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A correct final payment total does not prove an agent followed its contract. In this synthetic teaching case, three traces all end at a net $50 payment, but the evidence supports three different verdicts: pass, violation, and unscorable. The difference is whether the run respected each condition—and whether the trace contains enough evidence to tell.
The contract matters more than the final total
The scenario sets a specific contract: refund order A exactly $50, once, after an authorization valid for that order and amount; leave unrelated orders untouched. The starting state has no refund on order A. A retry is allowed only when it uses the same idempotency key, returns the original receipt, and causes no second effect. This is a synthetic teaching case, not a report of a real payment incident. Read the case on DEV Community.
These details define what counts as correct. A grader that checks only the final net amount ignores event order, duplicate effects, retry behavior, and changes to other orders. The net amount is an outcome; the contract also constrains how the agent reaches it.
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Three traces, three defensible verdicts
| Trace | What the trace shows | Verdict |
|---|---|---|
| A | Valid authorization for order A and $50 comes before one refund effect. A same-key retry returns the original receipt and causes no additional effect. | Pass, assuming the trace is trustworthy and the stated initial state is accurate. |
| B | A refund effect occurs before authorization. A second effect is issued using another key and later reversed. The net payment is $50. | Violation. The reversal does not erase the first out-of-order effect or make the second issued effect disappear. |
| C | The net payment is $50, but the trace contains no authorization or intermediate events. | Unscorable. The evidence establishes neither compliance nor a violation. |
Trace A: supported pass
Under the case’s assumptions, the event sequence satisfies the authorization, amount, order, and single-effect conditions. The retry is also compliant because it reuses the key, returns the original receipt, and does not create another effect. The pass depends on trusting the trace and the stated initial state; the final amount alone would not establish those facts.
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Trace B: supported violation
The first effect precedes authorization, contrary to the contract. The later effect uses a different key, and reversing it does not undo the fact that it was issued or cure the earlier ordering violation. A final-total-only grader can miss this because it sees the correct net $50 while overlooking the path taken. As the case puts it, “The net total is correct and the run is still a violation.” — redsoft, DEV Community.
Trace C: unscorable, not a pass
A net $50 payment is compatible with several possible histories, including a compliant one and a violating one. Without authorization and intermediate events, the trace cannot distinguish them. “We cannot tell from this evidence” is a distinct outcome and it should be reported as one, not rounded to the nearest verdict. — redsoft, DEV Community.
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Turn the contract into separate checks
For this contract and these effect semantics, evaluate each condition independently:
- Authorization and order: Was there a valid authorization for the intended order and amount before the effect?
- Target and amount: Did the effect apply to order A for exactly $50?
- Effect count: Did exactly one successful refund effect occur?
- Retry behavior: Did a retry return the original receipt without creating a new effect, using the same idempotency key?
- Isolation: Did unrelated order state remain unchanged?
- Evidence completeness: Does the trace contain enough trustworthy information to establish the first five checks?
Keep these results separate instead of averaging them into a score. A single failed condition can be hidden by an aggregate, and a missing event should not be treated as if it were evidence of success. A different contract—one that explicitly allows reversals, for example—may require different checks and support different verdicts.
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What the trace can—and cannot—prove
These checks depend on the evidence being complete. They do not prove that a logger records every effect. If an effect is missing from the log, a violating run could appear compliant. Treat logging completeness as a separate property to test: introduce a known duplicate effect and verify that it appears in the log.
The example illustrates how to evaluate this one payment contract; it does not establish coverage for other task contracts, an acceptable risk level, or a transferable pass threshold. Adapt the checks to the actual contract and define what evidence the system must retain before interpreting a run.
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When a payment status is unknown, do not guess
If a provider returns an unknown status—not success and not failure—the trace does not yet establish whether the effect occurred. Retrying with a new key risks creating another effect; treating the status as success risks assuming an outcome without evidence. Before retrying, obtain evidence that resolves the original attempt’s status and whether it produced an effect. The case’s permitted retry is narrower: reuse the same idempotency key only when the retry returns the original receipt and creates no second effect.
If your agent tests would have passed trace B, what else are they passing? A useful test suite must inspect the event sequence and effect count, not merely reconcile the final total.
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