feat: workflow rollback types + Python SDK (withRollback, saga pattern)

[dmmulroy]

Summary

Adds workflow rollback/saga support:

• TypeScript types: RollbackHandler<T>, RollbackStepConfig, withRollback method, TerminateOptions, rollingBack status
• Python SDK: step.with_rollback() decorator with undo=, depends=, concurrent= support

Note: Depends on internal gitlab workflows!750 which adds the underlying engine support.

TypeScript Types (types/defines/)

// rpc.d.ts
export type RollbackHandler<T> = {
  do: () => Promise<T>;
  undo: (err: unknown, value: T) => Promise<void>;
};

export type RollbackStepConfig = WorkflowStepConfig & {
  undoConfig?: WorkflowStepConfig;
};

// Added to WorkflowStep class:
withRollback<T>(name: string, handler: RollbackHandler<T>, config?: RollbackStepConfig): Promise<T>;

// workflows.d.ts - InstanceStatus.status now includes 'rollingBack'
// WorkflowInstance.terminate(options?: TerminateOptions)

Python SDK (src/pyodide/)

# Pattern A: Chained decorator
@step.with_rollback("create order")
async def create_order():
    return await db.insert(...)

@create_order.undo
async def _(err, order):
    await db.delete(order["id"])

# Pattern B: undo= parameter
@step.with_rollback("charge", undo=refund_handler, depends=[create_order])
async def charge_payment():
    return await stripe.charge(...)

API: step.with_rollback(name, *, undo=None, depends=None, concurrent=False, config=None, undo_config=None)

• Undo handler required (raises ValueError if missing)
• Supports DAG dependencies via depends= and concurrent=

Changed Files

• types/defines/rpc.d.ts - rollback types
• types/defines/workflows.d.ts - TerminateOptions, rollingBack status
• src/pyodide/internal/workers-api/src/workers/_workers.py - RollbackStep class
• src/pyodide/internal/workers-api/src/workers/__init__.py - exports
• src/workerd/server/tests/python/workflow-rollback/ - tests

Snapshot Regeneration Needed

Type snapshots need regeneration (just generate-types segfaults on macOS).

---

Note

This PR consolidates #5809 (Python SDK) and was written with AI assistance.

[anonrig]

Can you run "just generate-types" and push the changes files?

[codspeed-hq]

CodSpeed Performance Report

Merging this PR will not alter performance

_{Comparing dmmulroy:dillon/workflow-rollback-types (1dc9fe3) with main (a5c6178)}

Summary

✅ 70 untouched benchmarks
⏩ 129 skipped benchmarks¹

Footnotes

1. 129 benchmarks were skipped, so the baseline results were used instead. If they were deleted from the codebase, click here and archive them to remove them from the performance reports. ↩

[dmmulroy]

@anonrig I keep getting a segfaul trying to run just generate-types 😅 any chance you could pull/push that for me until i figure out what's going on? (will try in docker this weekend if i get time)

[smaldd14]

Looking forward to being able to implement saga pattern in my CF Workflows. In my day job, we utilize Temporal for durable execution which supports this, but I am trying to convince them to switch over.