diff --git a/.changeset/27512-draft-probe-creates-no-sqlite-file.md b/.changeset/27512-draft-probe-creates-no-sqlite-file.md
new file mode 100644
index 00000000000..01d4f7128ce
--- /dev/null
+++ b/.changeset/27512-draft-probe-creates-no-sqlite-file.md
@@ -0,0 +1,14 @@
+---
+'@objectstack/service-datasource': patch
+---
+
+fix(service-datasource): testing a datasource draft no longer creates its SQLite database file
+
+Clause-②: no
+Metadata-protocol: none
+
+"Test connection" on a datasource draft (`POST /api/v1/datasources/test`) saves nothing, yet for a file-backed SQLite draft it opened the database the way a server boot does, so the file, and every missing directory above it, was created on disk although no datasource was saved. A mistyped path left a stray database wherever the server process could write. Measured on every file-backed driver the default factory builds: `sqlite` / `sqlite3`, `sqlite-wasm`, and `turso` / `libsql` with a `file:` url.
+
+- **What the probe answers now.** A draft whose database file does not exist is refused: the probe answers `ok: false` with an error that names the file and says it does not exist. Nothing is created: neither the file nor its directory.
+- **What still works.** A draft naming an existing database file, or `:memory:`, probes as before. Saving a datasource still creates its file on connect, as do the boot restore and every hot pool: only the probe asks for an existing file.
+- **Whichever factory builds.** The check is the probe's own and runs before the driver factory is asked for anything, so it holds for a host-registered factory too. Nothing a host or an author can write changes: no exported type or function signature moves.
diff --git a/packages/services/service-datasource/src/__tests__/draft-probe-creates-no-database-file.test.ts b/packages/services/service-datasource/src/__tests__/draft-probe-creates-no-database-file.test.ts
new file mode 100644
index 00000000000..5abf4eabc35
--- /dev/null
+++ b/packages/services/service-datasource/src/__tests__/draft-probe-creates-no-database-file.test.ts
@@ -0,0 +1,190 @@
+// Copyright (c) 2026 ObjectStack. Licensed under the Apache-2.0 license.
+
+import { describe, it, expect, vi, beforeEach, afterEach } from 'vitest';
+import { existsSync, mkdtempSync, readdirSync, rmSync, writeFileSync } from 'node:fs';
+import { tmpdir } from 'node:os';
+import { join } from 'node:path';
+import { HonoHttpServer } from '@objectstack/plugin-hono-server';
+import type { IDatasourceAdminService, IDatasourceDriverFactory } from '../contracts/index.js';
+import { DatasourceAdminServicePlugin } from '../datasource-admin-plugin.js';
+import { registerDatasourceAdminRoutes } from '../admin-routes.js';
+import { createDefaultDatasourceDriverFactory } from '../default-datasource-driver-factory.js';
+import { ENTITLED_CREDENTIAL, createSessionAuthService, createGrantsEngine } from './entitled-caller.fixture.js';
+
+// [#10126] Pay the first transform of the dist-resolved workspace deps at module
+// load, not inside a clocked `it()` (see `scripts/check-test-source-alias.mjs`).
+import '@objectstack/spec/kernel';
+import '@objectstack/driver-sql';
+
+/**
+ * [#27512] The draft probe — `POST /api/v1/datasources/test`, the wizard's
+ * "Test connection" before Save — persists nothing, so it must leave nothing on
+ * disk either. For a file-backed SQLite draft it used to open the file the way
+ * a writing boot does: the file (and every missing directory above it) was
+ * created, although no datasource was saved. Measured on every file-backed
+ * SQL-family driver the default factory builds: `sqlite` (better-sqlite3),
+ * `sqlite-wasm`, and `turso` with a `file:` url.
+ *
+ * Driven through the real door: the real `HonoHttpServer`, the real admin
+ * routes, the real plugin probe and the default driver factory.
+ */
+
+const authService = createSessionAuthService();
+const grantsEngine = createGrantsEngine();
+
+async function mountDoor(driverFactory: IDatasourceDriverFactory = createDefaultDatasourceDriverFactory()) {
+  let admin: IDatasourceAdminService | undefined;
+  const ctx: any = {
+    getService: (name: string) => {
+      if (name === 'metadata') return { get: async () => undefined, list: async () => [] };
+      throw new Error(`no service ${name}`);
+    },
+    registerService: (name: string, svc: unknown) => {
+      if (name === 'datasource-admin') admin = svc as IDatasourceAdminService;
+    },
+    trigger: async () => {},
+    logger: { warn() {}, info() {} },
+  };
+  await new DatasourceAdminServicePlugin({ driverFactory }).init(ctx);
+
+  const server = new HonoHttpServer(0);
+  registerDatasourceAdminRoutes(
+    server,
+    {
+      getService: vi.fn((name: string) =>
+        name === 'auth'
+          ? authService
+          : name === 'objectql' || name === 'data'
+            ? grantsEngine
+            : name === 'datasource-admin'
+              ? admin
+              : undefined,
+      ),
+    } as any,
+    '/api/v1',
+  );
+  const app = server.getRawApp();
+  return (draft: Record<string, unknown>) =>
+    app.fetch(
+      new Request('http://local/api/v1/datasources/test', {
+        method: 'POST',
+        headers: { 'content-type': 'application/json', authorization: ENTITLED_CREDENTIAL },
+        body: JSON.stringify(draft),
+      }),
+    );
+}
+
+/** Every file-backed SQL-family driver id, and how its draft names the file. */
+const FILE_BACKED: Array<{ driver: string; config: (file: string) => Record<string, unknown> }> = [
+  { driver: 'sqlite', config: (file) => ({ filename: file }) },
+  { driver: 'sqlite3', config: (file) => ({ filename: file }) },
+  { driver: 'sqlite-wasm', config: (file) => ({ filename: file }) },
+  { driver: 'turso', config: (file) => ({ url: `file:${file}` }) },
+  { driver: 'libsql', config: (file) => ({ url: `file:${file}` }) },
+];
+
+let root: string;
+beforeEach(() => {
+  root = mkdtempSync(join(tmpdir(), 'ds-draft-probe-'));
+});
+afterEach(() => {
+  rmSync(root, { recursive: true, force: true });
+});
+
+describe('POST /api/v1/datasources/test — a draft probe leaves no database file (#27512)', () => {
+  for (const { driver, config } of FILE_BACKED) {
+    for (const where of ['probe.db', 'missing/dir/probe.db']) {
+      it(`${driver}: a missing '${where}' is reported, and neither the file nor its directory is created`, async () => {
+        const probe = await mountDoor();
+        const file = join(root, where);
+
+        const res = await probe({ name: 'draft', driver, config: config(file) });
+
+        // The probe's verdict door: 200 with `result.ok: false`, as for every
+        // other probe failure — the draft is refused, not the request.
+        expect(res.status).toBe(200);
+        const body = (await res.json()) as { success: boolean; data: { result: { ok: boolean; error?: string } } };
+        expect(body.success).toBe(true);
+        expect(body.data.result.ok).toBe(false);
+        // Names the missing file, so the admin knows WHAT the probe refused.
+        expect(body.data.result.error).toContain(file);
+        expect(body.data.result.error).toContain('does not exist');
+        // …and the filesystem is as the probe found it.
+        expect(existsSync(file)).toBe(false);
+        expect(readdirSync(root)).toEqual([]);
+      });
+    }
+  }
+
+  // Control: the refusal is about ABSENCE, not about file-backed SQLite. A
+  // database file that exists probes green, and is the only thing in the
+  // directory afterwards, as before.
+  it('control: an existing SQLite file still probes ok', async () => {
+    const probe = await mountDoor();
+    const file = join(root, 'existing.db');
+    const { SqlDriver } = await import('@objectstack/driver-sql');
+    const seed = new SqlDriver({ client: 'better-sqlite3', connection: { filename: file }, useNullAsDefault: true } as any);
+    await seed.connect();
+    await seed.disconnect();
+    expect(existsSync(file)).toBe(true);
+
+    const res = await probe({ name: 'draft', driver: 'sqlite', config: { filename: file } });
+
+    expect(res.status).toBe(200);
+    const body = (await res.json()) as { data: { result: { ok: boolean; error?: string } } };
+    expect(body.data.result).toMatchObject({ ok: true });
+    expect(readdirSync(root)).toEqual(['existing.db']);
+  });
+
+  // Control: an in-memory draft names no file, so nothing is refused.
+  it('control: a :memory: SQLite draft still probes ok', async () => {
+    const probe = await mountDoor();
+    const res = await probe({ name: 'draft', driver: 'sqlite', config: { filename: ':memory:' } });
+    expect(res.status).toBe(200);
+    const body = (await res.json()) as { data: { result: { ok: boolean } } };
+    expect(body.data.result.ok).toBe(true);
+  });
+});
+
+describe('the judgement is the probe\'s, whichever factory builds (#27512)', () => {
+  it('a host factory is never asked to build a draft whose file is missing', async () => {
+    const create = vi.fn(async () => ({ connect: async () => {}, ping: async () => {} }));
+    const probe = await mountDoor({ supports: () => true, create });
+    const file = join(root, 'missing/dir/probe.db');
+
+    for (const { driver, config } of FILE_BACKED) {
+      const res = await probe({ name: 'draft', driver, config: config(file) });
+      const body = (await res.json()) as { data: { result: { ok: boolean; error?: string } } };
+      expect(res.status, driver).toBe(200);
+      expect(body.data.result.ok, driver).toBe(false);
+    }
+    expect(create).not.toHaveBeenCalled();
+    expect(readdirSync(root)).toEqual([]);
+  });
+
+  it('a path that can be neither opened nor created is refused too, and nothing is written', async () => {
+    const probe = await mountDoor();
+    writeFileSync(join(root, 'blocker'), 'a regular file');
+    const file = join(root, 'blocker/probe.db');
+
+    const res = await probe({ name: 'draft', driver: 'sqlite', config: { filename: file } });
+
+    expect(res.status).toBe(200);
+    const body = (await res.json()) as { data: { result: { ok: boolean; error?: string } } };
+    expect(body.data.result.ok).toBe(false);
+    expect(body.data.result.error).toContain(file);
+    expect(readdirSync(root)).toEqual(['blocker']);
+  });
+
+  // Control: the default factory is untouched — Save, the boot restore and
+  // every hot pool build through it and still create the file on connect,
+  // which is what a datasource that is being SAVED is owed.
+  it('control: the default factory still creates a sqlite target on connect', async () => {
+    const factory = createDefaultDatasourceDriverFactory();
+    const file = join(root, 'created.db');
+    const handle = await factory.create({ driver: 'sqlite', config: { filename: file } });
+    await handle.connect?.();
+    await handle.disconnect?.();
+    expect(existsSync(file)).toBe(true);
+  });
+});
diff --git a/packages/services/service-datasource/src/datasource-admin-plugin.ts b/packages/services/service-datasource/src/datasource-admin-plugin.ts
index 7bb6c11d2d4..9c6083e902f 100644
--- a/packages/services/service-datasource/src/datasource-admin-plugin.ts
+++ b/packages/services/service-datasource/src/datasource-admin-plugin.ts
@@ -4,6 +4,7 @@ import type { Plugin, PluginContext } from '@objectstack/core';
 import { hashSpec, readLegacyOrganizationRows } from '@objectstack/metadata-core';
 import { applyConversionsToStoredItem } from '@objectstack/spec';
 import { registerMetadataTypeActions } from '@objectstack/spec/kernel';
+import { resolveDriverId } from '@objectstack/spec/data';
 import type {
   IDatasourceDriverFactory,
   TestConnectionResult,
@@ -21,6 +22,7 @@ import {
 import { datasourceConnectivityChanged } from './datasource-connectivity-change.js';
 import type { DatasourceConnectPolicy } from './contracts/connect-policy.js';
 import type { Logger } from './logger.js';
+import { resolveTursoUrl } from './turso-driver-config.js';
 import type { IDataEngine, IObjectQLEngine } from '@objectstack/spec/contracts';
 
 /**
@@ -872,6 +874,11 @@ export class DatasourceAdminServicePlugin implements Plugin {
     if (!factory.supports(input.driver)) {
       return { ok: false, error: `No driver factory supports driver '${input.driver}'.` };
     }
+    // [#27512] A probe persists nothing, so it may create nothing either.
+    // Judged before the factory builds anything: every file-backed driver
+    // opens its database the way a writing boot does and creates the file.
+    const fileRefusal = await absentDatabaseFileRefusal(input);
+    if (fileRefusal) return { ok: false, error: fileRefusal };
 
     let driver: any;
     try {
@@ -958,6 +965,62 @@ function servedOrigin(ctx: PluginContext, name: string): 'code' | 'runtime' {
   return codeDatasourceNamesOf(ctx)?.has(name) ? 'code' : 'runtime';
 }
 
+/**
+ * The database file a draft opens when its driver is file-backed, or
+ * `undefined` when it opens none — a server database, a remote libSQL url, an
+ * id no file-backed driver answers to. `:memory:` is returned as is; the
+ * judgement below leaves every `:`-prefixed name alone.
+ *
+ * Read as the default driver factory reads the same config: `sqlite` and
+ * `sqlite-wasm` open `config.filename` (`SqliteConfigSchema`, absent ⇒
+ * `:memory:`), and driver-turso's local engine opens the path of a `file:`
+ * url, its scheme matched in any letter case (`TursoDriver.toKnexConfig`).
+ */
+function probedDatabaseFile(input: ProbeInput): string | undefined {
+  const config = (input.config ?? {}) as Record<string, unknown>;
+  switch (resolveDriverId(input.driver)) {
+    case 'sqlite':
+    case 'sqlite-wasm':
+      return typeof config.filename === 'string' ? config.filename : ':memory:';
+    case 'turso': {
+      const url = resolveTursoUrl({ driver: input.driver, config });
+      return url.slice(0, 'file:'.length).toLowerCase() === 'file:' ? url.slice('file:'.length) : undefined;
+    }
+    default:
+      return undefined;
+  }
+}
+
+/**
+ * [#27512] Why the draft probe refuses to open a file-backed draft, or
+ * `undefined` when it may: the file the draft names does not exist, or can be
+ * neither opened nor created. Nothing is written to find out.
+ *
+ * The judgement is driver-sql's one write-free existence check,
+ * `resolveSqliteAbsentFileTarget`: under `'empty-in-memory'` it answers
+ * `openedEmptyInMemory` for an absent file and throws its
+ * `SqliteDatabaseFileError`, naming the file, for one that can be neither
+ * opened nor created — so no second `existsSync` is open-coded here.
+ *
+ * It lives in the probe, not in the driver factory, so it holds whichever
+ * factory the host registered, and a Save, the boot restore and every hot
+ * pool still open the file as before and create it.
+ */
+async function absentDatabaseFileRefusal(input: ProbeInput): Promise<string | undefined> {
+  const filename = probedDatabaseFile(input);
+  if (filename === undefined) return undefined;
+  const { resolveSqliteAbsentFileTarget } = await import('@objectstack/driver-sql');
+  try {
+    if (!resolveSqliteAbsentFileTarget(filename, 'empty-in-memory').openedEmptyInMemory) return undefined;
+  } catch (err) {
+    return errMsg(err);
+  }
+  return (
+    `SQLite database file '${filename}' does not exist. Testing a connection never creates it: `
+    + 'point the draft at an existing database file, or save the datasource to have it created.'
+  );
+}
+
 function errMsg(err: unknown): string {
   return err instanceof Error ? err.message : String(err);
 }