## Summary
v3 (the engine that ran the SDK v3 era, internally
`RunEngineVersion.V1`) is end-of-life. Following the removal of the v3
execution apps
([#4194](https://github.com/triggerdotdev/trigger.dev/pull/4194)) and
the legacy dev websocket
([#4198](https://github.com/triggerdotdev/trigger.dev/pull/4198)), this
removes the remaining v3 execution stack from the server.
Clients still on v3 (an old SDK or CLI that has not upgraded) keep
getting a clear "upgrade to v4" response. Triggers, batch triggers,
reschedules, and deploys that resolve to v3 are rejected with a graceful
4xx pointing at the migration guide, never a 5xx, so a stale client
cannot affect server health. Self-hosted instances still running v3
should stay on the 4.5.x release line until they migrate.
## What is removed
- The MarQS queue and its shared/dev queue consumers.
- The v3 socket.io namespaces (coordinator, provider, shared-queue) and
the v3 run lifecycle services (attempt, checkpoint, and batch-resume).
- The graphile-worker background job system; all live jobs already run
on `@trigger.dev/redis-worker`.
- The `DEPRECATE_V3_ENABLED` flag: v3 is now rejected unconditionally,
so the flag is gone.
- Unused v3 exports from `@trigger.dev/core` (the `v3/zodNamespace`
subpath and the legacy socket message catalogs) and the now-dead MarQS
environment variables.
## What stays
The v4 engine is untouched. The graceful v3 rejection boundary stays,
`determineEngineVersion` still detects a v3 project so it can reject it,
and the batch service plus batch-completion worker stay for current
clients. Live queue concurrency limits and metrics now read from the v4
run engine instead of MarQS, and a brand-new dev environment now
defaults to v4.
## Dependency cleanup
Removes webapp dependencies left unused by this change: `seedrandom` and
`semver` (only the removed v3 code used them) plus a set that was
already dead, their orphaned `@types` packages, and two dead files. Adds
a `knip:deps` script and a `knip.json` config so unused dependencies can
be found the same way going forward.
Adds support for **debounced task runs** - when triggering a task with a
debounce key, subsequent triggers with the same key will reschedule the
existing delayed run instead of creating new runs. This continues until
no new triggers occur within the delay window.
## Usage
```typescript
await myTask.trigger({ userId: "123" }, {
debounce: {
key: "user-123-update",
delay: "5s",
mode: "leading", // default
}
});
```
- **key**: Scoped to the task identifier
- **delay**: How long to wait before executing (supports duration
strings like `"5s"`, `"1m"`)
- **mode**: Either `"leading"` or `"trailing"`. Leading debounce will
use the payload and options from the first run created with the debounce
key. Trailing will use payload and options from the last run.
### "trailing" mode overrides
When using `mode: "trailing"` with debounce, the following options are
updated from the **last** trigger:
- **`payload`** - The task input data
- **`metadata`** - Run metadata
- **`tags`** - Run tags (replaces existing tags)
- **`maxAttempts`** - Maximum retry attempts
- **`maxDuration`** - Maximum compute time
- **`machine`** - Machine preset (cpu/memory)
## Behavior
- **First run wins**: The first trigger creates the run, subsequent
triggers push its execution time later
- **Idempotency keys take precedence**: If both are specified,
idempotency is checked first
- **Max duration**: Configurable via `DEBOUNCE_MAX_DURATION_MS` env var
(default: 10 minutes)
Works with `triggerAndWait` - parent runs correctly block on the
debounced run.
Eric Allam