@@ -0,0 +1,20 @@
+---
+'@objectstack/driver-sql': minor
+'@objectstack/service-datasource': minor
+---
+
+fix(driver-sql): a SQLite file whose bytes are not a SQLite database fails `connect()` at once, naming the file, and a development boot no longer moves it aside and replaces it with an empty database (#24960)
+
+`SqlDriver.connect()` runs `PRAGMA auto_vacuum` as the connection's first statement. On a file that is not a SQLite database (plain text, another format, a file encrypted by another engine) SQLite answers `SQLITE_NOTADB`, which `connect()` logged as "Failed to set PRAGMA auto_vacuum=INCREMENTAL" and swallowed. It resolved over a file it could not read. In production the first query failed later. On a development boot, `resolveSqliteDriver` (`@objectstack/service-datasource`) answered the failed probe by stepping down to wasm SQLite, whose open renamed the file to `<file>.corrupt-<timestamp>`, wrote an empty database in its place and read `connected`, under a warning that blamed the native addon.
+
+`connect()` now refuses such a file with a `SqliteDatabaseFileError` (`code: 'SQLITE_NOTADB'`, `filename`, a message naming the file), as it already did for `SQLITE_CANTOPEN`, in every mode and before anything is written. A declared datasource's boot prints `datasource '<name>': connect failed — <reason>`. `resolveSqliteDriver` classifies `SQLITE_NOTADB` as a file failure and re-throws it instead of stepping down, so the operator's file is left exactly as it was found. A real database file, an empty file and an absent file connect as before, and a native addon that cannot load still steps down to wasm SQLite.
+
+Clause-②: no (narrowing)
+
+<!-- adr-0087: not-required (no-migration-prescription) No metadata moves: no spec key, authorable spelling, object definition or stored shape is added, removed, renamed or re-shaped, and no exported declaration is removed or narrowed (`SqliteDatabaseFileError` keeps its shape; only the set of codes it is raised with grows by one), so there is nothing for `objectstack migrate meta` to rewrite. What changes is the answer `SqlDriver.connect()` gives for a SQLite file that is not a database: a rejection where it resolved. The remedy is the datasource's file, never a rewrite of a package source or a stored row. The other categories are closed on facts: both packages publish (not unpublished); no ADR-0087 id is named or touched (not registered or already-registered); and nothing exported is removed or narrowed (not runtime-interface-only, type-surface-only or runtime-export-retired). -->
+
+**BREAKING** (`SqlDriver.connect()`'s accept set narrows): a connect that resolved over a SQLite file that is not a database now rejects. It ships as `minor` under the launch-window convention for accept-set narrowings: during the launch window a breaking change does not take `major`, so the level does not say it breaks, and breaking-ness is carried by this banner and the disposition above.
+
+- **Before:** `connect()` resolved; in production the first query failed with `DATABASE_ERROR`, and on a development boot the file was renamed to `<file>.corrupt-<timestamp>` and an empty database was written in its place.
+- **Now:** `connect()` rejects with `SqliteDatabaseFileError`, `code: 'SQLITE_NOTADB'`, naming the file; the file is untouched.
+- **Fix:** point the datasource at a SQLite database file, or move the file aside yourself (an absent file is created empty on the next connect).
@@ -0,0 +1,100 @@
+// Copyright (c) 2026 ObjectStack. Licensed under the Apache-2.0 license.
+
+/**
+ * A declared SQLite file whose bytes are not a SQLite database fails
+ * `connect()` at once, naming the file, and the file is left exactly as it was
+ * found (#24960).
+ *
+ * Before: the connection's first statement (`PRAGMA auto_vacuum`) answered
+ * `SQLITE_NOTADB`, which `connect()` logged as "Failed to set PRAGMA
+ * auto_vacuum=INCREMENTAL" and swallowed, so it resolved over a file it could
+ * not read. In production the first query failed later; on a development boot
+ * the step-down (`resolveSqliteDriver` in `@objectstack/service-datasource`)
+ * answered with wasm SQLite, whose open moved the operator's file aside to
+ * `<file>.corrupt-<timestamp>` and wrote an empty database in its place, and
+ * the datasource read `connected`. `SQLITE_CANTOPEN` was already refused this
+ * way (#23696); `SQLITE_NOTADB` was left out.
+ *
+ * The refusal is the driver's own, so it holds whatever `NODE_ENV` says: both
+ * modes are pinned.
+ */
+
+import { describe, it, expect, beforeEach, afterEach, vi } from 'vitest';
+import { mkdtempSync, readdirSync, readFileSync, rmSync, writeFileSync } from 'node:fs';
+import { tmpdir } from 'node:os';
+import { join } from 'node:path';
+import { SqlDriver } from './sql-driver.js';
+import { SqliteDatabaseFileError } from './sqlite-database-file.js';
+
+const PLAIN_TEXT = 'archive notes — this file holds plain text, not a SQLite database\n';
+
+const drivers: SqlDriver[] = [];
+function make(filename: string): SqlDriver {
+  const d = new SqlDriver({ client: 'better-sqlite3', connection: { filename }, useNullAsDefault: true });
+  drivers.push(d);
+  return d;
+}
+
+/** `connect()`'s rejection, or a failure saying it resolved. */
+async function refusalOf(driver: SqlDriver): Promise<unknown> {
+  try {
+    await driver.connect();
+  } catch (error) {
+    return error;
+  }
+  throw new Error('connect() resolved for a file that is not a SQLite database');
+}
+
+let dir: string;
+beforeEach(() => { dir = mkdtempSync(join(tmpdir(), 'os-24960-')); });
+afterEach(async () => {
+  vi.unstubAllEnvs();
+  await Promise.all(drivers.splice(0).map((d) => d.disconnect().catch(() => {})));
+  rmSync(dir, { recursive: true, force: true });
+});
+
+describe('SqlDriver.connect — a declared SQLite file that is not a database (#24960)', () => {
+  for (const nodeEnv of ['development', 'production'] as const) {
+    it(`refuses a plain-text file with SQLITE_NOTADB, naming it, and leaves its bytes untouched (NODE_ENV=${nodeEnv})`, async () => {
+      vi.stubEnv('NODE_ENV', nodeEnv);
+      const filename = join(dir, 'archive.db');
+      writeFileSync(filename, PLAIN_TEXT);
+      const before = readFileSync(filename);
+
+      const error = await refusalOf(make(filename));
+
+      expect(error).toBeInstanceOf(SqliteDatabaseFileError);
+      const e = error as SqliteDatabaseFileError;
+      expect(e.code).toBe('SQLITE_NOTADB');
+      expect(e.filename).toBe(filename);
+      expect(e.message).toContain(filename);
+      expect(e.message).toContain((e.cause as Error).message);
+      // Nothing was written: the same bytes, and no sibling (journal, WAL,
+      // `.corrupt-*`) beside it.
+      expect(readFileSync(filename).equals(before)).toBe(true);
+      expect(readdirSync(dir)).toEqual(['archive.db']);
+    });
+  }
+
+  it('CONTROL: a real database file still connects and answers, and is not moved', async () => {
+    const filename = join(dir, 'real.db');
+    const seed = make(filename);
+    await seed.connect();
+    await seed.execute('CREATE TABLE t (a INTEGER)');
+    await seed.execute('INSERT INTO t (a) VALUES (7)');
+    await seed.disconnect();
+
+    const driver = make(filename);
+    await driver.connect();
+    expect(await driver.execute('SELECT a FROM t')).toEqual([{ a: 7 }]);
+    expect(readdirSync(dir).filter((name) => name.includes('.corrupt-'))).toEqual([]);
+  });
+
+  it('CONTROL: an empty file is an empty SQLite database, and connects', async () => {
+    const filename = join(dir, 'empty.db');
+    writeFileSync(filename, '');
+    const driver = make(filename);
+    await driver.connect();
+    expect(await driver.execute('SELECT 1 AS one')).toEqual([{ one: 1 }]);
+  });
+});
@@ -7059,6 +7059,9 @@ export class SqlDriver implements IDataDriver {
    * @returns whether the connection answered. The read is the first statement
    * any connection runs, so `false` says the connection itself is not answering —
    * not merely that space hygiene is unavailable.
+   * @throws {SqliteDatabaseFileError} when that first statement's answer is a
+   * verdict on the file itself ({@link SQLITE_FILE_REFUSALS}): it cannot be
+   * opened, or it is not a SQLite database.
    */
   private async applyAutoVacuumIncremental(): Promise<boolean> {
     try {
@@ -7082,15 +7085,24 @@ export class SqlDriver implements IDataDriver {
       // let the step-down message that follows explain the outcome. Any OTHER
       // PRAGMA failure keeps the full warning (with stack) as before.
       const code = (e as { code?: string } | null | undefined)?.code;
-      // The file itself cannot be opened or created (#23696): a directory that
-      // exists but refuses the file, a path SQLite cannot open. Every later
-      // statement would answer the same, so the connect fails here, naming the
-      // file — before, it logged and resolved, and the datasource counted as
-      // connected while it could not answer one query.
-      if (code === 'SQLITE_CANTOPEN') {
+      // The file itself is refused, and every later statement would answer the
+      // same, so the connect fails here, naming the file. Before, each of these
+      // logged and resolved, and the datasource counted as connected while it
+      // could not answer one query:
+      //   • SQLITE_CANTOPEN (#23696) — a directory that exists but refuses the
+      //     file, a path SQLite cannot open;
+      //   • SQLITE_NOTADB (#24960) — the file exists and opens, but its bytes
+      //     are not a SQLite database (plain text, a foreign format, a file
+      //     encrypted by another engine). On a development boot the step-down
+      //     used to answer it with wasm SQLite, whose open moved the
+      //     operator's file aside and wrote an empty database in its place.
+      //     The refusal is issued before anything is written: the file is left
+      //     exactly as it was found.
+      const refusal = code === undefined ? undefined : SqlDriver.SQLITE_FILE_REFUSALS.get(code);
+      if (refusal !== undefined) {
         const declared = (this.config as any).connection;
         const filename = this.sqliteFilename() ?? String(typeof declared === 'string' ? declared : declared?.filename);
-        throw new SqliteDatabaseFileError(filename, 'cannot be opened or created', e);
+        throw new SqliteDatabaseFileError(filename, refusal, e);
       }
       const msg = e instanceof Error ? e.message : String(e);
       const isNativeLoadFailure =
@@ -7109,6 +7121,19 @@ export class SqlDriver implements IDataDriver {
     }
   }
 
+  /**
+   * The SQLite codes the connection's first statement can answer that are a
+   * verdict on the FILE, each with the words {@link SqliteDatabaseFileError}
+   * names it with. Only a loaded addon answers with a SQLite code, so none of
+   * these is a native-addon load failure; and every rung of a step-down opens
+   * the same file, so no other engine can cure one (`resolveSqliteDriver` in
+   * `@objectstack/service-datasource` re-throws them).
+   */
+  private static readonly SQLITE_FILE_REFUSALS: ReadonlyMap<string, string> = new Map([
+    ['SQLITE_CANTOPEN', 'cannot be opened or created'],
+    ['SQLITE_NOTADB', 'is not a SQLite database, and was left as it is'],
+  ]);
+
   /** What `PRAGMA auto_vacuum` answers for INCREMENTAL (0 is NONE, 1 is FULL). */
   private static readonly SQLITE_AUTO_VACUUM_INCREMENTAL = 2;
 
 
@@ -5,13 +5,14 @@ import { mkdir, stat } from 'node:fs/promises';
 import { dirname, isAbsolute, resolve } from 'node:path';
 
 /**
- * A SQLite database file this driver cannot open or create (#23696).
+ * A SQLite database file this driver cannot open or create (#23696), or one
+ * whose bytes are not a SQLite database (#24960).
  *
  * Thrown by `SqlDriver.connect()`, so the boot's connect refusal (ADR-0062 D5,
  * `datasource '<name>': connect failed — <reason>`) carries the path and the
  * operating system's own answer instead of waiting for a plugin start timeout.
  * `code` is the underlying error's (`ENOENT`, `EACCES`, `ENOTDIR`,
- * `SQLITE_CANTOPEN`, …) and `cause` the error itself.
+ * `SQLITE_CANTOPEN`, `SQLITE_NOTADB`, …) and `cause` the error itself.
  */
 export class SqliteDatabaseFileError extends Error {
   readonly code: string | undefined;
 
@@ -0,0 +1,126 @@
+// Copyright (c) 2026 ObjectStack. Licensed under the Apache-2.0 license.
+
+/**
+ * A declared SQLite datasource whose file is not a SQLite database is refused
+ * at connect, naming the file, in development as in production. On a
+ * development boot the operator's file is neither renamed nor replaced, and
+ * nothing steps down to wasm SQLite or the in-memory driver (#24960).
+ *
+ * Before: `SqlDriver.connect()` swallowed the file's `SQLITE_NOTADB` and
+ * resolved, the probe's `SELECT 1` then failed as a `DATABASE_ERROR`, and in
+ * development `resolveSqliteDriver` stepped down to wasm SQLite. wasm's open
+ * moved the file aside to `<file>.corrupt-<timestamp>` and wrote an empty
+ * database in its place, under the warning "native better-sqlite3 unavailable
+ * (ABI mismatch or not built)", which named the wrong cause; the datasource
+ * read `connected`. Measured through `os migrate apply --yes` on the card.
+ *
+ * Real `better-sqlite3`, real wasm SQLite and real files in a scratch
+ * directory, as in `./sqlite-driver-fallback-file-open-failure.test.ts`.
+ */
+
+import { afterEach, beforeEach, describe, expect, it, vi } from 'vitest';
+import { mkdtempSync, readdirSync, readFileSync, rmSync, writeFileSync } from 'node:fs';
+import { tmpdir } from 'node:os';
+import { join } from 'node:path';
+import { resolveSqliteDriver, type ResolvedSqliteDriver } from '../sqlite-driver-fallback.js';
+import { DatasourceConnectionService } from '../datasource-connection-service.js';
+import { createDefaultDatasourceDriverFactory } from '../default-datasource-driver-factory.js';
+
+const PLAIN_TEXT = 'archive notes — this file holds plain text, not a SQLite database\n';
+
+let dir: string;
+let filename: string;
+let bytes: Buffer;
+const opened: ResolvedSqliteDriver[] = [];
+
+beforeEach(() => {
+  dir = mkdtempSync(join(tmpdir(), 'os-24960-'));
+  filename = join(dir, 'archive.db');
+  writeFileSync(filename, PLAIN_TEXT);
+  bytes = readFileSync(filename);
+});
+
+afterEach(async () => {
+  vi.restoreAllMocks();
+  vi.unstubAllEnvs();
+  await Promise.all(opened.splice(0).map((r) => r.driver?.disconnect?.().catch(() => {})));
+  rmSync(dir, { recursive: true, force: true });
+});
+
+/** `promise`'s rejection; a failure naming the engine when it resolves instead. */
+async function rejectionOf(promise: Promise<ResolvedSqliteDriver>): Promise<any> {
+  let resolved: ResolvedSqliteDriver;
+  try {
+    resolved = await promise;
+  } catch (error) {
+    return error;
+  }
+  opened.push(resolved);
+  throw new Error(`resolved to engine '${resolved.engine}' for a file that is not a SQLite database`);
+}
+
+/** The driver's refusal of the file: its own error name, SQLite's code, and the file. */
+function expectNotADatabaseRefusal(error: any): void {
+  expect(error?.name).toBe('SqliteDatabaseFileError');
+  expect(error?.code).toBe('SQLITE_NOTADB');
+  expect(error?.filename).toBe(filename);
+  expect(String(error?.message)).toContain(filename);
+}
+
+/** The operator's file is exactly as it was, and nothing was written beside it. */
+function expectFileUntouched(): void {
+  expect(readFileSync(filename).equals(bytes)).toBe(true);
+  expect(readdirSync(dir)).toEqual(['archive.db']);
+}
+
+describe('resolveSqliteDriver in development: a file that is not a SQLite database (#24960)', () => {
+  it('rejects with the driver\'s refusal, never wasm or memory, and leaves the file as it was', async () => {
+    const warn = vi.fn();
+    expectNotADatabaseRefusal(await rejectionOf(resolveSqliteDriver({ filename, dev: true, warn })));
+    // No step-down notice: the "native better-sqlite3 unavailable" warning
+    // named the wrong cause, and no rung was tried.
+    expect(warn).not.toHaveBeenCalled();
+    expectFileUntouched();
+  });
+});
+
+describe('resolveSqliteDriver in production: a file that is not a SQLite database (#24960)', () => {
+  it('returns native unprobed, and its connect() refuses the file', async () => {
+    const warn = vi.fn();
+    const resolved = await resolveSqliteDriver({ filename, dev: false, warn });
+    opened.push(resolved);
+    expect(resolved.engine).toBe('better-sqlite3');
+    let refusal: unknown;
+    await resolved.driver.connect().catch((e: unknown) => { refusal = e; });
+    expectNotADatabaseRefusal(refusal);
+    expect(warn).not.toHaveBeenCalled();
+    expectFileUntouched();
+  });
+});
+
+describe('DatasourceConnectionService: a declared SQLite datasource on a file that is not a database (#24960)', () => {
+  for (const mode of ['development', 'production'] as const) {
+    it(`${mode}: reports a failed connection state naming the file, registers no driver, and leaves the file as it was`, async () => {
+      vi.stubEnv('NODE_ENV', mode);
+      const registered: string[] = [];
+      const engine = {
+        registerDriver: (driver: { name?: string }) => { registered.push(String(driver?.name)); },
+        getDriverByName: (name: string) => (registered.includes(name) ? {} : undefined),
+      };
+      const service = new DatasourceConnectionService({
+        factory: () => createDefaultDatasourceDriverFactory({ dev: mode === 'development' }),
+        engine: () => engine as any,
+      });
+
+      await service.connectDeclared({
+        datasources: [{ name: 'archive', driver: 'sqlite', config: { filename }, autoConnect: true }],
+      });
+
+      const state = service.getConnectionState('archive');
+      expect(state?.availability).toBe('failed');
+      expect(state?.reason).toContain(filename);
+      expect(registered).toEqual([]);
+      expectFileUntouched();
+    });
+  }
+});