diff --git a/packages/sdk/src/authored-flow-loader.ts b/packages/sdk/src/authored-flow-loader.ts
index dde721aee..23193dcec 100644
--- a/packages/sdk/src/authored-flow-loader.ts
+++ b/packages/sdk/src/authored-flow-loader.ts
@@ -1,6 +1,6 @@
-import { accessSync, constants } from 'node:fs';
+import { accessSync, constants, realpathSync } from 'node:fs';
 import { createRequire } from 'node:module';
-import { resolve } from 'node:path';
+import { dirname, resolve } from 'node:path';
 import { pathToFileURL } from 'node:url';
 import {
   getAuthoredFlowDefinition,
@@ -9,7 +9,7 @@ import {
 } from './authored-flow.js';
 
 export class AuthoredFlowLoadError extends Error {
-  constructor(message: string) {
+  constructor(message: string, readonly kind: 'invalid_spec' | 'use_not_found' | 'use_invalid' | 'use_cycle' = 'invalid_spec') {
     super(message);
     this.name = 'AuthoredFlowLoadError';
   }
@@ -28,10 +28,67 @@ export interface LoadedAuthoredFlow {
    * `getAuthoredFlowDefinition` import.
    */
   readonly getDefinition: GetFlowDefinition;
+  /** Dependency-first load order, each canonical absolute path appearing once. */
+  readonly graph: readonly LoadedAuthoredFlowNode[];
+}
+
+export interface LoadedAuthoredFlowNode {
+  readonly path: string;
+  readonly handle: FlowHandle;
+  readonly getDefinition: GetFlowDefinition;
+  readonly use: readonly string[];
 }
 
 /** Import and validate a direct-run module without executing its authored body. */
 export async function loadAuthoredFlow(path: string): Promise<LoadedAuthoredFlow> {
+  const loaded = new Map<string, LoadedAuthoredFlowNode>();
+  const visiting = new Set<string>();
+  async function visit(sourcePath: string, isRoot = false): Promise<LoadedAuthoredFlowNode> {
+    let absolutePath: string;
+    try {
+      absolutePath = realpathSync(sourcePath);
+      accessSync(absolutePath, constants.R_OK);
+    } catch {
+      throw new AuthoredFlowLoadError(`Flow "${sourcePath}" is not readable.`, isRoot ? 'invalid_spec' : 'use_not_found');
+    }
+    if (visiting.has(absolutePath)) {
+      throw new AuthoredFlowLoadError(`Flow use cycle: ${[...visiting, absolutePath].join(' -> ')}`, 'use_cycle');
+    }
+    const cached = loaded.get(absolutePath);
+    if (cached !== undefined) return cached;
+    visiting.add(absolutePath);
+    try {
+      const { handle, getDefinition } = await importAuthoredFlow(absolutePath);
+      const dependencies: string[] = [];
+      for (const entry of getDefinition(handle).header.use ?? []) {
+        // Validate again at the SDK boundary: the author's surface package may
+        // be a different version from the runtime loading the graph.
+        if (!/^(?:\.\/|\.\.\/).+\.flow\.ts$/.test(entry) || /[?#\\\\]/.test(entry)) {
+          throw new AuthoredFlowLoadError(`Flow "${absolutePath}" use must contain relative .flow.ts paths.`, 'use_invalid');
+        }
+        const child = await visit(resolve(dirname(absolutePath), entry));
+        if (dependencies.includes(child.path)) {
+          throw new AuthoredFlowLoadError(`Flow "${absolutePath}" declares the same use path more than once.`, 'use_invalid');
+        }
+        dependencies.push(child.path);
+      }
+      const node = Object.freeze({ path: absolutePath, handle, getDefinition, use: Object.freeze(dependencies) });
+      loaded.set(absolutePath, node);
+      return node;
+    } catch (error) {
+      if (error instanceof AuthoredFlowLoadError && error.kind === 'invalid_spec' && !isRoot) {
+        throw new AuthoredFlowLoadError(error.message, 'use_invalid');
+      }
+      throw error;
+    } finally {
+      visiting.delete(absolutePath);
+    }
+  }
+  const root = await visit(resolve(path), true);
+  return Object.freeze({ handle: root.handle, getDefinition: root.getDefinition, graph: Object.freeze([...loaded.values()]) });
+}
+
+async function importAuthoredFlow(path: string): Promise<Pick<LoadedAuthoredFlow, 'handle' | 'getDefinition'>> {
   const absolutePath = resolve(path);
   try {
     accessSync(absolutePath, constants.R_OK);
diff --git a/packages/sdk/tests/authored-use-loader.test.ts b/packages/sdk/tests/authored-use-loader.test.ts
new file mode 100644
index 000000000..4f083417b
--- /dev/null
+++ b/packages/sdk/tests/authored-use-loader.test.ts
@@ -0,0 +1,59 @@
+import { mkdtempSync, mkdirSync, rmSync, symlinkSync, writeFileSync } from 'node:fs';
+import { tmpdir } from 'node:os';
+import { join, resolve } from 'node:path';
+import { afterEach, describe, expect, it } from 'vitest';
+import { loadAuthoredFlow } from '../src/authored-flow-loader.js';
+
+const directories: string[] = [];
+afterEach(() => {
+  for (const directory of directories.splice(0)) rmSync(directory, { recursive: true, force: true });
+});
+
+function fixture(files: Record<string, string[]>): string {
+  const directory = mkdtempSync(join(tmpdir(), 'flows-use-'));
+  directories.push(directory);
+  mkdirSync(join(directory, 'node_modules', '@relayflows'), { recursive: true });
+  symlinkSync(resolve('node_modules/@relayflows/surface'), join(directory, 'node_modules/@relayflows/surface'));
+  writeFileSync(join(directory, 'package.json'), '{"type":"module"}');
+  for (const [name, use] of Object.entries(files)) {
+    writeFileSync(join(directory, `${name}.flow.ts`), `
+      import { flow } from '@relayflows/surface';
+      export default flow(${JSON.stringify(name)}, { use: ${JSON.stringify(use)} }, async f => {
+        throw new Error('loader must never execute authored bodies');
+      });
+    `);
+  }
+  return directory;
+}
+
+describe('authored use graph loader', () => {
+  it('loads a diamond in dependency order with one node per canonical path', async () => {
+    const directory = fixture({
+      root: ['./mid1.flow.ts', './mid2.flow.ts'],
+      mid1: ['./leaf.flow.ts'], mid2: ['./leaf.flow.ts'], leaf: [],
+    });
+    const loaded = await loadAuthoredFlow(join(directory, 'root.flow.ts'));
+    expect(loaded.graph.map(node => node.handle.name)).toEqual(['leaf', 'mid1', 'mid2', 'root']);
+    expect(loaded.graph[1]?.use).toEqual(loaded.graph[2]?.use);
+    expect(Object.isFrozen(loaded.graph)).toBe(true);
+  });
+
+  it('refuses a transitive use cycle before executing any body', async () => {
+    const directory = fixture({ a: ['./b.flow.ts'], b: ['./a.flow.ts'] });
+    await expect(loadAuthoredFlow(join(directory, 'a.flow.ts'))).rejects.toMatchObject({ kind: 'use_cycle' });
+  });
+
+  it('refuses a missing declared flow', async () => {
+    const directory = fixture({ root: ['./missing.flow.ts'] });
+    await expect(loadAuthoredFlow(join(directory, 'root.flow.ts'))).rejects.toMatchObject({ kind: 'use_not_found' });
+  });
+
+  it.each([
+    'throw new Error("import failed");',
+    'export default { name: "forged" };',
+  ])('refuses a declared module that cannot supply a flow: %s', async source => {
+    const directory = fixture({ root: ['./invalid.flow.ts'] });
+    writeFileSync(join(directory, 'invalid.flow.ts'), source);
+    await expect(loadAuthoredFlow(join(directory, 'root.flow.ts'))).rejects.toMatchObject({ kind: 'use_invalid' });
+  });
+});
diff --git a/packages/surface/src/flow.ts b/packages/surface/src/flow.ts
index fa1f358d8..1323f004d 100644
--- a/packages/surface/src/flow.ts
+++ b/packages/surface/src/flow.ts
@@ -2,6 +2,8 @@ import type { Ctx } from "./context.js";
 
 /** Optional escalation header; the empty header is the common case. */
 export interface FlowHeader {
+  /** Relative paths to reusable authored flows composed by this body. */
+  use?: string[];
   identity?: string;
   memory?: { script?: boolean; agent?: boolean };
   budget?: string;
@@ -12,6 +14,7 @@ export interface FlowHeader {
 export type FlowBody<Input = unknown> = (f: Ctx, input: Input) => Promise<void>;
 
 export interface ReadonlyFlowHeader {
+  readonly use?: readonly string[];
   readonly identity?: string;
   readonly memory?: Readonly<{ script?: boolean; agent?: boolean }>;
   readonly budget?: string;
@@ -114,6 +117,7 @@ function isStoredDefinition(
 
 function freezeHeader(header: FlowHeader): ReadonlyFlowHeader {
   const unknownFields = Object.keys(header).filter((field) => ![
+    "use",
     "identity",
     "memory",
     "budget",
@@ -137,6 +141,7 @@ function freezeHeader(header: FlowHeader): ReadonlyFlowHeader {
           : { mcp: Object.freeze([...header.tools.mcp]) }),
       });
   return Object.freeze({
+    ...(header.use === undefined ? {} : { use: Object.freeze([...header.use]) }),
     ...(header.identity === undefined ? {} : { identity: header.identity }),
     ...(memory === undefined ? {} : { memory }),
     ...(header.budget === undefined ? {} : { budget: header.budget }),
@@ -150,12 +155,20 @@ function assertFlowHeader(value: unknown, flowName: string): asserts value is Fl
   assertHeaderObject(value, at);
   assertKnownKeys(
     value,
-    ["identity", "memory", "budget", "tools", "workspace"],
+    ["use", "identity", "memory", "budget", "tools", "workspace"],
     at,
   );
   assertOptionalString(value, "identity", at);
   assertOptionalString(value, "budget", at);
   assertOptionalString(value, "workspace", at);
+  assertOptionalStringArray(value, "use", at);
+  if (value.use !== undefined) {
+    for (const path of value.use as string[]) {
+      if (!/^(?:\.\/|\.\.\/).+\.flow\.ts$/.test(path) || /[?#\\\\]/.test(path)) {
+        throw new TypeError(`${at}.use: expected relative .flow.ts paths`);
+      }
+    }
+  }
 
   if (value.memory !== undefined) {
     assertHeaderObject(value.memory, `${at}.memory`);
@@ -238,8 +251,13 @@ function assertOptionalStringArray(
   const candidate = value[key];
   if (
     candidate !== undefined
-    && (!Array.isArray(candidate) || candidate.some((item) => typeof item !== "string"))
+    && (!Array.isArray(candidate) || Array.from(candidate).some((item) => typeof item !== "string"))
   ) {
     throw new TypeError(`${at}.${key}: expected an array of strings`);
   }
+  if (key === "use" && Array.isArray(candidate)
+    && (candidate.some((item) => item.trim().length === 0)
+      || new Set(candidate).size !== candidate.length)) {
+    throw new TypeError(`${at}.${key}: expected unique nonempty paths`);
+  }
 }
diff --git a/packages/surface/tests/flow.test.ts b/packages/surface/tests/flow.test.ts
index 5c74aa81d..3d9af98da 100644
--- a/packages/surface/tests/flow.test.ts
+++ b/packages/surface/tests/flow.test.ts
@@ -10,6 +10,27 @@ import {
 import { getFlowDefinition } from "@relayflows/surface/runtime";
 
 describe("flow", () => {
+  it("retains an immutable copy of declared relative flow imports", () => {
+    const use = ["./reviewer.flow.ts", "../shared/helper.flow.ts"];
+    const handle = flow("chief", { use }, async () => undefined);
+    use.push("./later.flow.ts");
+    expect(getFlowDefinition(handle).header.use).toEqual([
+      "./reviewer.flow.ts", "../shared/helper.flow.ts",
+    ]);
+    expect(Object.isFrozen(getFlowDefinition(handle).header.use)).toBe(true);
+  });
+
+  it.each([
+    null, "./reviewer.flow.ts", [42], [""], [" "],
+    ["./reviewer.flow.ts", "./reviewer.flow.ts"],
+    ["reviewer.flow.ts"], ["@team/reviewer"], ["/reviewer.flow.ts"],
+    ["./reviewer.ts"], ["./reviewer.flow.ts?other.flow.ts"],
+    Array(1),
+  ])("refuses malformed use declarations: %j", (use) => {
+    expect(() => flow("chief", { use } as FlowHeader, async () => undefined))
+      .toThrow("header.use");
+  });
+
   it("defines a flow with the empty header as the default", () => {
     const body = async (_f: Ctx): Promise<void> => undefined;
     const definition = flow("release-note", body);