diff --git a/packages/workflow-protocol/package.json b/packages/workflow-protocol/package.json
new file mode 100644
index 0000000..c0aebdc
--- /dev/null
+++ b/packages/workflow-protocol/package.json
@@ -0,0 +1,18 @@
+{
+  "name": "@uncaged/workflow-protocol",
+  "version": "0.1.0",
+  "type": "module",
+  "exports": {
+    ".": {
+      "types": "./dist/index.d.ts",
+      "import": "./src/index.ts"
+    }
+  },
+  "peerDependencies": {
+    "zod": "^4.0.0"
+  },
+  "devDependencies": {
+    "zod": "^4.0.0",
+    "typescript": "^5.8.3"
+  }
+}
diff --git a/packages/workflow-protocol/src/index.ts b/packages/workflow-protocol/src/index.ts
new file mode 100644
index 0000000..5992630
--- /dev/null
+++ b/packages/workflow-protocol/src/index.ts
@@ -0,0 +1,40 @@
+// ── Types ──────────────────────────────────────────────────────────
+
+export type {
+	Result,
+	CasStore,
+	WorkflowRoleSchema,
+	WorkflowRoleDescriptor,
+	WorkflowDescriptor,
+	RoleMeta,
+	RoleOutput,
+	StartStep,
+	RoleStep,
+	ThreadContext,
+	ModeratorContext,
+	AgentContext,
+	ExtractContext,
+	WorkflowCompletion,
+	WorkflowResult,
+	LlmProvider,
+	ProviderConfig,
+	ResolvedModel,
+	WorkflowConfig,
+	ExtractFn,
+	AgentFn,
+	AgentBinding,
+	WorkflowRuntime,
+	WorkflowFn,
+	RoleDefinition,
+	Moderator,
+	WorkflowDefinition,
+	AdvanceOutcome,
+} from "./types.js";
+
+// ── Constants ──────────────────────────────────────────────────────
+
+export { START, END } from "./types.js";
+
+// ── Constructor functions ──────────────────────────────────────────
+
+export { ok, err } from "./result.js";
diff --git a/packages/workflow-protocol/src/result.ts b/packages/workflow-protocol/src/result.ts
new file mode 100644
index 0000000..f9b25c0
--- /dev/null
+++ b/packages/workflow-protocol/src/result.ts
@@ -0,0 +1,9 @@
+import type { Result } from "./types.js";
+
+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-protocol/src/types.ts b/packages/workflow-protocol/src/types.ts
new file mode 100644
index 0000000..07bf57e
--- /dev/null
+++ b/packages/workflow-protocol/src/types.ts
@@ -0,0 +1,167 @@
+import type * as z from "zod/v4";
+
+// ── Constants ──────────────────────────────────────────────────────
+
+export const START = "__start__" as const;
+export const END = "__end__" as const;
+
+// ── Result ─────────────────────────────────────────────────────────
+
+export type Result<T, E = Error> = { ok: true; value: T } | { ok: false; error: E };
+
+// ── CAS ────────────────────────────────────────────────────────────
+
+export type CasStore = {
+	put(content: string): Promise<string>;
+	get(hash: string): Promise<string | null>;
+	delete(hash: string): Promise<void>;
+	list(): Promise<string[]>;
+};
+
+// ── Workflow Descriptor ────────────────────────────────────────────
+
+export type WorkflowRoleSchema = Record<string, unknown>;
+
+export type WorkflowRoleDescriptor = {
+	description: string;
+	schema: WorkflowRoleSchema;
+};
+
+export type WorkflowDescriptor = {
+	description: string;
+	roles: Record<string, WorkflowRoleDescriptor>;
+};
+
+// ── Role & Thread ──────────────────────────────────────────────────
+
+export type RoleMeta = Record<string, Record<string, unknown>>;
+
+export type RoleOutput = {
+	role: string;
+	contentHash: string;
+	meta: Record<string, unknown>;
+	refs: string[];
+};
+
+export type StartStep = {
+	role: typeof START;
+	content: string;
+	meta: { maxRounds: number };
+	timestamp: number;
+};
+
+export type RoleStep<M extends RoleMeta> = {
+	[K in keyof M & string]: {
+		role: K;
+		meta: M[K];
+		contentHash: string;
+		refs: string[];
+		timestamp: number;
+	};
+}[keyof M & string];
+
+export type ThreadContext<M extends RoleMeta = RoleMeta> = {
+	threadId: string;
+	depth: number;
+	start: StartStep;
+	steps: RoleStep<M>[];
+};
+
+export type ModeratorContext<M extends RoleMeta = RoleMeta> = ThreadContext<M>;
+
+export type AgentContext<M extends RoleMeta = RoleMeta> = ModeratorContext<M> & {
+	currentRole: {
+		name: string;
+		systemPrompt: string;
+	};
+};
+
+export type ExtractContext<M extends RoleMeta = RoleMeta> = AgentContext<M> & {
+	agentContent: string;
+};
+
+// ── Workflow Completion ────────────────────────────────────────────
+
+export type WorkflowCompletion = {
+	returnCode: number;
+	summary: string;
+};
+
+export type WorkflowResult = WorkflowCompletion & {
+	rootHash: string;
+};
+
+// ── LLM Provider ───────────────────────────────────────────────────
+
+export type LlmProvider = {
+	baseUrl: string;
+	apiKey: string;
+	model: string;
+};
+
+export type ProviderConfig = {
+	baseUrl: string;
+	apiKey: string;
+};
+
+export type ResolvedModel = {
+	baseUrl: string;
+	apiKey: string;
+	model: string;
+};
+
+export type WorkflowConfig = {
+	maxDepth: number;
+	supervisorInterval: number;
+	providers: Record<string, ProviderConfig>;
+	models: Record<string, string>;
+};
+
+// ── Functions ──────────────────────────────────────────────────────
+
+export type ExtractFn = <T extends Record<string, unknown>>(
+	schema: z.ZodType<T>,
+	prompt: string,
+	ctx: ExtractContext,
+) => Promise<T>;
+
+export type AgentFn = (ctx: AgentContext) => Promise<string>;
+
+export type AgentBinding = {
+	agent: AgentFn;
+	overrides: Partial<Record<string, AgentFn>> | null;
+};
+
+// ── Workflow Runtime & Definition ──────────────────────────────────
+
+export type WorkflowRuntime = {
+	cas: CasStore;
+	extract: ExtractFn;
+};
+
+export type WorkflowFn = (
+	thread: ThreadContext,
+	runtime: WorkflowRuntime,
+) => AsyncGenerator<RoleOutput, WorkflowCompletion>;
+
+export type RoleDefinition<Meta extends Record<string, unknown>> = {
+	description: string;
+	systemPrompt: string;
+	extractPrompt: string;
+	schema: z.ZodType<Meta>;
+	extractRefs: ((meta: Meta) => string[]) | null;
+};
+
+export type Moderator<M extends RoleMeta> = (
+	ctx: ModeratorContext<M>,
+) => (keyof M & string) | typeof END;
+
+export type WorkflowDefinition<M extends RoleMeta> = {
+	description: string;
+	roles: { [K in keyof M & string]: RoleDefinition<M[K]> };
+	moderator: Moderator<M>;
+};
+
+export type AdvanceOutcome<M extends RoleMeta> =
+	| { kind: "complete"; completion: WorkflowCompletion }
+	| { kind: "yield"; output: RoleOutput; step: RoleStep<M> };
diff --git a/packages/workflow-protocol/tsconfig.json b/packages/workflow-protocol/tsconfig.json
new file mode 100644
index 0000000..75eba9f
--- /dev/null
+++ b/packages/workflow-protocol/tsconfig.json
@@ -0,0 +1,8 @@
+{
+  "extends": "../../tsconfig.json",
+  "compilerOptions": {
+    "rootDir": "src",
+    "outDir": "dist"
+  },
+  "include": ["src"]
+}