diff --git a/packages/cli-workflow/src/cli-dispatch.ts b/packages/cli-workflow/src/cli-dispatch.ts
index 2032eac..b88a54a 100644
--- a/packages/cli-workflow/src/cli-dispatch.ts
+++ b/packages/cli-workflow/src/cli-dispatch.ts
@@ -1,5 +1,6 @@
 import { printCliError, printCliLine, printCliWarn } from "./cli-output.js";
 import { cmdAdd, formatAddSuccess, parseAddArgv } from "./cmd-add.js";
+import { cmdCasGet, cmdCasList, cmdCasPut, cmdCasRm } from "./cmd-cas.js";
 import { cmdFork, parseForkArgv } from "./cmd-fork.js";
 import { cmdHistory } from "./cmd-history.js";
 import { cmdKill } from "./cmd-kill.js";
@@ -33,6 +34,10 @@ function usage(): string {
     "  uncaged-workflow thread <id>",
     "  uncaged-workflow thread rm <id>",
     "  uncaged-workflow fork <thread-id> [--from-role <role>]",
+    "  uncaged-workflow cas get <thread-id> <hash>",
+    "  uncaged-workflow cas put <thread-id> <content>",
+    "  uncaged-workflow cas list <thread-id>",
+    "  uncaged-workflow cas rm <thread-id> <hash>",
   ].join("\n");
 }
 
@@ -276,6 +281,95 @@ async function dispatchFork(storageRoot: string, argv: string[]): Promise<number
   return 0;
 }
 
+async function dispatchCasGet(storageRoot: string, rest: string[]): Promise<number> {
+  const threadId = rest[0];
+  const hash = rest[1];
+  if (threadId === undefined || hash === undefined || rest.length > 2) {
+    printCliError(`${usage()}\n\nerror: cas get requires <thread-id> <hash>`);
+    return 1;
+  }
+  const result = await cmdCasGet(storageRoot, threadId, hash);
+  if (!result.ok) {
+    printCliError(result.error);
+    return 1;
+  }
+  printCliLine(result.value);
+  return 0;
+}
+
+async function dispatchCasPut(storageRoot: string, rest: string[]): Promise<number> {
+  const threadId = rest[0];
+  const content = rest[1];
+  if (threadId === undefined || content === undefined || rest.length > 2) {
+    printCliError(`${usage()}\n\nerror: cas put requires <thread-id> <content>`);
+    return 1;
+  }
+  const result = await cmdCasPut(storageRoot, threadId, content);
+  if (!result.ok) {
+    printCliError(result.error);
+    return 1;
+  }
+  printCliLine(result.value);
+  return 0;
+}
+
+async function dispatchCasList(storageRoot: string, rest: string[]): Promise<number> {
+  const threadId = rest[0];
+  if (threadId === undefined || rest.length > 1) {
+    printCliError(`${usage()}\n\nerror: cas list requires <thread-id>`);
+    return 1;
+  }
+  const result = await cmdCasList(storageRoot, threadId);
+  if (!result.ok) {
+    printCliError(result.error);
+    return 1;
+  }
+  for (const hash of result.value) {
+    printCliLine(hash);
+  }
+  return 0;
+}
+
+async function dispatchCasRm(storageRoot: string, rest: string[]): Promise<number> {
+  const threadId = rest[0];
+  const hash = rest[1];
+  if (threadId === undefined || hash === undefined || rest.length > 2) {
+    printCliError(`${usage()}\n\nerror: cas rm requires <thread-id> <hash>`);
+    return 1;
+  }
+  const result = await cmdCasRm(storageRoot, threadId, hash);
+  if (!result.ok) {
+    printCliError(result.error);
+    return 1;
+  }
+  printCliLine(`removed cas entry ${hash}`);
+  return 0;
+}
+
+const CAS_SUBCOMMAND_TABLE: Record<
+  string,
+  (storageRoot: string, rest: string[]) => Promise<number>
+> = {
+  get: dispatchCasGet,
+  put: dispatchCasPut,
+  list: dispatchCasList,
+  rm: dispatchCasRm,
+};
+
+async function dispatchCas(storageRoot: string, argv: string[]): Promise<number> {
+  const sub = argv[0];
+  if (sub === undefined) {
+    printCliError(`${usage()}\n\nerror: unknown cas subcommand: (none)`);
+    return 1;
+  }
+  const handler = CAS_SUBCOMMAND_TABLE[sub];
+  if (handler === undefined) {
+    printCliError(`${usage()}\n\nerror: unknown cas subcommand: ${sub}`);
+    return 1;
+  }
+  return handler(storageRoot, argv.slice(1));
+}
+
 type DispatchFn = (storageRoot: string, argv: string[]) => Promise<number>;
 
 const COMMAND_TABLE: Record<string, DispatchFn> = {
@@ -293,6 +387,7 @@ const COMMAND_TABLE: Record<string, DispatchFn> = {
   threads: dispatchThreads,
   thread: dispatchThreadBranch,
   fork: dispatchFork,
+  cas: dispatchCas,
 };
 
 export async function runCli(storageRoot: string, argv: string[]): Promise<number> {
diff --git a/packages/cli-workflow/src/cmd-cas.ts b/packages/cli-workflow/src/cmd-cas.ts
new file mode 100644
index 0000000..b62a427
--- /dev/null
+++ b/packages/cli-workflow/src/cmd-cas.ts
@@ -0,0 +1,67 @@
+import { dirname, join } from "node:path";
+
+import { createThreadCas, err, ok, type Result } from "@uncaged/workflow";
+
+import { resolveThreadDataPath } from "./thread-scan.js";
+
+function resolveCasDir(threadDataPath: string, threadId: string): string {
+  return join(dirname(threadDataPath), `${threadId}.cas`);
+}
+
+export async function cmdCasGet(
+  storageRoot: string,
+  threadId: string,
+  hash: string,
+): Promise<Result<string, string>> {
+  const dataPath = await resolveThreadDataPath(storageRoot, threadId);
+  if (dataPath === null) {
+    return err(`thread not found: ${threadId}`);
+  }
+  const cas = createThreadCas(resolveCasDir(dataPath, threadId));
+  const content = await cas.get(hash);
+  if (content === null) {
+    return err(`cas entry not found: ${hash}`);
+  }
+  return ok(content);
+}
+
+export async function cmdCasPut(
+  storageRoot: string,
+  threadId: string,
+  content: string,
+): Promise<Result<string, string>> {
+  const dataPath = await resolveThreadDataPath(storageRoot, threadId);
+  if (dataPath === null) {
+    return err(`thread not found: ${threadId}`);
+  }
+  const cas = createThreadCas(resolveCasDir(dataPath, threadId));
+  const hash = await cas.put(content);
+  return ok(hash);
+}
+
+export async function cmdCasList(
+  storageRoot: string,
+  threadId: string,
+): Promise<Result<string[], string>> {
+  const dataPath = await resolveThreadDataPath(storageRoot, threadId);
+  if (dataPath === null) {
+    return err(`thread not found: ${threadId}`);
+  }
+  const cas = createThreadCas(resolveCasDir(dataPath, threadId));
+  const hashes = await cas.list();
+  return ok(hashes);
+}
+
+export async function cmdCasRm(
+  storageRoot: string,
+  threadId: string,
+  hash: string,
+): Promise<Result<void, string>> {
+  const dataPath = await resolveThreadDataPath(storageRoot, threadId);
+  if (dataPath === null) {
+    return err(`thread not found: ${threadId}`);
+  }
+  const cas = createThreadCas(resolveCasDir(dataPath, threadId));
+  await cas.delete(hash);
+  return ok(undefined);
+}
diff --git a/packages/cli-workflow/src/cmd-thread.ts b/packages/cli-workflow/src/cmd-thread.ts
index af5c6b1..1422d89 100644
--- a/packages/cli-workflow/src/cmd-thread.ts
+++ b/packages/cli-workflow/src/cmd-thread.ts
@@ -1,4 +1,4 @@
-import { unlink } from "node:fs/promises";
+import { rm, unlink } from "node:fs/promises";
 import { dirname, join } from "node:path";
 
 import { err, ok, type Result } from "@uncaged/workflow";
@@ -33,10 +33,12 @@ export async function cmdThreadRemove(
   const dir = dirname(dataPath);
   const infoPath = join(dir, `${threadId}.info.jsonl`);
   const runningPath = join(dir, `${threadId}.running`);
+  const casPath = join(dir, `${threadId}.cas`);
 
   await unlink(dataPath);
   await unlink(infoPath).catch(() => {});
   await unlink(runningPath).catch(() => {});
+  await rm(casPath, { recursive: true, force: true });
 
   return ok(undefined);
 }
diff --git a/packages/workflow-template-solve-issue/__tests__/solve-issue-template.test.ts b/packages/workflow-template-solve-issue/__tests__/solve-issue-template.test.ts
index e1cd604..2dd12f9 100644
--- a/packages/workflow-template-solve-issue/__tests__/solve-issue-template.test.ts
+++ b/packages/workflow-template-solve-issue/__tests__/solve-issue-template.test.ts
@@ -16,11 +16,25 @@ import { createSolveIssueRun, solveIssueModerator } from "../src/index.js";
 import type { SolveIssueMeta } from "../src/roles.js";
 
 const DEFAULT_PHASES: PlannerMeta["phases"] = [
-  { hash: "4KNMR2PX", title: "Do the work", name: "phase-a", description: "Do the work", acceptance: "Done" },
+  {
+    hash: "4KNMR2PX",
+    title: "Do the work",
+    name: "phase-a",
+    description: "Do the work",
+    acceptance: "Done",
+  },
 ];
 
 const EXPECT_PLANNER_META: PlannerMeta = {
-  phases: [{ hash: "7BQST3VW", title: "placeholder phase", name: "phase-1", description: "placeholder", acceptance: "placeholder" }],
+  phases: [
+    {
+      hash: "7BQST3VW",
+      title: "placeholder phase",
+      name: "phase-1",
+      description: "placeholder",
+      acceptance: "placeholder",
+    },
+  ],
 };
 
 const EXPECT_CODER_META: CoderMeta = {
@@ -179,8 +193,20 @@ describe("solveIssueModerator", () => {
 
   test("multiple planner phases → coder until all complete, then reviewer", () => {
     const phases: PlannerMeta["phases"] = [
-      { hash: "AA000001", title: "first phase", name: "p1", description: "first", acceptance: "a1" },
-      { hash: "AA000002", title: "second phase", name: "p2", description: "second", acceptance: "a2" },
+      {
+        hash: "AA000001",
+        title: "first phase",
+        name: "p1",
+        description: "first",
+        acceptance: "a1",
+      },
+      {
+        hash: "AA000002",
+        title: "second phase",
+        name: "p2",
+        description: "second",
+        acceptance: "a2",
+      },
     ];
     expect(solveIssueModerator(makeCtx(20, [plannerStep(phases)]))).toBe("coder");
     expect(solveIssueModerator(makeCtx(20, [plannerStep(phases), coderStep("p1")]))).toBe("coder");
@@ -191,10 +217,34 @@ describe("solveIssueModerator", () => {
 
   test("one-shot coder reports only last phase name → reviewer (moderator treats as all phases done)", () => {
     const phases: PlannerMeta["phases"] = [
-      { hash: "BB000001", title: "setup branch", name: "setup-branch", description: "branch", acceptance: "branch exists" },
-      { hash: "BB000002", title: "write tests", name: "write-tests", description: "tests", acceptance: "tests pass" },
-      { hash: "BB000003", title: "verify", name: "verify", description: "verify", acceptance: "ok" },
-      { hash: "BB000004", title: "commit and pr", name: "commit-and-pr", description: "pr", acceptance: "pr open" },
+      {
+        hash: "BB000001",
+        title: "setup branch",
+        name: "setup-branch",
+        description: "branch",
+        acceptance: "branch exists",
+      },
+      {
+        hash: "BB000002",
+        title: "write tests",
+        name: "write-tests",
+        description: "tests",
+        acceptance: "tests pass",
+      },
+      {
+        hash: "BB000003",
+        title: "verify",
+        name: "verify",
+        description: "verify",
+        acceptance: "ok",
+      },
+      {
+        hash: "BB000004",
+        title: "commit and pr",
+        name: "commit-and-pr",
+        description: "pr",
+        acceptance: "pr open",
+      },
     ];
     expect(
       solveIssueModerator(makeCtx(20, [plannerStep(phases), coderStep("commit-and-pr")])),
@@ -203,8 +253,20 @@ describe("solveIssueModerator", () => {
 
   test("completedPhase sentinel when not a planned name → reviewer", () => {
     const phases: PlannerMeta["phases"] = [
-      { hash: "CC000001", title: "first phase", name: "p1", description: "first", acceptance: "a1" },
-      { hash: "CC000002", title: "second phase", name: "p2", description: "second", acceptance: "a2" },
+      {
+        hash: "CC000001",
+        title: "first phase",
+        name: "p1",
+        description: "first",
+        acceptance: "a1",
+      },
+      {
+        hash: "CC000002",
+        title: "second phase",
+        name: "p2",
+        description: "second",
+        acceptance: "a2",
+      },
     ];
     expect(solveIssueModerator(makeCtx(20, [plannerStep(phases), coderStep("all-done")]))).toBe(
       "reviewer",
@@ -213,8 +275,20 @@ describe("solveIssueModerator", () => {
 
   test("incomplete phases → END when max rounds exhausted", () => {
     const phases: PlannerMeta["phases"] = [
-      { hash: "DD000001", title: "first phase", name: "p1", description: "first", acceptance: "a1" },
-      { hash: "DD000002", title: "second phase", name: "p2", description: "second", acceptance: "a2" },
+      {
+        hash: "DD000001",
+        title: "first phase",
+        name: "p1",
+        description: "first",
+        acceptance: "a1",
+      },
+      {
+        hash: "DD000002",
+        title: "second phase",
+        name: "p2",
+        description: "second",
+        acceptance: "a2",
+      },
     ];
     const steps: ModeratorContext<SolveIssueMeta>["steps"] = [plannerStep(phases), coderStep("p1")];
     expect(solveIssueModerator(makeCtx(3, steps))).toBe(END);
diff --git a/packages/workflow/__tests__/cas.test.ts b/packages/workflow/__tests__/cas.test.ts
new file mode 100644
index 0000000..679e242
--- /dev/null
+++ b/packages/workflow/__tests__/cas.test.ts
@@ -0,0 +1,92 @@
+import { afterEach, beforeEach, describe, expect, test } from "bun:test";
+import { mkdtemp, rm } from "node:fs/promises";
+import { tmpdir } from "node:os";
+import { join } from "node:path";
+
+import { createThreadCas } from "../src/cas.js";
+import { hashString } from "../src/hash.js";
+
+describe("createThreadCas", () => {
+  let casDir: string;
+
+  beforeEach(async () => {
+    casDir = await mkdtemp(join(tmpdir(), "cas-test-"));
+  });
+
+  afterEach(async () => {
+    await rm(casDir, { recursive: true, force: true });
+  });
+
+  test("put returns consistent hash for same content", async () => {
+    const cas = createThreadCas(casDir);
+    const h1 = await cas.put("hello world");
+    const h2 = await cas.put("hello world");
+    expect(h1).toBe(h2);
+    expect(h1).toHaveLength(13);
+  });
+
+  test("put returns hash matching hashString", async () => {
+    const cas = createThreadCas(casDir);
+    const content = "some content to store";
+    const h = await cas.put(content);
+    expect(h).toBe(hashString(content));
+  });
+
+  test("get returns stored content", async () => {
+    const cas = createThreadCas(casDir);
+    const content = "line1\nline2\nline3";
+    const h = await cas.put(content);
+    const retrieved = await cas.get(h);
+    expect(retrieved).toBe(content);
+  });
+
+  test("get returns null for missing hash", async () => {
+    const cas = createThreadCas(casDir);
+    const result = await cas.get("0000000000000");
+    expect(result).toBeNull();
+  });
+
+  test("delete removes entry", async () => {
+    const cas = createThreadCas(casDir);
+    const h = await cas.put("to be deleted");
+    await cas.delete(h);
+    const result = await cas.get(h);
+    expect(result).toBeNull();
+  });
+
+  test("delete on missing hash does not throw", async () => {
+    const cas = createThreadCas(casDir);
+    await cas.delete("0000000000000");
+  });
+
+  test("list returns all stored hashes", async () => {
+    const cas = createThreadCas(casDir);
+    const h1 = await cas.put("aaa");
+    const h2 = await cas.put("bbb");
+    const h3 = await cas.put("ccc");
+    const hashes = await cas.list();
+    expect(hashes.sort()).toEqual([h1, h2, h3].sort());
+  });
+
+  test("list returns empty array when cas dir does not exist", async () => {
+    const cas = createThreadCas(join(casDir, "nonexistent"));
+    const hashes = await cas.list();
+    expect(hashes).toEqual([]);
+  });
+
+  test("put is idempotent — same content written twice causes no error", async () => {
+    const cas = createThreadCas(casDir);
+    const h1 = await cas.put("idempotent");
+    const h2 = await cas.put("idempotent");
+    expect(h1).toBe(h2);
+    const content = await cas.get(h1);
+    expect(content).toBe("idempotent");
+  });
+
+  test("different content produces different hashes", async () => {
+    const cas = createThreadCas(casDir);
+    const h1 = await cas.put("alpha");
+    const h2 = await cas.put("beta");
+    expect(h1).not.toBe(h2);
+  });
+});
diff --git a/packages/workflow/src/cas.ts b/packages/workflow/src/cas.ts
new file mode 100644
index 0000000..8e422ea
--- /dev/null
+++ b/packages/workflow/src/cas.ts
@@ -0,0 +1,70 @@
+import { mkdir, readdir, readFile, rename, unlink, writeFile } from "node:fs/promises";
+import { join } from "node:path";
+
+import { hashString } from "./hash.js";
+
+export type CasStore = {
+  put(content: string): Promise<string>;
+  get(hash: string): Promise<string | null>;
+  delete(hash: string): Promise<void>;
+  list(): Promise<string[]>;
+};
+
+export function createThreadCas(casDir: string): CasStore {
+  async function ensureDir(): Promise<void> {
+    await mkdir(casDir, { recursive: true });
+  }
+
+  function filePath(hash: string): string {
+    return join(casDir, `${hash}.txt`);
+  }
+
+  return {
+    async put(content: string): Promise<string> {
+      const hash = hashString(content);
+      await ensureDir();
+      const target = filePath(hash);
+      const tmp = `${target}.tmp.${Date.now()}`;
+      await writeFile(tmp, content, "utf8");
+      await rename(tmp, target);
+      return hash;
+    },
+
+    async get(hash: string): Promise<string | null> {
+      try {
+        return await readFile(filePath(hash), "utf8");
+      } catch (e) {
+        const errObj = e as NodeJS.ErrnoException;
+        if (errObj.code === "ENOENT") {
+          return null;
+        }
+        throw e;
+      }
+    },
+
+    async delete(hash: string): Promise<void> {
+      try {
+        await unlink(filePath(hash));
+      } catch (e) {
+        const errObj = e as NodeJS.ErrnoException;
+        if (errObj.code === "ENOENT") {
+          return;
+        }
+        throw e;
+      }
+    },
+
+    async list(): Promise<string[]> {
+      try {
+        const entries = await readdir(casDir);
+        return entries.filter((name) => name.endsWith(".txt")).map((name) => name.slice(0, -4));
+      } catch (e) {
+        const errObj = e as NodeJS.ErrnoException;
+        if (errObj.code === "ENOENT") {
+          return [];
+        }
+        throw e;
+      }
+    },
+  };
+}
diff --git a/packages/workflow/src/hash.ts b/packages/workflow/src/hash.ts
index 7d2c51c..3f85984 100644
--- a/packages/workflow/src/hash.ts
+++ b/packages/workflow/src/hash.ts
@@ -15,3 +15,10 @@ export function hashWorkflowBundleBytes(data: Uint8Array): string {
   const digest = XXH.h64(0).update(buf).digest();
   return encodeUint64AsCrockford(digestToUint64(digest));
 }
+
+/** XXH64 (seed 0) over a UTF-8 string, encoded as 13-char Crockford Base32. */
+export function hashString(content: string): string {
+  const buf = Buffer.from(content, "utf8");
+  const digest = XXH.h64(0).update(buf).digest();
+  return encodeUint64AsCrockford(digestToUint64(digest));
+}
diff --git a/packages/workflow/src/index.ts b/packages/workflow/src/index.ts
index 47d4564..131de9c 100644
--- a/packages/workflow/src/index.ts
+++ b/packages/workflow/src/index.ts
@@ -7,6 +7,7 @@ export {
 } from "./base32.js";
 export { buildDescriptor } from "./build-descriptor.js";
 export { validateWorkflowBundle, type WorkflowBundleValidationInput } from "./bundle-validator.js";
+export { type CasStore, createThreadCas } from "./cas.js";
 export { createWorkflow } from "./create-workflow.js";
 export {
   type ExecuteThreadIo,
@@ -25,7 +26,7 @@ export {
   selectForkHistoricalSteps,
 } from "./fork-thread.js";
 export { stringifyWorkflowDescriptor } from "./generate-descriptor.js";
-export { hashWorkflowBundleBytes } from "./hash.js";
+export { hashString, hashWorkflowBundleBytes } from "./hash.js";
 export {
   type LlmError,
   llmErrorToCause,