postcept 0.3.1

Python client for Postcept, Proof-of-Completion for AI agents. Verify high-risk agent actions against the system of record and get a signed completion receipt.

Postcept Python SDK

Submit Proof-of-Completion verifications for your AI agents' high-risk actions.

pip install postcept

Usage

from postcept import Postcept

pc = Postcept(api_key="pcpt_sk_...")  # create a key in the dashboard

# After your agent issues a refund, prove it actually completed:
result = pc.verify_refund(
    operation_id="refund_8F31",        # stable across retries
    agent_id="SupportAgent-04",
    refund_id="re_4md82k",
    amount_cents=12000,
    currency="usd",
    customer="[e-mail]",
    idempotency_key="refund_8F31",     # safe to retry
)

print(result["result"])                # "verified" | "incomplete" | "duplicated" | "mismatched" | "policy_failed"
print(result["lifecycle"])             # "pending_finality" | "finalized" | "unobserved" | "reversed" | ...
print(result["safe_to_claim_complete"])  # True only when verified and the provider state is terminal
print(result["claim_reason"])          # why it isn't safe, e.g. "pending_finality"
print(result["receipt"]["id"])         # signed completion receipt

Act on safe_to_claim_complete, not on the raw result. When it is False, claim_reason tells you what to say. pending_finality means the provider is still settling, so tell the customer "processing" and re-check later. Anything else means the work is not done, so surface the gap and recover.

Cancellations work the same way:

pc.verify_cancellation(
    operation_id="cancel_2240",
    agent_id="SupportAgent-04",
    subscription_id="sub_9Kd21",
    customer="[e-mail]",
)

Read your Verified Completion Rate:

pc.verified_completion_rate()  # {"claimed": 1240, "verified": 1167, "verified_completion_rate": 0.9411, ...}

Notes

• Auth: pass an organization API key (pcpt_sk_...). All data is scoped to that org.
• Idempotency: pass idempotency_key so retried submissions return the original verification instead of creating a duplicate.
• Errors: non-2xx responses raise PostceptError (.status_code, .detail).
• Base URL: defaults to https://api.postcept.com. Override with Postcept(api_key=..., base_url=...) for staging.
• Use as a context manager (with Postcept(...) as pc:) to close the HTTP client.

Verifying lifecycle webhooks

Postcept can push signed lifecycle events (a verification created, a previously verified refund later reversed) to an endpoint you register in the dashboard or via POST /v1/webhook-endpoints. Verify every delivery against the raw request body before acting on it:

from postcept import verify_webhook_signature

# In your handler, BEFORE parsing the JSON:
ok = verify_webhook_signature(
    payload=raw_body_bytes,
    header=request.headers["Postcept-Signature"],
    secret=os.environ["POSTCEPT_WEBHOOK_SECRET"],
)

Stale timestamps are rejected (replay protection, 5-minute default). Delivery is at-least-once and unordered: de-duplicate by the Postcept-Event-Id header. During a secret rotation the header carries a signature for both the new and the previous secret, so you can switch without dropping deliveries.

Guarded actions

Run your action in your own code, then verify it, and get a customer-safe status:

result = pc.guard_refund(
    lambda: stripe.Refund.create(charge="ch_1P09x", amount=12000),  # YOUR code
    operation_id="refund_8F31", agent_id="SupportAgent-04",
    refund_id="re_4md82k", amount_cents=12000, customer="[e-mail]",
)

result.action                  # whatever your function returned
result.safe_to_claim_complete  # True only when verified AND final
result.status                  # "completed" | "processing" | "failed" | "unverified" | "unreachable"
result.customer_message        # a non-false sentence for that status

Postcept never runs your action or holds write authority. guard_refund never raises for a non-verified or unreachable outcome (they're in the result). A raise from your own action propagates. A pending refund yields status="processing", never "done".

OpenTelemetry

Export Postcept outcomes to your existing observability tool. Attach the standard postcept.* attributes to your own span (no OTel dependency forced):

from opentelemetry import trace
from postcept import postcept_span_attributes

result = pc.verify_refund(...)
trace.get_current_span().set_attributes(postcept_span_attributes(result))

Works with any OTel-compatible backend (LangSmith, Phoenix, Datadog, Honeycomb, plain OTLP).