diff --git a/packages/protocol/src/__tests__/thread-index.test.ts b/packages/protocol/src/__tests__/thread-index.test.ts
index 2d58e7e..be2bf5c 100644
--- a/packages/protocol/src/__tests__/thread-index.test.ts
+++ b/packages/protocol/src/__tests__/thread-index.test.ts
@@ -1,6 +1,7 @@
 import { describe, expect, test } from "vitest";
 import {
   createThreadIndexEntry,
+  markThreadCompleted,
   markThreadSuspended,
   normalizeThreadIndexEntry,
   parseThreadsIndex,
@@ -16,6 +17,8 @@ describe("thread-index", () => {
       head: "0123456789ABC",
       suspendedRole: null,
       suspendMessage: null,
+      status: "idle",
+      completedAt: null,
     });
   });
 
@@ -29,6 +32,40 @@ describe("thread-index", () => {
       head: "0123456789ABC",
       suspendedRole: "worker",
       suspendMessage: "Please clarify: Which API?",
+      status: "idle",
+      completedAt: null,
+    });
+  });
+
+  test("normalizeThreadIndexEntry preserves status and completedAt from new data", () => {
+    const entry = normalizeThreadIndexEntry({
+      head: "0123456789ABC",
+      suspendedRole: null,
+      suspendMessage: null,
+      status: "completed",
+      completedAt: 1234567890,
+    });
+    expect(entry).toEqual({
+      head: "0123456789ABC",
+      suspendedRole: null,
+      suspendMessage: null,
+      status: "completed",
+      completedAt: 1234567890,
+    });
+  });
+
+  test("normalizeThreadIndexEntry defaults status=idle, completedAt=null for old data", () => {
+    const entry = normalizeThreadIndexEntry({
+      head: "0123456789ABC",
+      suspendedRole: null,
+      suspendMessage: null,
+    });
+    expect(entry).toEqual({
+      head: "0123456789ABC",
+      suspendedRole: null,
+      suspendMessage: null,
+      status: "idle",
+      completedAt: null,
     });
   });
 
@@ -47,10 +84,24 @@ describe("thread-index", () => {
       head: "0123456789ABC",
       suspendedRole: "worker",
       suspendMessage: "Please clarify: Which API?",
+      status: "suspended",
     });
   });
 
-  test("updateThreadHead clears suspend metadata", () => {
+  test("serialize completed entry as object", () => {
+    const entry = markThreadCompleted(
+      createThreadIndexEntry("0123456789ABC"),
+      "completed",
+      1234567890,
+    );
+    expect(serializeThreadIndexEntry(entry)).toEqual({
+      head: "0123456789ABC",
+      status: "completed",
+      completedAt: 1234567890,
+    });
+  });
+
+  test("updateThreadHead clears suspend metadata and resets status to idle", () => {
     const suspended = markThreadSuspended(
       createThreadIndexEntry("OLDHEAD0123456"),
       "worker",
@@ -61,6 +112,44 @@ describe("thread-index", () => {
       head: "NEWHEAD01234567",
       suspendedRole: null,
       suspendMessage: null,
+      status: "idle",
+      completedAt: null,
+    });
+  });
+
+  test("markThreadSuspended sets status to suspended", () => {
+    const entry = createThreadIndexEntry("0123456789ABC");
+    const suspended = markThreadSuspended(entry, "worker", "Waiting for input");
+    expect(suspended).toEqual({
+      head: "0123456789ABC",
+      suspendedRole: "worker",
+      suspendMessage: "Waiting for input",
+      status: "suspended",
+      completedAt: null,
+    });
+  });
+
+  test("markThreadCompleted sets status and completedAt", () => {
+    const entry = createThreadIndexEntry("0123456789ABC");
+    const completed = markThreadCompleted(entry, "completed", 1234567890);
+    expect(completed).toEqual({
+      head: "0123456789ABC",
+      suspendedRole: null,
+      suspendMessage: null,
+      status: "completed",
+      completedAt: 1234567890,
+    });
+  });
+
+  test("markThreadCompleted with cancelled status", () => {
+    const entry = createThreadIndexEntry("0123456789ABC");
+    const cancelled = markThreadCompleted(entry, "cancelled", 9876543210);
+    expect(cancelled).toEqual({
+      head: "0123456789ABC",
+      suspendedRole: null,
+      suspendMessage: null,
+      status: "cancelled",
+      completedAt: 9876543210,
     });
   });
 
@@ -71,6 +160,7 @@ describe("thread-index", () => {
         head: "HEAD00000000002",
         suspendedRole: "reviewer",
         suspendMessage: "Need input",
+        status: "suspended",
       },
     };
     const parsed = parseThreadsIndex(raw);
diff --git a/packages/protocol/src/index.ts b/packages/protocol/src/index.ts
index 9f8bffa..d62c170 100644
--- a/packages/protocol/src/index.ts
+++ b/packages/protocol/src/index.ts
@@ -5,6 +5,7 @@ export {
 } from "./schemas.js";
 export {
   createThreadIndexEntry,
+  markThreadCompleted,
   markThreadSuspended,
   normalizeThreadIndexEntry,
   parseThreadsIndex,
diff --git a/packages/protocol/src/thread-index.ts b/packages/protocol/src/thread-index.ts
index 91daaaf..f5f0720 100644
--- a/packages/protocol/src/thread-index.ts
+++ b/packages/protocol/src/thread-index.ts
@@ -15,10 +15,14 @@ export function normalizeThreadIndexEntry(raw: unknown): ThreadIndexEntry | null
   }
   const suspendedRole = rec.suspendedRole;
   const suspendMessage = rec.suspendMessage;
+  const status = rec.status;
+  const completedAt = rec.completedAt;
   return {
     head: head as CasRef,
     suspendedRole: typeof suspendedRole === "string" ? suspendedRole : null,
     suspendMessage: typeof suspendMessage === "string" ? suspendMessage : null,
+    status: typeof status === "string" ? (status as "idle" | "running" | "suspended" | "completed" | "cancelled") : "idle",
+    completedAt: typeof completedAt === "number" ? completedAt : null,
   };
 }
 
@@ -27,6 +31,8 @@ export function createThreadIndexEntry(head: CasRef): ThreadIndexEntry {
     head,
     suspendedRole: null,
     suspendMessage: null,
+    status: "idle",
+    completedAt: null,
   };
 }
 
@@ -35,6 +41,8 @@ export function updateThreadHead(_entry: ThreadIndexEntry, head: CasRef): Thread
     head,
     suspendedRole: null,
     suspendMessage: null,
+    status: "idle",
+    completedAt: null,
   };
 }
 
@@ -47,21 +55,58 @@ export function markThreadSuspended(
     head: entry.head,
     suspendedRole,
     suspendMessage,
+    status: "suspended",
+    completedAt: null,
+  };
+}
+
+export function markThreadCompleted(
+  entry: ThreadIndexEntry,
+  status: "completed" | "cancelled",
+  now: number,
+): ThreadIndexEntry {
+  return {
+    head: entry.head,
+    suspendedRole: null,
+    suspendMessage: null,
+    status,
+    completedAt: now,
   };
 }
 
 /** Serialize for variable store — compact string when not suspended. */
 export function serializeThreadIndexEntry(
   entry: ThreadIndexEntry,
-): string | Record<string, string> {
-  if (entry.suspendedRole === null || entry.suspendMessage === null) {
+): string | Record<string, string | number> {
+  // Compact string only for idle status with no suspend metadata
+  if (entry.status === "idle" && entry.suspendedRole === null && entry.suspendMessage === null && entry.completedAt === null) {
     return entry.head;
   }
-  return {
+
+  // Build object representation
+  const obj: Record<string, string | number> = {
     head: entry.head,
-    suspendedRole: entry.suspendedRole,
-    suspendMessage: entry.suspendMessage,
   };
+
+  // Include suspend metadata if present
+  if (entry.suspendedRole !== null) {
+    obj.suspendedRole = entry.suspendedRole;
+  }
+  if (entry.suspendMessage !== null) {
+    obj.suspendMessage = entry.suspendMessage;
+  }
+
+  // Always include status if not idle
+  if (entry.status !== "idle") {
+    obj.status = entry.status;
+  }
+
+  // Include completedAt if present
+  if (entry.completedAt !== null) {
+    obj.completedAt = entry.completedAt;
+  }
+
+  return obj;
 }
 
 export function parseThreadsIndex(raw: unknown): ThreadsIndex {
@@ -80,8 +125,8 @@ export function parseThreadsIndex(raw: unknown): ThreadsIndex {
 
 export function serializeThreadsIndex(
   index: ThreadsIndex,
-): Record<string, string | Record<string, string>> {
-  const out: Record<string, string | Record<string, string>> = {};
+): Record<string, string | Record<string, string | number>> {
+  const out: Record<string, string | Record<string, string | number>> = {};
   for (const [threadId, entry] of Object.entries(index)) {
     out[threadId] = serializeThreadIndexEntry(entry);
   }
diff --git a/packages/protocol/src/types.ts b/packages/protocol/src/types.ts
index 82b39f7..333eeac 100644
--- a/packages/protocol/src/types.ts
+++ b/packages/protocol/src/types.ts
@@ -118,6 +118,8 @@ export type ThreadIndexEntry = {
   head: CasRef;
   suspendedRole: string | null;
   suspendMessage: string | null;
+  status: ThreadStatus;
+  completedAt: number | null;
 };
 
 /** uwf thread steps — single step entry */