Proposal: Transaction Protocol for idempotent, auditable agent pipelines

Problem

Haystack pipelines lack transaction guarantees. When a step fails mid-execution, there's no standard way to:

1. Know exactly what completed and what didn't
2. Resume from failure point (idempotency)
3. Roll back partial work (compensation)

For production deployments in regulated environments, this is a hard requirement.

Proposed Solution

Transaction Protocol (L7) from Works With Agents (CC BY 4.0): idempotency, rollback, and immutable audit trails.

from haystack import Pipeline
from works_with_agents import TransactionProtocol

pipeline = Pipeline()
pipeline.add_component(embedder, ...)
pipeline.add_component(retriever, ...)
pipeline.add_component(generator, ...)

tx = TransactionProtocol.begin("doc-qna-pipeline")
try:
    result = pipeline.run({"query": "What is GDP?"})
    tx.commit(result)  # Signed, hashed, timestamped
except PipelineError:
    tx.rollback()  # Compensation per component

Provides: idempotency tokens, step-level audit trail, compensation actions, cryptographic signatures for tamper-proof evidence.

Why Haystack: pipeline architecture = natural transaction boundaries. Production users need this. Zero breaking changes — wrapper pattern.

Spec: https://workswithagents.dev/specs/transaction.md
SDK: pip install works-with-agents

Would a PR adding Transaction Protocol support to Haystack be welcome?

Start by reading Haystack's Pipeline API alongside the linked Transaction Protocol specification and SDK documentation. The proposal names no Haystack files or tests and leaves the integration, compensation behavior, audit guarantees, and acceptance criteria undefined, so the scope and definition of done require maintainer agreement first.