fix: don't leak a user-provided fs into the inner initdb instance

.changeset/fix-initdb-fs-option-leak.md

@@ -0,0 +1,5 @@
+---
+'@electric-sql/pglite': patch
+---
+
+Fix `PGlite.create({ fs })` on a fresh database calling the provided filesystem's `init()` twice: the inner initdb instance no longer inherits the user-provided `fs` and always runs on its own scratch filesystem. Previously any VFS holding exclusive resources (e.g. OPFS sync access handles) failed with a contention error on first create.

packages/pglite/src/pglite.ts

@@ -558,6 +558,11 @@ export class PGlite
           pgInitDbOpts.dataDir = undefined
           pgInitDbOpts.extensions = undefined
           pgInitDbOpts.loadDataDir = undefined
+          // The initdb instance must run on its own scratch filesystem: a
+          // user-provided `fs` must not leak into it, or its second `init()`
+          // collides with resources the outer instance already holds (e.g. an
+          // OPFS VFS's sync access handles, which are exclusive per file).
+          pgInitDbOpts.fs = undefined
           const pg_initDb = await PGlite.create(pgInitDbOpts)
 
           // Initialize the database

packages/pglite/tests/initdb-fs-option.test.ts

@@ -0,0 +1,31 @@
+import { describe, it, expect } from 'vitest'
+import { PGlite, MemoryFS } from '../dist/index.js'
+
+// Regression test: creating a fresh database with a user-provided `fs` option
+// boots an inner PGlite instance to run initdb. That inner instance must run
+// on its own scratch filesystem — if the user's `fs` leaks into it, the
+// filesystem's `init()` runs twice against the same backing resources, which
+// breaks any VFS holding exclusive resources (e.g. OPFS sync access handles).
+describe('initdb with user-provided fs option', () => {
+  it('does not re-init the provided fs for the inner initdb instance', async () => {
+    class CountingFS extends MemoryFS {
+      initCount = 0
+      async init(...args: Parameters<MemoryFS['init']>) {
+        this.initCount++
+        return super.init(...args)
+      }
+    }
+
+    const fs = new CountingFS()
+    const pg = await PGlite.create({ fs })
+
+    expect(fs.initCount).toBe(1)
+
+    // The store initialized and works end-to-end on the provided fs.
+    await pg.exec('CREATE TABLE t (id int)')
+    await pg.exec('INSERT INTO t VALUES (1)')
+    const res = await pg.query<{ id: number }>('SELECT id FROM t')
+    expect(res.rows).toEqual([{ id: 1 }])
+    await pg.close()
+  })
+})