@@ -0,0 +1,20 @@
+---
+'@objectstack/runtime': patch
+'@objectstack/cli': patch
+---
+
+fix(runtime,cli): `os start` and `os dev` refuse a SQLite database whose directory cannot be made, at once, instead of hanging
+
+Clause-②: no
+
+**What was wrong.** The standalone host (`createStandaloneStack`, which `os start`, `os dev`'s standalone boot and every embedder run) prepared the directory of a file-backed SQLite database with Node's recursive `mkdirSync`. Node's recursive mkdir never returns when a level answers `ENOENT` although its parent exists: for `OS_DATABASE_URL=file:/proc/os-x/ctl.db` it looped `mkdir("/proc/os-x")` and `mkdir("/proc")` without end, holding the event loop. `os start` printed `→ Starting server...` and hung with no timeout and no message. The `sqlite-wasm` arm (`wasm-sqlite://…`, or `OS_DATABASE_DRIVER=sqlite-wasm`) did the same. `os dev` hung the same way in its own process when its default database lived under a state directory that cannot be made (for example `OS_HOME=/proc/os-x`).
+
+**What an operator sees now.** The boot exits non-zero within its normal start-up time, naming the database file, the directory and the operating system's error:
+
+```text
+✗ [StandaloneStack] SQLite database file '/proc/os-x/ctl.db' cannot be created: its directory '/proc/os-x' could not be made: ENOENT: no such file or directory, mkdir '/proc/os-x'
+```
+
+`os dev` with an unusable state directory prints `✗ The default database '…/data/objectstack.db' cannot be created: its directory '…/data' could not be made: …`, followed by the remedy: point `OS_HOME` at a directory that can be created, or choose the database with `--database`.
+
+Nothing else changes. A creatable path is still made, every missing level of it. The read-only boot (`os migrate plan` over an absent database file) still creates no directory. The refusal names the path, never the database URL.
@@ -0,0 +1,146 @@
+// Copyright (c) 2026 ObjectStack. Licensed under the Apache-2.0 license.
+//
+// `os dev` refuses a unified-default database directory it cannot make — at
+// once, naming the database file, the directory and the operating system's
+// code — instead of looping in Node's recursive mkdir (#23737).
+//
+// ## The defect, measured on `origin/main` 43567a8fcb
+//
+// `os dev` prepared `<state dir>/data/` for its unified-default SQLite file with
+// `fs.mkdirSync(dir, { recursive: true })`. Under `OS_HOME=/proc/os-23737` that
+// call looped `mkdir("/proc/os-23737") = ENOENT`, `mkdir("/proc") = EEXIST`,
+// retry, in the `os dev` process itself: 64,440 failing calls in 25 s under
+// `strace`, and the command never reached its next line.
+//
+// ## Why every case runs in ONE bounded child process
+//
+// The loop was SYNCHRONOUS: it holds the event loop, so no timer fires and a
+// vitest timeout cannot end it. A regression to it would hang this worker
+// rather than fail, so `prepareDevDatabaseDirectory` (the function `os dev`'s
+// boot awaits) runs from source in a `node --import tsx` child bounded by
+// `spawnSync`'s timeout with SIGKILL. All cases share that one child because
+// importing `dev.ts` costs about 7 s of the child's wall (measured, cold and
+// warm tsx cache alike), and this worker never imports it at all.
+//
+// ## What is asserted
+//
+//   1. `/proc/<missing>/` (where `/proc/self` exists — Linux, which CI is): the
+//      child settles inside the bound and the refusal carries `ENOENT`, naming
+//      the file and the directory — the shape that looped.
+//   2. A path through a regular file: refused with `ENOTDIR`, naming the file.
+//   3. CONTROL: a creatable unified-default path three levels deep is made.
+//   4. CONTROL: any other source is left to the serve child — nothing is made.
+
+import { describe, it, expect, beforeAll, afterAll } from 'vitest';
+import { spawnSync } from 'node:child_process';
+import { existsSync, mkdtempSync, rmSync, statSync, writeFileSync } from 'node:fs';
+import { tmpdir } from 'node:os';
+import { dirname, join, resolve } from 'node:path';
+import { fileURLToPath, pathToFileURL } from 'node:url';
+
+const HERE = dirname(fileURLToPath(import.meta.url));
+const PKG_ROOT = resolve(HERE, '../..');
+const SUBJECT = pathToFileURL(resolve(HERE, 'dev.ts')).href;
+
+/** The child's whole budget; the loop it guards against never ends. */
+const CHILD_BOUND_MS = 45_000;
+
+interface Outcome {
+  label: string;
+  outcome: 'returned' | 'rejected';
+  code?: string;
+  message?: string;
+}
+
+const PROC_DIR = `/proc/os-23737-${process.pid}/data`;
+const PROC_FILE = `${PROC_DIR}/objectstack.db`;
+const RUNS_PROC = existsSync('/proc/self');
+
+let root: string;
+let outcomes: Map<string, Outcome>;
+
+beforeAll(() => {
+  root = mkdtempSync(join(tmpdir(), 'os-23737-dev-'));
+  writeFileSync(join(root, 'plain'), '');
+  const cases: Array<{ label: string; url: string; source: string }> = [
+    ...(RUNS_PROC ? [{ label: 'proc', url: `file:${PROC_FILE}`, source: 'unified-default' }] : []),
+    { label: 'through-file', url: `file:${join(root, 'plain', 'data', 'objectstack.db')}`, source: 'unified-default' },
+    { label: 'creatable', url: `file:${join(root, 'home', 'a', 'data', 'objectstack.db')}`, source: 'unified-default' },
+    { label: 'other-source', url: `file:${join(root, 'env', 'a', 'data', 'objectstack.db')}`, source: 'env' },
+  ];
+  const script = [
+    'const [subject, json] = process.argv.slice(1);',
+    'const { prepareDevDatabaseDirectory } = await import(subject);',
+    'const out = [];',
+    'for (const { label, url, source } of JSON.parse(json)) {',
+    '  try { await prepareDevDatabaseDirectory({ url, source }); out.push({ label, outcome: "returned" }); }',
+    '  catch (e) { out.push({ label, outcome: "rejected", code: e?.code, message: String(e?.message) }); }',
+    '}',
+    'process.stdout.write("\\nDEV-DIR-OUTCOMES " + JSON.stringify(out) + "\\n");',
+  ].join('\n');
+  const t0 = Date.now();
+  const child = spawnSync(
+    process.execPath,
+    ['--import', 'tsx', '--input-type=module', '-e', script, SUBJECT, JSON.stringify(cases)],
+    {
+      cwd: PKG_ROOT,
+      env: {
+        PATH: process.env.PATH ?? '',
+        ...(process.env.TMPDIR ? { TMPDIR: process.env.TMPDIR } : {}),
+      },
+      encoding: 'utf8',
+      timeout: CHILD_BOUND_MS,
+      killSignal: 'SIGKILL',
+      maxBuffer: 16 * 1024 * 1024,
+    },
+  );
+  if (child.signal) {
+    throw new Error(
+      `prepareDevDatabaseDirectory had not settled after ${Date.now() - t0} ms (child killed by ${child.signal}) — ` +
+        `the directory prep is looping again. stderr tail: ${String(child.stderr).slice(-2000)}`,
+    );
+  }
+  const line = String(child.stdout).split('\n').find((l) => l.startsWith('DEV-DIR-OUTCOMES '));
+  if (!line) {
+    throw new Error(`child exited ${child.status} without a result. stderr tail: ${String(child.stderr).slice(-2000)}`);
+  }
+  const parsed: Outcome[] = JSON.parse(line.slice('DEV-DIR-OUTCOMES '.length));
+  outcomes = new Map(parsed.map((o) => [o.label, o]));
+}, CHILD_BOUND_MS + 15_000);
+
+afterAll(() => {
+  if (root) rmSync(root, { recursive: true, force: true });
+});
+
+function outcomeOf(label: string): Outcome {
+  const found = outcomes.get(label);
+  if (!found) throw new Error(`no outcome recorded for case '${label}'`);
+  return found;
+}
+
+describe('prepareDevDatabaseDirectory — os dev\'s unified-default directory (#23737)', () => {
+  it.runIf(RUNS_PROC)('refuses /proc/<missing>/ at once with ENOENT, naming the file and the directory', () => {
+    const o = outcomeOf('proc');
+    expect(o.outcome).toBe('rejected');
+    expect(o.code).toBe('ENOENT');
+    expect(o.message).toContain(`'${PROC_FILE}'`);
+    expect(o.message).toContain(`'${PROC_DIR}'`);
+  });
+
+  it('refuses a path through a regular file with ENOTDIR, naming the file', () => {
+    const o = outcomeOf('through-file');
+    expect(o.outcome).toBe('rejected');
+    expect(o.code).toBe('ENOTDIR');
+    expect(o.message).toContain(`'${join(root, 'plain', 'data', 'objectstack.db')}'`);
+  });
+
+  it('CONTROL: a creatable unified-default path three levels deep is made', () => {
+    expect(outcomeOf('creatable').outcome).toBe('returned');
+    expect(statSync(join(root, 'home', 'a', 'data')).isDirectory()).toBe(true);
+  });
+
+  it('CONTROL: any other source is left to the serve child — nothing is made', () => {
+    expect(outcomeOf('other-source').outcome).toBe('returned');
+    expect(existsSync(join(root, 'env'))).toBe(false);
+  });
+});
@@ -90,6 +90,69 @@ export async function resolveDevDatabase(opts: {
   });
 }
 
+/**
+ * Make the directory of `os dev`'s unified-default SQLite database
+ * (`<state dir>/data/`), bounded — or reject at once, naming the database
+ * file, the directory and the operating system's code (#23737).
+ *
+ * Only the `unified-default` source is prepared here; every other source is
+ * the serve child's to open (and its standalone host prepares the directory
+ * with the same bounded walk).
+ *
+ * ## Why not `fs.mkdirSync(dir, { recursive: true })`
+ *
+ * Node's recursive mkdir (v22.22.0, measured; sync and async alike) never
+ * returns when a level answers `ENOENT` although its parent exists. Under
+ * `OS_HOME=/proc/os-23737` this command looped `mkdir("/proc/os-23737")` ↔
+ * `mkdir("/proc")` in its own process (64,440 failing calls in 25 s) and never
+ * reached its next line.
+ *
+ * The walk is the one `driver-sql`'s connect and the runtime's standalone host
+ * run (neither is on a package entry, hence this module-level copy): find the
+ * nearest level that exists, create the missing ones top-down with a
+ * NON-recursive `mkdir`, accept `EEXIST` on a created level (a concurrent
+ * creator), and reject on anything else.
+ */
+export async function prepareDevDatabaseDirectory(
+  resolved: Pick<ResolvedProjectDatabaseUrl, 'url' | 'source'>,
+): Promise<void> {
+  if (resolved.source !== 'unified-default') return;
+  const filename = resolved.url.replace(/^file:/, '');
+  const directory = path.resolve(path.dirname(filename));
+  try {
+    const missing: string[] = [];
+    let level = directory;
+    for (;;) {
+      try {
+        if (!(await fs.promises.stat(level)).isDirectory() && missing.length === 0) await fs.promises.mkdir(level);
+        break;
+      } catch (e) {
+        if ((e as { code?: unknown } | null)?.code !== 'ENOENT') throw e;
+        missing.push(level);
+        const parent = path.dirname(level);
+        if (parent === level) break;
+        level = parent;
+      }
+    }
+    for (const each of missing.reverse()) {
+      try {
+        await fs.promises.mkdir(each);
+      } catch (e) {
+        if ((e as { code?: unknown } | null)?.code !== 'EEXIST') throw e;
+      }
+    }
+  } catch (e) {
+    const code = (e as { code?: unknown } | null)?.code;
+    const reason = e instanceof Error ? e.message : String(e);
+    throw Object.assign(
+      new Error(
+        `The default database '${filename}' cannot be created: its directory '${directory}' could not be made: ${reason}`,
+      ),
+      { code: typeof code === 'string' ? code : undefined, filename, directory, cause: e },
+    );
+  }
+}
+
 /**
  * The `os dev` MCP connect hint — the three lines a reader PASTES (#3167,
  * #16734).
@@ -573,8 +636,15 @@ export default class Dev extends Command {
         // prompt (CI-safe), never silent (#6469).
         console.log(chalk.yellow(`  ⚠ ${resolvedDb.notice}`));
       }
-      if (resolvedDb.source === 'unified-default') {
-        fs.mkdirSync(path.dirname(resolvedDb.url.replace(/^file:/, '')), { recursive: true });
+      // Bounded, and refused at once when the directory cannot be made (#23737).
+      try {
+        await prepareDevDatabaseDirectory(resolvedDb);
+      } catch (error: any) {
+        printError(error?.message ?? String(error));
+        console.error(chalk.yellow(
+          '  Point OS_HOME at a directory that can be created, or choose the database with --database.',
+        ));
+        process.exit(1);
       }
       const effectiveDb = resolvedDb.url;
       // `dev` has a resolved artifact by this point (it compiled one, or was