I have a system I'm building on celld that uses Workflows extensively, which ran into this (a flaw in the KV layer). The below MWE is from Fable 5.1/Opus 5.5, the diagnosis is rewritten in my own prose.

This has been tested against `celld 0.6.0` but it also exists in earlier versions, too.

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`ctx.storage.kv.list()` gives you a key/value iterator, backed by a SQLite prepared statement object. At some point in time, the LTX replicator will checkpoint the database backing the iterator, after which the statement object becomes invalid. However, this then breaks _everything_ and causes the DO itself to become unusable; all `kv.put()` or storage calls or SQL statement calls after this point will fail. The only way this can be undone is by opening a new `kv.list()` iterator in order to finalize/collect the old one so it can go away.

Workflows can hit this quite reliably. `step.waitForEvent` returns from inside a `kv.list()` loop when it consumes an event, so a Workflow that waits for events and writes about 4 MB afterwards starts failing `status()` and `sendEvent()` with `storage.transaction: database is locked`.

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MWE: `wrangler.jsonc` & `index.js`

```json { "name": "kv-list-cursor-lock", "main": "index.js", "no_bundle": true, "compatibility_date": "2026-08-20", "durable_objects": { "bindings": [{ "name": "REPRO", "class_name": "Repro" }] }, "migrations": [{ "tag": "v1", "new_sqlite_classes": ["Repro"] }] } ```

```javascript import { DurableObject } from "cloudflare:workers";

export class Repro extends DurableObject { leak() { const kv = this.ctx.storage.kv; kv.put("a", 1); kv.put("b", 2);

// leak the cursor, then commit about ~3 MiB, going past the 1000-page threshold & forcing a checkpoint for (const _ of kv.list()) break; for (let i = 0; i < 200; i++) kv.put("blob" + i, "x".repeat(16384)); } put() { try { this.ctx.storage.kv.put("c", 3); return "ok"; } catch (e) { return e.message; } } drain() { for (const _ of this.ctx.storage.kv.list()); } }

export default { async fetch(request, env) { const repro = env.REPRO.getByName(new URL(request.url).pathname); await repro.leak(); const before = await repro.put(); // this will fail with "database is locked" await repro.drain(); // a new kv.list finalizes the old cursor and removes it const after = await repro.put(); // this will succeed return Response.json({ before, after }); }, }; ```

## Actual output

``` $ celld dev . --host 127.0.0.1 --port 8787 --no-watch & $ curl http://127.0.0.1:8787/run1 {"before":"storage.put: database is locked","after":"ok"} ```

## Expected output

I expect both `before` and `after` to return `ok` and not violate any other consistency guarantees, etc.