+      afterResult.value.prompt,
+    );
+    await saveThreadsIndex(storageRoot, freshIndex);
     return buildStepOutputFromEvaluation(
       workflowHash,
       threadId,
@@ -1202,6 +1293,8 @@ async function cmdThreadStepOnce(
     head: newHead,
     status,
     currentRole,
+    suspendedRole: null,
+    suspendMessage: null,
     done,
     background: null,
   };
@@ -1209,7 +1302,7 @@ async function cmdThreadStepOnce(
 
 async function resolveHeadHash(storageRoot: string, threadId: ThreadId): Promise<CasRef> {
   const index = await loadThreadsIndex(storageRoot);
-  const activeHead = index[threadId];
+  const activeHead = index[threadId]?.head;
   if (activeHead !== undefined) {
     return activeHead;
   }
@@ -1262,8 +1355,8 @@ export type CancelOutput = {
  */
 export async function cmdThreadStop(storageRoot: string, threadId: ThreadId): Promise<StopOutput> {
   const index = await loadThreadsIndex(storageRoot);
-  const head = index[threadId];
+  const entry = index[threadId];
-  if (head === undefined) {
+  if (entry === undefined) {
     fail(`thread not active: ${threadId}`);
   }
 
@@ -1292,10 +1385,11 @@ export async function cmdThreadCancel(
   threadId: ThreadId,
 ): Promise<CancelOutput> {
   const index = await loadThreadsIndex(storageRoot);
-  const head = index[threadId];
+  const entry = index[threadId];
-  if (head === undefined) {
+  if (entry === undefined) {
     fail(`thread not active: ${threadId}`);
   }
+  const head = entry.head;
 
   // Check if thread is running in background and terminate it
   const runningMarker = await isThreadRunning(storageRoot, threadId);

packages/cli-workflow/src/store.ts

@@ -5,7 +5,18 @@ import { join } from "node:path";
 
 import type { BootstrapCapableStore, Hash } from "@ocas/core";
 import { createFsStore } from "@ocas/fs";
-import type { CasRef, ThreadId, ThreadListItem, ThreadsIndex } from "@uncaged/workflow-protocol";
+import type {
+  CasRef,
+  ThreadId,
+  ThreadIndexEntry,
+  ThreadListItem,
+  ThreadsIndex,
+} from "@uncaged/workflow-protocol";
+import {
+  createThreadIndexEntry,
+  parseThreadsIndex,
+  serializeThreadsIndex,
+} from "@uncaged/workflow-protocol";
 import { parse, stringify } from "yaml";
 
 import { registerUwfSchemas, type UwfSchemaHashes } from "./schemas.js";
@@ -234,16 +245,7 @@ export async function loadThreadsIndex(storageRoot: string): Promise<ThreadsInde
   try {
     const text = await readFile(path, "utf8");
     const raw = parse(text) as unknown;
-    if (raw === null || typeof raw !== "object" || Array.isArray(raw)) {
+    return parseThreadsIndex(raw);
-      return {};
-    }
-    const index: ThreadsIndex = {};
-    for (const [threadId, head] of Object.entries(raw as Record<string, unknown>)) {
-      if (typeof head === "string") {
-        index[threadId as ThreadId] = head;
-      }
-    }
-    return index;
   } catch (e) {
     const err = e as NodeJS.ErrnoException;
     if (err.code === "ENOENT") {
@@ -253,10 +255,25 @@ export async function loadThreadsIndex(storageRoot: string): Promise<ThreadsInde
   }
 }
 
-export async function saveThreadsIndex(storageRoot: string, index: ThreadsIndex): Promise<void> {
+/** Accept legacy CasRef values for test convenience. */
+export type ThreadsIndexInput = Record<ThreadId, ThreadIndexEntry | CasRef>;
+
+function normalizeThreadsIndexInput(index: ThreadsIndexInput): ThreadsIndex {
+  const normalized: ThreadsIndex = {};
+  for (const [threadId, value] of Object.entries(index)) {
+    normalized[threadId as ThreadId] =
+      typeof value === "string" ? createThreadIndexEntry(value as CasRef) : value;
+  }
+  return normalized;
+}
+
+export async function saveThreadsIndex(
+  storageRoot: string,
+  index: ThreadsIndexInput,
+): Promise<void> {
   const path = getThreadsPath(storageRoot);
   await mkdir(storageRoot, { recursive: true });
-  const text = stringify(index, { indent: 2 });
+  const text = stringify(serializeThreadsIndex(normalizeThreadsIndexInput(index)), { indent: 2 });
   await writeFile(path, text, "utf8");
 }
 

packages/workflow-protocol/src/__tests__/thread-index.test.ts

@@ -0,0 +1,79 @@
+import { describe, expect, test } from "vitest";
+import {
+  createThreadIndexEntry,
+  markThreadSuspended,
+  normalizeThreadIndexEntry,
+  parseThreadsIndex,
+  serializeThreadIndexEntry,
+  serializeThreadsIndex,
+  updateThreadHead,
+} from "../thread-index.js";
+
+describe("thread-index", () => {
+  test("parse legacy string head hash", () => {
+    const entry = normalizeThreadIndexEntry("0123456789ABC");
+    expect(entry).toEqual({
+      head: "0123456789ABC",
+      suspendedRole: null,
+      suspendMessage: null,
+    });
+  });
+
+  test("parse suspended object entry", () => {
+    const entry = normalizeThreadIndexEntry({
+      head: "0123456789ABC",
+      suspendedRole: "worker",
+      suspendMessage: "Please clarify: Which API?",
+    });
+    expect(entry).toEqual({
+      head: "0123456789ABC",
+      suspendedRole: "worker",
+      suspendMessage: "Please clarify: Which API?",
+    });
+  });
+
+  test("serialize non-suspended entry as compact string", () => {
+    const entry = createThreadIndexEntry("0123456789ABC");
+    expect(serializeThreadIndexEntry(entry)).toBe("0123456789ABC");
+  });
+
+  test("serialize suspended entry as object", () => {
+    const entry = markThreadSuspended(
+      createThreadIndexEntry("0123456789ABC"),
+      "worker",
+      "Please clarify: Which API?",
+    );
+    expect(serializeThreadIndexEntry(entry)).toEqual({
+      head: "0123456789ABC",
+      suspendedRole: "worker",
+      suspendMessage: "Please clarify: Which API?",
+    });
+  });
+
+  test("updateThreadHead clears suspend metadata", () => {
+    const suspended = markThreadSuspended(
+      createThreadIndexEntry("OLDHEAD0123456"),
+      "worker",
+      "Waiting",
+    );
+    const resumed = updateThreadHead(suspended, "NEWHEAD01234567");
+    expect(resumed).toEqual({
+      head: "NEWHEAD01234567",
+      suspendedRole: null,
+      suspendMessage: null,
+    });
+  });
+
+  test("parseThreadsIndex round-trip", () => {
+    const raw = {
+      "01THREAD0000000000000001": "HEAD00000000001",
+      "01THREAD0000000000000002": {
+        head: "HEAD00000000002",
+        suspendedRole: "reviewer",
+        suspendMessage: "Need input",
+      },
+    };
+    const parsed = parseThreadsIndex(raw);
+    expect(serializeThreadsIndex(parsed)).toEqual(raw);
+  });
+});

packages/workflow-protocol/src/index.ts

@@ -3,6 +3,15 @@ export {
   STEP_NODE_SCHEMA,
   WORKFLOW_SCHEMA,
 } from "./schemas.js";
+export {
+  createThreadIndexEntry,
+  markThreadSuspended,
+  normalizeThreadIndexEntry,
+  parseThreadsIndex,
+  serializeThreadIndexEntry,
+  serializeThreadsIndex,
+  updateThreadHead,
+} from "./thread-index.js";
 export type {
   AgentAlias,
   AgentConfig,
@@ -29,6 +38,7 @@ export type {
   Target,
   ThreadForkOutput,
   ThreadId,
+  ThreadIndexEntry,
   ThreadListItem,
   ThreadStatus,
   ThreadStepsOutput,

packages/workflow-protocol/src/thread-index.ts

@@ -0,0 +1,89 @@
+import type { CasRef, ThreadId, ThreadIndexEntry, ThreadsIndex } from "./types.js";
+
+/** Normalize a legacy head hash or entry object into {@link ThreadIndexEntry}. */
+export function normalizeThreadIndexEntry(raw: unknown): ThreadIndexEntry | null {
+  if (typeof raw === "string") {
+    return createThreadIndexEntry(raw as CasRef);
+  }
+  if (raw === null || typeof raw !== "object" || Array.isArray(raw)) {
+    return null;
+  }
+  const rec = raw as Record<string, unknown>;
+  const head = rec.head;
+  if (typeof head !== "string") {
+    return null;
+  }
+  const suspendedRole = rec.suspendedRole;
+  const suspendMessage = rec.suspendMessage;
+  return {
+    head: head as CasRef,
+    suspendedRole: typeof suspendedRole === "string" ? suspendedRole : null,
+    suspendMessage: typeof suspendMessage === "string" ? suspendMessage : null,
+  };
+}
+
+export function createThreadIndexEntry(head: CasRef): ThreadIndexEntry {
+  return {
+    head,
+    suspendedRole: null,
+    suspendMessage: null,
+  };
+}
+
+export function updateThreadHead(_entry: ThreadIndexEntry, head: CasRef): ThreadIndexEntry {
+  return {
+    head,
+    suspendedRole: null,
+    suspendMessage: null,
+  };
+}
+
+export function markThreadSuspended(
+  entry: ThreadIndexEntry,
+  suspendedRole: string,
+  suspendMessage: string,
+): ThreadIndexEntry {
+  return {
+    head: entry.head,
+    suspendedRole,
+    suspendMessage,
+  };
+}
+
+/** Serialize for threads.yaml — compact string when not suspended. */
+export function serializeThreadIndexEntry(
+  entry: ThreadIndexEntry,
+): string | Record<string, string> {
+  if (entry.suspendedRole === null || entry.suspendMessage === null) {
+    return entry.head;
+  }
+  return {
+    head: entry.head,
+    suspendedRole: entry.suspendedRole,
+    suspendMessage: entry.suspendMessage,
+  };
+}
+
+export function parseThreadsIndex(raw: unknown): ThreadsIndex {
+  if (raw === null || typeof raw !== "object" || Array.isArray(raw)) {
+    return {};
+  }
+  const index: ThreadsIndex = {};
+  for (const [threadId, value] of Object.entries(raw as Record<string, unknown>)) {
+    const entry = normalizeThreadIndexEntry(value);
+    if (entry !== null) {
+      index[threadId as ThreadId] = entry;
+    }
+  }
+  return index;
+}
+
+export function serializeThreadsIndex(
+  index: ThreadsIndex,
+): Record<string, string | Record<string, string>> {
+  const out: Record<string, string | Record<string, string>> = {};
+  for (const [threadId, entry] of Object.entries(index)) {
+    out[threadId] = serializeThreadIndexEntry(entry);
+  }
+  return out;
+}

packages/workflow-protocol/src/types.ts

@@ -105,10 +105,21 @@ export type StepOutput = {
   status: ThreadStatus;
   /** The current or next role. Null when completed, cancelled, suspended, or next is $END. */
   currentRole: string | null;
+  /** Role whose output triggered suspension. Null when thread is not suspended. */
+  suspendedRole: string | null;
+  /** Rendered suspend prompt for the user. Null when thread is not suspended. */
+  suspendMessage: string | null;
   done: boolean;
   background: boolean | null;
 };
 
+/** Active thread entry in ~/.uncaged/workflow/threads.yaml */
+export type ThreadIndexEntry = {
+  head: CasRef;
+  suspendedRole: string | null;
+  suspendMessage: string | null;
+};
+
 /** uwf thread steps — single step entry */
 export type StepEntry = {
   hash: CasRef;
@@ -200,4 +211,4 @@ export type WorkflowConfig = {
 };
 
 /** ~/.uncaged/workflow/threads.yaml */
-export type ThreadsIndex = Record<ThreadId, CasRef>;
+export type ThreadsIndex = Record<ThreadId, ThreadIndexEntry>;

packages/workflow-util-agent/src/context.ts

@@ -163,7 +163,7 @@ export async function buildContext(
   const { store, schemas } = agentStore;
 
   const index = await loadThreadsIndex(storageRoot);
-  const headHash = index[threadId];
+  const headHash = index[threadId]?.head;
   if (headHash === undefined) {
     fail(`thread not found in threads.yaml: ${threadId}`);
   }
@@ -212,7 +212,7 @@ export async function buildContextWithMeta(
   const { store, schemas } = agentStore;
 
   const index = await loadThreadsIndex(storageRoot);
-  const headHash = index[threadId];
+  const headHash = index[threadId]?.head;
   if (headHash === undefined) {
     fail(`thread not found in threads.yaml: ${threadId}`);
   }

packages/workflow-util-agent/src/storage.ts

@@ -12,11 +12,11 @@ import type {
   ProviderAlias,
   ProviderConfig,
   Scenario,
-  ThreadId,
   ThreadsIndex,
   WorkflowConfig,
   WorkflowName,
 } from "@uncaged/workflow-protocol";
+import { parseThreadsIndex } from "@uncaged/workflow-protocol";
 import { parse } from "yaml";
 
 import { registerAgentSchemas } from "./schemas.js";
@@ -207,16 +207,7 @@ export async function loadThreadsIndex(storageRoot: string): Promise<ThreadsInde
   try {
     const text = await readFile(path, "utf8");
     const raw = parse(text) as unknown;
-    if (!isRecord(raw)) {
+    return parseThreadsIndex(raw);
-      return {};
-    }
-    const index: ThreadsIndex = {};
-    for (const [threadId, head] of Object.entries(raw)) {
-      if (typeof head === "string") {
-        index[threadId as ThreadId] = head;
-      }
-    }
-    return index;
   } catch (e) {
     const err = e as NodeJS.ErrnoException;
     if (err.code === "ENOENT") {