diff --git a/packages/rstack/src/configLayers.ts b/packages/rstack/src/configLayers.ts
new file mode 100644
index 00000000..4bb403c4
--- /dev/null
+++ b/packages/rstack/src/configLayers.ts
@@ -0,0 +1,71 @@
+import type {
+  ConfigParams as AppConfigParams,
+  RsbuildConfig,
+} from '@rsbuild/core';
+import type { ConfigParams as LibConfigParams, RslibConfig } from '@rslib/core';
+import type { RslintConfig } from '@rslint/core';
+import type { UserConfig as RspressConfig } from '@rspress/core';
+import type { RstestConfig } from '@rstest/core';
+import type { Configs } from './config.ts';
+import type { FmtConfig } from './fmt/types.ts';
+import type { StagedConfig } from './staged.ts';
+
+/** Internal definitions, including the deferred lint factory created by define.lint. */
+export type ConfigLayer = Readonly<Configs>;
+
+/** Ordered from the lowest to the highest precedence; no tool merge rules here. */
+export type ConfigLayers = readonly ConfigLayer[];
+
+type ConfigValues = {
+  app: RsbuildConfig;
+  lib: RslibConfig;
+  doc: RspressConfig;
+  test: RstestConfig;
+  lint: RslintConfig;
+  fmt: FmtConfig;
+  staged: StagedConfig;
+};
+
+type ConfigArgs<K extends keyof Configs> = K extends 'app'
+  ? [params: AppConfigParams]
+  : K extends 'lib'
+    ? [params: LibConfigParams]
+    : [];
+
+/** Collect definitions without running factories or modifying the supplied layers. */
+export const createConfigLayers = (
+  project: ConfigLayer,
+  inherited: ConfigLayers = [],
+): ConfigLayers => [...inherited, project];
+
+/**
+ * Resolve only the requested tool, in layer order. Missing definitions contribute
+ * nothing; defaults and merging belong to the tool adapter. Each call evaluates
+ * its factories anew, without caching across native parameters or loads.
+ */
+export const resolveConfigLayers = async <K extends keyof Configs>(
+  layers: ConfigLayers,
+  kind: K,
+  ...args: ConfigArgs<K>
+): Promise<ConfigValues[K][]> => {
+  const configs: ConfigValues[K][] = [];
+
+  for (const layer of layers) {
+    const definition = layer[kind];
+    if (definition === undefined) {
+      continue;
+    }
+
+    // A staged function generates tasks from file names; it is not a factory.
+    if (kind !== 'staged' && typeof definition === 'function') {
+      const factory = definition as (
+        ...args: ConfigArgs<K>
+      ) => ConfigValues[K] | Promise<ConfigValues[K]>;
+      configs.push(await factory(...args));
+    } else {
+      configs.push(definition as ConfigValues[K]);
+    }
+  }
+
+  return configs;
+};
diff --git a/packages/rstack/tests/config/layers.test.ts b/packages/rstack/tests/config/layers.test.ts
new file mode 100644
index 00000000..0f79d934
--- /dev/null
+++ b/packages/rstack/tests/config/layers.test.ts
@@ -0,0 +1,170 @@
+import type { ConfigParams } from 'rstack/app';
+import { expect, rs, test } from 'rstack/test';
+import {
+  createConfigLayers,
+  resolveConfigLayers,
+  type ConfigLayer,
+} from '../../src/configLayers.ts';
+
+test('collects inherited layers before the project without resolving definitions', () => {
+  const factory = rs.fn(() => ({}));
+  const base = Object.freeze({ app: factory });
+  const team = Object.freeze({ test: factory });
+  const project = Object.freeze({ app: factory });
+  const inherited = Object.freeze([base, team]);
+
+  const layers = createConfigLayers(project, inherited);
+
+  expect(layers).toEqual([base, team, project]);
+  expect(layers[0]).toBe(base);
+  expect(layers[2]).toBe(project);
+  expect(inherited).toEqual([base, team]);
+  expect(createConfigLayers(project)).toEqual([project]);
+  expect(factory).not.toHaveBeenCalled();
+});
+
+test.each(['app', 'lib'] as const)(
+  'passes native parameters unchanged to every %s factory',
+  async (kind) => {
+    const params: ConfigParams = {
+      command: 'build',
+      env: 'production',
+      envMode: 'staging',
+      meta: { caller: 'test' },
+    };
+    const baseConfig = { root: 'base' };
+    const projectConfig = { root: 'project' };
+    const base = rs.fn((_params: ConfigParams) => baseConfig);
+    const project = rs.fn((_params: ConfigParams) =>
+      Promise.resolve(projectConfig),
+    );
+    const layers = createConfigLayers({ [kind]: project }, [{ [kind]: base }]);
+
+    const configs = await resolveConfigLayers(layers, kind, params);
+
+    expect(configs).toEqual([baseConfig, projectConfig]);
+    expect(configs[0]).toBe(baseConfig);
+    expect(configs[1]).toBe(projectConfig);
+    expect(base).toHaveBeenCalledExactlyOnceWith(params);
+    expect(project).toHaveBeenCalledExactlyOnceWith(params);
+    expect(base.mock.calls[0][0]).toBe(params);
+    expect(project.mock.calls[0][0]).toBe(params);
+  },
+);
+
+test('awaits layers sequentially and only resolves the selected tool', async () => {
+  const started = Promise.withResolvers<void>();
+  const ready = Promise.withResolvers<void>();
+  const baseConfig = Object.freeze({ retry: 2 });
+  const projectConfig = Object.freeze({ retry: 1 });
+  const unrelated = rs.fn(() => {
+    throw new Error('Unselected tool must stay lazy');
+  });
+  const project = rs.fn(() => projectConfig);
+  const layers = createConfigLayers({ test: project, app: unrelated }, [
+    {
+      async test() {
+        started.resolve();
+        await ready.promise;
+        return baseConfig;
+      },
+      fmt: unrelated,
+    },
+  ]);
+
+  const resolving = resolveConfigLayers(layers, 'test');
+  await started.promise;
+  try {
+    expect(project).not.toHaveBeenCalled();
+  } finally {
+    ready.resolve();
+  }
+  const configs = await resolving;
+
+  expect(configs).toEqual([baseConfig, projectConfig]);
+  expect(configs[0]).toBe(baseConfig);
+  expect(configs[1]).toBe(projectConfig);
+  expect(project).toHaveBeenCalledExactlyOnceWith();
+  expect(unrelated).not.toHaveBeenCalled();
+});
+
+test.each(['doc', 'test', 'lint', 'fmt'] as const)(
+  'resolves %s values and factories without injecting arguments',
+  async (kind) => {
+    const values = {
+      doc: { title: 'Docs' },
+      test: { retry: 2 },
+      lint: [],
+      fmt: { singleQuote: true },
+    };
+    const factory = rs.fn(() => Promise.resolve(values[kind]));
+    const layers = createConfigLayers({ [kind]: factory }, [
+      { [kind]: values[kind] },
+    ]);
+
+    const configs = await resolveConfigLayers(layers, kind);
+
+    expect(configs).toEqual([values[kind], values[kind]]);
+    expect(configs[0]).toBe(values[kind]);
+    expect(configs[1]).toBe(values[kind]);
+    expect(factory).toHaveBeenCalledExactlyOnceWith();
+  },
+);
+
+test('skips missing definitions while preserving explicitly empty configs', async () => {
+  const emptyConfig = {};
+  const emptyLint: ConfigLayer = { lint: [] };
+  const layers = createConfigLayers({ test: emptyConfig }, [{}, emptyLint]);
+
+  expect(await resolveConfigLayers(layers, 'test')).toEqual([emptyConfig]);
+  expect(await resolveConfigLayers(layers, 'lint')).toEqual([[]]);
+  expect(await resolveConfigLayers(layers, 'fmt')).toEqual([]);
+});
+
+test('preserves staged task generators without invoking them', async () => {
+  const task = rs.fn((_files: readonly string[]) => 'rs lint');
+  const generator = rs.fn((_files: readonly string[]) =>
+    Promise.resolve(['rs fmt']),
+  );
+  const tasks = { '*.ts': task };
+  const layers = createConfigLayers({ staged: generator }, [{ staged: tasks }]);
+
+  const configs = await resolveConfigLayers(layers, 'staged');
+
+  expect(configs[0]).toBe(tasks);
+  expect(configs[1]).toBe(generator);
+  expect(task).not.toHaveBeenCalled();
+  expect(generator).not.toHaveBeenCalled();
+});
+
+test('stops at a failed factory and preserves its error', async () => {
+  const error = new Error('Invalid shared config');
+  const project = rs.fn(() => ({}));
+  const layers = createConfigLayers({ fmt: project }, [
+    {
+      fmt: () => Promise.reject(error),
+    },
+  ]);
+
+  await expect(resolveConfigLayers(layers, 'fmt')).rejects.toBe(error);
+  expect(project).not.toHaveBeenCalled();
+});
+
+test('keeps simultaneous resolutions with different parameters independent', async () => {
+  const factory = rs.fn(async ({ env }: ConfigParams) => {
+    await Promise.resolve();
+    return { root: env };
+  });
+  const layers = createConfigLayers({ app: factory });
+
+  const configs = await Promise.all([
+    resolveConfigLayers(layers, 'app', { command: 'build', env: 'production' }),
+    resolveConfigLayers(layers, 'app', { command: 'dev', env: 'development' }),
+  ]);
+
+  expect(configs).toEqual([
+    [{ root: 'production' }],
+    [{ root: 'development' }],
+  ]);
+  expect(factory).toHaveBeenCalledTimes(2);
+});