diff --git a/docs/rfc-001-workflow-engine.md b/docs/rfc-001-workflow-engine.md
index ff2804d..1ba54a0 100644
--- a/docs/rfc-001-workflow-engine.md
+++ b/docs/rfc-001-workflow-engine.md
@@ -202,7 +202,99 @@ No concurrency control or timeout settings in the registry — those belong to e
 |---------|-------------|
 | `uncaged-workflow fork <thread-id> [--from-role <role>]` | Fork from a historical thread state |
 
-## 8. Design Decisions & Rationale
+## 8. Workflow Execution Model: Role, Moderator, Agent
+
+A workflow is a finite-state automaton driven by three concepts:
+
+### Core Types
+
+```typescript
+/** Sentinel values for automaton control flow. */
+const START = "__start__" as const;
+const END = "__end__" as const;
+
+/** Maps role names → their meta types. Single generic drives all inference. */
+type RoleMeta = Record<string, Record<string, unknown>>;
+
+/** Typed output of a Role execution. */
+type RoleResult<Meta> = { content: string; meta: Meta };
+
+/** Engine start frame: initial prompt + thread identity. */
+type StartStep = {
+  role: START;
+  content: string;              // the user prompt
+  meta: { maxRounds: number; threadId: string };
+  timestamp: number;
+};
+
+/** A completed role step in the thread. */
+type RoleStep<M extends RoleMeta> = {
+  [K in keyof M & string]: { role: K; meta: M[K]; content: string; timestamp: number };
+}[keyof M & string];
+
+/** Thread-scoped context passed to roles and moderator. */
+type ThreadContext<M extends RoleMeta = RoleMeta> = {
+  threadId: string;
+  start: StartStep;
+  steps: RoleStep<M>[];
+};
+
+/**
+ * A Role — receives full thread context, returns typed content + meta.
+ * Implementation can be an agent, LLM call, script, HTTP request, etc.
+ */
+type Role<Meta> = (ctx: ThreadContext) => Promise<RoleResult<Meta>>;
+
+/**
+ * An Agent — raw string output interface for LLM/CLI adapters.
+ * Structured meta is extracted by the role's extract layer.
+ */
+type AgentFn = (ctx: ThreadContext, systemPrompt: string) => Promise<string>;
+
+/**
+ * The Moderator — a pure routing function.
+ * Receives the full thread context (start + all prior steps).
+ * On initial call, `steps` is empty.
+ * Returns the next role name or END to terminate.
+ */
+type Moderator<M extends RoleMeta> = (ctx: ThreadContext<M>) => (keyof M & string) | END;
+
+/** Complete workflow definition as authored by users. */
+type WorkflowDefinition<M extends RoleMeta> = {
+  name: string;
+  roles: { [K in keyof M & string]: Role<M[K]> };
+  moderator: Moderator<M>;
+};
+```
+
+### Execution Flow
+
+```
+START (prompt) → Moderator → Role A → Moderator → Role B → ... → Moderator → END
+```
+
+1. Engine creates a `StartStep` with the user prompt and maxRounds
+2. Moderator is called with `steps = []`, returns the first role name
+3. Role executes, appends a `RoleStep` to the thread
+4. Moderator is called again with updated steps, returns next role or END
+5. Repeat until END or maxRounds reached
+
+### Responsibilities
+
+| Component | Responsibility | Purity |
+|-----------|---------------|--------|
+| **Moderator** | Route to next role based on thread state | Pure function, no side effects |
+| **Role** | Execute a step (call LLM, run script, etc.) | Async, may have side effects |
+| **AgentFn** | Low-level LLM/CLI invocation adapter | Async, side effects |
+
+### Key Constraints
+
+- Moderator is **synchronous and pure** — no I/O, no state mutation
+- Roles receive the **full thread context** (not just the last message)
+- Round count = `steps.length`; max rounds in `start.meta.maxRounds`
+- The `meta` field on each step is **typed per role** via the `RoleMeta` generic
+
+## 9. Design Decisions & Rationale
 
 ### Why single-file ESM?
 - Hash = version. No ambiguity.
diff --git a/packages/cli-workflow/tsconfig.json b/packages/cli-workflow/tsconfig.json
new file mode 100644
index 0000000..3160acf
--- /dev/null
+++ b/packages/cli-workflow/tsconfig.json
@@ -0,0 +1,21 @@
+{
+  "compilerOptions": {
+    "target": "ES2022",
+    "lib": ["ES2022"],
+    "module": "NodeNext",
+    "moduleResolution": "NodeNext",
+    "strict": true,
+    "exactOptionalPropertyTypes": true,
+    "esModuleInterop": true,
+    "skipLibCheck": true,
+    "forceConsistentCasingInFileNames": true,
+    "declaration": true,
+    "declarationMap": true,
+    "sourceMap": true,
+    "composite": true,
+    "outDir": "dist",
+    "rootDir": "src"
+  },
+  "references": [{ "path": "../workflow" }],
+  "include": ["src/**/*.ts"]
+}
diff --git a/packages/workflow/package.json b/packages/workflow/package.json
index 3d4529f..f82b3c5 100644
--- a/packages/workflow/package.json
+++ b/packages/workflow/package.json
@@ -7,5 +7,13 @@
   "scripts": {
     "build": "echo 'TODO'",
     "test": "bun test"
+  },
+  "dependencies": {
+    "acorn": "^8.16.0",
+    "xxhashjs": "^0.2.2",
+    "yaml": "^2.8.4"
+  },
+  "devDependencies": {
+    "@types/acorn": "^6.0.4"
   }
 }
diff --git a/packages/workflow/src/base32.ts b/packages/workflow/src/base32.ts
new file mode 100644
index 0000000..683abe7
--- /dev/null
+++ b/packages/workflow/src/base32.ts
@@ -0,0 +1,77 @@
+import { err, ok, type Result } from "./result.js";
+
+/** Crockford Base32 alphabet (no I, L, O, U). */
+export const CROCKFORD_BASE32_ALPHABET = "0123456789ABCDEFGHJKMNPQRSTVWXZ";
+
+const DECODE_MAP: Record<string, number> = (() => {
+  const map: Record<string, number> = {};
+  for (let i = 0; i < CROCKFORD_BASE32_ALPHABET.length; i++) {
+    map[CROCKFORD_BASE32_ALPHABET[i]] = i;
+  }
+  return map;
+})();
+
+function padBitCount(bitLength: number): number {
+  const r = bitLength % 5;
+  return r === 0 ? 0 : 5 - r;
+}
+
+/**
+ * Encode an integer using exactly `bitLength` significant bits, MSB-first,
+ * with the minimum number of leading zero bits so the total is a multiple of 5.
+ */
+export function encodeCrockfordBase32Bits(value: bigint, bitLength: number): string {
+  if (bitLength <= 0) {
+    throw new Error("bitLength must be positive");
+  }
+  const padBits = padBitCount(bitLength);
+  const totalBits = bitLength + padBits;
+  const charCount = totalBits / 5;
+  const shifted = value << BigInt(padBits);
+  let result = "";
+  for (let i = 0; i < charCount; i++) {
+    const shift = totalBits - 5 * (i + 1);
+    const quintet = Number((shifted >> BigInt(shift)) & 0x1fn);
+    result += CROCKFORD_BASE32_ALPHABET[quintet];
+  }
+  return result;
+}
+
+export function decodeCrockfordBase32Bits(encoded: string, bitLength: number): Result<bigint, Error> {
+  if (bitLength <= 0) {
+    return err(new Error("bitLength must be positive"));
+  }
+  const padBits = padBitCount(bitLength);
+  const totalBits = encoded.length * 5;
+  if (totalBits !== bitLength + padBits) {
+    return err(new Error("encoded length does not match bitLength"));
+  }
+  let shifted = 0n;
+  for (let i = 0; i < encoded.length; i++) {
+    const ch = encoded[i];
+    if (ch === undefined) {
+      return err(new Error("invalid encoded string"));
+    }
+    const upper = ch.toUpperCase();
+    const val = DECODE_MAP[upper];
+    if (val === undefined) {
+      return err(new Error(`invalid Crockford Base32 character: ${ch}`));
+    }
+    shifted = (shifted << 5n) | BigInt(val);
+  }
+  return ok(shifted >> BigInt(padBits));
+}
+
+/** XXH64-sized value (13 Crockford chars). */
+export function encodeUint64AsCrockford(value: bigint): string {
+  const masked = value & 0xffff_ffff_ffff_ffffn;
+  return encodeCrockfordBase32Bits(masked, 64);
+}
+
+export function decodeCrockfordToUint64(encoded: string): Result<bigint, Error> {
+  const decoded = decodeCrockfordBase32Bits(encoded, 64);
+  if (!decoded.ok) {
+    return decoded;
+  }
+  return ok(decoded.value & 0xffff_ffff_ffff_ffffn);
+}
diff --git a/packages/workflow/src/bundle-validator.ts b/packages/workflow/src/bundle-validator.ts
new file mode 100644
index 0000000..7f16a36
--- /dev/null
+++ b/packages/workflow/src/bundle-validator.ts
@@ -0,0 +1,142 @@
+import { isBuiltin } from "node:module";
+
+import * as acorn from "acorn";
+import type { Node, Program } from "acorn";
+
+import { err, ok, type Result } from "./result.js";
+
+export type WorkflowBundleValidationInput = {
+  /** Absolute or relative path (used for `.esm.js` suffix checks). */
+  filePath: string;
+  /** UTF-8 source of the bundle. */
+  source: string;
+};
+
+function endsWithEsmJs(path: string): boolean {
+  return path.endsWith(".esm.js");
+}
+
+function isAllowedImportSpecifier(spec: string): boolean {
+  if (spec.length === 0) {
+    return false;
+  }
+  if (spec.startsWith(".") || spec.startsWith("/")) {
+    return false;
+  }
+  return isBuiltin(spec);
+}
+
+function walk(node: Node, visit: (n: Node) => void): void {
+  visit(node);
+  for (const key of Object.keys(node)) {
+    const val = (node as Record<string, unknown>)[key];
+    if (val === null || val === undefined) {
+      continue;
+    }
+    if (Array.isArray(val)) {
+      for (const item of val) {
+        if (item !== null && typeof item === "object" && "type" in item) {
+          walk(item as Node, visit);
+        }
+      }
+    } else if (typeof val === "object" && "type" in val) {
+      walk(val as Node, visit);
+    }
+  }
+}
+
+function programHasDefaultExport(body: readonly Node[]): boolean {
+  for (const stmt of body) {
+    if (stmt.type === "ExportDefaultDeclaration") {
+      return true;
+    }
+  }
+  return false;
+}
+
+/**
+ * Validate RFC-001 bundle rules: single-file ESM shape, default export,
+ * no dynamic `import()`, static imports restricted to Node builtins.
+ */
+export function validateWorkflowBundle(input: WorkflowBundleValidationInput): Result<void, string> {
+  if (!endsWithEsmJs(input.filePath)) {
+    return err('workflow bundle file must use the ".esm.js" suffix');
+  }
+
+  let ast: Node;
+  try {
+    ast = acorn.parse(input.source, {
+      ecmaVersion: 2022,
+      sourceType: "module",
+      locations: false,
+    }) as Node;
+  } catch (e) {
+    const message = e instanceof Error ? e.message : String(e);
+    return err(`failed to parse module: ${message}`);
+  }
+
+  if (ast.type !== "Program") {
+    return err("internal error: expected Program root");
+  }
+
+  const program = ast as Program;
+  if (!programHasDefaultExport(program.body)) {
+    return err("workflow bundle must have a default export");
+  }
+
+  let walkError: string | null = null;
+  walk(ast, (n) => {
+    if (walkError !== null) {
+      return;
+    }
+    if (n.type === "ImportExpression") {
+      walkError = "dynamic import() is not allowed in workflow bundles";
+      return;
+    }
+    if (n.type === "ImportDeclaration") {
+      const src = n.source;
+      if (src.type !== "Literal" || typeof src.value !== "string") {
+        walkError = "only static string import specifiers are allowed";
+        return;
+      }
+      if (!isAllowedImportSpecifier(src.value)) {
+        walkError = `disallowed import specifier "${src.value}" (only Node built-ins are allowed)`;
+      }
+      return;
+    }
+    if (n.type === "ExportNamedDeclaration" && n.source !== null && n.source !== undefined) {
+      const src = n.source;
+      if (src.type !== "Literal" || typeof src.value !== "string") {
+        walkError = "only static string re-export specifiers are allowed";
+        return;
+      }
+      if (!isAllowedImportSpecifier(src.value)) {
+        walkError = `disallowed re-export specifier "${src.value}" (only Node built-ins are allowed)`;
+      }
+      return;
+    }
+    if (n.type === "ExportAllDeclaration") {
+      const src = n.source;
+      if (src.type !== "Literal" || typeof src.value !== "string") {
+        walkError = "only static string export-all specifiers are allowed";
+        return;
+      }
+      if (!isAllowedImportSpecifier(src.value)) {
+        walkError = `disallowed export-all specifier "${src.value}" (only Node built-ins are allowed)`;
+      }
+      return;
+    }
+    if (n.type === "CallExpression") {
+      const c = n.callee;
+      if (c.type === "Identifier" && c.name === "require") {
+        walkError = "require() is not allowed in workflow bundles";
+      }
+    }
+  });
+
+  if (walkError !== null) {
+    return err(walkError);
+  }
+
+  return ok(undefined);
+}
diff --git a/packages/workflow/src/hash.ts b/packages/workflow/src/hash.ts
new file mode 100644
index 0000000..7d2c51c
--- /dev/null
+++ b/packages/workflow/src/hash.ts
@@ -0,0 +1,17 @@
+import { Buffer } from "node:buffer";
+
+import XXH from "xxhashjs";
+
+import { encodeUint64AsCrockford } from "./base32.js";
+
+function digestToUint64(digest: { toString(radix?: number): string }): bigint {
+  const hex = digest.toString(16).padStart(16, "0");
+  return BigInt(`0x${hex}`);
+}
+
+/** XXH64 (seed 0) over bundle bytes, encoded as 13-char Crockford Base32. */
+export function hashWorkflowBundleBytes(data: Uint8Array): string {
+  const buf = Buffer.from(data.buffer, data.byteOffset, data.byteLength);
+  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 322c6a9..93e00a4 100644
--- a/packages/workflow/src/index.ts
+++ b/packages/workflow/src/index.ts
@@ -1,2 +1,32 @@
-// @uncaged/workflow - core library
-export {};
+export {
+  CROCKFORD_BASE32_ALPHABET,
+  decodeCrockfordBase32Bits,
+  decodeCrockfordToUint64,
+  encodeCrockfordBase32Bits,
+  encodeUint64AsCrockford,
+} from "./base32.js";
+export { validateWorkflowBundle, type WorkflowBundleValidationInput } from "./bundle-validator.js";
+export { hashWorkflowBundleBytes } from "./hash.js";
+export {
+  createLogger,
+  type CreateLoggerOptions,
+  type LogFn,
+  type LoggerSink,
+} from "./logger.js";
+export {
+  getRegisteredWorkflow,
+  listRegisteredWorkflowNames,
+  parseWorkflowRegistryYaml,
+  readWorkflowRegistry,
+  registerWorkflowVersion,
+  stringifyWorkflowRegistryYaml,
+  unregisterWorkflow,
+  workflowRegistryPath,
+  writeWorkflowRegistry,
+  type WorkflowHistoryEntry,
+  type WorkflowRegistryEntry,
+  type WorkflowRegistryFile,
+} from "./registry.js";
+export { err, ok, type Result } from "./result.js";
+export { getDefaultWorkflowStorageRoot } from "./storage-root.js";
+export { generateUlid } from "./ulid.js";
diff --git a/packages/workflow/src/logger.ts b/packages/workflow/src/logger.ts
new file mode 100644
index 0000000..7f70316
--- /dev/null
+++ b/packages/workflow/src/logger.ts
@@ -0,0 +1,57 @@
+import { appendFileSync } from "node:fs";
+
+const TAG_LENGTH = 8;
+
+function assertValidLogTag(tag: string): void {
+  if (tag.length !== TAG_LENGTH) {
+    throw new Error(`log tag must be exactly ${TAG_LENGTH} characters`);
+  }
+  for (let i = 0; i < tag.length; i++) {
+    const ch = tag[i];
+    if (ch === undefined) {
+      throw new Error("log tag validation failed");
+    }
+    const upper = ch.toUpperCase();
+    if (!/[0-9A-HJKMNP-TV-Z]/.test(upper)) {
+      throw new Error(`invalid Crockford Base32 character in log tag: ${ch}`);
+    }
+  }
+}
+
+export type LoggerSink =
+  | { kind: "stderr" }
+  | { kind: "file"; path: string };
+
+export type CreateLoggerOptions = {
+  sink: LoggerSink;
+};
+
+export type LogFn = (tag: string, content: string) => void;
+
+/** Append one JSONL log record: `{ tag, content, timestamp }` per RFC-001. */
+export function createLogger(options: CreateLoggerOptions): LogFn {
+  if (options.sink.kind === "stderr") {
+    return (tag: string, content: string) => {
+      assertValidLogTag(tag);
+      const line =
+        `${JSON.stringify({
+          tag: tag.toUpperCase(),
+          content,
+          timestamp: Date.now(),
+        })}\n`;
+      process.stderr.write(line);
+    };
+  }
+
+  const filePath = options.sink.path;
+  return (tag: string, content: string) => {
+    assertValidLogTag(tag);
+    const line =
+      `${JSON.stringify({
+        tag: tag.toUpperCase(),
+        content,
+        timestamp: Date.now(),
+      })}\n`;
+    appendFileSync(filePath, line, "utf8");
+  };
+}
diff --git a/packages/workflow/src/registry.ts b/packages/workflow/src/registry.ts
new file mode 100644
index 0000000..d9f073b
--- /dev/null
+++ b/packages/workflow/src/registry.ts
@@ -0,0 +1,164 @@
+import { mkdir, readFile, writeFile } from "node:fs/promises";
+import { dirname, join } from "node:path";
+
+import { parseDocument, stringify } from "yaml";
+
+import { err, ok, type Result } from "./result.js";
+
+export type WorkflowHistoryEntry = {
+  hash: string;
+  timestamp: number;
+};
+
+export type WorkflowRegistryEntry = {
+  hash: string;
+  timestamp: number;
+  history: WorkflowHistoryEntry[];
+};
+
+export type WorkflowRegistryFile = {
+  workflows: Record<string, WorkflowRegistryEntry>;
+};
+
+export function workflowRegistryPath(storageRoot: string): string {
+  return join(storageRoot, "workflow.yaml");
+}
+
+function emptyRegistry(): WorkflowRegistryFile {
+  return { workflows: {} };
+}
+
+function normalizeRegistry(raw: unknown): Result<WorkflowRegistryFile, Error> {
+  if (raw === null || typeof raw !== "object") {
+    return err(new Error("registry root must be a mapping"));
+  }
+  const root = raw as Record<string, unknown>;
+  const workflowsRaw = root.workflows;
+  if (workflowsRaw === null || workflowsRaw === undefined || typeof workflowsRaw !== "object") {
+    return err(new Error('registry must contain a "workflows" mapping'));
+  }
+  const workflows: Record<string, WorkflowRegistryEntry> = {};
+  for (const [name, entryRaw] of Object.entries(workflowsRaw)) {
+    if (entryRaw === null || typeof entryRaw !== "object") {
+      return err(new Error(`workflow "${name}" must be a mapping`));
+    }
+    const e = entryRaw as Record<string, unknown>;
+    const hash = e.hash;
+    const timestamp = e.timestamp;
+    const historyRaw = e.history;
+    if (typeof hash !== "string") {
+      return err(new Error(`workflow "${name}" must have a string hash`));
+    }
+    if (typeof timestamp !== "number" || !Number.isFinite(timestamp)) {
+      return err(new Error(`workflow "${name}" must have a finite numeric timestamp`));
+    }
+    if (!Array.isArray(historyRaw)) {
+      return err(new Error(`workflow "${name}" must have a history array`));
+    }
+    const history: WorkflowHistoryEntry[] = [];
+    for (let i = 0; i < historyRaw.length; i++) {
+      const h = historyRaw[i];
+      if (h === null || typeof h !== "object") {
+        return err(new Error(`workflow "${name}" history[${i}] must be a mapping`));
+      }
+      const he = h as Record<string, unknown>;
+      if (typeof he.hash !== "string" || typeof he.timestamp !== "number" || !Number.isFinite(he.timestamp)) {
+        return err(new Error(`workflow "${name}" history[${i}] must have hash and timestamp`));
+      }
+      history.push({ hash: he.hash, timestamp: he.timestamp });
+    }
+    workflows[name] = { hash, timestamp, history };
+  }
+  return ok({ workflows });
+}
+
+export function parseWorkflowRegistryYaml(text: string): Result<WorkflowRegistryFile, Error> {
+  if (text.trim() === "") {
+    return ok(emptyRegistry());
+  }
+  let doc: unknown;
+  try {
+    doc = parseDocument(text).toJSON();
+  } catch (e) {
+    return err(e instanceof Error ? e : new Error(String(e)));
+  }
+  return normalizeRegistry(doc);
+}
+
+export function stringifyWorkflowRegistryYaml(registry: WorkflowRegistryFile): string {
+  return `${stringify(registry, { indent: 2 })}\n`;
+}
+
+export async function readWorkflowRegistry(storageRoot: string): Promise<Result<WorkflowRegistryFile, Error>> {
+  const path = workflowRegistryPath(storageRoot);
+  let text: string;
+  try {
+    text = await readFile(path, "utf8");
+  } catch (e) {
+    const errObj = e as NodeJS.ErrnoException;
+    if (errObj.code === "ENOENT") {
+      return ok(emptyRegistry());
+    }
+    return err(errObj instanceof Error ? errObj : new Error(String(e)));
+  }
+  return parseWorkflowRegistryYaml(text);
+}
+
+export async function writeWorkflowRegistry(
+  storageRoot: string,
+  registry: WorkflowRegistryFile,
+): Promise<Result<void, Error>> {
+  const path = workflowRegistryPath(storageRoot);
+  try {
+    await mkdir(dirname(path), { recursive: true });
+    await writeFile(path, stringifyWorkflowRegistryYaml(registry), "utf8");
+  } catch (e) {
+    return err(e instanceof Error ? e : new Error(String(e)));
+  }
+  return ok(undefined);
+}
+
+export function listRegisteredWorkflowNames(registry: WorkflowRegistryFile): string[] {
+  return Object.keys(registry.workflows).sort();
+}
+
+export function getRegisteredWorkflow(
+  registry: WorkflowRegistryFile,
+  name: string,
+): WorkflowRegistryEntry | null {
+  const entry = registry.workflows[name];
+  if (entry === undefined) {
+    return null;
+  }
+  return entry;
+}
+
+/** Register or upgrade a workflow version, moving the previous head into `history`. */
+export function registerWorkflowVersion(
+  registry: WorkflowRegistryFile,
+  name: string,
+  hash: string,
+  timestamp: number,
+): WorkflowRegistryFile {
+  const prev = registry.workflows[name];
+  const baseHistory = prev === undefined ? [] : prev.history;
+  const history: WorkflowHistoryEntry[] =
+    prev === undefined
+      ? baseHistory
+      : [{ hash: prev.hash, timestamp: prev.timestamp }, ...baseHistory];
+  const next: WorkflowRegistryEntry = { hash, timestamp, history };
+  return {
+    workflows: { ...registry.workflows, [name]: next },
+  };
+}
+
+export function unregisterWorkflow(
+  registry: WorkflowRegistryFile,
+  name: string,
+): Result<WorkflowRegistryFile, Error> {
+  if (registry.workflows[name] === undefined) {
+    return err(new Error(`workflow not registered: ${name}`));
+  }
+  const { [name]: _removed, ...rest } = registry.workflows;
+  return ok({ workflows: rest });
+}
diff --git a/packages/workflow/src/result.ts b/packages/workflow/src/result.ts
new file mode 100644
index 0000000..39e40a2
--- /dev/null
+++ b/packages/workflow/src/result.ts
@@ -0,0 +1,9 @@
+export type Result<T, E = Error> = { ok: true; value: T } | { ok: false; error: E };
+
+export function ok<T>(value: T): Result<T, never> {
+  return { ok: true, value };
+}
+
+export function err<E>(error: E): Result<never, E> {
+  return { ok: false, error };
+}
diff --git a/packages/workflow/src/storage-root.ts b/packages/workflow/src/storage-root.ts
new file mode 100644
index 0000000..81c20d8
--- /dev/null
+++ b/packages/workflow/src/storage-root.ts
@@ -0,0 +1,7 @@
+import { homedir } from "node:os";
+import { join } from "node:path";
+
+/** Default filesystem root for workflow data (`~/.uncaged/workflow`). */
+export function getDefaultWorkflowStorageRoot(): string {
+  return join(homedir(), ".uncaged", "workflow");
+}
diff --git a/packages/workflow/src/ulid.ts b/packages/workflow/src/ulid.ts
new file mode 100644
index 0000000..60938cf
--- /dev/null
+++ b/packages/workflow/src/ulid.ts
@@ -0,0 +1,28 @@
+import { encodeCrockfordBase32Bits } from "./base32.js";
+
+const ULID_TIME_BITS = 48;
+const ULID_RANDOM_BITS = 80;
+
+function readRandomUint80(): bigint {
+  const bytes = new Uint8Array(10);
+  crypto.getRandomValues(bytes);
+  let x = 0n;
+  for (let i = 0; i < bytes.length; i++) {
+    x = (x << 8n) | BigInt(bytes[i]);
+  }
+  return x & ((1n << 80n) - 1n);
+}
+
+/**
+ * Generate a ULID using Crockford Base32: 10 timestamp chars + 16 random chars.
+ * Timestamp uses 48 bits of Unix time in milliseconds.
+ */
+export function generateUlid(nowMs: number): string {
+  if (!Number.isFinite(nowMs) || nowMs < 0 || nowMs >= 2 ** ULID_TIME_BITS) {
+    throw new Error("nowMs must be a finite number in [0, 2^48)");
+  }
+  const time = BigInt(Math.floor(nowMs));
+  const rand = readRandomUint80();
+  const payload = (time << BigInt(ULID_RANDOM_BITS)) | rand;
+  return encodeCrockfordBase32Bits(payload, ULID_TIME_BITS + ULID_RANDOM_BITS);
+}
diff --git a/packages/workflow/tsconfig.json b/packages/workflow/tsconfig.json
new file mode 100644
index 0000000..944ec14
--- /dev/null
+++ b/packages/workflow/tsconfig.json
@@ -0,0 +1,20 @@
+{
+  "compilerOptions": {
+    "target": "ES2022",
+    "lib": ["ES2022"],
+    "module": "NodeNext",
+    "moduleResolution": "NodeNext",
+    "strict": true,
+    "exactOptionalPropertyTypes": true,
+    "esModuleInterop": true,
+    "skipLibCheck": true,
+    "forceConsistentCasingInFileNames": true,
+    "declaration": true,
+    "declarationMap": true,
+    "sourceMap": true,
+    "composite": true,
+    "outDir": "dist",
+    "rootDir": "src"
+  },
+  "include": ["src/**/*.ts", "xxhashjs.d.ts"]
+}
diff --git a/packages/workflow/xxhashjs.d.ts b/packages/workflow/xxhashjs.d.ts
new file mode 100644
index 0000000..beee6d4
--- /dev/null
+++ b/packages/workflow/xxhashjs.d.ts
@@ -0,0 +1,17 @@
+declare module "xxhashjs" {
+  type Digest = {
+    toString(radix?: number): string;
+  };
+
+  type Hasher64 = {
+    update(data: Buffer): Hasher64;
+    digest(): Digest;
+  };
+
+  type XXH = {
+    h64(seed: number): Hasher64;
+  };
+
+  const XXH: XXH;
+  export default XXH;
+}