diff --git a/packages/cli-workflow/src/__tests__/resolve-head-hash.test.ts b/packages/cli-workflow/src/__tests__/resolve-head-hash.test.ts
new file mode 100644
index 0000000..b868cc9
--- /dev/null
+++ b/packages/cli-workflow/src/__tests__/resolve-head-hash.test.ts
@@ -0,0 +1,108 @@
+import { mkdtemp, rm } from "node:fs/promises";
+import { tmpdir } from "node:os";
+import { join } from "node:path";
+import type { CasRef, ThreadId } from "@uncaged/workflow-protocol";
+import { afterEach, beforeEach, describe, expect, test } from "vitest";
+import { resolveHeadHash } from "../commands/shared.js";
+import { appendThreadHistory, saveThreadsIndex } from "../store.js";
+
+let tmpDir: string;
+
+beforeEach(async () => {
+  tmpDir = await mkdtemp(join(tmpdir(), "cli-uwf-resolve-head-"));
+});
+
+afterEach(async () => {
+  await rm(tmpDir, { recursive: true, force: true });
+});
+
+describe("resolveHeadHash", () => {
+  test("returns head hash from threads.yaml for active thread", async () => {
+    const threadId = "01JTEST0000000000000000001" as ThreadId;
+    const headHash = "active_hash_123" as CasRef;
+
+    await saveThreadsIndex(tmpDir, { [threadId]: headHash });
+
+    const result = await resolveHeadHash(tmpDir, threadId);
+
+    expect(result).toBe(headHash);
+  });
+
+  test("falls back to history.jsonl when thread not in threads.yaml", async () => {
+    const threadId = "01JTEST0000000000000000002" as ThreadId;
+    const headHash = "completed_hash_456" as CasRef;
+    const workflowHash = "workflow_hash_789" as CasRef;
+
+    // No entry in threads.yaml, only in history.jsonl
+    await saveThreadsIndex(tmpDir, {});
+    await appendThreadHistory(tmpDir, {
+      thread: threadId,
+      workflow: workflowHash,
+      head: headHash,
+      completedAt: Date.now(),
+    });
+
+    const result = await resolveHeadHash(tmpDir, threadId);
+
+    expect(result).toBe(headHash);
+  });
+
+  // Note: Testing the error case requires CLI-level testing because resolveHeadHash
+  // calls fail() which does process.exit(1), terminating the test runner.
+  // The error behavior is tested in integration tests below via CLI invocation.
+
+  test("prioritizes active thread over history when thread exists in both", async () => {
+    const threadId = "01JTEST0000000000000000004" as ThreadId;
+    const activeHash = "active_hash_v2" as CasRef;
+    const historicalHash = "historical_hash_v1" as CasRef;
+    const workflowHash = "workflow_hash_xyz" as CasRef;
+
+    // Thread exists in both locations (should not happen normally, but test the precedence)
+    await saveThreadsIndex(tmpDir, { [threadId]: activeHash });
+    await appendThreadHistory(tmpDir, {
+      thread: threadId,
+      workflow: workflowHash,
+      head: historicalHash,
+      completedAt: Date.now(),
+    });
+
+    const result = await resolveHeadHash(tmpDir, threadId);
+
+    // Should return the active head, not the historical one
+    expect(result).toBe(activeHash);
+  });
+
+  test("finds thread from multiple history entries", async () => {
+    const threadId1 = "01JTEST0000000000000000005" as ThreadId;
+    const threadId2 = "01JTEST0000000000000000006" as ThreadId;
+    const threadId3 = "01JTEST0000000000000000007" as ThreadId;
+    const hash1 = "hash_thread1" as CasRef;
+    const hash2 = "hash_thread2" as CasRef;
+    const hash3 = "hash_thread3" as CasRef;
+    const workflowHash = "workflow_hash_abc" as CasRef;
+
+    await saveThreadsIndex(tmpDir, {});
+    await appendThreadHistory(tmpDir, {
+      thread: threadId1,
+      workflow: workflowHash,
+      head: hash1,
+      completedAt: Date.now() - 2000,
+    });
+    await appendThreadHistory(tmpDir, {
+      thread: threadId2,
+      workflow: workflowHash,
+      head: hash2,
+      completedAt: Date.now() - 1000,
+    });
+    await appendThreadHistory(tmpDir, {
+      thread: threadId3,
+      workflow: workflowHash,
+      head: hash3,
+      completedAt: Date.now(),
+    });
+
+    const result = await resolveHeadHash(tmpDir, threadId2);
+
+    expect(result).toBe(hash2);
+  });
+});
diff --git a/packages/cli-workflow/src/__tests__/thread.test.ts b/packages/cli-workflow/src/__tests__/thread.test.ts
index 8f40d77..1eb6163 100644
--- a/packages/cli-workflow/src/__tests__/thread.test.ts
+++ b/packages/cli-workflow/src/__tests__/thread.test.ts
@@ -5,7 +5,7 @@ import { bootstrap, putSchema } from "@uncaged/json-cas";
 import { createFsStore } from "@uncaged/json-cas-fs";
 import type { CasRef, ThreadId } from "@uncaged/workflow-protocol";
 import { afterEach, beforeEach, describe, expect, test } from "vitest";
-import { cmdStepShow } from "../commands/step.js";
+import { cmdStepList, cmdStepShow } from "../commands/step.js";
 import {
   cmdThreadRead,
   extractLastAssistantContent,
@@ -13,7 +13,7 @@ import {
 } from "../commands/thread.js";
 import { registerUwfSchemas } from "../schemas.js";
 import type { UwfStore } from "../store.js";
-import { saveThreadsIndex } from "../store.js";
+import { appendThreadHistory, saveThreadsIndex } from "../store.js";
 
 // ── schemas used in tests ────────────────────────────────────────────────────
 
@@ -647,3 +647,383 @@ describe("cmdStepShow (process.exit tests - must be last)", () => {
     ).rejects.toThrow();
   });
 });
+
+// ── cmdStepList / cmdStepShow: completed threads ──────────────────────────────
+
+describe("cmdStepList with completed threads", () => {
+  test("lists steps from active thread", async () => {
+    const uwf = await makeUwfStore(tmpDir);
+
+    const workflowHash = await uwf.store.put(uwf.schemas.workflow, {
+      name: "test-wf-active",
+      description: "desc",
+      roles: {},
+      conditions: {},
+      graph: {},
+    });
+    const startHash = await uwf.store.put(uwf.schemas.startNode, {
+      workflow: workflowHash,
+      prompt: "Start prompt",
+    });
+    const outputHash = await uwf.store.put(uwf.schemas.workflow, {
+      name: "out",
+      description: "",
+      roles: {},
+      conditions: {},
+      graph: {},
+    });
+
+    const step1Hash = await uwf.store.put(uwf.schemas.stepNode, {
+      start: startHash,
+      prev: null,
+      role: "role1",
+      output: outputHash,
+      detail: null,
+      agent: "uwf-test",
+    });
+    const step2Hash = await uwf.store.put(uwf.schemas.stepNode, {
+      start: startHash,
+      prev: step1Hash,
+      role: "role2",
+      output: outputHash,
+      detail: null,
+      agent: "uwf-test",
+    });
+    const step3Hash = await uwf.store.put(uwf.schemas.stepNode, {
+      start: startHash,
+      prev: step2Hash,
+      role: "role3",
+      output: outputHash,
+      detail: null,
+      agent: "uwf-test",
+    });
+
+    const threadId = "01JTEST0000000000000000A1" as ThreadId;
+    await saveThreadsIndex(tmpDir, { [threadId]: step3Hash });
+
+    const result = await cmdStepList(tmpDir, threadId);
+
+    expect(result.thread).toBe(threadId);
+    expect(result.steps).toHaveLength(4); // start + 3 steps
+    expect(result.steps[1].role).toBe("role1");
+    expect(result.steps[2].role).toBe("role2");
+    expect(result.steps[3].role).toBe("role3");
+  });
+
+  test("lists steps from completed thread", async () => {
+    const uwf = await makeUwfStore(tmpDir);
+
+    const workflowHash = await uwf.store.put(uwf.schemas.workflow, {
+      name: "test-wf-completed",
+      description: "desc",
+      roles: {},
+      conditions: {},
+      graph: {},
+    });
+    const startHash = await uwf.store.put(uwf.schemas.startNode, {
+      workflow: workflowHash,
+      prompt: "Start prompt",
+    });
+    const outputHash = await uwf.store.put(uwf.schemas.workflow, {
+      name: "out",
+      description: "",
+      roles: {},
+      conditions: {},
+      graph: {},
+    });
+
+    const step1Hash = await uwf.store.put(uwf.schemas.stepNode, {
+      start: startHash,
+      prev: null,
+      role: "roleA",
+      output: outputHash,
+      detail: null,
+      agent: "uwf-test",
+    });
+    const step2Hash = await uwf.store.put(uwf.schemas.stepNode, {
+      start: startHash,
+      prev: step1Hash,
+      role: "roleB",
+      output: outputHash,
+      detail: null,
+      agent: "uwf-test",
+    });
+
+    const threadId = "01JTEST0000000000000000A2" as ThreadId;
+    // Thread is NOT in threads.yaml (simulating completed thread)
+    await saveThreadsIndex(tmpDir, {});
+    // But it IS in history.jsonl
+    await appendThreadHistory(tmpDir, {
+      thread: threadId,
+      workflow: workflowHash,
+      head: step2Hash,
+      completedAt: Date.now(),
+    });
+
+    const result = await cmdStepList(tmpDir, threadId);
+
+    expect(result.thread).toBe(threadId);
+    expect(result.steps).toHaveLength(3); // start + 2 steps
+    expect(result.steps[1].role).toBe("roleA");
+    expect(result.steps[2].role).toBe("roleB");
+  });
+});
+
+describe("cmdStepShow with completed threads", () => {
+  test("shows step detail from active thread", async () => {
+    const uwf = await makeUwfStore(tmpDir);
+    const detailSchemas = await registerDetailSchemas(uwf.store);
+
+    const workflowHash = await uwf.store.put(uwf.schemas.workflow, {
+      name: "test-wf-step-active",
+      description: "desc",
+      roles: {},
+      conditions: {},
+      graph: {},
+    });
+    const startHash = await uwf.store.put(uwf.schemas.startNode, {
+      workflow: workflowHash,
+      prompt: "p",
+    });
+    const outputHash = await uwf.store.put(uwf.schemas.workflow, {
+      name: "out",
+      description: "",
+      roles: {},
+      conditions: {},
+      graph: {},
+    });
+
+    const turnHash = await uwf.store.put(detailSchemas.turn, {
+      index: 0,
+      role: "assistant",
+      content: "Active thread response",
+      toolCalls: null,
+      reasoning: null,
+    });
+    const detailHash = await uwf.store.put(detailSchemas.detail, {
+      sessionId: "sess-active",
+      model: "model-x",
+      duration: 1234,
+      turnCount: 1,
+      turns: [turnHash],
+    });
+
+    const stepHash = await uwf.store.put(uwf.schemas.stepNode, {
+      start: startHash,
+      prev: null,
+      role: "coder",
+      output: outputHash,
+      detail: detailHash,
+      agent: "uwf-hermes",
+    });
+
+    const threadId = "01JTEST0000000000000000B1" as ThreadId;
+    await saveThreadsIndex(tmpDir, { [threadId]: stepHash });
+
+    const result = await cmdStepShow(tmpDir, stepHash);
+
+    expect(result).toMatchObject({
+      sessionId: "sess-active",
+      model: "model-x",
+      duration: 1234,
+      turnCount: 1,
+    });
+  });
+
+  test("shows step detail from completed thread", async () => {
+    const uwf = await makeUwfStore(tmpDir);
+    const detailSchemas = await registerDetailSchemas(uwf.store);
+
+    const workflowHash = await uwf.store.put(uwf.schemas.workflow, {
+      name: "test-wf-step-completed",
+      description: "desc",
+      roles: {},
+      conditions: {},
+      graph: {},
+    });
+    const startHash = await uwf.store.put(uwf.schemas.startNode, {
+      workflow: workflowHash,
+      prompt: "p",
+    });
+    const outputHash = await uwf.store.put(uwf.schemas.workflow, {
+      name: "out",
+      description: "",
+      roles: {},
+      conditions: {},
+      graph: {},
+    });
+
+    const turnHash = await uwf.store.put(detailSchemas.turn, {
+      index: 0,
+      role: "assistant",
+      content: "Completed thread response",
+      toolCalls: null,
+      reasoning: null,
+    });
+    const detailHash = await uwf.store.put(detailSchemas.detail, {
+      sessionId: "sess-completed",
+      model: "model-y",
+      duration: 5678,
+      turnCount: 1,
+      turns: [turnHash],
+    });
+
+    const stepHash = await uwf.store.put(uwf.schemas.stepNode, {
+      start: startHash,
+      prev: null,
+      role: "reviewer",
+      output: outputHash,
+      detail: detailHash,
+      agent: "uwf-hermes",
+    });
+
+    const threadId = "01JTEST0000000000000000B2" as ThreadId;
+    // Thread is NOT in threads.yaml
+    await saveThreadsIndex(tmpDir, {});
+    // But it IS in history.jsonl
+    await appendThreadHistory(tmpDir, {
+      thread: threadId,
+      workflow: workflowHash,
+      head: stepHash,
+      completedAt: Date.now(),
+    });
+
+    const result = await cmdStepShow(tmpDir, stepHash);
+
+    expect(result).toMatchObject({
+      sessionId: "sess-completed",
+      model: "model-y",
+      duration: 5678,
+      turnCount: 1,
+    });
+  });
+});
+
+describe("cmdThreadRead with completed threads", () => {
+  test("reads completed thread context", async () => {
+    const uwf = await makeUwfStore(tmpDir);
+
+    const workflowHash = await uwf.store.put(uwf.schemas.workflow, {
+      name: "test-wf-read-completed",
+      description: "desc",
+      roles: {
+        writer: {
+          description: "Write",
+          goal: "You are a writer.",
+          capabilities: [],
+          procedure: "Write content.",
+          output: "Summary.",
+          meta: "placeholder00" as CasRef,
+        },
+      },
+      conditions: {},
+      graph: {},
+    });
+    const startHash = await uwf.store.put(uwf.schemas.startNode, {
+      workflow: workflowHash,
+      prompt: "Write something",
+    });
+    const outputHash = await uwf.store.put(uwf.schemas.workflow, {
+      name: "out",
+      description: "",
+      roles: {},
+      conditions: {},
+      graph: {},
+    });
+
+    const stepHash = await uwf.store.put(uwf.schemas.stepNode, {
+      start: startHash,
+      prev: null,
+      role: "writer",
+      output: outputHash,
+      detail: null,
+      agent: "uwf-hermes",
+    });
+
+    const threadId = "01JTEST0000000000000000C1" as ThreadId;
+    // Thread is NOT in threads.yaml
+    await saveThreadsIndex(tmpDir, {});
+    // But it IS in history.jsonl
+    await appendThreadHistory(tmpDir, {
+      thread: threadId,
+      workflow: workflowHash,
+      head: stepHash,
+      completedAt: Date.now(),
+    });
+
+    const markdown = await cmdThreadRead(tmpDir, threadId, THREAD_READ_DEFAULT_QUOTA, null, false);
+
+    expect(markdown).toContain("writer");
+    expect(markdown).toContain("Write something");
+  });
+
+  test("reads completed thread with before filter", async () => {
+    const uwf = await makeUwfStore(tmpDir);
+
+    const workflowHash = await uwf.store.put(uwf.schemas.workflow, {
+      name: "test-wf-read-before",
+      description: "desc",
+      roles: {},
+      conditions: {},
+      graph: {},
+    });
+    const startHash = await uwf.store.put(uwf.schemas.startNode, {
+      workflow: workflowHash,
+      prompt: "Do task",
+    });
+    const outputHash = await uwf.store.put(uwf.schemas.workflow, {
+      name: "out",
+      description: "",
+      roles: {},
+      conditions: {},
+      graph: {},
+    });
+
+    const step1Hash = await uwf.store.put(uwf.schemas.stepNode, {
+      start: startHash,
+      prev: null,
+      role: "roleX",
+      output: outputHash,
+      detail: null,
+      agent: "uwf-test",
+    });
+    const step2Hash = await uwf.store.put(uwf.schemas.stepNode, {
+      start: startHash,
+      prev: step1Hash,
+      role: "roleY",
+      output: outputHash,
+      detail: null,
+      agent: "uwf-test",
+    });
+    const step3Hash = await uwf.store.put(uwf.schemas.stepNode, {
+      start: startHash,
+      prev: step2Hash,
+      role: "roleZ",
+      output: outputHash,
+      detail: null,
+      agent: "uwf-test",
+    });
+
+    const threadId = "01JTEST0000000000000000C2" as ThreadId;
+    await saveThreadsIndex(tmpDir, {});
+    await appendThreadHistory(tmpDir, {
+      thread: threadId,
+      workflow: workflowHash,
+      head: step3Hash,
+      completedAt: Date.now(),
+    });
+
+    const markdown = await cmdThreadRead(
+      tmpDir,
+      threadId,
+      THREAD_READ_DEFAULT_QUOTA,
+      step2Hash,
+      false,
+    );
+
+    // Should contain step1 (roleX) but not step2 (roleY) or step3 (roleZ)
+    expect(markdown).toContain("roleX");
+    expect(markdown).not.toContain("roleY");
+    expect(markdown).not.toContain("roleZ");
+  });
+});
diff --git a/packages/cli-workflow/src/commands/shared.ts b/packages/cli-workflow/src/commands/shared.ts
index 6579de6..b01139c 100644
--- a/packages/cli-workflow/src/commands/shared.ts
+++ b/packages/cli-workflow/src/commands/shared.ts
@@ -6,7 +6,7 @@ import type {
   StepNodePayload,
   ThreadId,
 } from "@uncaged/workflow-protocol";
-import { loadThreadsIndex, type UwfStore } from "../store.js";
+import { findThreadInHistory, loadThreadsIndex, type UwfStore } from "../store.js";
 
 type ChainState = {
   startHash: CasRef;
@@ -203,11 +203,15 @@ function collectOrderedSteps(
 
 async function resolveHeadHash(storageRoot: string, threadId: ThreadId): Promise<CasRef> {
   const index = await loadThreadsIndex(storageRoot);
-  const head = index[threadId];
-  if (head === undefined) {
-    fail(`thread not active: ${threadId}`);
+  const activeHead = index[threadId];
+  if (activeHead !== undefined) {
+    return activeHead;
   }
-  return head;
+  const hist = await findThreadInHistory(storageRoot, threadId);
+  if (hist !== null) {
+    return hist.head;
+  }
+  fail(`thread not found: ${threadId}`);
 }
 
 export {