Proposal: Transaction Protocol for idempotent, auditable agent pipelines

[vystartasv]

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?